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Title: Anatomy of the Cat

Author: Jacob Reighard
H. S. Jennings

Illustrator: Louise Burridge Jennings

Release date: December 1, 2018 [eBook #58394]

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK ANATOMY OF THE
CAT ***

Please see the Transcriber’s Notes at
the end of this text.
For some illustrations, larger versions
are available by clicking the link in the
illustration caption (Fig. nnn) (not
available in all formats).

ANATOMY OF THE CAT

BY
JACOB REIGHARD
Professor of Zoology in the University of Michigan

AND

H. S. JENNINGS
Instructor in Zoology in the University of Michigan

WITH

ONE HUNDRED AND SEVENTY-THREE ORIGINAL FIGURES

DRAWN BY

LOUISE BURRIDGE JENNINGS

NEW YORK

HENRY HOLT AND COMPANY
1901

Copyright, 1901,

BY

HENRY HOLT & CO.

ROBERT DRUMMOND, PRINTER, NEW YORK.

PREFACE.

Although the cat has long been in common use for the practical study of
mammalian anatomy, a clear, correct, not too voluminous account of its
structure, such as should be in the hands of students in the laboratory, has
remained a desideratum. A number of works have been published on the cat,
some of them of much value, yet there is none which fulfils exactly the
conditions mentioned. The books which have appeared on this subject are the
following:
1. Strauss-Durckheim, H. Anatomie descriptive et comparative du Chat. 2
vols. Paris, 1845.
2. Mivart, St. George. The Cat: an Introduction to the Study of Back-boned
Animals, especially Mammals. New York, 1881.
3. Wilder, Burt G., and Gage, Simon H. Anatomical Technology as applied
to the Domestic Cat. New York, 1882.
4. Gorham, F. P., and Tower, R. W. A Laboratory Guide for the Dissection of
the Cat. New York, 1895.
5. Jayne, H. Mammalian Anatomy. Vol. I. Philadelphia, 1898.
The first of these works treats only of the muscles and bones, and is not
available for American students. Its excellent plates (or Williams’s outline
reproductions of the same) should be in every laboratory.
The second book named is written in such general terms that its descriptions
are not readily applicable to the actual structures found in the dissection of the
cat, and experience has shown that it is not fitted for a laboratory handbook. It
contains, in addition to a general account of the anatomy of the cat, also a
discussion of its embryology, psychology, palæontology, and classification.
The book by Wilder and Gage professedly uses the cat as a means of
illustrating technical methods and a special system of nomenclature. While of
much value in many ways, it does not undertake to give a complete account of
the anatomy of the animal.
The fourth work is a brief laboratory guide.
The elaborate treatise by Jayne, now in course of publication, is a
monumental work, which will be invaluable for reference, but is too

voluminous to place in the hands of students. At present only the volume on
the bones has been published.
As appears from the above brief characterization, none of these books gives
a complete description of the anatomy of the cat in moderate volume and
without extraneous matter. This is what the present work aims to do.
In the year 1891-92, Professor Reighard prepared a partial account of the
anatomy of the cat, which has since been in use, in typewritten form, in
University of Michigan classes. It has been used also at the Universities of
Illinois, Nebraska, and West Virginia, and in Dartmouth College, and has
proven so useful for college work in Mammalian Anatomy that it was decided
to complete it and prepare it for publication. This has been done by Dr.
Jennings.
The figures, which are throughout original, are direct reproductions of ink
drawings, made under the direction of Dr. Jennings by Mrs. Jennings.
The book is limited to a description of the normal anatomy of the cat. The
direct linear action of each muscle taken alone has been given in the
description of muscles; other matters belonging to the realm of physiology, as
well as all histological matter, have been excluded. It was felt that the
monumental work of Jayne on the anatomy of the cat, now in course of
publication, forms the best repository for a description of variations and
abnormalities, so that these have been mentioned in the present volume only
when they are so frequent as to be of much practical importance.
Except where the contrary is stated, the descriptions are based throughout on
our own dissections and observations and are in no sense a compilation. For
this reason we have not thought it necessary to collect the scattered references
to the anatomy of the cat that may occur in the literature. A collection of such
references may be found in Wilder and Gage’s Anatomical Technology. In
addition to the works already referred to, we have of course made use of the
standard works on human and veterinary anatomy. Among these should be
mentioned as especially useful the Anatomie des Hundes by Ellenberger and
Baum. Other publications which have been of service in the preparation of the
work are Windle and Parson’s paper On the Myology of the Terrestrial
Carnivora, in the Proceedings of the Zoological Society of London for 1897
and 1898, T. B. Stowell’s papers on the nervous system of the cat in the
Proceedings of the American Philosophical Society (1881, 1886, 1888) and in
the Journal of Comparative Neurology (vol. I.), and F. Clasen’s Die Muskeln
und Nerven des proximalen Abschnitts der vorderen Extremität der Katze, in
Nova Acta der Ksl. Leop.-Carol. Deutschen Akademie der Naturforscher, Bd.
64.

Nomenclature.—The question of nomenclature has been one of difficulty.
What is desired is a uniform set of anatomical names,—a system that shall be
generally used by anatomists. At present the greatest diversity prevails as to the
names to be applied to the different structures of the body. The only set of
terms which at the present time seems to have any chance of general
acceptance is that proposed by the German Anatomical Society at their
meeting in Basel in 1895, and generally designated by the abbreviation BNA.
This system has therefore been adopted, in its main features, for use in the
present work. It seems impossible at the present time, however, to impose any
one set of terms absolutely upon anatomists of all nations, and we have felt it
necessary to use for certain familiar structures, in place of the BNA terms,
names that have come to have a fixed place in English anatomy, and may
almost be considered component parts of the English language. The German
anatomists have expressly recognized the fact that this would be to a greater or
less degree necessary among anatomists of different nations, and have
characterized their list as for the present tentative, and capable of farther
development. The only purpose of a name is that it shall furnish a key to a
common understanding; where the BNA name does not furnish such a key to
English readers, and where there is a term in established English usage that
does serve this purpose and seems unlikely to be supplanted, we have used the
latter. But we have endeavored to make the number of these exceptions as
small as possible, and in such cases we have usually cited at the same time the
term proposed by the German society, followed by the abbreviation BNA.
When, on the other hand, we have adopted a BNA term for which there is also
a commonly used English equivalent, the latter has likewise usually been cited
in parenthesis.
In deciding whether or not to use in a given case the BNA term many
difficult cases arose. Will the common English name innominate bone (os
innominatum) be replaced by the BNA term os coxæ or coxal bone? We have
held this to be highly improbable, and have therefore used the term innominate
bone, merely citing os coxæ (BNA) as a synonym. In the same way we have
used centrum as a designation of a part of a vertebra, in place of corpus
(BNA); premaxillary bone or premaxilla in place of os incisivum (BNA);
malar bone in place of os zygomaticum (BNA); trapezoid as a name of one of
the bones of the carpus, in place of os multangulum minus (BNA), etc. In other
cases where it has seemed probable that the BNA term would come into
common use, though now unfamiliar, this and the more common English
expression are both used or used alternatively; such has been the case, for
example, with the Gasserian ganglion or semilunar ganglion (BNA). In naming

the cerebral sulci and gyri the system in use for man is not well fitted for
bringing out the plan of those in the brain of the cat, so that it was necessary to
reject the BNA names for these structures.
As to the use of the Latin terms and their equivalents in English form, we
have made a practice of employing in the text sometimes one, sometimes the
other; this has the advantage of giving variety, and of impressing the
interchangeability of the Latin and English forms on the mind of the student.
Where a given structure is called by two equally well-known names, we have
used both, holding that the student should become familiar with each and
recognize their identity of meaning.
In general we have maintained the principle that the primary purpose of such
a work as the present is not to illustrate or defend any particular system of
nomenclature, but to aid in obtaining a knowledge of the structures themselves.
With this end in view, we have used such terms as would in our judgment best
subserve this purpose, making the BNA system, as the one most likely to
prevail, our basis. In applying the system we have had to keep in mind a
number of sometimes conflicting principles. In some cases the judgment of
other anatomists will doubtless differ from our own; but this we feel to be
inevitable. The matter of an absolutely uniform nomenclature is not ripe for
settlement at the present time.
Some further explanation is needed in regard to the topographical terms, or
terms of direction, used in the present work. We have adopted the BNA terms
in this matter also. The terms superior, inferior, anterior, and posterior have
been avoided, as these terms do not convey the same meaning in the case of
the cat as they do in man, owing to the difference in the posture of the body. In
place of these terms are used dorsal and ventral, cranial and caudal. As terms
of direction these, of course, must have an absolutely fixed meaning,
signifying always the same direction without necessary reference to any given
structure. For example, cranial means not merely toward the cranium, but
refers to the direction which is indicated by movement along a line from the
middle of the body, toward the cranium; after the head or cranium is reached,
the term still continues in force for structures even beyond the cranium. Thus
the tip of the nose is considered to be craniad of the cranium itself. Lateral
signifies away from the middle plane; medial toward it. Inner and outer or
internal and external are used only with reference to the structure of separate
organs, not with reference to the median plane of the body.
In describing the limbs the convexity of the joint (the elbow or knee) is
considered as dorsal, the concavity being therefore ventral. Medial refers to
that side of the limb which in the normal position is toward the middle of the

body; lateral to the outer side. Terms of direction which are derived only from
the structure of the limb itself are in some cases more convenient than the
usual ones. In the fore limbs the terms radial (referring to the side on which
the radius lies) and ulnar (referring to the side on which the ulna lies) are used;
in the hind limbs the terms tibial and fibular are used in a similar manner.
Distal means toward the free end of a limb or other projecting structure;
proximal, toward the attached end.
For all these terms an adverbial form ending in -ad has been employed.
Experience has shown this to be very useful in practice, and while not
expressly recommended by the BNA, it is not condemned. Terms ending in -al
are therefore adjectives; those ending in -ad are adverbs.
In compounding these terms of direction, the hyphen has been omitted in
accordance with the usage recommended by the Standard Dictionary. Thus
dorsoventral is written in place of dorso-ventral, etc. The student will perhaps
be assisted in understanding these compounds if he notes that the first
component always ends in -o, so that the letter o practically serves the purpose
of a hyphen in determining how the word is to be divided.
In one particular the BNA nomenclature is not entirely consistent. While
recommending or at least permitting the use of the general terms dorsal and
ventral in place of the human posterior and anterior, and cranial and caudal in
place of superior and inferior, it retains the words anterior, posterior,
superior, and inferior as parts of the names of definite organs. For example, we
have the muscle serratus anterior in place of serratus ventralis; serratus
posterior inferior in place of serratus dorsalis caudalis. This is very
unfortunate, from a comparative standpoint, but we have felt it necessary to
retain the BNA terms in order that the structures of the cat may receive the
same names as the corresponding structures of man.
In the matter of orthography we have endeavored to follow the best English
anatomical usage, as exemplified in Gray’s Human Anatomy,—therefore
writing peroneus in place of peronæus, pyriformis in place of piriformis, etc.
The book is designed for use in the laboratory, to accompany the dissection
and study of the structures themselves. Anatomy cannot be learned from a
book alone, and no one should attempt to use the present work without at the
same time carefully dissecting the cat. On the other hand, anatomy can
scarcely be learned without descriptions and figures of the structures laid bare
in dissection, so that this or some similar work should be in the hands of any
one attempting to gain a knowledge of anatomy through the dissection of the
cat.

The figures have all been drawn from actual dissections, and have been
carefully selected with a view to furnishing the most direct assistance to the
dissector. It is hoped that no figures are lacking that are required for giving the
students the necessary points of departure for an intelligent dissection of any
part of the body. The fore limb is illustrated somewhat more fully than the hind
limb, because it was thought that the fore limb would usually be dissected first;
the hind limb will be easily dissected, with the aid of the figures given, after
the experience gained in dissecting the fore limb.
As the book is designed to accompany the dissection of the specimen in the
laboratory, it was deemed best to give succinct specific directions for the
dissection of the different systems of organs, together with suggestions as to
methods of preserving and handling the material. These are included in an
appendix.

CONTENTS.

PAGE
The Skeleton of the Cat 1
I. The Vertebral Column 1
Thoracic Vertebræ 1
Lumbar Vertebræ 7
Sacral Vertebræ: Sacrum 8
Caudal Vertebræ 11
Cervical Vertebræ 11
Ligaments of the Vertebral Column 16
II. The Ribs 18
III. The Sternum 20
IV. The Skull 21
Occipital Bone 22
Interparietal 25
Sphenoid 25
Presphenoid 29
Temporal 30
Parietal 36
Frontal 37
Maxillary 39
Premaxillary 41
Nasal 42
Ethmoid 42
Vomer 44
Palatine 45
Lachrymal 46
Malar 47
Mandible 47
Hyoid 49
The Skull as a Whole 49

Cavities of the Skull 57
Joints and Ligaments of the Skull 61
V. The Thoracic Extremities 62
Scapula 62
Clavicle 64
Humerus 64
Radius 67
Ulna 68
Carpus 69
Bones of the Hand 71
Joints and Ligaments of the Thoracic Limbs 73
VI. The Pelvic Extremities 76
Innominate Bones 76
Femur 79
Patella 80
Tibia 80
Fibula 82
Tarsus 82
Bones of the Foot 85
Joints and Ligaments of the Pelvic Limbs 86
The Muscles 93
I. Muscles of the Skin 93
II. Muscles of the Head 96
A. Superficial Muscles 96
B. Deep Muscles 107
a. Muscles of Mastication 107
b. Muscles of Hyoid Bone 112
III. Muscles of the Body 115
1. Muscles of the Back 115
A. Muscles of the Shoulder 115
B. Muscles of the Vertebral Column 123
a. Muscles of the Lumbar and Thoracic Region 126
b. Dorsal Muscles of the Cervical Region 131
C. Muscles of the Tail 136
2. Muscles on the Ventral Side of the Vertebral Column 138

A. Lumbar and Thoracic Regions 138
B. Muscles on the Ventral Side of the Neck 139
3. Muscles of the Thorax 144
A. Breast Muscles (Connecting the Arm and Thorax) 144
B. Muscles of the Wall of the Thorax 148
4. Abdominal Muscles 153
IV. Muscles of the Thoracic Limbs 156
1. Muscles of the Shoulder 156
A. Lateral Surface 156
B. Medial Surface 161
2. Muscles of the Brachium or Upper Arm 164
3. Muscles of the Antibrachium or Forearm 172
Fascia of the Forearm 172
A. Muscles on the Ulnar and Dorsal Side of the
Forearm 173
B. Muscles on the Radial and Ventral Side of the
Forearm 179
4. Muscles of the Hand 184
A. Between the Tendons 184
B. Muscles of the Thumb 184
C. Between the Metacarpals 185
D. Special Muscles of the Second Digit 185
E. Special Muscles of the Fifth Digit 185
V. Muscles of the Pelvic Limbs 186
1. Muscles of the Hip 186
A. On the Lateral Surface of the Hip 186
Fascia of the Thigh 186
B. On the Medial Surface of the Hip 192
2. Muscles of the Thigh 194
3. Muscles of the Lower Leg 203
A. On the Ventral Side 203
B. On the Dorsal and Lateral Surfaces 209
4. Muscles of the Foot 212
A. Muscles on the Dorsum of the Foot 212
B. Muscles on the Sole of the Foot 212
C. Muscles of the Tarsus 215

The Viscera 217
I. The Body Cavity 217
II. Alimentary Canal 221
1. Mouth 221
Glands of the Mouth 223
Teeth 224
Tongue 226
Muscles of the Tongue 228
Soft Palate 229
Muscles of the Soft Palate 230
2. Pharynx 231
Muscles of the Pharynx 232
3. Œsophagus 234
4. Stomach 234
5. Small Intestine 236
6. Large Intestine 237
7. Liver, Pancreas, and Spleen 239
III. Respiratory Organs 243
1. Nasal Cavity 243
2. Larynx 246
Cartilages of the Larynx 247
Muscles of the Larynx 249
3. Trachea 251
4. Lungs 252
Thyroid Gland 254
Thymus Gland 254
IV. Urogenital System 255
1. Excretory Organs 255
Kidneys 255
Ureter 256
Bladder 256
(Suprarenal Bodies) 257
2. Genital Organs 257
A. Male 257
B. Female 263

Muscles of the Urogenital Organs, Rectum, and Anus 268
a. Muscles Common to the Male and Female 268
b. Muscles Peculiar to the Male 271
c. Muscles Peculiar to the Female 272
The Circulatory System 274
I. The Heart 274
II. The Arteries 280
1. Pulmonary Artery 280
2. Aorta 281
A. Thoracic Aorta and its Branches 281
Common Carotid Artery 283
Subclavian Artery 290
B. Abdominal Aorta and its Branches 301
External Iliac Artery and its Branches 309
III. The Veins 315
1. Veins of the Heart 315
2. Vena Cava Superior and its Branches 316
Veins of the Brain and Spinal Cord 324
3. Vena Cava Inferior and its Branches 325
Portal Vein 326
IV. Lymphatic System 330
1. Lymphatics of the Head 331
2. Lymphatics of the Neck 332
3. Lymphatics of the Thoracic Limbs 332
4. Lymphatics of the Thorax and Abdomen 333
5. Lymphatics of the Pelvic Limbs 334
The Nervous System 335
I. The Central Nervous System 336
1. Spinal Cord 336
2. The Brain 339
(1) Myelencephalon 344
(2) Metencephalon 347
(3) Mesencephalon 351
(4) Diencephalon 352
(5) Telencephalon 357

II. The Peripheral Nervous System 369
1. Cranial Nerves 369
I. Olfactory Nerve 369
II. Optic Nerve 369
III. Oculomotor Nerve 369
IV. Trochlear Nerve 370
V. Trigeminal Nerve 370
VI. Abducens 375
VII. Facial Nerve 375
VIII. Auditory Nerve 377
IX. Glossopharyngeal Nerve 378
X. Vagus Nerve 378
XI. Accessory Nerve 382
XII. Hypoglossal Nerve 383
2. Spinal Nerves 383
A. Cervical Nerves 383
The Brachial Plexus 386
B. Thoracic Nerves 393
C. Lumbar Nerves 394
Lumbar Plexus 395
D. Sacral Nerves and Sacral Plexus 399
E. Nerves of the Tail 404
3. Sympathetic System 404
Sense Organs and Integument 409
I. The Eye 409
II. The Ear 415
III. Olfactory Organ 426
IV. Organ of Taste 426
V. Integument 427
Appendix: Practical Directions 429
Index 473

LIST OF ILLUSTRATIONS.

FIG. PAGE
1. Skeleton 2
2. Fourth Thoracic Vertebra 3
3. Fourth Thoracic Vertebra 3
4. Thoracic Vertebræ 5
5. Lumbar Vertebræ 7
6. Sacrum 9
7. Sacrum 9
8. Caudal Vertebra 11
9. Caudal Vertebra 11
10. Cervical Vertebræ 12
11. Sixth Cervical Vertebra 13
12. Atlas 13
13. Axis 15
14. Ligaments of the Odontoid Process 18
15. Rib 19
16. Sternum 20
17. Occipital Bone 22
18. Occipital Bone 22
19. Interparietal 25
20. Sphenoid 25
21. Presphenoid 29
22. Temporal 31
23. Temporal 31
24. Tympanic Bulla 33
25. Petrous Bone 34
26. Frontal 37
27. Maxillary Bone 39
28. Maxillary Bone 39
29. Premaxillary 41

30. Nasal 42
31. Ethmoid and Vomer 43
32. Ethmoid and Vomer 43
33. Palatine 45
34. Lachrymal 46
35. Malar 46
36. Mandible 48
37. Mandible 48
38. Hyoid 49
39. Skull, Dorsal Surface 50
40. Skull, Side View 53
41. Skull, Ventral Surface 55
42. Cavities of Skull 57
43. Skull, Median Section 60
44. Scapula 62
45. Scapula 62
46. Clavicle 64
47. Humerus 65
48. Humerus 65
49. Radius and Ulna 68
50. Radius and Ulna 68
51. Bones of the Hand 70
52. Ligaments of the Elbow 74
53. Ligaments of the Elbow 74
54. Innominate Bone of Kitten 76
55. Innominate Bone 77
56. Femur 79
57. Tibia and Fibula 81
58. Bones of the Foot 83
59. Calcaneus 83
60. Knee-joint 89
61. Knee-joint 89
62. Muscles of the Skin 94
63. Muscles on Dorsal Side of Head 97
64. Muscles of Face 102

65. Ventral Muscles of Thorax, Neck, and Head 109
66. Pterygoid and Palatal Muscles 112
67. Muscles of Tongue, Hyoid, and Pharynx 114
68. First Layer of Body Muscles 117
69. Deep Muscles of the Vertebræ and Ribs 125
70. Dorsal Muscles of Lumbar and Caudal Regions 127
71. Deep Muscles of Neck 135
72. Muscles on the Ventral Surface of the Cervical Vertebræ 143
73. Second Layer of Body Muscles 149
74. Diaphragm 152
75. Lateral Muscles of Arm 158
76. Origin of Lateral Muscles on Scapula 160
77. Medial Muscles of Arm 162
78. Origin of Medial Muscles on Scapula 163
79. Deep Medial Muscles of Arm 167
80. Deep Lateral Muscles of Arm 169
81. Areas of Origin of Muscles on Ventral Surface of Humerus 171
82. Areas of Origin of Muscles on Medial Side of Humerus 171
83. Areas of Origin of Muscles on Dorsal Surface of Left Humerus 171
84. Tendons on Back of Hand 175
85. Deep Muscles of Forearm 177
86. Insertions of Muscles on Radius and Ulna 178
87. Insertions of Muscles on Radius and Ulna 182
88. Mm. Lumbricales, etc. 183
89. Deep Muscles of Palm of Hand 184
90. Lateral Muscles of the Leg 192
91. Medial Muscles of the Leg 197
92. Deep Medial Muscles of Thigh 200
93. Teeth of the Upper Jaw 225
94. Teeth of the Lower Jaw 226
95. Tongue, Epiglottis, etc. 227
96. Muscles of Tongue, Hyoid, and Pharynx 229
97. Stomach 235
98. Colon and Cæcum 238
99. Ileocolic Valve 238

100. Liver 240
101. Liver 240
102. Pancreas and Spleen 242
103. Cartilages of Nose 244
104. Cartilages of Larynx 247
105. Muscles of Larynx 250
106. Bronchi 253
107. Thymus Gland 254
108. Kidney 255
109. Section of Kidney 255
110. Testis 260
111. Male Genital Organs 262
112. Female Urogenital Organs 265
113. Muscles of Urogenital Organs and Anus in Male 270
114. Muscles of Urogenital Organs of Female 272
115. Heart 276
116. Heart 276
117. Inside of Heart 278
118. Vessels of Thorax 282
119. Common Carotid and Internal Jugular 284
120. Branches of External Carotid 288
121. Arteries of Brain 291
122. Vessels and Nerves of the Axilla 295
123. Vessels and Nerves of the Arm 299
124. Palmar Arch 301
125. Cœliac Artery 302
126. Abdominal Blood-vessels 305
127. Medial Vessels and Nerves of the Leg 310
128. Deep Arteries of Foot 314
129. Thoracic Blood-vessels 317
130. Superficial Vessels and Nerves of the Forearm 319
131. Blood-vessels of the Face 322
132. Portal Vein 327
133. Spinal Cord, cranial portion 336
134. Section of Spinal Cord 337

135. Origin of Spinal Nerves 337
136. Cauda Equina, etc. 338
137. Brain, Dorsal View 340
138. Brain, Ventral View 342
139. Diagram of Brain 343
140. Diagram of Brain 343
141. Dorsal View of Midbrain and ’Tween-brain 350
142. Ventral View of Midbrain and ’Tween-brain 352
143. Longitudinal Section of Brain 356
144. Lateral View of Brain 358
145. Diagram of Sulci and Gyri 359
146. Diagram of Sulci and Gyri 361
147. Corpus Callosum 363
148. Fornix, Hippocampus, and Corpus Striatum 364
149. Transverse Section of Brain 366
150. Transverse Section of Brain 366
151. Transverse Section of Brain 366
152. Transverse Section of Brain 367
153. Transverse Section of Brain 367
154. Cranial Nerves 374
155. Nerves of Face 376
156. Cranial Nerves in the Neck 379
157. Sympathetic and Vagus in the Thorax 381
158. Nerves of the Neck 384
159. Brachial Plexus 387
160. Nerves and Vessels of Axilla 389
161. Nerves and Vessels of Forearm 391
162. Lumbar and Sacral Nerves 398
163. Great Sciatic Nerve 401
164. Sympathetic and Vagus in Abdomen 407
165. Nictitating Membrane 410
166. Muscles of Eyeball 411
167. Diagram of Eye 413
168. Cartilage of External Ear 417
169. Muscles of External Ear 419

170. Tympanic Membrane 422
171. Malleus and Incus 423
172. Stapes 424
173. Membranous Labyrinth 425

ANATOMY OF THE CAT.

THE SKELETON OF THE CAT.

The skeleton of the cat consists of 230 to 247 bones exclusive of the
sesamoid bones (44) and the chevron bones (8). These are divided as follows:
head 35-40, vertebral column 52-53, ribs 26, sternum 1-8, pelvis 2-8, upper
extremities 62, lower extremities 54-56. The number of bones varies with the
age of the individual, being fewer in the old than in the young animal, owing to
the fact that in an old animal some bones that were originally separate have
united.

I. THE VERTEBRAL COLUMN. COLUMNA VERTEBRALIS.

The vertebral column, spinal column, or back-bone, consists of a varying
number of separate bones, the vertebræ. At its cranial end are seven vertebræ
(cervical, Fig. 1, c) which are without ribs and support the head; caudad of
these are thirteen rib-bearing vertebræ (thoracic, Fig. 1, m); caudad of these
are seven that are again without ribs (lumbar, Fig. 1, o); these are followed by
three vertebræ (sacral, Fig. 1, x) which are united into a single bone, the
sacrum, which supports the pelvic arch. Following the sacral vertebræ are
twenty-two or twenty-three small ribless vertebræ which support the tail
(caudal, Fig. 1, y).

Fig. 1.—Skeleton of Cat.
a, skull; b, hyoid; c, cervical vertebræ; d, clavicle; e, scapula; f, sternum; g, humerus; h, radius; i,
ulna; j, carpus; k, metacarpus; l, phalanges; m, thoracic vertebræ; n, ribs; o, lumbar vertebræ; p,
innominate bones; q, femur; r, patella; s, fibula; t, tibia; u, tarsus; v, metatarsus; w, phalanges; x,
sacrum; y, caudal vertebræ.

Thoracic Vertebræ. Vertebræ thoracales (Fig. 4).—The thoracic
vertebræ are most typical, and the fourth one of these may therefore be first
described (Figs. 2 and 3). It forms an oval ring which has numerous processes
and surrounds an opening which is the vertebral foramen (a). The ventral one-
third of this ring is much thickened and forms the centrum or body (corpus)
(b) of the vertebra. The centrum is a semicylinder, the plane face of which
bounds the vertebral canal, while the curved surface is concave longitudinally
and is directed ventrad. The dorsal plane surface of the centrum is marked by a
median longitudinal ridge on either side of which is an opening (nutrient
foramen) for a blood-vessel. The ends are nearly plane, the caudal being
slightly concave; they are harder and smoother than the other surfaces. They
may be easily separated in a young specimen as thin plates of bone known as
epiphyses.

Fig. 2.—Fourth Thoracic Vertebra, Cranial Fig. 3.—Fourth Thoracic Vertebra, Side View.
End.
a, vertebral foramen; b, centrum; c, caudal, and d, cranial, costal demifacets; e, radix or pedicle;
f, lamina; g, transverse process; h, cranial articular facet; i, caudal articular facet; j, caudal articular
process; k, spinous process.

At the caudal end of the centrum, at its dorsolateral angle, is a smooth area
on each side continuous with the surface of the epiphysis and bounded
dorsolaterally by a sharp ridge of bone (c). It is a costal demifacet. In
corresponding positions at the cranial end of the centrum are two demifacets
not limited by bony ridges (d). When the centra of two contiguous thoracic
vertebræ are placed together in the natural position the cranial costal
demifacets of one together with the caudal demifacets of the other form two
costal facets (Fig. 4, e), one on each side, and each receives the head of a rib.
The dorsal two-thirds of the vertebral ring forms the vertebral arch which
is continued dorsally into the long, bluntly pointed spinous process (Figs. 2
and 3, k) for attachment of muscles.
The vertebral arch (each half of which is sometimes called a
neurapophysis) rises on each side from the cranial two-thirds of the
dorsolateral angle of the centrum, as a thickened portion, the radix or pedicle
(Figs. 2 and 3, e), which forms the ventral half of the lateral boundary of the
vertebral canal. From the dorsal end of each radix a flat plate of bone, the
lamina (f), extends caudomediad to join its fellow of the opposite side and
form the vertebral arch. Owing to the fact that the radix rises from only the
cranial two-thirds of the centrum there is left in the caudal border of the

vertebral arch a notch bounded by the radix, the lamina, and the centrum.
There is also a slight excavation of the cranial border of the radix. When the
vertebræ are articulated in the natural position, these notches form the
intervertebral foramina (Fig. 4, d), for the exit of the spinal nerves.
At the junction of radix and lamina the arch is produced craniolaterad into a
short process, the transverse process (g), knobbed at the end. On the ventral
face of its free end the transverse process bears a smooth facet, the transverse
costal facet or tubercular facet (Fig. 4, c), for articulation with the tubercle of a
rib.
On the dorsal face of each lamina at its cranial border is a smooth oval area,
the cranial articular facet (superior articular facet of human anatomy) (Figs.
2 and 3, h). Its long axis is oblique and it looks dorsolaterad. The slight
projections of the cranial edge of the laminæ on which the facets are situated
are the inconspicuous cranial articular processes (prezygapophyses).
On the ventral surface of each lamina at the caudal border, near the middle
line is a similar area, the caudal articular facet (inferior articular facet of
human anatomy) (i); these occupy the ventral surfaces of two projections
which form the caudal (inferior) articular processes (postzygapophyses) (j).
These are separated by a median notch. When the vertebræ are in their natural
position the caudal articular facets lie dorsad of the cranial facets and fit
against them. They thus strengthen the joint between contiguous vertebræ,
while permitting slight rotary motion.

Fig. 4.—Thoracic Vertebræ, Side View.
a, spinous processes; b, cranial articular processes; c, transverse costal facets; d, intervertebral
foramina; e, costal facets; f, accessory processes; g, mammillary processes; h, caudal articular
processes.

Differential Characters of the Thoracic Vertebræ (Fig. 4).—Following
the thoracic vertebræ caudad there is to be seen a gradual increase in the size
of the centra brought about by an increase in their craniocaudal and transverse
measurements. The dorsoventral measurements remain nearly the same. The
costal facets (Fig. 4, e) shift caudad so that on the eleventh, twelfth, and
thirteenth thoracic vertebræ each lies entirely on the cranial end of its centrum,
while the caudal end of the centrum immediately preceding is not marked by
any part of it. In the eleventh thoracic vertebra each costal facet is usually still
confluent with the smooth cranial end of the centrum. In the twelfth vertebra
the facets are separated by smooth ridges from the cranial end of the vertebra,
while in the thirteenth vertebra they are separated by rough ridges.
The spinous processes (a) of the first four are of about the same length. They
then decrease in length to the twelfth, while the twelfth and thirteenth are
slightly longer than the eleventh. The first ten slope more or less caudad, while
the spinous process of the tenth (anticlinal) vertebra is vertical and those of
the eleventh, twelfth, and thirteenth point craniad.
Each of the transverse processes of the seventh thoracic vertebra shows a
tendency to divide into three tubercles; one of these is directed craniad, the
mammillary process (or metapophysis), one caudad, the accessory process (or
anapophysis), while the third (transverse process proper) looks ventrad and
bears the transverse costal facet. This division becomes more prominent in the
succeeding vertebræ, being most marked in the ninth and tenth. In the
eleventh, twelfth, and thirteenth vertebræ the mammillary (g) and accessory (f)
processes are very pronounced, while the transverse costal facet and that part
of the transverse process which bears it have disappeared. The ribs of the
eleventh, twelfth, and thirteenth vertebræ are thus attached to their respective
centra by their heads alone.
The cranial articular processes (b) are prominent on the first two thoracic
vertebræ; back of these they are very small as far as the eleventh, so that the
articular facets seem to be borne merely upon the dorsal surface of the cranial
edge of the laminæ. In the eleventh, twelfth, and thirteenth the cranial articular
processes are large, bearing the articular facets on their medial surfaces, while
the mammillary processes appear as tubercles on the lateral surfaces of the
articular processes. The caudal articular processes (h) are prominent in the first
thoracic, then smaller until the tenth is reached; in the tenth, eleventh, twelfth,
and thirteenth they are large and their facets are borne laterally, so as to face
the corresponding cranial facets. Thus from the tenth to the thirteenth thoracic
vertebra rotary motion is very limited, owing to the interlocking of the articular
processes.

The Lumbar Vertebræ. Vertebræ lumbales (Fig. 5).—The last thoracic
vertebræ form the transition to the typical lumbar vertebræ. These are larger
than the thoracic vertebræ. The centra are of the form of the centra of the
thoracic vertebræ, and increase in length to the sixth, but the seventh is about
the length of the first. They increase in breadth to the last.

Fig. 5.—Lumbar Vertebræ.
a, cranial articular processes; b, mammillary processes; c, caudal articular processes; d,
accessory processes; e, transverse processes; f, spinous processes.

The cranial articular processes (Fig. 5, a) are prominent and directed
craniodorsad; they have the facets on their medial surfaces, while their
dorsolateral surfaces bear the mammillary processes (b) as prominent
tubercles. The caudal articular processes (c) are likewise large; their facets look
laterad. When the vertebræ are articulated they are received between the
medially directed cranial processes.
The accessory processes (d) are well developed on the first vertebra,
diminish in size to the fifth or sixth, and are absent on the seventh and
sometimes on the sixth.
The transverse processes (more properly pseudo-transverse processes) (e)
arise from the lateral surface of the centra; are flat and are directed
ventrocraniolaterad. The first is small, and they increase in length and breadth
from the first to the sixth, those of the last being slightly smaller than in the
sixth. The free ends of the last four are curved craniad.
The spinous processes (f) are flat and directed craniodorsad. They increase
in length to the fifth and then decrease. The first five are knobbed at the end. In
a dorsal view the spinous process and cranial articular processes of each
vertebra are seen to interlock with the caudal articular processes and accessory
processes of the preceding vertebra in such a way as to prevent rotary motion,

and this arrangement may be traced craniad as far as the eleventh thoracic
vertebra.
Sacral Vertebræ. Vertebræ sacrales (Figs. 6 and 7).—The three sacral
vertebræ are united in the adult into a single bone, the os sacrum, or sacrum.
In a kitten the three vertebræ are separate, while in an animal almost mature
the first two are united and the third is still separate. The sacrum lies between
the last lumbar and the first caudal vertebræ and articulates laterally with the
two innominate bones. It is pyramidal, with the base of the pyramid directed
craniad, and is perforated by a depressed longitudinal canal, the sacral canal,
which is a continuation of the vertebral canal, and by four large foramina
dorsally and four ventrally. It may be described as having a cranial end or base
and a caudal end or apex, a dorsal, a ventral, and two lateral surfaces.
The base is slightly oblique and presents a smooth transversely oval
articular facet (the cranial end of the centrum of the first sacral vertebra), for
articulation with the centrum of the last lumbar vertebra. Dorsad of this is the
sacral canal, more depressed than the vertebral arch craniad of it. It supports a
spinous process (Fig. 6, a) which is directed dorsad. At the junction of its
lamina and radix is seen the prominent cranial articular process (b) with
sometimes slight indications of a mammillary process on its lateral surface.
Laterad of the articular facet is seen the cranial face of the expanded “pseudo-
transverse process” (c) of the first sacral vertebra. The ventral border of the
base is concave ventrad, forming an arc of about 120 degrees. The apex shows
the caudal end of the last sacral centrum. Dorsad of this are the vertebral arch
with a very short spinous process (a′), and the caudal articular processes (d).
Laterad of the centrum appears the laterally directed thin transverse process
(e).

Fig. 6.—Sacrum, Dorsal Surface. Fig. 7.—Sacrum, Ventral Surface.
Fig. 6.—1, 2, 3, the three sacral vertebræ. a, a′, spinous processes; b, cranial articular process of
first sacral vertebra; c, expanded transverse process of first sacral vertebra; d, caudal articular
processes of third sacral vertebra; e, transverse processes of third sacral vertebra; f, tubercles
formed by fused articular processes of the vertebræ; g, dorsal (or posterior) sacral foramina.
Fig. 7.—1, 2, 3, the three sacral vertebræ. a, the transverse ridges formed by the union of the
centra; b, cranial articular processes of first vertebra; c, transverse process of first vertebra; d,
caudal articular processes of third vertebra; e, transverse processes of third sacral vertebra; f, f′,
ventral (or anterior) sacral foramina; g, notch which helps to form third ventral sacral foramen.

The ventral or pelvic surface (Fig. 7) is smooth, concave craniad, convex
caudad, and crossed by two transverse ridges (a) along which are seen the
ossified remains of the intervertebral fibro-cartilages. At the ends of the first
ridge is a pair of nearly circular ventral (or anterior) sacral foramina (f) for
the passage of sacral nerves. At the end of the second ridge is a pair of ventral
sacral foramina (f′), smaller than the first pair and continued laterocaudad into
shallow grooves for the ventral rami of the sacral nerves. That portion of the
bone lying laterad of a line joining the medial borders of these two pairs of
foramina is known as the lateral mass of the sacrum and is composed of the
fused transverse processes of the sacral vertebræ. At the caudal margin of the
ventral surface there is a notch between the lateral mass and the centrum (g).
When the caudal vertebræ are articulated, this notch helps to form a foramen
for the third sacral nerve.
The dorsal surface (Fig. 6) is narrower at its cranial end than is the ventral
surface. Its cranial border bears laterally a pair of cranial articular processes (b)
with their medially directed facets and between them it is concave, so that a

large dorsal opening is left into the vertebral canal between the last lumbar
vertebra and the sacrum. Caudad of the articular processes are two pairs of
tubercles (f). These are the fused cranial and caudal articular processes of the
sacral vertebræ. Caudad of them are the caudal articular processes of the last
sacral vertebra (d). Craniolaterad of the middle and cranial tubercles are dorsal
(posterior) sacral foramina (g) for the transmission of the dorsal rami of the
sacral nerves. Three spinous processes (a) appear between these rows of
tubercles. They decrease in height caudad. That part of the surface included
between the spinous process and the tubercles is made up of the fused laminæ
of the sacral vertebræ. That part between the tubercles and a line joining the
lateral margins of the dorsal (posterior) sacral foramina is formed by the fused
radices of the sacral vertebræ.
The lateral surface may be divided into two parts. Craniad is a large rough
triangular area with equal sides and with one of its angles directed
ventrocraniad. It is the lateral face of the pseudo-transverse process of the first
sacral vertebra (Fig. 6, c). A smooth curved surface (the auricular facet) along
its ventral edge articulates with the ilium, while the dorsal portion is rough for
attachment of ligaments. Caudad is the narrow longitudinal triangular area of
the lateral faces of the fused transverse processes of the second and third sacral
vertebræ.
Caudal Vertebræ. Vertebræ caudales (Fig. 1, y, and Figs. 8 and 9).—The
caudal vertebræ (21-23 in number) decrease gradually in size to the last one.
Caudad they become longer and more slender and lose the character of
vertebræ. They become finally reduced to mere centra,—slender rods of bone
knobbed or enlarged at their two ends (Fig. 8). The last one is more pointed
than the others and bears at its caudal end a small separate conical piece, the
rudiment of an additional vertebra.

Fig. 8. Fig. 9.
Fig. 8.—Caudal Vertebra, from near the caudal end of the tail.
Fig. 9.—Fourth Caudal Vertebra, ventral view. a, transverse processes;
b, cranial articular processes; c, hæmal processes; d, chevron bone.

The parts of a typical vertebra—vertebral arch, transverse processes, cranial
and caudal articular processes—may be recognized in the vertebræ as far back
as the eighth or ninth. The transverse processes (Fig. 9, a) are directed caudad
and decrease rapidly in length. They are very small on the ninth vertebra, but
may be recognized for a considerable distance back of this. The spinous
process disappears at about the fourth caudal vertebra, and the vertebral canal
becomes gradually smaller caudad, until on the eighth or ninth vertebra it
becomes merely a groove open dorsad.
Caudad of the third vertebra for a considerable distance, each centrum bears
on each lateral face at its cranial end a short anterior transverse process, and
on its ventral face at its cranial end a pair of rounded tubercles, hæmal
processes (c), which articulate with a small pyramidal chevron bone (d) so as
to enclose a canal. These structures disappear caudad.
Cervical Vertebræ. Vertebræ cervicales (Fig. 10).—The cervical vertebræ
number seven. The first two of these are so peculiar as to require a separate
description, so that the last five may be first considered.
Passing craniad from the fourth thoracic vertebra to the third cervical there
is a gradual transition. The centra of the cervical vertebræ are broader and
thinner than those of the thoracic vertebræ, while the vertebral arches and
vertebral canal are larger (Fig. 11). The caudal end of each centrum is concave

and looks dorsocaudad when the centrum is held with its long axis horizontal.
The cranial end of the centrum is convex and looks ventrocraniad when the
centrum is horizontal. These peculiarities are more marked in the third vertebra
than in the seventh. The spinous processes grow rapidly shorter as we pass
craniad; the fifth, sixth, and seventh are directed dorsocraniad, the third and
fourth dorsad.

Fig. 10.—Cervical Vertebræ, Side View.

a, spinous processes; b, cranial articular processes; c, caudal articular facet; d, intervertebral
foramina; e, transverse process proper; f, processus costarius; g, wing of the atlas; h, dorsal arch of
the atlas; i, atlantal foramen.

The caudal articular processes are situated at the junction of the radices and
laminæ; their facets (Fig. 10, c) look ventrocaudolaterad. The cranial articular
processes also become more prominent than is the rule in the thoracic
vertebræ; they are borne at the junction of radix and lamina and have their
facets (Fig. 11, b) directed dorsomediad. The cranial and caudal articular
processes of each side are joined by a prominent ridge which is most
pronounced in the third, fourth, and fifth vertebræ.
The characteristic feature of the cervical vertebræ is their transverse process,
so called. In each of them it arises by two roots, one from the centrum and one

from the arch. These two roots, which are broad and thin, converge and unite
so as to enclose a canal or foramen, the foramen transversarium (Fig. 11, g),
for the vertebral artery. Laterad of the foramen the two parts of the process are,
in the third cervical, almost completely united, the dorsal part being, however,
distinguishable as a tubercle at the caudolateral angle of the thin plate formed
by the process as a whole. This dorsal component is the transverse process
proper (Figs. 10 and 11, e), while the ventral portion represents a rib, and is
hence known as the processus costarius (f). The expanded plate formed by the
union of these two processes is directed nearly ventrad and somewhat craniad
in the third, fourth, and fifth vertebræ. The two components of the process
gradually separate as we pass caudad; in the fourth and fifth vertebræ the part
which represents the transverse process proper forms a very prominent tubercle
at the caudolateral angle of the plate formed by the processus costarius. In the
sixth (Fig. 11) the two parts are almost completely separated; the dorsal part
forms (e) a slender knobbed process, while the processus costarius is divided
into two portions (f and f′) by a broad lateral notch. In the seventh the ventral
part (processus costarius) is usually quite lacking, though sometimes
represented by a slender spicule of bone. In the former case the foramen
transversarium is of course likewise lacking.

Fig. 11.—Sixth Cervical Vertebra, Fig. 12.—Atlas, Ventral View.
Cranial End.

Fig. 11.—a, spinous process; b, cranial articular facet; c, lamina; d, radix or pedicle; e, transverse
process proper; f, f′, processus costarius; g, foramen transversarium; h, centrum; i, vertebral canal.
Fig. 12.—a, ventral arch; b, tuberculum anterius; c, lateral masses; d, transverse processes; e,
cranial articular facets; f, groove connecting the foramen transversarium with the atlantal foramen;
g, atlantal foramen; h, caudal articular facets.

The Atlas (Fig. 10, 1; Fig. 12).—The first cervical vertebra or atlas has
somewhat the form of a seal ring. The centrum is absent; it has united with the
second vertebra to form the odontoid process or dens. Its place is taken in the
atlas by a narrow flat arch of bone, narrower at the ends than in the middle, the
ventral arch (Fig. 12, a) of the atlas. This connects the lateral, thicker portions
of the ring ventrally and bears on its caudal margin a blunt tubercle
(tuberculum anterius, Fig. 12, b). Laterally the ring is thickened, forming
thus the lateral masses (c) which are continued into the broad thin transverse
processes (Fig. 10, g; Fig. 12, d). Each lateral mass bears at its cranial end on
its medial surface a concave, pear-shaped facet, cranial (or superior) articular
facet, (Fig. 12, e) for articulation with the condyles of the skull. These facets
look craniomediad. Dorsad of each is a foramen, the atlantal foramen (Fig. 10,
i; Fig. 12, g), which pierces the dorsal arch at its junction with the lateral mass.
Caudal to the facet, on the medial face of each lateral mass, within the
vertebral canal, is a tubercle. To the two tubercles are attached the transverse
ligament (Fig. 14, b) which holds in place the odontoid process (dens) of the
axis.
That part of the lateral mass which bears the articular facet projects craniad
of the dorsal arch and is separated by a deep triangular notch from the
transverse process. Along the bottom of this notch runs a groove (Fig. 12, f),
convex craniad, which connects the cranial end of the foramen transversarium
and the atlantal foramen. The vertebral artery passes along it. The foramen
transversarium is circular. It is bounded laterally by the lateral masses, and
dorsally by the dorsal arch.
The dorsal arch (Fig. 10, h) is two to three times as broad as the ventral, has
a thick convex cranial border with a median notch, and a thin concave caudal
border.

Fig. 13.—Axis or Epistropheus, Side View.

a, odontoid process or dens; b, cranial articular
facets; c, spinous process; d, caudal articular
facet; e, transverse process; f, foramen
transversarium.

The caudal articular facets (Fig. 12, h) are borne by the caudal ends of the
lateral masses. They are slightly concave, triangular, and look caudomediad, so
that their dorsal borders form with the caudal border of the dorsal arch nearly a
semicircle. The transverse processes are flat and directed laterad. The attached
margin of each is about two-thirds the length of the thinner free margin. The
somewhat thicker caudal end of the transverse process projects further caudad
than any other part of the vertebra and is separated by a slight notch from the
caudal articular facet. From the bottom of this notch the foramen
transversarium extends craniad and opens at the middle of the ventral face of
the transverse process.
Epistropheus or Axis (Fig. 10, 2; Fig. 13).—The second cervical vertebra
(epistropheus or axis) is not so wide as the atlas but is much longer. Craniad
the centrum is continued into a slender conical, toothlike projection, the dens
or odontoid process (Fig. 13, a) which represents the centrum of the atlas. The
dens is smooth below for articulation with the ventral arch of the atlas. It is
rougher above. Laterad of the dens the centrum bears a pair of large cranial
articular facets (b) which look craniolaterad. These have each the form of a
right-angled triangle with rounded angles, one side of the triangle being nearly
horizontal. Each is separated from the articular face of the dens by a roughened
groove. The spinous process (c) runs the length of the vertebral arch. It extends
craniad of the vertebral arch nearly as far as the dens, as a flat rounded
projection. Caudad of the vertebral arch it projects for a short distance as a
stout triangular spine. The caudal articular facets (d) are borne on thickenings
of the caudolateral portions of the arch; they face almost directly ventrad. The
transverse process (e) is slender and triangular and directed nearly caudad. Its
apex reaches no farther than the caudal or articular face of the centrum. Its
base is traversed by the foramen transversarium (f).
Differential Characters of the Cervical Vertebræ.—It is possible to
identify each of the cervical vertebræ:
The first by the absence of the centrum.
The second by the dens or odontoid process.
The third by the small spinous process and slightly marked tubercle of the
transverse process, and by a median tubercle on the cranial border of the
vertebral arch.

The fourth by the spinous process directed dorsad, and the short thick
tubercle of the transverse process not trifid.
The fifth by the spinous process directed craniad, and the more slender
spine-like tubercle of the transverse process not trifid.
The sixth by the trifid transverse process.
The seventh by the long spinous process and the slender simple transverse
process, and by the usual absence of the foramen transversarium.

LIGAMENTS OF THE VERTEBRAL COLUMN.

Fibro-cartilagines intervertebrales.—The separate vertebræ (except the
atlas and axis) are united by the disk-shaped intervertebral fibro-cartilages,
which are situated between the centra of the vertebræ. Each consists of a
central pulpy portion and a fibrous outer portion, covered by strong
intercrossing tendinous fibers which unite with the periosteum of the vertebræ.
Ligamentum longitudinale anterius.—On the ventral face of the centra of
the vertebræ, from the atlas to the sacrum, lies a longitudinal ligament, the
anterior longitudinal ligament. It is very small, almost rudimentary, in the
cervical region: large and strong in the thoracic and lumbar regions.
Ligamentum longitudinale posterius (Fig. 14, a).—A corresponding
ligament (posterior longitudinal ligament) lies on the dorsal surface of the
centra (therefore within the vertebral canal). It is enlarged between each pair of
vertebræ and closely united to the intervertebral fibro-cartilages.
Ligamentum supraspinale.—Between the tips of the spinous processes of
the thoracic and lumbar vertebræ extend ligamentous fibers. They are not
united to form a distinct band, and can hardly be distinguished from the
numerous tendinous fibers of the supraspinous muscles. Together they
represent the supraspinous ligament. From the tip of the spinous process of
the first thoracic vertebra to the caudal end of the spine of the axis extends a
slender strand representing the ligamentum nuchæ or cervical supraspinous
ligament. It is imbedded in the superficial muscles of this region, some of
which take origin from it.
Ligamentous fibers are also present between the spinous processes of the
vertebræ (ligamenta interspinalia): between the transverse processes
(ligamenta intertransversaria), and between the vertebral arches (ligamenta
flava).
Capsulæ articulares.—The joints between the articular processes are
furnished with articular capsules attached about the edges of the articular

surfaces. These are larger and looser in the cervical region.
Atlanto-occipital Articulation.—The joint between the atlas and the
occipital condyles has a single articular capsule, which is attached about the
borders of the articular surfaces of the two bones. This capsule is of course
widest laterally, forming indeed two partially separated sacs, which are,
however, continuous by a narrow portion across the ventral middle line. This
capsule communicates with that which covers the articular surface of the dens,
and through this with the capsule between the atlas and axis. That portion of
the capsule which covers the space between the ventral arch of the atlas and
the occipital bone represents the anterior atlanto-occipital membrane; it is
strengthened by a slender median ligamentous strand. The posterior atlanto-
occipital membrane covers in the same way the space between the dorsal arch
of the atlas and the dorsal edge of the foramen magnum. In it a number of
different sets of fibers, with regard to direction and to degree of development,
may be distinguished; these have sometimes been considered separate
ligaments.
The lateral ligaments of the atlas begin at the lateral angle of the cranial
margin of the atlas, at about the junction of its dorsal and ventral arches, and
pass cranioventrad to the jugular processes.
Articulation between the Axis and Atlas.—The articular capsule is large
and loose, being attached to dorsal and ventral borders of the atlas, about the
articular surfaces of the axis, and to the cranial projection of the spine of the
atlas. It also passes craniad along the ventral side of the dens and
communicates here with the capsule of the atlanto-occipital articulation. In the
dorsal part of the capsule a short strong ligamentous strand is developed,
connecting the caudal border of the dorsal arch of the atlas with the tip of the
cranial projection of the spinous process of the axis.

Fig. 14.—Ligaments of the Odontoid Process or Dens.

First three cervical vertebræ and base of the skull, with dorsal surface
removed. a, ligamentum longitudinale posterius; b, transverse ligament of
the atlas; c, ligamenta alaria; d, odontoid process; e, occipital condyles; 1,
2, 3, the first three cervical vertebræ; 4, basal portion of the occipital bone.

The dens or odontoid process is held in place by the transverse ligament
(Fig. 14, b) of the atlas, which passes across the process as it lies within the
vertebral canal of the atlas. The transverse ligament is attached at its two
ends to the medial surface of the sides of the atlas at about the region where
the dorsal and ventral arches of the atlas unite.
From the cranial end of the odontoid process the two ligamenta alaria
(Fig. 14, c) diverge craniolaterad to the rough ventromedial angle of the
condyles of the occipital bone.

II. RIBS. COSTÆ (Figs. 1 and 15.)

The cat has thirteen pairs of ribs. One of the fifth pair (Fig. 15) may be
taken as typical. It is a curved flattened rod of bone attached at its dorsal
end to the vertebral column, and at its ventral end to a cartilage (costal
cartilage, Fig. 15, f) which serves to unite it to the sternum.
The most convex portion of the bone is known as the angle (e). Each rib
presents a convex lateral and a concave medial surface, a cranial and a

caudal border. The borders are broad dorsad and narrow ventrad, while the
surfaces are narrow dorsad and broad ventrad. The rib has thus the
appearance of having been twisted.
The rib ends dorsad in a globular head or capitulum (a), by which it
articulates with the costal demifacets of two contiguous thoracic vertebræ.
Between the capitulum and angle on the lateral surface is an elevated area,
the tubercle, marked by the smooth tubercular facet (c) for articulation with
the transverse process of a vertebra. The constricted portion between the
head and tubercle is known as the neck (collum) (d). The angle is marked
by a projecting process (e) (angular process) on its lateral border, for
attachment of a ligament.

Fig. 15.—Fifth Rib of Left Side,
Cranial View.
a, head; b, tubercle; c, tubercular facet;
d, neck; e, angle, with angular process; f,
cartilage.

The ribs increase in length to the ninth (the ninth and tenth are of the
same length) and then decrease to the last. They decrease in breadth behind
the fifth. The first is nearly in a dorsoventral plane, while the others have
their dorsal ends inclined slightly craniad.
The tubercles become less prominent as we
pass caudad and are absent on the last two or
three ribs, which do not articulate with the
transverse process.
The first nine ribs (true ribs or costæ veræ)
are attached separately to the sternum by their
costal cartilages. The last four (false ribs or costæ
spuriæ) are not attached separately to the
sternum. The costal cartilages of the tenth,
eleventh, and twelfth are united to one another at
their sternal ends. They may be united also to the
ninth costal cartilage or to the sternum by a
common cartilage of insertion, or they may be
quite free from the sternum. The thirteenth costal
cartilages are free (floating ribs).
Ligaments of the Ribs.—The articular
surfaces between the head of the rib and the
centra, and between the tubercle and the
transverse process of the vertebra, have each an
articular capsule. There are also a number of
small ligamentous bands from the tuberosity and
the neck of the rib to the transverse process of the
vertebra.

III. STERNUM. (Fig. 16.)
Fig. 16.—Sternum, Ventral
The sternum consists of three portions, a View.
cranial piece or manubrium (a), a caudal piece a, manubrium; b, the separate
or xiphoid process (c), and a middle portion or pieces forming the body; c, bony
body (corpus), which is divided into a number of part of the xiphoid process (the
expanded cartilaginous portion
segments (b). not being shown); d, facet for
To the sternum are united the ventral ends of attachment of first rib.
the first nine ribs. It thus forms the median ventral boundary of the thorax.

Since the thorax decreases in dorsoventral measurement craniad, the long
axis of the sternum is inclined from its caudal end dorsocraniad, and if
continued would strike the vertebral column in the region of the first
cervical vertebra.
The manubrium (a) makes up about one-fifth the whole length of the
sternum and projects craniad of the first rib. It has the form of a dagger and
presents a dorsal surface and two lateral surfaces, the latter uniting ventrad
to form a sharp angle. In the middle of the lateral surface near the dorsal
margin is an oval articular surface (d) borne on a triangular projection. It
looks caudodorsad and is for the first costal cartilage.
The caudal end articulates with the body by a synchondrosis and presents
a slightly marked oval facet on each side for the second costal cartilage.
The body consists of six cylindrical pieces (b) enlarged at their ends and
movably united by synchondroses. They increase in breadth from the first,
and decrease slightly in length and thickness. At the caudal end of each near
its ventral border there is a pair of facets looking caudolaterad. They are for
the costal cartilages.
The xiphoid process (c) is a broad thin plate of cartilage at its caudal end;
bony and cylindrical at its cranial end. It is attached by its base to the last
segment of the body by a considerable cartilaginous interval, while the
opposite end is free and directed caudoventrad.
The cartilage of the ninth rib is attached to the lateral face of the cartilage
between the xiphoid and the body, and just caudad of this the common
cartilage of insertion of the tenth, eleventh, and twelfth costal cartilages is
attached, if present.

IV. THE SKULL.

The bones of the head consist of the skull proper together with a number
of separate bones forming part of the visceral skeleton; these are the lower
jaw, the hyoid, and the ear-bones.
The skull proper is considered as divided into cranial and facial
portions. The former includes all the bones which take part in bounding the
cranial cavity or cavity of the brain; the latter includes the bones which
support the face.
The cranial portion of the skull includes all that part enclosing the large
cavity which contains the brain. For convenience this portion may be

considered as made up of three segments, each of which forms a ring
surrounding a part of the cranial cavity. The first or caudal segment or ring
consists of the occipital bone (with the interparietal) surrounding the
foramen magnum. The second segment consists of the sphenoid ventrad, the
parietals laterad and dorsad. Between the first and second segments are
intercalated laterally the temporal bones containing the auditory organ. The
third segment or ring consists of the presphenoid ventrad, of the frontals
laterad and dorsad. The cranial opening of this ring is closed by the lamina
cribrosa of the ethmoid.
The cranial portion of the skull therefore contains eleven separate bones:
one occipital, one interparietal, two temporals, one sphenoid, two parietals,
one presphenoid, two frontals, and one ethmoid.
The facial portion of the skull is much smaller than the cranial, and lies
craniad of the latter; it encloses the nasal cavity. It contains the following
thirteen bones: two palatines, one vomer, two maxillaries, two lachrymals,
two premaxillaries, two nasals, two malar or zygomatic bones. The two
halves of the mandible or lower jaw are frequently included in the facial
portion of the skull, making in all fifteen separate bones in this part of the
skull.
In the following the bones of the skull are first described separately, then
an account is given of the skull as a whole.
Occipital Bone. Os occipitale (Figs. 17 and 18).—The occipital bone
forms the most caudal portion of the cranium, entering into the formation of
its caudal wall and of its base. It connects the cranium with the vertebral
column and surrounds a large opening, the foramen magnum (d), by
means of which the cranial cavity communicates with the vertebral canal.

Fig. 17.—Occipital Bone, Caudal or Outer Fig. 18.—Occipital Bone, Inner Surface.
Surface.

a, basilar portion; b, lateral portions; c, squamous portion; d, foramen magnum; e, occipital
condyles; f, jugular processes; g, jugular notch; h, lambdoidal ridge; i, external occipital crest; j,
external occipital protuberance.

In young kittens four portions may be distinguished in this bone. These
are, a basal portion (the basioccipital bone), two lateral portions (the
exoccipital bones), and a dorsal portion (the supraoccipital bone). These
four bones remain separate through life in many lower vertebrates. In the
adult cat they are completely united into a single bone, but it is convenient
to describe this bone as made up of four parts: a basal portion (a) (pars
basilare), corresponding to the basioccipital, two lateral portions (b)
(partes laterales), corresponding to the exoccipitals, and a squamous
portion (c) (squama occipitalis) corresponding to the supraoccipital.
The basilar portion (a) as seen from the dorsal or ventral surface is
oblong and flattened. It is broadest at the junction of its middle and last
thirds, and tapers toward both ends. It presents a cranial end and a caudal
end, a dorsal, a ventral, and two lateral surfaces. Its caudal end, which helps
to form the ventral boundary of the foramen magnum, is concave from side
to side. The cranial end is transversely elongate, about five times as broad
as high, pointed laterally and roughened for attachment to the caudal end of

the body of the sphenoid, which has a corresponding form. The joint is a
synchondrosis.
The dorsal surface is concave from side to side, forming a longitudinal
groove in which rest the pons and medulla. The concavity is more
pronounced caudad, where the bone is thinner at its middle.
The ventral surface is marked by three parallel longitudinal ridges. One
of them is median and expands caudad into a smooth triangular elevated
area which extends to the foramen magnum. The other two ridges run near
the lateral edges of the bone. Between them and the median ridge the
surface is smooth and is depressed caudad. Laterad of each lateral ridge is a
rough triangular surface overlaid in the natural state by the medial edge of
the tympanic bulla.
The lateral surfaces are smooth and sharp and abut against the petrous
portion of the temporal bone. They pass into the lateral portions of the
occipital caudad.
The lateral portions (b) of the occipital arise from the caudal margin of
the basilar portion in the transverse plane; a short distance laterad of the line
of junction they turn dorsad at an angle of nearly ninety degrees. They form
the lateral boundaries of the foramen magnum and pass dorsally into the
squamous portion.
The external surface of each presents an elongated elevated spirally
curved surface, the occipital condyle (c), for articulation with the atlas. A
small part of each condyle is formed from the basal portion. The two
condyles are separated from one another ventrally by a narrow notch, and
each extends (laterad) along the border of the foramen magnum to a point
slightly dorsad of the transverse diameter of the latter.
Laterad of each condyle the bone is elevated into a blunt triangular
projection, the jugular process (f), which covers the caudal end of the
tympanic bulla. Between the jugular process and the condyle is a deep
depression.
The internal surface (Fig. 18) is concave dorsoventrally, following the
outline of the foramen magnum. It is convex from side to side. It is smooth
except at its outer margin, which is rough for articulation with the mastoid
portion of the temporal bone. The cranial face of the jugular process (f)
shows a rough concavity for the reception of the bulla tympani. Mediad of
the jugular process is a notch (jugular notch) (g) which when the bones are
articulated forms part of the boundary of the jugular foramen. Mediad of

this notch is a foramen which forms one end of the hypoglossal canal. It
passes dorsocaudad into the cranial cavity and transmits the hypoglossal
nerve. Dorsad of the hypoglossal canal is the cranial opening of the
condyloid canal, which passes caudad and opens just craniad of the dorsal
end of the condyle. It transmits a vein. The outer border of this portion is
rough for articulation with the petrous and mastoid portions of the temporal.
The squamous portion (c) has the form of a sector of a circle whose arc
is a little more than ninety degrees. The central angle of the sector is
truncated and bounds the foramen magnum dorsally. The arc of the sector
forms the dorsal margin of the bone, while along the radii it passes into the
lateral portions. Its dorsal portion is thick and porous; its ventral portion
near the foramen magnum is thin and compact.
The external surface (Fig. 17) is marked by a prominent ridge, the
lambdoidal ridge (h), parallel with the dorsal border and near to it. The
narrow portion of the outer surface that lies dorsad of the ridge forms an
angle of about ninety degrees with the remainder of the surface.
A median crest (i) extends ventrad from the middle of the lambdoidal
ridge toward the foramen magnum; this is the external occipital crest. At
its junction with the lambdoidal ridge it is elevated into a tubercle, the
external occipital protuberance (j).
The inner surface (Fig. 18) presents depressions for the convolutions of
the cerebellum.
The dorsal border is thick and rough for articulation with the parietals
and interparietal. The ventral border abuts on the foramen magnum and is
thin and smooth.
Interparietal Bone. Os interparietale (Fig. 19).—This is a small
triangular bone lying between the parietals, with its apex directed craniad,
and its base in contact with the squamous portion of the occipital.
Its dorsal surface is arrow-shaped and has its posterior border notched. It
is marked by a median crest (part of the sagittal crest) which is continued
craniad from the middle of the lambdoidal crest.
The ventral surface is irregularly triangular, smooth, and concave. The
three borders are rough for articulation with the parietals and occipital.

Fig. 19.—Interparietal Fig. 20.—Sphenoid Bone, Dorsal or Internal Surface.
Bone, Outer Surface.

Fig. 19, showing the sagittal crest running craniocaudad across its middle.
Fig. 20.—a, body; b, wings; c, pterygoid process; d, tuberculum sellæ; e, dorsum sellæ; f, sella
turcica; g, notch which aids in forming the foramen lacerum; h, longitudinal groove of alisphenoid;
i, notch which aids in forming the orbital fissure; j, foramen rotundum; k, foramen ovale.

Sphenoid Bone. Os sphenoidale (Fig. 20).—The sphenoid bone of man
is represented in the cat by two entirely distinct bones,—one cranial, the
other caudal. The cranial portion may be designated as the presphenoid
(Fig. 21); the caudal part will be described as the sphenoid (proper) (Fig.
20).
The sphenoid bone in the kitten is in three parts: a central portion, the
basisphenoid, and two lateral portions, the alisphenoids. In many lower
vertebrates these three bones are permanently distinct, but in the adult cat
they are united to form the sphenoid bone. To these there is added a fourth
element, separate in many vertebrates as the pterygoid bone. The sphenoid
may thus be described as composed of a central portion, the body (a)
(basisphenoid), and of two thin expanded wings (b) (alisphenoids, alæ
magnæ of the human sphenoid); each of which has arising from it a thin
curved process, the pterygoid process (c), directed craniad and largely
made up of the pterygoid bone.
The body of the sphenoid (a) lies in the middle line of the base of the
skull. It is wedge-shaped, with the converging sides of the wedge directed
laterad and its apex pointed craniad.

It has six surfaces, of which the dorsal and a part of the laterals look into
the cranial cavity. The cranial end articulates with the body of the
presphenoid, and the caudal with the body of the occipital.
The dorsal surface is triangular, with one apex of the triangle truncated,
elevated, and directed craniad. This elevation is the tuberculum sellæ (d).
Just caudad of the middle the surface presents a rectangular elevation with
rounded angles, the dorsum sellæ (e). The cranial end of the dorsum sellæ
presents at each dorsolateral angle a very small smooth tubercle which
represents one of the posterior clinoid processes of man. Between this
elevation and the elevated cranial end of this surface there is a deep
excavation, the sella turcica (f), in which in the natural state is lodged the
hypophysis. Near the cranial end of the sella is a small foramen, probably
nutrient. At the caudal end of the body a slight notch (g) separates it from
the wing: this notch forms a part of the foramen lacerum. Against this
notch fits the apex of the petrous bone, and from it a groove (carotid
groove) is continued mediocraniad to the sella turcica.
The ventral surface (Fig. 41, 3) is triangular, smooth, and nearly flat; it is
marked by a median ridge which is the continuation craniad of the ridge on
the ventral face of the basilar portion of the occipital.
Its caudal angles are separated from the rest of the bone by sharp
triangular elevations, laterad of which are rough triangular areas, overlaid
when the bones are articulated by a triangular spine from the tympanic
bulla.
Its lateral surfaces are mostly covered by the wings. They appear at the
sides of the elevated cranial end of the dorsal surface as triangular areas.
The caudal end is concave, rough, and has the form of the cranial end of
the basilar part of the occipital.
The cranial end is nearly square and rough for articulation with the body
of the presphenoid.
The Wing (alisphenoid; ala magna of the human sphenoid) (Fig. 20, b).
—This is a thin quadrilateral plate of bone attached by its medial border to
nearly the whole of the lateral surface of the body. Its middle portion lies
nearly in the same plane as the body, but its ends are curved dorsad so that
its internal surface is concave and its external surface is convex. The
curvature is most pronounced near the long lateral border, so that this
border forms nearly a semicircle.

The internal surface supports the occipital lobe of the cerebrum. It is
marked by a rounded groove (h) which is parallel with the lateral surface of
the body. The dorsal margin of the groove projects mediad in the form of a
sharp ridge which is broadest caudad, where it often reaches nearly to the
posterior clinoid process. The groove passes craniad into three foramina.
The first (cranial) of these, the orbital fissure (i), is large and lies between
the wing, the body, and the pterygoid process. It is incomplete, but is
completed by the presphenoid. The second foramen is small and rounded; it
is the foramen rotundum (j). The third, foramen ovale (k), is larger and
oval and penetrates the wing through about the middle of its longitudinal
axis. Another minute foramen penetrates the sphenoid between the wing
and the body of the bone, just laterad of the tuberculum sellæ. This foramen
is continuous craniad with a groove on the dorsal surface of the pterygoid
process; the groove and foramen constitute the pterygoid canal. It
transmits a nerve.
The external surface shows the orbital fissure, the foramen rotundum and
the foramen ovale, bounded ventrally by a sharp ridge, which is continued
onto the pterygoid process. Between this ridge and the body the surface is
longitudinally grooved for the tuba auditiva or Eustachian tube.
The semicircular margin of the bone articulates with the squamous
portion of the temporal. At the junction of its caudal and middle third there
is sometimes a toothlike projection which underlies the root of the zygoma.
The whole of the cranial margin, except the lateral end, articulates with
the wing of the presphenoid. At this end the angle formed by the junction of
lateral and cranial borders is produced into a flat process, which passes
dorsocaudad between the squamous portion of the temporal and the frontal,
and articulates by the roughened internal surface of its free end with a
similar process from the parietal.
The caudal margin laterad of the groove is bevelled and roughened at the
expense of the dorsal surface and is overlaid by the ventral end of the
tentorium. Mediad of the groove it projects caudad as a slender point, the
lingula of the sphenoid. This is received into a narrow cleft between the
apex of the petrous bone and the bulla tympani.
The pterygoid process (c) is a nearly square, thin plate of bone. The
medial surface is smooth and concave, the lateral face is convex and
marked by two parallel ridges. The medial one of these is continued craniad
from the bony septum which separates the orbital fissure from the foramen

rotundum, and the lateral one from the septum which separates the foramen
rotundum from the foramen ovale. A sharp triangular spine projects laterad
from near the caudal end of the lateral ridge.
The two ridges and that part of the lateral surface of the bone included
between them form a part of the sphenoid bone known as the pterygoid
process of the sphenoid bone, in those cases where the pterygoid is a
separate bone.
The remainder of the process is equivalent to the pterygoid bone of other
vertebrates.
Between the caudal margin of this bone and the lateral of the two ridges,
i.e., between the pterygoid bone and the pterygoid process of the sphenoid,
is a long deep fossa, the internal pterygoid fossa (Fig. 40, s). The
laterocaudal margin of the pterygoid process projects caudad, as a curved
triangular spine, the hamulus or hamular process (Fig. 40, t; Fig. 43, i).
The Presphenoid Bone. Os presphenoidale (Fig. 21).—In a young cat
this bone is in three pieces, a basal portion (presphenoid) and two wings
(orbitosphenoid bones). These bones remain distinct throughout life in
many lower vertebrates, but in the adult cat they fuse to form a single bone.
We may nevertheless conveniently describe this bone as made up of a body
(a) (the basisphenoid), and two wings (b), the orbitosphenoids (the alæ
parvæ of the human sphenoid).

Fig. 21.—Presphenoid Bone, Ventral
View.

a, body; b, wings; c, optic foramina.

The body (a) lies in the base of the skull in the median line, craniad of
the basisphenoid. It has the form of a rectangular prism about twice as long
as broad. It is hollow, and the cavity is divided by a median longitudinal
partition into two cavities (sphenoidal sinuses, Fig. 43, l). The sphenoidal

sinuses are continued craniad into the cavities of the ethmoid. The body has
six surfaces:
The dorsal or internal surface (Fig. 42, n) looks into the cranial cavity
and is continuous with the dorsal surface of the wings. The caudal end of
the body is depressed, and when united to the basisphenoid aids in forming
the cranial wall of the sella turcica. At each caudolateral angle is a short
spine, the anterior clinoid process. At about one-third the length of the
bone from the caudal end is a transverse groove (chiasmatic groove, Fig.
42, m) for the optic chiasma. Its ends lead into two round foramina (the
optic foramina, Fig. 42, l; Fig. 21, c) which pass craniolaterad between the
body and the wings of the presphenoid and transmit the optic nerve and the
ophthalmic artery.
The ventral surface (Fig. 21) is hour-glass-shaped and marked by a
smooth median ridge, continuous with the ridge on the basisphenoid and
overlaid at its cranial end by the vomer. The caudal end presents a rough
triangular area on each side, for articulation with the pterygoid process of
the sphenoid bone, while the cranial end has similar areas overlaid by the
nasal portion of the palatine bones.
The lateral surface looks towards the orbitotemporal fossa. It is notched
near the caudal end by the ventral border of the optic foramen (c). Caudad
of this foramen the surface presents an oblique groove which forms in the
natural condition the medial boundary of the orbital fissure.
Craniad of the optic foramen the surface is smooth and marked near its
ventral border by a longitudinal ridge which forms part of the dorsal
boundary of a fossa, the external pterygoid fossa (Fig. 40, p).
The caudal end presents ventrally a quadrangular rough surface for
articulation with the body of the sphenoid. The cranial end presents the two
sphenoidal sinuses separated by a median partition.
The median partition articulates by its free border with the lamina
perpendicularis of the ethmoid. At its ventral end is the abruptly truncate
end of the median ridge of the ventral surface, which is continuous with the
ventral cartilaginous portion of the lamina perpendicularis. The lateral walls
of the sphenoidal sinuses are continued craniad of the dorsal and ventral
walls and of the median partition, and articulate ventrally with the nasal
portion of the palatine bones, and dorsally with the orbital plate of the
frontal. Between them is received the caudal ends of the labyrinths of the
ethmoid in the middle, while between their dorsal edges is received the

caudal end of the cribriform plate, and between their ventral edges the
expanded end of the vomer.
The wings (b) arise each from nearly the whole of the dorsolateral angle
of the body. They form prominent nearly horizontal triangular projections
over the optic foramina.
The dorsal and ventral surfaces are smooth and continuous respectively
with the dorsal and lateral surfaces of the body. The dorsal surface looks
into the cranial cavity, while the ventral looks into the orbitotemporal fossa.
Craniad of the apex of the wing its border articulates with the ventral
edge of the orbital portion of the frontal bone. Caudad of the apex the
border articulates with the cranial border of the wing of the sphenoid.
Temporal Bone. Os temporale (Figs. 22 and 23).—This forms a part of
the lateral wall of the cranium, filling the gap between the occipital and the
sphenoidal segments. It is made up of three portions which are distinct in
kittens but somewhat firmly united in adult cats. In lower vertebrates these
portions are distinct bones called the Squamous, the Petrous, and the
Tympanic bones. In the cat they may be described as the squamous (a),
petrous (b), and tympanic (c) portions of the temporal bone.

Fig. 22.—Temporal Bone, External Surface. Fig. 23.—Temporal Bone, Internal Surface.

a, squamous portion; b, petrous portion; c, c′, tympanic portion (c, entotympanic; c′,
ectotympanic); d, zygomatic process; e, mastoid portion of the petrous; f, mandibular fossa; g,
postmandibular process; h, tuberculum articulare; i, external auditory meatus; j, stylomastoid
foramen; k, pit for tympanohyal bone; l, mastoid process; m, grooves bounding the jugular

foramen; n, internal auditory meatus; o, appendicular fossa; p, hiatus facialis; q, styliform process
of tympanic bulla.

The squamous portion (a) (squama temporalis) is thin and oval or has
the form of an equilateral triangle with rounded angles, with a curved
process, the zygomatic process (d), arising from its ventral border. Its outer
surface (Fig. 22) is convex and smooth and gives origin to part of the
temporal muscle. Its inner surface (Fig. 23) is concave and smooth except
near the margins, where it is bevelled and rough. The roughened border is
broader dorsad and caudad. The ventral margin of the bone is turned
mediad at its cranial end so that the lateral face of the inverted portion looks
ventrad. By this portion of its lateral face the squamous rests upon the
tympanic bulla, and its edge articulates with the tentorium and the wing of
the sphenoid. The remaining (caudal) portion of the ventral border overlies
the mastoid portion (e) of the petrous. By the remainder of its border the
bone articulates with the parietal dorsad and with the wing of the sphenoid
craniad. The roughened portion of its inner surface overlies the margins of
both these bones.
The zygomatic process (d) is formed by the confluence of two roots. One
of these starts from the ventral end of the lambdoidal ridge and passes along
the ventral margin of the squama dorsad of the external auditory meatus.
The other arises abruptly from the cranioventral angle of the bone. The
process thus formed is at first broad and passes horizontally laterad and
slightly craniad. It soon grows more slender and turns gradually craniad,
while at the same time it twists so that the surface which is dorsal at the
base becomes medial at the tip; the posterior root which is continuous with
the caudal border at the base is continuous with the dorsal border at the
apex. On the ventral surface of the base is a transversely elongated concave
articular surface, the mandibular fossa (f), for the condyloid process of the
lower jaw. Caudad of this is a sharp transverse ridge, the postmandibular
or postglenoid process (g), and craniad of the lateral end of the fossa a
slight tubercle, the tuberculum articulare (h). Near its apex the zygomatic
process is more slender and its ventral border is bevelled for articulation
with the malar or zygomatic bone.
The tympanic (Figs. 22 and 23, c; Fig. 24) is expanded into a large
hollow olive-shaped bone which is known as the auditory bulla and
encloses the tympanic cavity. Its substance is very compact. Unlike the

tympanic of most other mammals it is developed from two bones, known as
the ectotympanic (Fig. 22, c′) and entotympanic (c). These are strongly
marked in young kittens, and can usually be easily distinguished in adult
cats. The entotympanic (Figs. 22 and 23, c) forms the larger part of the
bulla, constituting its ventral and medial surfaces; it is thin, smooth, and
transparent. The ectotympanic (Fig. 22, c′) surrounds the external auditory
meatus: it is thicker and more opaque than the entotympanic. The bulla lies
ventrad of the squamous, and in an external view conceals a large part of
the petrous.
On its lateral surface it presents near the dorsal border an irregular oval
opening, that of the external auditory meatus (Fig. 22, i), which leads into
the tympanic cavity. Caudad of the external auditory meatus is a nearly
dorsoventral groove, which, when the bone is articulated, forms a part of
the boundary of the stylomastoid foramen (Fig. 22, j); just ventrad of this
groove is a pit (k) which lodges the tip of the tympanohyal bone.
Craniad the bone is produced into a short spine, the styliform process
(q), which lies in a horizontal groove in the ventral surface of the
basisphenoid. Laterad of this spine is a groove for the tuba auditiva or
Eustachian tube.

Fig. 24.—Tympanic Bulla, Isolated,
Medial Surface.

a, inner end of auditory meatus; b,
partition dividing tympanic cavity; c,
styliform process.

The medial surface (Fig. 24) presents in the middle near its ventral
margin a short triangular spine which lies in the natural state against the
ventral surface of the basilar portion of the occipital.

Caudad of this spine the surface is marked by two or three vertical
parallel grooves (Fig. 23, m). They indicate the portion of the bone which
bounds the jugular foramen, and are possibly impressions of the ninth,
tenth, and eleventh nerves.
The dorsal two-thirds of the medial surface is lacking in the disarticulated
bulla (Fig. 24), so that the cavity of the bone is exposed. This opening is in
the natural state closed by the petrous bone. The caudal end is rough where
it is overlaid by the jugular process.
On the inner surface of the tympanic bulla is seen the thickened margin
of the inner end of the auditory meatus (Fig. 24, a). To it is attached the
membrana tympana. In the median dorsal line this margin is notched for the
reception of the incus and head of the malleus. From the lateral wall of the
cavity at the line of junction of the ectotympanic and entotympanic a thin
bony partition (b) rises. It runs almost directly mediad; is concave dorsally
and divides the tympanic cavity into two chambers.
The Petrous Portion (Fig. 23, b, and Fig. 25).—This consists of two
parts, a very dense part (the petrous portion proper, Fig. 25), which has the
form of a triangular pyramid and encloses the auditory labyrinth, and a less
dense part, the mastoid portion (Figs. 22 and 23, e), which is flattened and
triangular and is attached by its base to the base of the pyramid.
The petrous portion may be described as having a base and three sides,
lateral, dorsal, and medial. It completes the medial wall of the tympanic
bulla, so that it is not possible to see it from the exterior of a skull except
through the auditory meatus (Fig. 22, i). When the bones of the skull are
articulated its dorsal surface is covered by the tentorium and alisphenoid. Its
lateral face looks into the tympanic cavity, while the medial face looks into
the cranial cavity.

Fig. 25.—Petrous Bone of Right Side, Lateral Surface, Enlarged.
a, fenestra cochleæ; b, promontory; c, fenestra vestibuli; d, fossa for the
tensor tympani muscle; e, fossa for incus and malleus; f, fossa continuous
with stylomastoid foramen; g, foramen leading to facial canal.

Its lateral face (Fig. 25) (medial wall of the tympanic cavity) presents just
ventrad of the middle of its base a large circular foramen, the fenestra
cochleæ (a) (or fenestra rotunda), which looks caudolaterad; it leads into
the cochlea. The fenestra cochleæ lies at the summit of a nipple-like
elevation, the promontory (b), which is continued toward the apex of the
bone as a gradually diminishing semicylindrical ridge, due to the presence
within it of the bony cochlea. Dorsad of the fenestra cochleæ is the much
smaller fenestra vestibuli (c) (or ovalis) which leads into the vestibule. It is
occupied in the natural condition by the base of the stapes.
Dorsocraniad of the fenestra vestibuli is a large fossa (d) which contains
the tensor tympani muscle. Dorsocaudad of this, partly bounded by the
squamous portion of the temporal, is another large fossa (e), the cranial end
of which is occupied by the incus, while its caudal end is occupied by the
head of the malleus.
Nearly caudad of this fossa and separated from it by an oblique bony
septum is a third fossa (f) which is narrow and curved. It is continuous with
a notch in the mastoid portion of the bone. When the tympanic is articulated
the notch is converted into a foramen (stylomastoid foramen, Fig. 22, j)
for the exit of the seventh nerve. The fossa gives passage to the seventh
nerve and also lodges the stapedius muscle. A groove may be traced from
the stylomastoid foramen to the caudal border of the fossa for the tensor
tympani muscle, where it passes into a canal (g). The groove and canal are
parts of the canalis facialis or facial canal (aqueductus Fallopii) for the
passage of the seventh nerve through the petrous bone.
The medial surface (Fig. 23, b) of the petrous portion shows near its
middle a fossa, the internal auditory meatus (n). This is divided by a
partition of bone into a dorsal and ventral part. The dorsal portion is the
beginning of the facial canal (aqueductus Fallopii) by which the seventh
nerve passes through the petrous bone to emerge at the stylomastoid
foramen. The ventral portion shows at its bottom several small foramina for
the auditory nerve.

Dorsocaudad of the internal auditory meatus is a deep fossa (o) for a
small lobe, the so-called appendicular lobe, of the cerebellum. This may be
called the appendicular fossa.
The dorsal surface is triangular and presents near its apex a foramen—the
hiatus facialis (p), the opening of a canal which joins the canalis facialis
and transmits the superficial petrosal branch of the nerve of the pterygoid
canal (Vidian nerve). That part of the dorsal surface which lies caudad of
the hiatus facialis is known as the tegmen tympani.
The base of the petrous is attached to the mastoid portion (Fig. 23, e).
(For an account of the structures within the petrous bone and the
tympanic cavity, see the description of the internal and middle ear.)
The mastoid portion (Figs. 22 and 23, c) is attached by its base to the
pyramidal petrous portion, with which it forms an angle of about 120
degrees. It appears in the lateral wall of the skull between the parietal bone
and the occipital (Fig. 40, d). The lambdoidal ridge is continued on its outer
surface to the caudal border of the external auditory meatus. Caudad of the
stylomastoid foramen it forms a slight nipple-like eminence, the mastoid
process (Fig. 22, l). Its inner face looks into the cranial cavity.
Parietal Bone. Os parietale (Figs. 39, 40, and 43, 3).—The parietal
bones form the larger part of the lateral and dorsal boundary of the cranial
cavity. Each is a thin rectangular bone, compact and curved and with a
deeply notched shelf of bone, the tentorium (Fig. 42, e, and Fig. 43, f),
projecting inward from near the caudal margin.
The outer surface is smooth and convex. The highest part of the
convexity, a little caudad of the middle of the bone, is known as the
parietal tubercle or eminence (Fig. 39, d); it marks the point of beginning
ossification. An obscure curved ridge (Fig. 39, e), running from the
caudodorsal angle or a point craniad of it craniolaterad, indicates the
boundary of the origin of the temporal muscle. Near the ventral border the
surface is roughened and is covered in the natural state by a part of the
squamous portion of the temporal bone.
The inner surface (Fig. 43, 3 and 3′) is smooth and marked by ridges and
grooves for the convolutions of the cerebrum. Near the medial border is a
ridge which, when the bone is articulated with that of the opposite side,
forms a shallow groove for the superior sagittal sinus. Beginning near the
middle of the ventral margin and passing dorsad is a groove for the middle
meningeal artery. The tentorium (Fig. 43, f) arises from the inner surface

near its caudal margin and projects mediad as a thin curved or notched shelf
of bone which separates the cerebellar fossa (Fig. 43, I) of the cranium from
the cerebral fossa (Fig. 43, II). When the parietals are articulated there is
left between the tentoria a large foramen by means of which the two fossæ
communicate. The foramen is bounded laterally and dorsally by the free
margins of the tentoria, while the ventral end of each tentorium articulates
with the alisphenoid, and its dorsal end with the opposite tentorium.
The medial border is straight and is united by suture to the opposite bone.
The cranial border is bevelled at the expense of the inner surface and
articulates with the frontal. Just ventrad of the middle of the border projects
a sharp spine which fits into a corresponding notch in the caudal border of
the frontal.
The ventral border is concave, sharp, and bevelled at the expense of the
outer surface, for articulation with the squamous portion of the temporal,
except near the cranial end, where it articulates with the wing of the
sphenoid.
The caudal border is thick and porous medially, but thin laterally, and
bevelled at the expense of the inner surface for articulation with the
interparietal and mastoid portion of the temporal.
Frontal Bone. Os frontale (Figs. 39, 40, and 41, 5; Fig. 43, 8; Fig. 26).
—The frontal bones meet one another in the median dorsal line so as to
form the roof of the skull between the parietal and nasal bones. A part
extends also ventrad, forming a large part of the medial wall of the orbit and
a part of the temporal fossa.
The bone may be divided into two portions, a plate forming the cranial
portion of the roof of the skull and a part of the roof of the nasal cavity, the
frontal plate (Fig. 40, 5), and a part descending into the orbit, the orbital
plate (Fig. 40, 5′).
The frontal plate (Fig. 40, 5) is a right-angled triangle with the
hypothenuse lateral. Its dorsal surface is convex and smooth. The cranial
two-thirds of its lateral border is separated from the orbital fossa by a ridge,
the supraorbital arch or margin (Fig. 39, i; Fig. 40, o); the caudal third
passes gradually into the temporal fossa. At its cranial angle is a triangular
projection, the frontal spine or nasal spine (Fig. 26, a), which fits into a
space between the nasal and maxillary bones.

Fig. 26.—Frontal Bone, Medial Surface.

a, frontal spine; b, transverse ridge; c, surface
applied to the ethmoid; d, vertical plate of medial
border.

The ventral surface is concave and smooth over its caudal one-half and
helps to form the cranial part of the brain-case. It presents slight ridges and
depressions for convolutions of the cerebrum. At its narrowed middle
region the ventral surface is marked by a thick transverse ridge (Fig. 26, b).
Caudally the ridge descends by a gentle slope to the level of the ventral
surface of the bone. The cranial end of the ridge is pierced by an oval
foramen through which the frontal sinus (Fig. 43, m, m′), which lies within
the ridge, communicates with the spaces in the ethmoid bone (nasal cavity).
Craniad of the ridge the surface (Fig. 26, c) is rough and, together with the
raised medial border of the bone and the orbital plate, encloses a rectangular
space which in the natural state receives a portion of the labyrinth of the
ethmoid. The ventral surface is marked at its medial edge by a thin
longitudinal ridge which, when the bones are articulated, is continuous with
one of the vertical lamellæ of the ethmoid.
The medial border forms a vertical plate (d), broadest craniad and
roughened for articulation with its fellow of the opposite side except at its
cranial end, where it articulates with the border of the nasal bone.
The caudal border is roughened, bevelled at the expense of the outer
surface, and articulated with the parietal bone except at its ventral end,
where it articulates with the alisphenoid.
The lateral border is smooth, and it is here that the orbital plate is joined
to the frontal plate at right angles. Along its cranial two-thirds this union is
marked by a sharp ridge, the supraorbital margin (Fig. 40, o) or arch. This
ridge extends caudolaterad as a triangular projection, the zygomatic (or
postorbital) process (Fig. 40, n), which is flattened on its cranioventral face

near its extremity and forms part of the boundary of the orbital fossa. At its
cranial end the lateral border articulates with the nasal and maxillary bones.
The orbital plate (Fig. 40, 5′) arises from the ventral surface of the lateral
border of the frontal plate. It is directed ventrad, is smooth and concave on
its outer surface, and forms the dorsal portion of the medial wall of the
orbital fossa. Near its ventral border it bears the small ethmoidal foramen,
for the artery of the same name.
On the caudal one-half of its inner surface (Fig. 26) it assists the caudal
part of the dorsal plate in forming the brain-case. The cranial one-half of its
inner surface is marked off from the remainder of the surface by a sharp
irregular ridge which is for articulation with the cribriform plate of the
ethmoid. Craniad of this the surface is marked by ridges and looks into the
nasal cavity.
The cranial margin is produced dorsally in the form of a blunt triangular
spine. Mediad of this spine the bone articulates with the lachrymal bone.
The ventral border articulates by its cranial one-third with the orbital
plate of the palatine, and by its caudal two-thirds with the body and wing of
the presphenoid.
Maxillary Bone. Maxilla (Figs. 27 and 28).—The maxillary bone forms
the cranial and lateral portions of the roof of the mouth. The bones of
opposite sides meet craniad, but diverge caudad to enclose the palatal plates
of the palatine bones. Each consists of a thick prismatic ventral portion or
body (a) and a thin flat plate, the frontal process (b), extending dorsad
from the cranial part of the bone.

Fig. 27.—Maxillary Bone, Lateral Surface. Fig. 28.—Maxillary Bone, Medial Surface.

a, body; b, frontal process; c, infraorbital foramen; d, elevation for root of canine tooth; e, canine
tooth; f, first premolar; g, second premolar; h, third premolar; i, molar tooth; j, zygomatic process;
k, beginning of lachrymal canal; l, ridge to which the ventral nasal concha is attached; m, nasal
crest of palatine process.

The body (a) has the form of a triangular prism whose broader dorsal
face looks into the nasal cavity and orbit, while the ventral face looks into
the mouth, and the lateral face toward the cheek. From the junction of the
dorsal and lateral surfaces at the cranial end the large flat curved frontal
process (b) passes dorsad, while the teeth are implanted along the border,
alveolar border or process, formed by the junction of the ventral and
lateral surfaces.
The lateral surface is continuous with the lateral surface of the frontal
process and shows at the base of the frontal process on its caudal border the
large infraorbital foramen (Fig. 27, c), for the vessels and nerves of the
same name. Near the medial end of the surface is a cylindrical elevation (d)
for the root of the canine tooth (e).
The ventral surface is smooth and looks into the roof of the mouth.
On the dorsal surface caudal and cranial halves may be distinguished.
The caudal one-half enters into the floor of the orbit. The lateral edge of this
portion is divided into two laminæ, between which is received the end of
the malar bone. Caudad this edge is prolonged into the short dorsally

directed zygomatic process (j). The cranial half of the dorsal surface looks
into the nasal cavity and is separated from the caudal half by a sharp
vertical lamina of bone which runs caudomediad from the base of the nasal
process. To the dorsal edge of this lamina are articulated the lachrymal bone
and a part of the palatine. At the point where the lamina joins the base of the
nasal process a foramen is seen leading into a canal, the nasolachrymal
canal (k). Craniad of the lamina the surface is concave. Where it becomes
continuous with the inner edge of the frontal process there is attached to it a
thin bone, the ventral nasal concha (or maxilloturbinal), which is rolled
into an irregular spiral. The nasolachrymal canal opens ventrad of its cranial
end.
The cranial third of this part of the bone projects further mediad than
does the rest of the medial border, forming thus the broad palatine process.
This is rough on its medial edge for articulation with the premaxillary and
the palatine process of the opposite bone. This medial edge rises also
dorsally into a low ridge, the nasal crest (m), which is roughened for
articulation with the vomer. The caudal two-thirds of the medial edge
articulates with the palatine bone.
The cranial end of the bone articulates with the premaxilla.
The caudal end is smooth.
The frontal process (b) presents on its inner surface, which looks into the
nasal cavity, certain transverse ridges which are in relation with the ethmoid
bone. Its outer surface is smooth. By its cranial border it articulates with the
nasal bone dorsally and with the premaxillary bone ventrally.

Fig. 29.—Premaxillary Bone,
Obliquely Craniolateral
Aspect.

a, the three incisor teeth; b,
palatal portion of the bone; c,
nasal process.

Its dorsal end articulates medially with the nasal spine of the frontal
bone, and caudally with the orbital plate of the same bone.
Premaxillary Bone. (Os incisivum BNA.) Premaxilla (Fig. 29).—The
premaxillary bones bear the incisor teeth and form the cranial portion of the
roof of the mouth.
Each consists of an irregular, horizontal palatal portion (b) and of a
perpendicular nasal process (c) which forms part of the lateral boundary of
the nares and enters into the formation of the lateral wall of the nasal cavity.
The palatal portion has in its caudal border a deep notch for the foramen
incisivum or anterior palatine canal, which lies between it and the maxillary
and transmits blood-vessels and nerves. It articulates with the maxillary
bone by this border.
The medial border is raised into a thin crest of bone which, besides
forming the medial wall of the foramen incisivum or anterior palatine canal,
articulates by its medial border with the bone of the opposite side, forming
a sort of median trough (sulcus palatinus) which projects dorsad into the
nasal cavity and receives the ventral border of the nasal septum. The caudal
end of this border articulates laterad with the maxilla, dorsad with the
vomer.
Its craniolateral border bears the incisor teeth (a).
The nasal process (c) presents three surfaces, all elongated and triangular;
one, the medial surface, is smooth and concave and looks into the nasal
cavity. Its dorsal border is rough for articulation with the nasal bone dorsad,
and smooth ventrad where it aids in forming the nares.
The lateral surface is smooth.
The caudal surface is rough for articulation with the maxillary bone.
Nasal Bone. Os nasale (Fig. 30).—The nasal bones fill the space
between the nasal process of the premaxillary, the frontal process of the
maxillary, and the nasal spine of the frontal bone (Fig. 39, 7). They thus
form part of the dorsal wall of the nasal cavity near the middle line.

Fig. 30.—Nasal Bone,
Dorsal View.

Each may be described as consisting of two elongated triangular lamellæ,
one vertical, the other horizontal. The vertical lamella is curved slightly
ventrad and has its apex directed craniad. It is applied by its medial surface
against the vertical lamella of the opposite bone, the two thus forming a
median vertical partition, the nasal crest (Fig. 43, 12), which extends
ventrad into the nasal cavity and, by joining the dorsal edge of the lamina
perpendicularis, helps to form the internasal septum.
The horizontal lamella is attached to the dorsal margin of the vertical
lamella in such a way that its apex lies opposite the base of the vertical
lamella. It helps to roof in the nasal cavity, and by its base forms a part of
the dorsal boundary of the narial opening. By its lateral margin it articulates
with the nasal spine of the frontal at its caudal end, with the frontal process
of the maxillary at its middle, and with the nasal process of the premaxilla
at its cranial end. The lateral angle of its base projects in a curved line
which forms the dorsal part of the lateral boundary of the narial opening.
From the lateral border of the horizontal lamella a bony plate curves
ventrad and mediad, enclosing a narrow fossa which receives a part of the
ethmoid. This is the concha nasalis superior (nasoturbinal bone).
Ethmoid Bone. Os ethmoidale (Figs. 31 and 32).—The ethmoid bone
closes in the cranial cavity at its cranial end and extends forward into the
nasal cavity, which it largely fills.
It consists of a median vertical portion, the lamina perpendicularis (Fig.
43, n; Fig. 42, p), forming a part of the nasal septum, of two lateral portions
made of thin sheets of bone variously folded and united—the labyrinths (or

ethmoturbinals), which fill the greater part of the nasal cavity; and of a
transverse perforated plate, the cribriform plate (lamina cribrosa), attached
to the caudal end of the lamina perpendicularis and the labyrinths.
The lamina perpendicularis (Fig. 43, n; Fig. 42, p) is a flat four-sided
bone. By its caudal margin it is continuous with the cribriform plate; by its
ventral margin it is enclosed by the halves of the vomer; by its dorsal
margin it unites with the crest formed by the vertical portion of the nasal
bone craniad and with the vertical lamina of the medial margin of the
frontal caudad, while its cranial margin is continued into the septal cartilage
of the nose. Its lateral faces are smooth and free.
The lamina cribrosa or cribriform plate (Fig. 42, o) is elongated heart-
shaped, with the apex of the heart ventrad. Its caudal face is concave and
looks into the cranial cavity. It presents three irregular longitudinal rows of
holes, one median and two lateral, for the passage of the olfactory fibres
from the cranial cavity into the nasal cavity. Its cranial face is continuous
along the medial line with the lamina perpendicularis, and at the sides with
the labyrinths.
The notch in the heart is directed dorsad and receives the vertical lamina
of the medial border of the frontal bone. The apex of the heart articulates
with the cranial end of the dorsal surface of the presphenoid. Its lateral
margins are articulated with the ethmoidal ridges on the medial surface of
the frontal bone.

Fig. 31.—Ethmoid and Vomer, Side View. Fig. 32.—Ethmoid and Vomer, Ventral View.

a, vomer; b, vertical cells of the labyrinth of the ethmoid; c, horizontal cell of the same; d, part of
the ethmoid that forms the lamina papyracea; e, edge of cribriform plate.

The labyrinths (Figs. 31 and 32) are attached to the cranial face of the
lamina cribrosa, one on each side of the lamina perpendicularis. Each is
made of thin bony plates irregularly folded so as to enclose spaces, the
ethmoid cells. In each may be distinguished a cranial portion (b), in which
the cells are nearly vertical, and a caudal portion (c), in which the cells are
nearly horizontal.
The medial surfaces are separated by a space from the lamina
perpendicularis. This space is broadest along the junction of the horizontal
and vertical portions of the labyrinth. There are thus formed two
passageways which correspond to the superior meati of human anatomy.
The lateral surfaces come into contact with the frontal process of the
maxillary and the orbital plate of the frontal bone. On the lateral surface of
each labyrinth there is a thin irregular lamina of bone lying in a
dorsoventral longitudinal plane and closing in some of the ethmoid cells
laterally (d). A small part of this lamina, situated near the caudoventral
angle of the bone, appears in the orbital fossa on the external surface of the
skull between the presphenoid, palatine, and frontal bones or between the
lachrymal, palatine, and frontal bones. Sometimes in the entire skull two
such pieces may be seen, one in each of these positions. This corresponds to
the lamina papyracea of human anatomy.
The dorsocaudal angle of each bone is received into the space between
the orbital plate of the frontal and the vertical lamina of the medial border
of the frontal. Its ventrocaudal angle is received between the cranial
extensions of the lateral walls of the presphenoid, while its ventral surface
is overlaid caudally by the expanded portion of the vomer, to which it is
attached at its caudolateral angles.
Vomer (Figs. 31 and 32, a).—The vomer consists of two thin laminæ of
bone which ensheath the ventral margin of the lamina perpendicularis (or
the cartilaginous plate which continues ventrad from this margin) and unite
ventrad of it; the two thus form a trough open dorsad.
Each becomes horizontal near its caudal end and at the same time
expands. The expanded portion lies ventrad of the labyrinth of the ethmoid,
closing in some of its cells: its lateral angles are united with the labyrinths.

At its caudal end the bone articulates with the body of the presphenoid,
and each half of it is produced caudad near the middle line into a triangular
spine which lies ventrad of the body of the presphenoid. The horizontal
portion of the bone helps to separate the olfactory and respiratory passages
of the nasal chamber, while its vertical portion contributes to the formation
of the nasal septum.
The ventral margin formed by the junction of the two halves of the bone
is smooth and free caudad, but at its cranial end is broad and rough for
articulation with the palatal processes of the maxillæ.
Palatine Bone. Os palatinum (Fig. 33).—The palate bone or palatine
bone consists of two portions, a horizontal or palatal portion (a) and a
perpendicular or nasal portion (b), uniting at an angle of about forty-five
degrees.

Fig. 33.—Palatine Bone, Dorsal View.

a, horizontal portion; b, perpendicular portion; c, maxillary
spine; d, posterior nasal spine; e, sphenopalatine foramen; f,
caudal opening of posterior palatine canal.

The horizontal portions (a) of the two bones are received between the
maxillary bones and form the caudal and medial part of the roof of the
mouth. Each is irregularly quadrilateral in form, with the caudolateral angle
produced caudad into a long process which is continuous with the
perpendicular portion of the bone. The lateral margin of the horizontal
portion articulates over its cranial half with the maxillary bone. At about its

middle a short thick maxillary spine (c) projects caudolaterad. The
remainder of the lateral margin is directly continuous with the perpendicular
plate of the bone. The medial margin is rough for articulation with the
corresponding margin of the opposite palatine; the caudal angle of this
margin projects caudad as the short posterior nasal spine (d). The caudal
margin forms a free edge which bounds the choanæ; it passes laterally into
the perpendicular portion.
The ventral surface (Fig. 41, 8) looks into the mouth. Near the middle of
its craniolateral margin are two or more small foramina (Fig. 41, q) which
form the cranial termination of the posterior palatine canal. The dorsal
surface is smooth and looks into the nasal cavity.
The perpendicular or nasal portion (Fig. 33, b) of the palatine is thin and
irregularly quadrilateral in form. It is attached by its cranial two-thirds to
the dorsal surface of the horizontal portion. The outer surface is concave
and looks into the orbital fossa. The inner surface is convex and looks into
the nasal cavity.
The perpendicular portion is marked by two foramina just craniad of the
middle. The larger dorsal oval foramen is the sphenopalatine foramen (e).
The smaller ventral foramen is the caudal opening of the posterior palatine
canal (f). From this opening the canal passes craniomediad, lying in the
substance of the palatine bone; it opens on the ventral surface of the
horizontal portion at the small openings previously described (Fig. 41, q).
By its cranial margin it articulates with the lachrymal bone. By its dorsal
margin it articulates craniad with the orbital plate of the frontal: with the
lamina papyracea at its middle, and with the body of the presphenoid
caudad. The caudal half of the dorsal margin is partially divided into two
lamellæ with a rough surface between them: this rough surface lies against
the ventral surface of the presphenoid. The caudal margin articulates with
the pterygoid portion of the sphenoid.
Lachrymal Bone. Os lachrymale (Fig. 34; Fig. 39, 10).—The lachrymal
bone is a thin pentagonal scale of bone filling the interval between the
horizontal plate of the palatine, the maxillary, and the orbital plate of the
frontal. Its outer surface looks into the orbit, its inner surface into the nasal
cavity.

Fig. 34.—Lachrymal Bone of Left Side, Fig. 35.—Malar Bone of Right Side, Lateral
External Surface. Surface.

Fig. 34.—a, notch forming the beginning of the lachrymal canal.
Fig. 35.—a, ridge for origin of the masseter muscle; b, frontal process; c, zygomatic process.

Near the middle of its cranial border it is notched obliquely by a foramen
(a), the beginning of the nasolachrymal canal.
Malar Bone. Jugal Bone. Os zygomaticum (Fig. 35).—The malar or
zygomatic bone is a flat curved plate of bone which forms the lateral wall
of the orbit and together with the zygomatic process of the temporal forms
the zygomatic arch. Its outer surface is smooth and marked by a
longitudinal ridge (a) for attachment of the masseter muscle.
At its caudal end the bone is continued into two processes: one, the
frontal process or orbital process (b), is a triangular spine of bone directed
caudomediad; when the bones are articulated it lies opposite the zygomatic
process of the frontal to which it is joined by a ligament (orbital ligament).
The other, zygomatic process (c) of the malar bone, extends ventrocaudad
and articulates with a similar process from the temporal to form the
zygomatic arch above mentioned.
Its inner surface is smooth and looks into the orbit, except that of the
zygomatic process, which looks into the temporal fossa.
Its cranial border is roughened at the expense of both surfaces and
articulates with the maxillary bone. Its other borders are smooth except the
dorsal border of the zygomatic process, which is roughened for attachment
to the zygomatic process of the temporal.
The Mandible. Mandibula (Figs. 36 and 37).—The mandible (or
inferior maxillary bone) is composed of two halves which come together at

the cranial end and form the lower jaw. At its caudal end each half
articulates with the temporal bone at the mandibular fossa, and at its cranial
end it joins the opposite bone, the suture being known as the symphysis of
the jaw (symphysis menti) (Fig. 37, a).
Each half consists of a horizontal portion, the body (b), bearing teeth on
one of its borders (the alveolar border), and of a vertical portion, the
ramus (c).
The body (b) has the form of a flattened cylinder and has two surfaces
and two borders. The lateral surface (Fig. 36) is smooth and presents near
its cranial end a foramen (or sometimes two), the mental foramen (d),
forming the cranial termination of the mandibular canal. At its caudal end is
a deep fossa continuing on to the ramus, the coronoid fossa, or masseteric
fossa (e).

Fig. 36.—Mandible, Lateral Surface.

Fig. 37.—Mandible, Medial Surface.

a, symphysis; b, body; c, ramus; d, mental foramina; e, coronoid fossa; f, mandibular foramen; g,
angular process; h, coronoid process; i, condyloid process; 1, 2, 3, the three incisor teeth; 4, the
canine tooth; 5, 6, the premolars; 7, the molar tooth.

The medial surface (Fig. 37) is smooth and has near its caudal end a
foramen, the mandibular foramen (f), which communicates with the
mandibular canal leading lengthwise through the bone to the mental
foramen. The cranial end is roughened for attachment to the bone of the
opposite side.
The ventral border is smooth and rounded; it ends caudally in a blunt
point, the angular process (g). The dorsal (alveolar) border is slightly
curved and bears the sockets (alveoli) for the teeth. It is continuous with the
cranial margin of the coronoid process.
The ramus is divided into two portions, the coronoid process (h) and the
condyloid process (i). The coronoid process (h) extends dorsocaudad as a
thin plate of bone with smooth surfaces and borders. Its outer surface is
partly occupied by the coronoid fossa (e). The condyloid process (i) has the
form of a semicylindrical transverse piece of bone attached to the caudal
margin of the coronoid process. It articulates with the mandibular fossa of
the temporal bone.
Hyoid Bone. Os hyoideum (Fig. 38 and Fig. 104).—The hyoid bone
forms the support for the tongue and gives origin to muscles passing to the
tongue and larynx. It also supports the thyroid cartilage (Fig. 104, 1).

Fig. 38.—Hyoid Bone, Dorsal View.

a, body; b, c, d, e, cranial cornu; f, caudal cornu; b, ceratohyal; c,
epihyal; d, stylohyal; e, tympanohyal; f, thyrohyal.

It consists of a transverse bony bar, the body (Fig. 38, a) and of two
cornua or horns attached to each end of the body.
The cranial cornu (lesser cornu of human anatomy) is the longer (Fig. 38,
b-e). Each arises from the cranial face of the body at its lateral end, curves
laterad, and then caudodorsad. It consists of four bony pieces movably
united by cartilage.
The terminal piece is the tympanohyal (e); it is imbedded in the
tympanic bulla just ventrad of the stylomastoid foramen. It is not therefore
seen attached to the cornu after the latter has been separated from the skull.
The other pieces become successively shorter toward the body, and are
called stylohyal (d), epihyal (c), and ceratohyal (b).
The caudal cornua (f) (greater cornua of human anatomy) arise from the
ends of the body. Each consists of a single piece of bone, the thyrohyal (f),
which passes caudolaterad; its free end is united to a process of the thyroid
cartilage (Fig. 104, 1).
The Skull as a Whole.—In the following description of the skull as a
whole the mandible, hyoid, and ear-bones are not included.
The skull forms a bony box which contains the brain and is produced
craniad into the facial portion which encloses the nasal cavity and forms the
framework of the face.
In dorsal view (Fig. 39) the skull presents a smooth convex surface,
broadest caudad, with the two zygomatic arches (g) curving out some

distance laterally. The following bones are visible in dorsal view: the
occipital (1), interparietal (2), parietals (3), temporals (4), frontals (5), malar
or zygomatic bones (6), nasals (7), maxillaries (8), premaxillaries (9), and
lachrymals (10).

Fig. 39.—Skull, Dorsal Surface.

1, occipital bone; 2, interparietal bone; 3, parietal bones; 4, temporal; 5, frontal; 6, malar; 7,
nasal; 8, maxillary; 9, premaxillary; 10, lachrymal, a, lambdoidal ridge; b, external occipital
tubercle; c, sagittal crest; d, parietal eminence; e, line which forms the dorsal boundary of the
temporal fossa; f, zygomatic process of the frontal; g, zygomatic arch; h, frontal process of the
malar; i, supraorbital arch; j, nares; k, foramen incisivum or anterior palatine foramen; l,
sphenopalatine foramen; m, zygomatic process of the temporal; n, infraorbital foramen; o, opening
of lachrymal duct.

The caudal boundary of the dorsal surface is marked by the prominent
lambdoidal ridge (a) which passes from the middle cranioventrad along
each side to the root of the zygomatic arch: it is borne by the occipital and
temporal bones. From the middle of the lambdoidal ridge a second ridge,
the sagittal crest (c), passes craniad in the middle line across the
interparietal bone: it varies greatly in extent, reaching in a very old and
muscular cat to the cranial border of the parietals, while in kittens it does
not exist. The most prominent portions of the skull in this region, just
craniad of the middle of the parietal bones, are known as the parietal
tubercles or eminences (d). A faint curved line (e) runs from the cranial end
of the sagittal crest craniolaterad to the base of the zygomatic process of the
frontal: it marks the dorsal boundary of the origin of the temporal muscle,
and may therefore be considered the dorsal boundary of the temporal fossa.
This fossa extends from its dorsal boundary as far laterad and caudad as the
lambdoidal ridge (a), and as far craniad as a line connecting the tip of the
zygomatic process of the frontal (f) with the frontal process of the malar (h).
The temporal muscle takes origin from its surface.
The middle portion of the dorsal surface is formed by the frontals (5).
Each frontal presents laterally a prominent zygomatic process (f),
extending ventrolaterad toward a corresponding (frontal) process (h) of the
malar bone. These two processes mark the boundary between the orbital
fossa (craniad) and the temporal fossa (caudad). Craniad of the zygomatic
process of the frontal a sharp margin separates the dorsal surface of the
skull from the wall of the orbital fossa: this is the supraorbital arch or
margin (i).
The cranial portion of the dorsal surface is formed by the maxillary (8),
nasal (7), and premaxillary bones (9). Just craniad of the nasals, bounded
ventrad and craniad by the premaxillaries, appears the large opening of the
nares (j), leading into the nasal cavity.
The zygomatic arch (g) is formed by the zygomatic process of the
temporal (m) and the malar or zygomatic bone (6). Each presents near its
middle a prominent dorsocaudally directed process, the frontal process (h)
of the malar bone. The zygomatic arch forms the lateral boundary of the
temporal and orbital fossæ, which are separated by a line connecting the
frontal process of the malar (h) and the zygomatic process of the frontal (f).
A portion of the floor of the orbit and the opening of the lachrymal canal
(o) may also be seen in dorsal view; they are described in connection with

the lateral surface.
The caudal surface of the skull is formed largely by the occipital bone
(Fig. 17), surrounding the foramen magnum (Fig. 17, d). At the sides of the
foramen magnum are the two prominent curved occipital condyles (e) for
articulation with the atlas. Craniolaterad of the condyles, separated from
them by a deep notch, are the jugular processes (f) of the occipital, closely
applied to the caudal ends of the tympanic bullæ.
Dorsad of the foramen magnum are faint indications of a median ridge
running dorsad, the external occipital crest (Fig. 17, i); this rises at its
junction with the lambdoidal ridge to form the prominent external occipital
tubercle (Fig. 39, b). The dorsal and dorsolateral boundaries of the
posterior surface are formed by the lambdoidal ridge (Fig. 17, h; Fig. 39, a).
The lateral surface of the skull (Fig. 40) is much more complicated than
the dorsal and posterior surfaces. Caudally the occipital condyles (a) and
external occipital crest (b) are visible; dorsocaudad the sagittal crest (c).
Extending from the caudal end of the sagittal crest the lambdoidal ridge
(d) is seen passing ventrocraniad to the tympanic bulla, thence craniad to
the root of the zygomatic arch. In the ventral part of the caudal region the
tympanic bulla (e) is visible with the jugular process (f) of the occipital
pressed close against its caudal end. Just craniad of the jugular process the
mastoid process (g) of the temporal rests against the side of the bulla.
Beneath the cranial edge of this process is the opening of the stylomastoid
foramen (h) for the seventh nerve, while just ventrad of the foramen is the
small pit (i) in the tympanic bulla for the reception of the tympanohyal
bone. Craniad of the stylomastoid foramen is the large opening of the
external auditory meatus (j), leading into the middle ear.
Immediately dorsocraniad of the external auditory meatus the zygomatic
arch begins as the zygomatic process (k) of the temporal bone. On the
cranial surface of the base of this process is the deep mandibular fossa (l)
for the condyle of the mandible. This fossa is bounded caudally by the
prominent postmandibular process (m).

Fig. 40.—Skull, Side View.

1, occipital bone; 2, interparietal; 3, parietal; 4, temporal; 5, 5′, frontal; 6, malar; 7, sphenoid; 8,
palatine; 9, presphenoid; 10, maxillary; 11, nasal; 12, premaxillary; 13, incisor teeth; 14, canine; 15,
16, 17, premolars; 18, molar. a, occipital condyle; b, external occipital crest; c, sagittal crest; d,
lambdoidal ridge; e, tympanic bulla; f, jugular process; g, mastoid process; h, stylo-mastoid
foramen; i, pit for tympanohyal bone; j, external auditory meatus; k, zygomatic process of temporal
bone; l, mandibular fossa; m, postmandibular process; n, zygomatic process of the frontal; o,
supraorbital margin; p, external pterygoid fossa; q, sphenopalatine foramen; r, orbital fissure; s,
internal pterygoid fossa; t, hamulus; u, foramen ovale; v, foramen rotundum; w, optic foramen; x,
opening of lachrymal canal; y, infraorbital foramen.

All that portion of the lateral surface of the skull which lies craniodorsad
of the lambdoidal ridge may be divided (excluding the zygomatic arch) into
three main parts, the temporal fossa, the orbital fossa, and the face. The
boundaries of the temporal fossa have been given. The orbital fossa is
bounded externally by a prominent semicircular ridge formed chiefly by the
zygomatic arch, the zygomatic process of the frontal (n), and the
supraorbital arch (o) of the frontal, which may be traced to the cranial root
of the zygomatic arch. The orbital fossa may be considered to end caudally
and ventrally at the level of the optic foramen (w); ventrad of it are certain
smaller fossæ. Immediately ventrad is the long external pterygoid fossa
(p), from which arises part of the external pterygoid muscle. This fossa
begins at the sphenopalatine foramen (q) and extends caudad to the orbital

fissure (r); it is separated by a ridge from the orbital fossa. Caudoventrad of
the external pterygoid fossa and separated from it by a sharp ridge is the
small narrow internal pterygoid fossa (s), which extends ventrad without
interruption on to the surface of the hamulus (t) and caudad to within two or
three millimeters of the tympanic bulla. From it the internal pterygoid
muscle takes origin. The hamulus (t) projects caudoventrad in this region,
forming a prominent feature in a lateral view.
Four foramina leading into the cranial cavity are visible in a lateral view
of the skull, craniad of the tympanic bulla. The one nearest the bulla is the
foramen ovale (u) for the third division of the fifth nerve; next craniad of
this is the foramen rotundum (v) for the second division of the fifth nerve.
These two foramina pierce the alisphenoid: just craniad of them, between
the alisphenoid and the orbitosphenoid, is the large orbital fissure (r)
(foramen lacerum anterius), which transmits the third, fourth, and sixth
cranial nerves and the first division of the fifth. Dorsocraniad of the orbital
fissure is the optic foramen (w), for the optic nerve.
Ventrad of the cranial portion of the orbit is the large sphenopalatine
foramen (q), for the nerves and arteries of the same name. Just craniad of
this is the small caudal opening of the posterior palatine canal, which
passes through the substance of the palatine bone and opens on its ventral
surface near its cranial margin. Just dorsad of the cranial root of the
zygomatic arch is the opening of the lachrymal canal (x), while the root of
the arch is pierced by the large infraorbital foramen (y), which transmits
the infraorbital nerves and artery from the orbit.
The teeth (13-18), implanted along the alveolar border of the maxillary
and premaxillary, form a prominent feature in a lateral view: they are
described in the account of the alimentary canal.
The ventral surface of the skull (Fig. 41) is very complex. It is separated
by the orbits into a caudal and a cranial portion, united by a narrow median
trough-like part. Laterad of this trough-like part are visible parts of the orbit
and the zygomatic arches, which do not properly belong to the ventral
surface and have already been described.

Fig. 41.—Skull, Ventral View.

1, occipital bone; 2, temporal; 3, sphenoid; 4, presphenoid; 5, frontal; 6, malar; 7, vomer; 8,
palatine; 9, maxillary; 10, premaxillary. a, foramen magnum; b, occipital condyles; c, jugular
process; d, tympanic bulla; e, mastoid process; f, stylomastoid foramen; g, external auditory
meatus; h, jugular foramen; i, styliform process; j, groove for Eustachian tube; k, foramen ovale; l,
foramen rotundum; m, pterygoid process of sphenoid; n, perpendicular plate of palatine; o, choanæ
or posterior nares; p, zygomatic arch; q, cranial end of posterior palatine canal; r, palatine grooves;
s, foramina incisiva or anterior palatine foramina; t, opening of pterygoid canal.

Caudally there appear in the ventral view the foramen magnum (a),
occipital condyles (b), and jugular processes (c). In front of the jugular
processes the two tympanic bullæ (d) form prominent features, with the
mastoid process (e), the stylomastoid foramen (f), and the external auditory

meatus (g) on their lateral surfaces. All these structures have been
described. The tympanic bullæ (d) are placed with long axes directed
craniomediad, so that they converge toward their cranial ends. At the
caudomedial angle of each bulla is the large jugular foramen (h), for the
ninth, tenth, and eleventh nerves. Opening into the mediocaudal margin of
the jugular foramen is the smaller hypoglossal foramen, for the twelfth
nerve.
The craniomedial end of the tympanic bulla projects craniad as the
styliform process (i). Just laterad of this process is the opening (j) into the
tympanic bulla by which the tuba auditiva or Eustachian tube passes into
the middle ear. A faint groove for the tube passes craniomediad from this
opening, on the surface of the sphenoid. Craniolaterad of the opening for
the tuba auditiva is the foramen ovale (k); craniad of this the foramen
rotundum (l) is faintly indicated. On the surface of the sphenoid just
craniad of the styliform process of the bulla tympani is the minute opening
of the pterygoid canal (t). The orbital fissure and optic foramen are not
seen in the ventral view.
The middle region of the ventral surface is narrow: it is formed by a
trough-like fossa which is bounded laterally by the pterygoid processes (m)
of the sphenoid and the perpendicular plates of the palatines (n). Ventrad of
this lies, in the natural condition, the soft palate, converting the fossa into
the nasal portion of the pharynx or nasopharynx. Craniad this fossa is
bounded by the free caudal edges of the palatines; beneath which the fossa
communicates with the nasal cavity by the two choanæ (o). Laterad of this
median fossa are visible in the ventral view parts of the temporal and orbital
fossæ, bounded laterally by the zygomatic arches (p).
The cranial part of the ventral surface is a somewhat triangular plane area
formed by the palatal portions of the palatines (8), maxillaries (9), and
premaxillaries (10), which together constitute the hard palate (palatum
durum). Laterad and craniad this area is bounded by the alveolar borders of
the maxillaries and premaxillaries bearing the teeth. The hard palate is
marked near the cranial border of the palatine bones with two or more
foramina which form the cranial termination of the posterior palatine canal
(q). Two faint grooves pass from these foramina a short distance craniad,
gradually converging: these are known as the palatine grooves (r) (sulci
palatini). Near the cranial end of the hard palate are two large openings

close together near the middle line: these are the foramina incisiva (or
anterior palatine foramina) (s).

Fig. 42.—Skull, with Dorsal Surface Removed, showing the Cranial and Nasal Cavities.
a, foramen magnum; b, caudal end of hypoglossal canal; c, jugular foramen; d, internal auditory
meatus; e, tentorium, forming the cranial boundary of the cerebellar fossa; f, dorsum sellæ; g, sella
turcica; h, anterior clinoid processes; i, foramen ovale; j, foramen rotundum; k, orbital fissure; l,
optic foramen; m, chiasmatic groove; n, presphenoid bone; o, cribriform plate; p, lamina
perpendicularis of ethmoid; q, labyrinths of ethmoid; r, nares; s, foramina incisiva or anterior
palatine foramina; t, infraorbital foramen; u, opening of the lachrymal canal; v, caudal opening of
posterior palatine canal; w, sphenopalatine foramen; x, frontal process of the malar; y, zygomatic
process of the temporal; z, appendicular fossa, in the petrous bone.

Cavities of the Skull (Figs. 42 and 43).—The bones of the cranial
portion of the skull enclose the cranial cavity for the brain; the facial bones

enclose the nasal cavity, for the olfactory organ.
The cranial cavity is divisible into three principal fossæ: the cerebellar
fossa (Fig. 43, I) caudad, for the cerebellum; the cerebral fossa (II) in the
middle, for the cerebrum; the small olfactory fossa (III) at the cranial end
for the olfactory bulb of the brain.
The cerebellar fossa (I) is bounded caudally by the occipital bone
enclosing the foramen magnum (Fig. 42, a). Its ventral surface is formed by
the basilar portion of the occipital and the petrous portions of the temporals;
its lateral surface by the mastoid portions of the temporals and parts of the
parietals and occipital. Its roof is formed by the parietals and interparietal.
Craniad the cerebellar fossa is partly separated from the cerebral fossa by
the tentorium (Fig. 42, e; Fig. 43, f) formed by the two parietals: this
encloses a quadrangular opening by which the two fossæ communicate. The
caudal, dorsal, and lateral walls of the cerebellar fossa are deeply marked
by fossæ for the lobes of the cerebellum; the small appendicular fossa
(Fig. 43, e), forming a deep indentation in the petrous bone near its
dorsocaudal end, is particularly noticeable.
The following openings are found in the walls of the cerebellar fossa.
Caudad is the large foramen magnum (Fig. 42, a) by which the brain-cavity
communicates with the vertebral canal. Near the caudal margin of the
foramen magnum, on its lateral side, just mediad of the dorsal end of the
occipital condyle, is the caudal opening of the condyloid canal (Fig. 43, a)
which passes craniad through the substance of the occipital bone to open
just caudad of the petrous: it transmits a vein. The condyloid canal varies
greatly in size in different specimens. A few millimeters craniad of the edge
of the foramen magnum on the floor of the fossa is the small opening of the
hypoglossal canal (Figs. 42 and 43, b), for the twelfth nerve. Just craniad of
this, at the caudomedial border of the petrous, is the large jugular foramen
(c). On the petrous itself, near the middle, is the internal, auditory meatus
(d) divided into the dorsal facial canal for the seventh nerve, and a ventral
passage for the eighth nerve. At the cranial end of the cerebellar fossa is the
large opening bounded by the free edges of the tentorium.
The cerebral fossa forms much the largest part of the cranial cavity. It is
bounded by the parietals (Fig. 43, 3′), squamous portions of the temporals
(4), frontals (8), the sphenoid (5), and presphenoid (6). A slight rounded
ridge on its lateral wall at about the position of the suture between the
frontals and parietals separates a smaller cranial portion sometimes called

the anterior fossa, from a larger caudal portion sometimes known as the
middle fossa of the cranial cavity. The walls of the cerebral cavity are
marked with numerous ridges and shallow furrows for the cerebral
convolutions.
The floor of the cerebral cavity is bounded caudad by the prominent
dorsum sellæ (Fig. 42, f; Fig. 43, g), just craniad of which is the rounded
depression known as the sella turcica (Fig. 42, g; Fig. 43, h), for lodgment
of the hypophysis. A number of foramina pierce the floor of the cavity in
this region. Just ventrad of the cranial tip of the petrous portion of the
temporal is the small foramen lacerum (medius). Craniad and laterad of
this is a row of four foramina: the caudal one is the foramen ovale (Fig. 42,
i); then come in order the foramen rotundum (j), the orbital fissure (k), and
the optic foramen (Fig. 42, l; Fig. 43, k). The two optic foramina are
connected by the shallow transverse chiasmatic groove (Fig. 42, m), for the
optic chiasma. Another small foramen continues caudad from a groove on
the floor of the orbital fissure; this opens on the ventral surface of the
sphenoid, between the wing and the body of the bone. The groove and
foramen constitute the pterygoid canal, which transmits a nerve,—the
nerve of the pterygoid canal, or Vidian nerve.
The cranial cavity narrows at its cranial end to form the small olfactory
fossa (Fig. 43, III) which lodges the olfactory bulbs. This is bounded by the
frontals and the lamina cribrosa (Fig. 42, o) of the ethmoid; caudad it opens
directly into the cerebral fossa. Numerous openings through the lamina
cribrosa for the olfactory fibres connect the olfactory fossa with the nasal
cavity. The roof of the fossa is marked by a prominent median crest from
the united edges of the frontals.
The nasal cavity is almost completely filled by the ethmoid and vomer
and the conchæ nasales. Its roof is formed by the nasal bones and portions
of the frontals; its sides by the frontals, lachrymals, maxillaries,
premaxillaries, and palatine bones; its floor by the horizontal plates of the
palatines, maxillaries, and premaxillaries.

Fig. 43.—Skull, Median Longitudinal Section, showing the Cavities.

I, cerebellar fossa; II, cerebral fossa; III, olfactory fossa. 1, occipital bone; 2, interparietal; 3, 3′,
parietal; 4, temporal (4, squamous portion; 4′, petrous portion; 4″, tympanic portion); 5, sphenoid;
6, presphenoid; 7, palatine; 8, frontal; 9, maxillary; 10, premaxillary; 11, ethmoid; 12, nasal; 13,
incisor teeth; 14, canine; 15, 16, 17, premolars; 18, molar. a, condyloid canal; b, hypoglossal canal;
c, jugular foramen; d, internal auditory meatus; e, appendicular fossa; f, tentorium; g, dorsum sellæ;
h, sella turcica; i, hamular process; j, pterygoid process of sphenoid; k, optic foramen; l,
presphenoid sinus; m, m′, frontal sinus; n, lamina perpendicularis of the ethmoid (broken at cranial
edge).

The nasal cavity opens craniad by the large nares (Fig. 39, j; Fig. 42, r),
which are bounded by the premaxillary and nasal bones. In the natural
condition this opening is divided by a median cartilage which is continuous
with the lamina perpendicularis (Fig. 43, n) of the ethmoid, thus forming a
partition which divides the nasal cavity into two separate halves. From the
floor of the cranial part of the cavity rises a ridge formed of the nasal crests
of the maxillaries and premaxillaries, and the cranial portion of the vomer.
Farther caudad the vomer spreads out in a horizontal plane and separates
from the floor of the cavity, so that the nasal cavity is thereby divided by a
horizontal partition into dorsal and ventral portions. The ventral portion is
small, forming the inferior meatus of the nose; it ends caudally at the
choanæ (posterior nares, Fig. 41, o) which lead into the nasopharynx. That
portion of the nasal cavity lying dorsad of the vomer is almost completely

filled by the ethmoid and the conchæ nasales, superior and inferior. It is
bounded caudally by the lamina cribrosa of the ethmoid (Fig. 42, o). The
nasal cavity communicates with the cranial cavity by the foramina for the
olfactory fibres in the lamina cribrosa; with the nasopharynx by the choanæ;
with the exterior of the body by the nares; with the mouth-cavity by the
foramina incisiva or anterior palatine foramina (Fig. 42, s); with the orbit by
the sphenopalatine foramen and the nasolachrymal canal. It communicates
directly also with the frontal sinuses (Fig. 43, m, m′), the sphenoidal sinuses
(Fig. 43, l), and with the cells of the labyrinths of the ethmoid.

JOINTS AND LIGAMENTS OF THE SKULL.

Sutures of the Skull.—The bones of the skull join each other by means
of immovable articulations known as sutures. These sutures are designated
by combining the names of the bones between which they are situated: as,
sphenofrontal suture (sutura sphenofrontalis), between the sphenoid and
frontal; nasomaxillary suture (sutura nasomaxillaris), between the nasal
and maxillary bones. When a suture joins the two corresponding bones of
opposite sides the prefix inter is used, as the intermaxillary suture (sutura
intermaxillaris) between the maxillaries. The sutures bounding the
parietals have, however, received special names not derived in this manner.
The suture caudad of the parietals, separating them from the occipital and
interparietal, is known as the lambdoidal suture; that between the two
parietals is the sagittal suture; that separating the parietals and squamous
portions of the temporals is the squamous suture; that between the parietals
and frontals is the coronal suture. The suture separating the two frontals
also is known as the frontal suture, in place of interfrontal.
Articulations of the Mandible.—In man the two halves of the mandible
are united craniad, so as to form a single bone. In the cat the two halves are
separate, but articulate closely at the symphysis menti by a thin
interarticular cartilage.
The articulation of the mandible at the mandibular fossa of the temporal
is covered with a close articular capsule. The mandibular fossa is lined
with cartilage. A slender ligament passes from the angular process of the
mandible caudad to the external auditory meatus, being attached to the

latter about 8 millimeters from its medial end. This is the stylomandibular
ligament.

V. BONES OF THE THORACIC EXTREMITIES.

Scapula (Figs. 44 and 45).—The scapula may be described as a flat
triangular bone with one angle rounded. It lies beneath the muscles on the
lateral face of the thorax near its cranial end. From its lateral surface there
projects a flat ridge (Fig. 44, g), the spine of the scapula. The ventral end of
the ridge is free as a curved process, the acromion process (Fig. 44, j).

Fig. 44.—Scapula, Lateral Surface. Fig. 45.—Scapula, Medial Surface.

I, fossa supraspinata; II, fossa infraspinata; III, fossa subscapularis; IV, fossa for teres major. a,
vertebral border; b, coracoid border; c, glenoid border; d, glenoid angle and fossa; e,
coracovertebral angle; f, glenovertebral angle; g, spine; h, tuberosity of the spine; i, metacromion; j,
acromion; k, supraglenoidal tubercle; l, incisura scapulæ; m, coracoid process; n, groove indicating
portion of spine; o, o′, ridges for attachment of muscle-fibres.

The ventral angle of the scapula (d), the glenoid angle (lateral angle of
human anatomy), is much heavier than the others and bears a concave, pear-
shaped articular facet, the glenoid fossa, for articulation with the humerus.
The border with which this angle is more nearly continuous may be called
the glenoid border (c) (axillary border of human anatomy).
Near the narrower cranial end of the glenoid fossa is a small curved
projection of the bone, the coracoid process (Fig. 45, m). The border upon
which it lies is the coracoid border (b) (superior border of human
anatomy). The third border is turned toward the vertebral column and is the
vertebral border (a).
The angle between the glenoid and vertebral borders is the
glenovertebral angle (f) (inferior angle of human anatomy), and that
between the coracoid and vertebral borders the coracovertebral angle (e)
(medial angle of human anatomy).
The medial or costal surface (Fig. 45) is smooth and nearly flat. A
shallow furrow (n) marks the position of the spine of the scapula. Between
the furrow and the coracoid border are two oblique parallel ridges (o and o′)
for the insertion of muscle-fibres. Near the glenoid border is a well-marked
ridge separating the subscapular fossa (III), comprising the greater part of
the medial surface of the scapula, from the fossa in which the teres major
muscle has origin (IV). The surface presents several nutrient foramina
usually directed toward the glenoid angle.
The lateral surface (dorsal surface of human anatomy) (Fig. 44) is
divided by the spine (g) into two portions. The portion of the scapula
craniad of the spine and the cranial surface of the spine bound the
supraspinous fossa (fossa supraspinata) (I), while the surface caudad of
the spine and the caudal portion of the spine bound the infraspinous fossa
(fossa infraspinata) (II).
The spine (g) begins as a triangular elevated area in the middle of the
vertebral margin and runs toward the glenoid angle. It rises gradually for
about two-fifths of its length and then the margin becomes broader and the
spine remains of the same height to its glenoid end. There is a rough
thickening, the tuberosity (h) of the spine, situated on its free border about
midway between the tip of the acromion and the vertebral end of the spine.
The spine is inclined toward the glenoid margin so as to form an angle of
about 60 degrees with the caudal half of the lateral surface.

At the base of the acromion process (j) the margin of the spine presents a
flat triangular projection, the metacromion (i), directed toward the glenoid
border.
The acromion (j) continues in the direction of the spine. It is thicker than
the spine, smooth and rounded on both its surfaces and both its borders, and
its apex is connected by fibrous tissue to the clavicle.
The coracoid border (b) presents a slight rounded notch, the incisura
scapulæ or suprascapular notch (l), just dorsad of the glenoid angle, and at
its ventral end bears the coracoid process (m) which is directed
ventromediad.
The glenoid angle (d) is the only one requiring special mention. Between
the root of the coracoid process and the glenoid cavity it presents a tubercle,
the supraglenoidal or bicipital tubercle (k), for the tendon of origin of the
biceps muscle. The glenoid angle is separated by a contracted neck from the
rest of the bone. Between this angle and the inner margin of the acromion
there is left a deep notch, the great scapular notch.

Fig. 46.—Clavicle.

a, medial end; b, lateral end.

Clavicle. Clavicula (Fig. 46).—The clavicle in the cat is greatly reduced.
It is a slender curved rod of bone imbedded in the muscles of the shoulder
and connected by fibrous tissue to the apex of the acromion process. The
lateral end (b) is slightly enlarged.
Humerus (Figs. 47 and 48).—The humerus forms the support of the
upper arm and articulates by its proximal end with the scapula at the
glenoid cavity, and by its distal end with the radius and ulna, the bones of
the lower arm. It is a nearly cylindrical bone with enlarged ends, and is so
curved that its dorsal and ventral borders are hooked at the opposite ends so
that it has the form of an Italic f.
The proximal end of the bone bears on its dorsomedial portion a
thickening, the head of the humerus (a), which bears a smooth ovoid
articular facet by which the bone articulates with the glenoid cavity of the

scapula. The head is not separated from the body by a distinct anatomical
neck as in the human humerus.

Fig. 47.—Humerus, Ventral Side. Fig. 48.—Humerus, Medial Side.

a, head; b, greater tuberosity; c, lesser tuberosity; d, bicipital groove; e, pectoral ridge; f, deltoid
ridge; g, rough area for insertion of latissimus dorsi and teres major; h, nutrient foramen; i,
capitulum; j, trochlea; l, coronoid fossa; m, radial fossa; n, medial epicondyle; o, lateral epicondyle;
q, supracondyloid foramen.

Along the lateral border of the proximal end of the shaft is a high rough
ridge semicircular in side view, the great tuberosity (b). It gives attachment
to muscles and is marked on its dorsal border by a deep depression for the

tendon of the infraspinatus muscle. On the medial margin of the proximal
end closely associated with the head is a smaller elevation, the lesser
tuberosity (c), also for muscular attachment.
Between the greater and lesser tuberosities on the ventral surface is seen
a broad groove, the sulcus intertubercularis or bicipital groove (d), which
passes distad onto the surface of the shaft. In the natural state it is converted
into a canal by overlying tendons and lodges the tendon of the biceps
muscle.
The shaft is nearly cylindrical at its middle, but its dorsoventral diameter
is slightly greater than its mediolateral diameter. Its proximal end is
flattened mediolaterad, while its distal end is flattened dorsoventrad.
From the ventral margin of the greater tuberosity a ridge, the pectoral
ridge (e), is continued onto the surface of the shaft, and from the dorsal
margin another ridge, the deltoid ridge (f), passes distad and ventrad so as
to meet the pectoral ridge near the middle of the ventral surface of the bone.
On the medial margin of the bone near the junction of the first and second
fourths is a roughened area (g) for the attachment of the tendons of the
latissimus dorsi and teres major muscles, and on the same surface near the
junction of the second and last thirds is a nutrient foramen (h).
The distal end of the bone presents a smooth saddle-shaped articular
surface, which, in well-marked bones, is divided, when seen from the
ventral surface, by a slight nearly median ridge into two unequal portions,
lateral and medial (i and j). The lateral half is rounded and is called the
capitulum (i). It is broader ventrad than dorsad, and is not continued onto
the dorsal surface of the bone. It is for articulation with the proximal end of
the radius.
The medial half of the surface, the trochlea (j), is concave and passes
directly into the capitular surface laterad, but is limited mediad by a sharp
ridge. It is continued onto the dorsal surface of the bone, where it is limited
also laterad by a ridge. It articulates with the semilunar notch of the ulna.
Proximad of the trochlea the dorsal surface presents a deep fossa, the
olecranon fossa, which receives the olecranon of the ulna when the arm is
straightened. On the ventral surface (Fig. 47) are two shallower fossæ
separated by a longitudinal ridge. The one over the trochlea receives the
coronoid process of the ulna when the arm is bent, and is called thence the
coronoid fossa (l). The one over the capitulum, the radial fossa (m),
receives a triangular facet on the proximal end of the radius at the same

time. Between the radial and coronoid fossæ on one side and the olecranon
fossa on the other is only a thin plate of bone. On the medial surface of the
distal end is a considerable roughened elevation, the medial epicondyle (n)
(epitrochlea). It gives origin to flexor muscles and to the ulnar collateral
ligaments of the elbow-joint. Opposite the medial epicondyle over the
capitulum is the lateral epicondyle (o) for the origin of extensor muscles of
the forearm and of the radial collateral ligaments of the elbow-joint. From
the lateral epicondyle a ridge, the lateral supracondyloid ridge (p),
continues proximad, curving onto the dorsal surface of the bone and ending
about opposite the junction of the deltoid and pectoral ridges.
Proximad of the medial epicondyle the bone is pierced near its medial
margin by an oblique oval foramen, the supracondyloid foramen (q).
Radius (I, Figs. 49 and 50).—In the usual position the radius lies with its
proximal end on the lateral side of the arm, articulating with the capitulum
of the humerus. The proximal end is thus laterad of the proximal end of the
ulna. Its distal end, however, lies on the medial side of the distal end of the
ulna, so that the radius in the natural position crosses ventrad of the ulna.
The radius is a curved bone slightly flattened dorsoventrally, with
enlarged ends. It may be described as consisting of a shaft and of a
proximal and a distal end. Its proximal end presents on the ventral surface a
tuberosity, the bicipital tuberosity (c), for the insertion of the tendon of the
biceps muscle. Proximad of this the bone is contracted to form a neck (b)
which is surmounted by a head (a). The head has on its proximal surface a
depressed oval facet by which it articulates with the capitulum, and on its
ulnar border a long narrow facet, the articular circumference (d), for
articulation with the radial notch of the ulna; also a triangular facet (e),
which fits into the radial fossa of the humerus.
The shaft is convex dorsad and concave ventrad. The distal end is
somewhat pyramidal. From its medial or radial side a wedge-shaped
process, the styloid process (f), extends distad. The distal surface of the end
together with the lateral surface of the styloid process form a concave
articular cavity (g) which fits against the scapholunar bone.

Fig. 49.—Radius and Ulna, Dorsolateral Fig. 50.—Radius and Ulna, Ventromedial
View. View.

I, radius; II, ulna. a, head of radius; b, neck; c, bicipital tuberosity; d, articular circumference; e,
facet for radial fossa of humerus; f, styloid process of radius; g, facet for articulation of scapholunar
bone; h, semilunar (or great sigmoid) notch of ulna; i, coronoid process; j, olecranon; k, area for
insertion of brachialis and clavobrachial muscles; l, rough area for attachment of interosseous
membrane; m, styloid process of ulna.

The dorsal surface of the distal end is marked by longitudinal grooves for
tendons, and its lateral or ulnar surface bears a concave facet for articulation
with the ulna.
Ulna

(II, Figs. 49 and 50).—The ulna is a long slender bone, flattened
mediolaterad. It is enlarged at its proximal end and becomes gradually
smaller toward the distal end.
The proximal end is marked ventrally by a deep excavation, the
semilunar notch, or great sigmoid cavity (h). By the saddle-shaped
articular surface of the semilunar notch it articulates with the trochlea. This
articular surface is divided into two parts by a transverse non-articular area.
The distal boundary of the semilunar notch is a blunt process, the coronoid
process (i), which bears on its lateral surface a concave facet, the radial
notch, for the head of the radius.
The portion of the bone proximad of the semilunar notch is called the
olecranon (j). It fits into the olecranon fossa of the humerus when the arm
is straightened, and is rough at its end for the insertion of tendons.
The body of the ulna becomes triangular distad. The distal end is slightly
larger than the shaft just proximad of it, and bears on its radioventral side a
hemispherical head for articulation with the radius. Distad of the head the
bone continues as the flattened styloid process (m), which projects distad
from its dorsolateral side and is smooth on the medial side of its apex, for
articulation with the cuneiform bone of the wrist.
Carpus (Fig. 51).—The carpus (wrist) consists of seven bones arranged
in two rows, three in the proximal row and four in the distal row. Beginning
on the medial side of the hand (thumb or radial side), the first bone in the
proximal row is the scapholunar (a) (equal to the scaphoid or navicular
and lunar of the human hand). It articulates with the radius. The next is the
cuneiform (b), articulating with the styloid process of the ulna, and the
next, which is attached to the cuneiform and projects freely ventrad, is the
pisiform (c).
In the distal row the bone on the radial side is the trapezium (d); the next
is the trapezoid (e), the next the os magnum (f), and the last the unciform
(g). The distal row articulates with the metacarpals or bones of the palm of
the hand (1-5).
In the kitten the scapholunar is represented by three bones, the scaphoid
or navicular, on the radial side, the lunare, between the scaphoid and the
cuneiform, and a centrale, which lies distad of the other two.
Scapholunar Bone. Os scapholunaris (Fig. 51, a).—The scapholunar is a
quadrangular bone with the ventroradial angle produced into a blunt
process. Its proximal surface is smooth and articulates with the distal end of

the radius. The distal end is marked by oblique ridges and articulates with
the unciform, os magnum, trapezoid, and trapezium. The ulnar surface
articulates with the cuneiform, and the dorsal surface of the ventroradial
process with the radial sesamoid.
Cuneiform Bone. (Os triquetrum BNA) (Fig. 51, b).—The cuneiform
bone has the form of a flattened pyramid. Its base articulates with the
unciform, its proximoulnar surface with the pisiform except at its dorsal
margin, where it articulates with the styloid process of the ulna. On its
proximoradial surface is a smooth facet for articulation with the
scapholunar.
Pisiform Bone. Os pisiforme (Fig. 51, c).—The pisiform bone is about
twice as long as broad, with enlarged ends. Its dorsal end articulates with
the cuneiform, and on its proximal surface, separated from the above by a
smooth ridge, is a smooth facet for articulation with the styloid process of
the ulna.

Fig. 51.—Carpus, Metacarpus, and Phalanges, Dorsal Surface.

a, scapholunar bone; b, cuneiform; c, pisiform; d, trapezium; e,
trapezoid; f, os magnum; g, unciform; h, radial sesamoid; i, proximal
phalanges; j, second phalanges; k, distal phalanges; 1, 2, 3, 4, 5,
metacarpals in order from the radial side.

Unciform Bone. (Os hamatum BNA) (Fig. 51, g).—The unciform is a
wedge-shaped bone with the apex of the wedge directed proximad, and
smooth for articulation with the scapholunar. By a part of its ulnar surface it
articulates with the cuneiform, and by its radial surface with the os
magnum. Its distal end articulates with the fourth and fifth metacarpals.
Os magnum. (Os capitatum BNA) (Fig. 51, f).—The os magnum may be
described as an oblong plate bearing on its proximal surface a semicircular
ridge which crosses it diagonally. The proximal end of the bone articulates
with the scapholunar. Its distal end articulates with the third metacarpal

except near its ventroulnar angle, where it articulates with the fourth
metacarpal. Its ulnar surface articulates with the unciform. Its radial border
articulates with the trapezoid, the third metacarpal, and, by two facets, with
the second metacarpal.
Trapezoid. (Os multangulum minus BNA.) (Fig. 51, e).—The trapezoid is
somewhat wedge-shaped, with the apex of the wedge pointing ventrad. Its
proximal side articulates with the scapholunar, its distal side with the
second metacarpal, its ulnar side with the os magnum, and its radial side
with the trapezium.
Trapezium. (Os multangulum majus BNA.) (Fig. 51, d).—The trapezium
has the form of a triangular prism curved into a semicircle. The convex face
looks proximad and articulates by its ventral half with the scapholunar. The
ulnar surface articulates with the second metacarpal dorsally, and ventrally
with the trapezoid. Its radial surface articulates with the first metacarpal.
Bones of the Hand or Manus (Fig. 51, 1-5).—The Metacarpals.
Metacarpus.—The metacarpals are the five bones of the palm of the hand;
they are numbered from one to five, beginning with the thumb. They are
cylindrical elongated bones with enlarged ends. The distal end is called the
head, and the proximal end the base. Each head bears a hemispherical
articular facet which is marked over its ventral half by a prominent smooth
ridge. The surface dorsad of the ridge articulates with the proximal head of
a phalanx. The ridge and the surface at its sides are for a pair of sesamoid
bones.
The first metacarpal (1) is the shortest. Its head is oblique, and it
articulates by the ulnar half of its proximal surface with the trapezium (d);
by the radial half with the radial sesamoid (h).
The second metacarpal (2) is marked on the proximal part of its dorsal
surface by an oblique groove passing from the radial side distad to the ulnar
side. The base articulates with the trapezoid (e). The ulnar surface of the
proximal end articulates with the os magnum (f) and third metacarpal, while
the radial surface articulates with the trapezium (d).
The third metacarpal (3) is the longest, and its base is rhomboidal with a
projecting dorsoradial angle separated by a groove from the rhomboid
surface. The proximal end articulates with the os magnum (f) and second
metacarpal; the radial surface of the proximal end with the second, and the
ulnar surface with the fourth, metacarpal.

The fourth metacarpal (4) has a base similar in form to that of the third,
and when placed in position with the fifth the two form a hemispherical
facet which articulates with the unciform (g) and os magnum (f). The fourth
metacarpal articulates by its radial side with the third, and by its ulnar side
with the fifth.
The fifth metacarpal (5) articulates by its proximal end with the unciform
(g), and by the radial side of its proximal end with the fourth metacarpal.
Digits (Fig. 51).—The first digit of the hand is called the pollex (thumb),
the second the index, the third the medius, the fourth the annularis, the
fifth the minimus.
The first digit has two phalanges, each of the others three phalanges.
Phalanges (Fig. 51, i, j, k).—The phalanges of the proximal row (i) are
elongated, flattened dorsoventrally and curved so as to be longitudinally
convex dorsad. All have thickened ends. The proximal end is notched, and
its proximal surface looks dorsad and is concave for the head of the
metacarpal. The distal end is pulley-shaped, and the pulley surface extends
farther on to the ventral than on to the dorsal surface, and serves for
articulation with the middle phalanx.
The phalanges of the middle row (j) are like those of the proximal row,
but shorter. The proximal surface is triangular and marked by a median
facetted ridge. The whole surface is smooth and adapted to the distal end of
the phalanx of the first row. The distal end is transversely elongated, so as
to be cylindrical, and projects more toward the ulnar than toward the radial
side. The distal phalanx (k) articulates with this cylinder so that when it is
fully extended it lies on the ulnar side of the middle phalanx.
The distal phalanx (k) has the form of a quadrangular prism. It is
excavated on its proximal surface for articulation with the middle phalanx.
Its distal surface presents dorsad a deep excavation from the bottom of
which arises a compressed plate of bone having the form of a bird’s beak.
The depression receives the base of a claw, and the beak-like projection
supports the claw.
Sesamoid Bones of the Hand. Ossa sesamoidea.—The hand contains, in
addition to those already described, eleven small bones that are developed
in tendons.
One of these, the radial sesamoid (Fig. 51, h), is closely applied to the
radial end of the scapholunar bone. It is developed in the tendon of the
extensor brevis pollicis muscle.

The other ten occur in pairs as small flattened curved bones on the
ventral side of the joint between each metacarpal and the phalanx with
which it articulates.

JOINTS AND LIGAMENTS OF THE THORACIC LIMBS.

The shoulder-joint is an arthrodial or ball-and-socket joint. The bones
entering into its formation are the scapula and the humerus.
The capsular ligament or articular capsule is very ample and allows
for extended movement of the humerus. It is attached to the edge of the
glenoid fossa of the scapula and passing distad covers the head of the
humerus and is inserted at the line of junction of the shaft and the epiphysis
which forms the head of the bone. On the lateral side of the ventral surface
of the humerus the attachment continues distad about two centimeters along
the lateral edge of the bicipital groove. On the medial side the insertion
passes over the proximal end of the lesser tuberosity. A strong transverse
band passes from the greater tuberosity to the lesser tuberosity and bridges
the bicipital groove, converting it into a canal. The lateral and medial parts
of the capsule are strengthened by thicker bands of fibres, the more
prominent medial one of which passes from the coracoid process of the
scapula to the lesser tuberosity. To the capsule are closely united parts of the
supraspinatus, infraspinatus, coracobrachialis, and subscapularis muscles. A
synovial membrane lines the capsule within and forms a sheath around the
biceps tendon, so that the latter does not actually enter the synovial capsule.
The elbow-joint (Figs. 52 and 53) is a ginglymus or hinge-joint. The
bones which enter into it are the humerus, radius, and ulna.
The capsule of the joint forms a sac, with the following attachments to
the bones: (1) To the humerus it is attached at the proximal edge of the
coronoid and radial fossæ; to the sides of the capitulum and trochlea distad
of the two epicondyles, and to the distal edge of the olecranon fossa. (2) To
the ulna it is attached at the edges of the radial and semilunar notches; (3) to
the radius around the articular facet, two or three centimeters distad of the
border. Many of the muscles of this region are closely attached to the
capsule.

Fig. 52.—Ligaments of Elbow-joint, Medial Fig. 53.—Elbow-joint, Lateral View.
Side.

Fig. 52.—1, humerus; 2, ulna; 3, radius. a and b, the two medial collateral ligaments.
Fig. 53.—1, humerus; 2, radius; 3, ulna. a, dorsal collateral ligament; b, ventral collateral
ligament; c, annular ligament.

Closely connected with the capsule of the joint are the collateral
ligaments. The two medial collateral ligaments (Fig. 52) arise from the
medial epicondyle. One (b) passes distad and laterad to the interval between
the radius and ulna; here it divides, one branch going to the head of the
radius, while the other is attached to the lateral surface of the ulna at the
edge of the semilunar notch. The second medial ligament (a) lies dorsad of
the first; it passes to the medial surface of the ulna, at the distal edge of the
semilunar notch.
The two collateral ligaments on the lateral side (Fig. 53) arise from the
lateral epicondyle. The ventral one (b) passes almost directly distad and is
inserted into the lateral surface of the proximal end of the radius about one
centimeter from the articular surface; its inner surface is partly united to the
annular ligament (c) of the radius. The dorsal one (a) is attached to the
lateral border of the semilunar notch of the ulna.
Articulations of Radius and Ulna.—The proximal radio-ulnar
articulation (Fig. 53) is by a pivot-joint or trochoid. The two bones are
held in place by the annular ligament (Fig. 53, c). This is attached on the
lateral side to the dorsal border of the radial notch of the ulna, passes
around the head of the radius, receiving some ligamentous fibres which

come from the lateral epicondyle, and is attached to the coronoid process of
the ulna. The annular ligament is closely united with the capsule of the
joint.
The radius and ulna are united for about their middle third by the thin
interosseous membrane, which fills the interosseous space between their
adjacent edges.
The Wrist.—At the wrist or carpus there are in reality three joints, the
first between the radius and ulna proximad and the first row of carpals
distad, the second between the two rows of carpal bones, the third between
the distal row of carpals and the metacarpals. The first two are movable
joints; the third is not. Each of these three joints has a capsule, and the
bones entering into the joints are interconnected by numerous ligaments.
These ligaments are named by combining the names of the two bones
which they interconnect. Ligaments which interconnect bones of the same
row in the carpus are sometimes distinguished as interosseous ligaments, as
contrasted with intercarpal ligaments, which connect together bones of
different rows. According to their position the ligaments may also be
distinguished as dorsal, ventral, and lateral. Detailed descriptions and
figures of all these ligaments are given by Strauss-Durckheim.
Metacarpals.—The joint between the carpals and metacarpals has been
described. At the distal end of the metacarpals the articulations with the
phalanges have each a capsule. The joint is further strengthened by a double
lateral ligament on each side. The two sesamoid bones at each joint are
interconnected by a strong transverse ligament, and each is connected with
the head of the metacarpal and the base of the first phalanx by a lateral
ligament.
Phalanges.—Between the phalanges the joints possess capsules, and
each has a radial and an ulnar lateral ligament.

VI. BONES OF THE PELVIC EXTREMITIES.

Innominate Bones. Ossa innominata. (Os coxæ BNA) (Figs. 54 and
55).—The two innominate bones articulate with the sacrum and extend
thence caudoventrad and finally turn mediad and unite in the middle line,
forming the symphysis pubis. They thus form an arch, the pelvic arch,
pelvic girdle or pelvis, which is closed dorsad by the sacrum.

In the middle of the lateral surface of each bone is a hemispherical
depression, the acetabulum (Fig. 55, d), which receives the head of the
femur.

Fig. 54.—Innominate Bone of Kitten,
Ventrolateral View.

I, ilium; II, ischium; III, pubis; IV,
acetabular bone. a, acetabulum; b,
obturator foramen.

In the kitten each innominate bone is composed of three principal parts
united by sutures (Fig. 54). From the sacrum to the acetabulum is a single
bar, the ilium (I). Caudad of the acetabulum are two bars. The dorsal one of
these is the ischium (II), and the ventral one is the pubis (III). The ischium
enters into the formation of the acetabulum (a), but the pubis does not. The
two bones, however, are in contact at the ventral edge of the acetabulum.
From this point they diverge, but unite with one another again near the
middle line and thus enclose an oval foramen, the obturator foramen (b).
Wedged between the ilium, ischium, and pubis at their point of junction and
helping to form the acetabulum is a small irregular bone, the acetabular
bone (IV). In the adult cat these four parts are united into a single bone

which is nevertheless usually described, ignoring the acetabular piece, as
made up of ilium (Fig. 55, I), ischium (II), and pubis (III).

Fig. 55.—Innominate Bone of Adult Cat, Ventrolateral View.

I, ilium; II, ischium; III, pubis. a, crest of the ilium; b, posterior inferior
spine; c, great sciatic notch; d, acetabulum; d′, incisura acetabuli; e, spine
of the ischium; f, lesser sciatic notch; g, tuberosity of the ischium; h,
ramus of the ischium; i, ramus of the pubis; j, obturator foramen; k, pubic
tubercle; l, iliopectineal line; l′, ilio-pectineal eminence; m, anterior
superior process.

The ilium (I) is somewhat contracted at the middle and broader at its
ends. One end enters into the acetabulum (Fig. 55, d) and forms about one-

fifth the articular surface. This end is also the thickest part of the bone. The
lateral surface of the ilium is concave for the attachment of muscles. The
medial surface is smooth over its acetabular half and rough over its sacral
half. The rough portion is marked at its junction with the smooth portion by
the ear-shaped auricular impression by which the bone articulates directly
with the sacrum. The caudal half of that part of the medial surface craniad
of the auricular impression gives attachment to the ilio-sacral ligaments
which bind the ilium to the sacrum. The dorsal border is straight at its
cranial end and concave and rounded at its caudal end. Between the two
portions and at the dorsal edge of the auricular surface is a protuberance
corresponding to the posterior inferior spine (Fig. 55, b) of the human
ilium. The concavity of the dorsal border (c) corresponds to the great sciatic
notch of the human ilium. At its caudal end is the short spine of the
ischium (e), which is not a part of the ilium. The ventral border of the ilium
is broad caudad, becoming narrower craniad. The lateral margin of the
ventral border is continued to a tuberosity at the edge of the acetabulum; its
medial margin is called the iliopectineal line (l) and extends on the pubis to
the symphysis. An eminence, the iliopectineal eminence (l′), on the
iliopectineal line, lies opposite to the acetabulum at about the junction of
the ilium and pubis. The cranial end of the bone is thickened, forming the
crest (a) of the ilium. At the junction of the crest with the ventral border is a
projection, the anterior superior process (m) of human anatomy.
The pubis (III) (including the acetabular bone) enters into the formation
of the acetabulum (d) constituting about one-sixth the circumference, but
less than one-sixth its area. It may be described as a flat, curved bone,
contracted at the middle and expanded at the ends. The dorsal end enters
into the acetabulum; the ventral end unites with the opposite bone at the
symphysis pubis and sends caudad a projection, the ramus (i) of the pubis,
which unites with the ramus of the opposite bone to form about two-thirds
of the entire symphysis. At the sides of the symphysis a slightly marked
angle projects craniad from each of the pubic bones; these two together
constitute the pubic tubercle (k), for the origin of the rectus abdominis
muscle. The surfaces of the ramus are smooth. One of its borders is concave
and enters into the formation of the obturator foramen (j). Another of its
borders is the iliopectineal line (l). Its third border is rough for the
symphysis.

The ischium (II) has the form of a triangular prism contracted at the
middle. Its cranial end forms nearly two-thirds of the acetabulum. Its caudal
end bears dorsad a rough thickening, the tuberosity of the ischium (g).
From the caudal half of the ventral border of the bone a sickle-shaped
process, the ramus (h) of the ischium, curves medioventrad and then
craniad and joins the ramus of the pubis. Its medial border is rough and
enters into the symphysis, forming the caudal one-third. The lateral angle of
the bone is rounded. Its dorsal angle is marked near the cranial end by the
spine (e) of the ischium. The concavity between this spine and the
tuberosity corresponds to the lesser sciatic notch (f) of human anatomy.
The acetabulum (d) is cup-shaped. The ventral one-sixth of its border is
deficient and a broad groove extends from the deficiency to the bottom of
the cup. The deficiency, incisura acetabuli, or acetabular notch (d′), is
closed naturally by a ligament, and the groove gives origin to the ligament
(ligamentum teres) which attaches the head of the femur.

Fig. 56.—Left Femur, Ventral Side.

a, head; b, neck; c, depression for round ligament; d, great trochanter; e,
trochanteric fossa; f, intertrochanteric line; g, lesser trochanter; h, linea
aspera; i, medial condyle; j, lateral condyle; k, intercondyloid fossa; l,
lateral epicondyle.

Femur (Fig. 56).—The femur is the proximal bone of the posterior
extremity. It consists of enlarged proximal and distal ends connected by a
nearly cylindrical shaft. The proximal end presents on its medial side a
hemispherical head (a) which fits into the acetabulum. It is supported by a
neck (b) which is contracted near the head and expanded dorsoventrally
where it joins the remainder of the bone. The medial surface of the head
presents near its ventral border a depression (c) for the insertion of the
round ligament of the femur. Ventrad the articular surface of the head

extends as an acute projection onto the shaft, so that the whole articular
surface appears somewhat pear-shaped. On the lateral side of the proximal
end opposite the head is a projecting mass, the great trochanter (d),
forming the end of the shaft. On the medial side of the great trochanter at its
junction with the neck is a deep fossa, the trochanteric fossa or digital
fossa (e) for the insertion of muscles. From the ventral surface of the great
trochanter a ridge, the intertrochanteric line (f), is continued distad, ending
in a pyramidal projection, the lesser trochanter (g), which serves for the
insertion of muscles. A second ridge is continued to the lesser trochanter
from the neck. A slight but well-marked ridge, the spiral ridge or line, runs
round two sides of the neck parallel to the second ridge.
The shaft is nearly straight and cylindrical. A rough line is continued
along its ventral surface from the lesser trochanter, and a similar line along
its lateral surface from the greater trochanter; these unite ventrad to form
the linea aspera (h). On its ventral surface is a nutrient foramen, directed
proximad.
The shaft gradually widens distad and ends in two condyles (i and j)
which are continuous dorsad but separated ventrad by a deep notch, the
intercondyloid fossa (k). The distal surface of the shaft and condyles is
articular. This articular surface is larger on the lateral condyle (j). The part
of the articular surface on the end of the shaft (patellar surface) is for the
patella; that part of it on the condyles and separated by the notch is for the
tibia.
On the lateral surface of the lateral condyle is a slight prominence, the
lateral epicondyle (l), and on the medial surface of the medial condyle is
another prominence, the medial epicondyle; both are for the attachment of
ligaments.
Patella (Fig. 1, r).—The patella is a small flat bone with a pear-shaped
outline, having its apex distad. It lies against the articular surface at the
lower end of the shaft of the femur. It thus covers the knee-joint. The inner
surface is smooth and convex from side to side, but concave in a
proximodistal line. It fits against the lower end of the femur. Its outer
surface is rough and concave. It is a sesamoid bone inserted in the tendon of
the quadriceps femoris muscle.
Three other sesamoid bones are found in the region of the knee (see Fig.
61, p. 89). Two are in the tendons of the gastrocnemius muscle, proximad of

the two condyles of the femur. The third is in the tendon of the popliteus
muscle, just laterad of the lateral condyle of the femur.

Fig. 57.—Tibia and Fibula of Left Leg, Dorsal View.

I, tibia; II, fibula. a, medial condyle of the tibia; b, lateral condyle; c,
spine of the tibia; d, crest of the tibia; e, tubercle for attachment of the
patellar ligament; f, medial malleolus; g, projection of dorsal surface of the
tibia; h, head of fibula; i, lateral malleolus.

Tibia (I, Fig. 57).—The tibia is the longer of the two bones of the leg
between the knee and the ankle, and is the longest bone of the body. It has a
triangular shaft and enlarged proximal and distal ends.

The proximal end is curved ventrad and projects into two prominences,
the tuberosities, on either side. Each tuberosity bears on its proximal end
an articular facet for the condyles of the femur; these are known
respectively as the lateral and medial condyles (a and b) of the tibia. The
condyles are oval, convex dorsoventrad, and concave from side to side. The
two condyles are separated at the middle of their contiguous margins by a
bicuspid projection, the spine of the tibia (c). They are continuous dorsad,
but separated ventrad by a deep notch between the tuberosities, the
popliteal notch. On the distal side of the lateral condyle is an elongated
facet for the proximal end of the fibula.
The shaft is triangular, smallest at about its middle and enlarged at both
ends. It presents dorsal, medial, and lateral borders, and medial, lateral, and
ventral surfaces. The lateral surface is concave proximad. The medial
surface is convex. The two are continuous at the distal end. At their
proximal ends the border separating them is raised into a prominent ridge,
the crest (d) of the tibia, the proximal end of which contributes to increase
the proximal surface of the bone, and presents an oblong tubercle (e) for the
insertion of the ligamentum patellæ (ligament of the quadriceps femoris
muscle). The ventral surface is concave proximad where it abuts upon the
tuberosities. Its proximal half is crossed by two rough parallel lines, the
distal one of which crosses in a spiral course from the lateral to the medial
border; near its beginning is a nutrient foramen.
The distal end extends farther distad on its medial side. The extension is
the medial malleolus (f). The malleolus presents two grooves on its medial
surface for the tendons of muscles. On the lateral side of the distal end is an
oblique triangular facet for the distal end of the fibula. The ventral surface
of the distal end presents an oblique border which passes from the apex of
the malleolus proximolaterad. The dorsal surface extends into a V-shaped
projection (g) between the malleolus and the fibular facet. The distal end
presents an oblique ridge running from the apex of the V-shaped extension
of the dorsal surface to near the base of the medial malleolus. The ridge and
the concavities on either side of it, the medial one of which is deeper, fit
against the proximal trochlear surface of the astragalus.
Fibula (II, Fig. 57).—The fibula lies at the lateral side of the tibia in the
shank. It is a slender triangular bone with enlarged proximal and distal ends.
The proximal end or head (h) is flattened. It bears a facet on its
proximomedial surface for articulation with the tibia, and is longitudinally

grooved on the outer surface.
The shaft has a very sharp medial border. This border is turned toward
the tibia and gives attachment to the interosseous membrane, which runs
between the tibia and fibula.
The distal end is expanded to form the lateral malleolus (i). This bears a
facet on the proximal portion of its medial surface near its dorsal margin,
for the tibia, and distad of this is a second facet for the astragalus. The
ventral and lateral surfaces are grooved for tendons.
Tarsus (Fig. 58).—The tarsus consists of seven bones. The longest of
these, lying on the lateral side of the foot and forming the support of the
heel, is the calcaneus or os calcis (a). It articulates distad with a bone, the
cuboid (c), which bears the fourth and fifth metatarsals. Lying between the
calcaneus and the tibia is the astragalus or talus (b), the distal end of which
articulates with the boat-shaped navicular or scaphoid (d). The scaphoid
bears on its distal surface the three cuneiform bones, lateral (e), medial (g),
and intermediate, bearing the rudiment of the first metatarsal and the second
and third metatarsals.
Astragalus. (Talus BNA) (Fig. 58, b).—The astragalus may be divided
into body, neck, and head. The body is marked on its proximal surface by a
deep pulley-like groove for the articulation with the distal end of the tibia,
and on its lateral and medial surfaces by curved facets for articulation with
the malleoli of the tibia and fibula. This entire surface for articulation with
the bones of the leg is known as the trochlea. The lower surface is marked
by two facets separated by a groove; these are for articulation with
corresponding facets on the calcaneus. Distally the bone contracts to form
the neck and enlarges at the end, forming the head, which is smooth on its
distal surface for articulation with the navicular or scaphoid.
Calcaneus (Fig. 58, a, and Fig. 59).—The calcaneus (os calcis) is the
largest bone of the foot and forms the heel. It is two or three times as long
as broad and has six surfaces: dorsal, ventral, medial, lateral, proximal, and
distal. The proximal one-half of the dorsal surface (Fig. 59) is smooth,
while the distal half is broadened and bears two facets which are separated
by a groove. These articulate with the corresponding facets on the
astragalus. The medial facet is borne on a projection of the bone, the
sustentaculum tali (c). Distad of the facets the surface is rough. The ventral
surface is smooth. The proximal end (b) is grooved for the tendon of
Achilles. The lateral surface is smooth and marked by a grooved tubercle,

the peroneal tubercle (d), near the distal end. The medial surface is marked
by part of the articular facet for the astragalus, and also by the grooved
sustentaculum tali. The distal end (a) articulates with the cuboid.

Fig. 58.—Tarsus, Metatarsus, and Phalanges Fig. 59.—Calcaneus of Right Foot, Dorsal
of Left Foot, Ventral View. View.

a, calcaneus; b, astragalus; c, cuboid; d, a, distal facet for cuboid; b, proximal end
scaphoid; e, lateral cuneiform; g, medial with groove for tendon of Achilles; c,
cuneiform; h, peroneal groove, for the tendon sustentaculum tali; d, peroneal tubercle.
of the peroneus longus muscle; i, proximal

phalanges; j, second row of phalanges; k, distal
phalanges; l, sesamoid bones. 1, rudimentary
first (medial) metatarsal; 2, 3, 4, 5, the other
metatarsals.

Cuboid. Os cuboideum (Fig. 58, c).—The cuboid has somewhat the form
of a cube and articulates by its proximal end with the calcaneus (a), and by
its distal end with the fourth and fifth metatarsals. Its medial surface
articulates with the scaphoid (d) and lateral cuneiform (e). The ventral
surface is marked near its distal end by an oblique ridge, distad of which is
a deep groove, the peroneal groove (h), for the tendon of the peroneus
longus muscle.
Scaphoid. (Os naviculare pedis BNA) (Fig. 58, d).—The scaphoid is a
boat-shaped bone. Its proximal surface is marked by a concave facet for the
head of the astragalus (b), and its distal surface has three facets for the
lateral (e), intermediate and medial (g) cuneiform bones. At the junction of
the ventral with the medial surface is a prominent tubercle. The lateral
surface bears two linear facets for articulation with the calcaneus (a) and
cuboid (c).
Lateral Cuneiform. Ectocuneiform. Os cuneiforme tertium BNA (Fig. 58,
e).—The lateral cuneiform is a wedge-shaped bone with a hooked process
extending from the ventral sharp angle of the bone. It articulates by its
proximal end with the scaphoid (d), and by its distal end with the third
metatarsal. The medial surface bears near its distal end two facets for the
second metatarsal, and on its proximal end a facet for the intermediate
cuneiform. The caudal surface has a facet on its proximal end for the cuboid
(c).
Intermediate Cuneiform. Mesocuneiform. Os cuneiforme secundum BNA.
—The intermediate cuneiform is small and wedge-shaped, with the base of
the wedge dorsad. It lies between the lateral cuneiform and the medial
cuneiform, articulates by its proximal end with the middle facet of the
scaphoid, and bears on its distal end the second metatarsal. It is not visible
in ventral view.
Medial Cuneiform. Entocuneiform. Os cuneiforme primum BNA (Fig. 58,
g).—The medial cuneiform lies on the medial side of the foot. It is a flat

triangular bone about twice as long as broad, and broader at its proximal
end than at the distal end. It bears on its distal end the rudimentary first
metatarsal. The proximal end is oblique and bears a concave facet for the
lateral distal facet of the scaphoid (d). The lateral surface has a concave
facet at its proximal end for the intermediate cuneiform, while the distal
portion is applied against the medial surface of the second metatarsal.
Bones of the Foot or Pes (Fig. 58).—Metatarsals. Metatarsus (Fig. 58,
1-5).—The metatarsals are five in number. They bear a close resemblance to
the metacarpals, but they may be distinguished by their bases.
The first metacarpal (1) is rudimentary and conical. Its base has a facet
for the distal end of the medial cuneiform (g), while the outer surface fits
into a depression on the inner surface of the base of the second metatarsal.
The second (2). The proximal surface of the base is triangular,
corresponding to the distal end of the intermediate cuneiform. The medial
surface is marked by two concavities, one along the proximal border for the
distal end of the medial cuneiform, and one distad of this for the first
metatarsal. The lateral surface bears on the proximal margin an oblique
triangular facet dorsad and a similar facet ventrad, both for the lateral
cuneiform (e). Distad of these facets is a rough ridge.
The third (3). The proximal end of its base is a triangular facet with the
apex directed ventrad and the sides excavated. It is for the distal end of the
lateral cuneiform (e). Its medial surface presents a depression which
receives the ridge of the second metatarsal. On the lateral surface a short
distance distad of the proximal border is a triangular concave facet, and
near the proximal border ventrad a second concave facet. Both are for the
fourth metatarsal.
The fourth (4). The proximal end is convex, notched medially and
facetted for the cuboid (c). Its medial surface bears dorsad, a short distance
from its proximal end, a smooth tubercle, and ventrad a small convex facet.
Both articulate with facets on the lateral surface of the third metatarsal. The
lateral surface has a sinuous facet along its dorsal border, and ventrad of
this a depression. There is a second facet along the ventral border. Both
facets are for the fifth metatarsal, and the depression is for ligaments.
The fifth (5) has its base flattened and expanded so as to be wedge-
shaped, with the apex of the wedge directed proximad. Its dorsal end
extends into a tubercle. It thus presents only lateral and medial surfaces.
The medial surface shows two tubercles, one distad of the other. The distal

tubercle and the distal half of the proximal tubercle are facetted and fit into
the sinuous facet on the fourth metatarsal. A narrow facet on the ventral
border of the surface articulates with the facet on the ventral border of the
lateral surface of the fourth metatarsal. The proximal half of the distal
tubercle is facetted for the cuboid (c). The lateral surface is smooth, non-
articular, and obliquely grooved.
Phalanges (Fig. 58, i, j, k).—There are three phalanges in each of the
four digits, and these are almost identical with those described for the
manus.
Sesamoid Bones. Ossa sesamoidea (Fig. 58, l).—The sesamoid bones are
found at the joints between the metatarsals and phalanges, and are in all
respects like those of the manus.

JOINTS AND LIGAMENTS OF THE PELVIC LIMBS.

Ligaments of the Pelvis.—The ilium and sacrum are articulated at the
auricular facet of the ilium and the corresponding rough surface of the
sacrum. The joint is an amphiarthrosis, permitting very little movement. A
capsular ligament surrounds the articular surface, being attached to the
bones about its circumference; it is short and strong. Craniad of the capsule
is a thick very short ligament, composed of very strong transverse fibres
passing from the rough surface of the sacrum to the corresponding rough
surface of the ilium. This forms the lateral iliosacral ligament, which is
united at its caudal border to the capsule.
A strong, wide ligamentous band passes from the dorsal border of the
ilium to the sides of the sacrum. This is indistinctly subdivided into several
bands, which together represent the long and short posterior iliosacral
ligaments of man.
Symphysis pelvis.—The medial borders of the pubis and ilium meet in the
middle line ventrad of the pelvis and are here united by cartilage. The joint
is strengthened by numerous small bands which pass across the line of
junction from one side to the other; these occur on both surfaces.
The Hip-joint.—The hip-joint is an enarthrosis, or ball-and-socket joint
in which more than half the spherical head of the femur is received into the
acetabulum. The depth of the acetabulum is increased by a rim of
fibrocartilage about its margin, forming the labrum glenoidale. This passes

across the acetabular notch, forming the transverse ligament of the
acetabulum; beneath it blood-vessels and nerves pass into the acetabular
cavity.
The capsule of the joint is large and loose. It is attached about the
margin of the acetabulum, and passes over the head of the femur, to be
attached to the bone several millimeters distad of the head. It thus encloses
both the head and the neck of the femur.
The ligamentum teres, or round ligament, is a very strong, short
ligament which passes from the depression in the head of the femur to the
bottom of the acetabulum.
The Knee-joint (Figs. 60 and 61).—The joint between the femur and the
tibia is very complex. The surfaces of the condyles of the femur do not
correspond to those of the condyles of the tibia. Between the ends of the
two bones are placed two disks of cartilage, the menisci, or semilunar
cartilages (Fig. 60, c and d; Fig. 61, a and b), of such a form that the
congruity of articular surfaces is restored. Each meniscus has a proximal
surface corresponding to the form of one of the condyles of the femur, and a
distal surface corresponding to a condyle of the tibia. The menisci are held
in position by ligaments. The knee-joint permits not only backward and
forward movement, but also a small amount of rotary motion.
The joint has two capsules, one on the dorsal (convex) side, the other on
the ventral side. The two communicate only by a small passageway lying
within the joint between the ends of the bones. The dorsal one is attached to
the femur several millimeters proximad of the patellar surface and some
distance on each side of the latter. The patella is imbedded in its outer wall,
and it is attached to the tibia on the edges of the articular surface of the
latter, from the crest to the tuberosities. The capsule is also attached
laterally and medially to the sides of the menisci, and is closely united to
the patellar ligaments. Its cavity contains a mass of yellow fat.
The ventral capsule is attached to the borders of the articular surfaces of
the femur and tibia on their ventral sides, to the menisci, and to the
epicondyles of the femur and the tuberosities of the tibia. Its walls are
stronger and its cavity smaller than those of the dorsal capsule.
The ligaments of the knee-joint (Figs. 60 and 61), aside from the
capsules, may be classified into: (1) those which are connected with the
patella; (2) collateral ligaments (Fig. 60, i and j), which pass from the
epicondyles directly distad along the sides of the joint to the tibia or fibula;

(3) crucial ligaments (Fig. 60, g and h; Fig. 61, c and d), which cross within
the joint from one side of the femur to the opposite side of the tibia; (4)
ligaments which hold the menisci in place (Fig. 60, e and f; Fig. 61, e and f).
(1) Ligaments of the Patella.—The patella is imbedded in the dorsal
wall of the dorsal capsule of the joint. From its distal end a strong tendon or
ligament passes distad to the crest of the tibia. This is known as the
ligamentum patellæ: it may be considered a part of the tendon of M.
quadriceps femoris. On the lateral side the capsule of the joint is
strengthened by the transverse fibres of the tendon of M. plantaris, which
aid in holding the patella in place.
(2) Collateral Ligaments.—Of these there are two. The ligamentum
collaterale fibulare (Fig. 60, j) is attached to the lateral epicondyle of the
femur and passes distad across the tendon of the plantaris muscle to the
head of the fibula. Dorsad of the fibular ligament and parallel with it passes
the tendon of origin of the extensor longus digitorum. The ligamentum
collaterale tibiale (Fig. 60, i; Fig. 61, g) begins on the medial epicondyle of
the femur and passes distad to the lateral tuberosity of the tibia; part of it
passes one to one and a half centimeters distad of the tuberosity to be
attached to a rough ridge on the side of the tibia.

Fig. 60.—Knee-joint, from the Dorsal or Fig. 61.—Knee-joint, from the Ventral or
Patellar Side. Flexor Side.

Fig. 60.—The patella has been removed. 1, femur; 2, tibia; 3, fibula. a, patellar surface of femur;
b, tubercle for attachment of ligamentum patellæ; c, medial meniscus; d, lateral meniscus; e, f,
ligaments of the menisci; g, ligamentum cruciatum anterius; h, ligamentum cruciatum posterius; i,
ligamentum collaterale tibiale; j, ligamentum collaterale fibulare.
Fig. 61.—The capsule of the joint has been opened. 1, femur; 2, tibia (fibula not shown); 3,
sesamoid bone in lateral head of M. gastrocnemius; 4, sesamoid in medial head of M.
gastrocnemius; 5, tendon of M. popliteus, with sesamoid bone; 6, 7, lateral and medial condyles of
the femur, with the intercondyloid notch between them; 8, 9, lateral and medial condyles of the
tibia, with the popliteal notch between them; a, b, medial and lateral menisci; c, ligamentum
cruciatum anterius; d, ligamentum cruciatum posterius; e, f, ligaments of the lateral meniscus; g,
ligamentum collaterale tibiale.

(3) Crucial Ligaments.—There are two of these also. The ligamentum
cruciatum anterius, or anterior crucial ligament (Fig. 60, g; Fig. 61, c), is a
thick, strong ligament which begins on the dorsal part of the proximal end
of the tibia nearer the medial side (Fig. 60, g), and passes ventrad and
proximad, between the ends of the two bones forming the joint, into the
intercondyloid fossa of the femur, and becomes attached to the medial
surface of the lateral condyle of the femur (Fig. 61, c). It is composed of
two partially separated bands, forming a slight angle with one another. It is
crossed near its dorsal and ventral ends by two of the ligaments of the
menisci. The ligamentum cruciatum posterius, or posterior crucial
ligament (Fig. 60, h; Fig. 61, d), begins on the tibia at the edge of the
popliteal notch (Fig. 61, d), nearer the medial side, and passes dorsad and
proximad to be attached to the ventral edge of the patellar surface of the
femur, in the intercondyloid fossa (Fig. 60, h).
(4) Ligaments of the Menisci.—There are five of these, connecting the
menisci with the femur or tibia. One (Fig. 60, e) passes from the dorsal edge
of the medial meniscus (c) transversely across the anterior crucial ligament
(g) to the proximal end of the tibia nearer the lateral side. A second (Fig. 60,
f) passes from the dorsal margin of the lateral meniscus (d) transversely
beneath the anterior crucial ligament (g) to the proximal end of the tibia
nearer the ventral side and medial border. A third (Fig. 61, f) passes from
the ventral margin of the lateral meniscus obliquely across the anterior
crucial ligament (c) to the lateral side of the medial condyle of the femur.
The fourth (Fig. 61, e) is small, passing from the medial angle of the ventral
border of the lateral meniscus distad to the popliteal notch. The fifth passes
from the ventral border of the medial meniscus laterad beneath the posterior
crucial ligament to the proximal end of the tibia, nearer the ventral and
lateral sides.
Articulations between the Tibia and Fibula.—At the proximal end the
fibula is as it were suspended from the distal side of the overhanging lateral
tuberosity of the tibia by strong ligamentous tissue. The capsule of the joint
is formed by an extension of the capsule of the knee-joint which passes
between the tibia and fibula on the ventral side. Forming the dorsolateral
wall of this extension is a strong, thick ligament which passes directly from
the head of the fibula to the lateral surface of the lateral tuberosity of the
tibia. A second more delicate ligament passes from the head of the fibula

dorsoproximad to the tubercle laterad of the crest of the tibia, bridging a
groove through which passes the tendon of M. extensor longus digitorum.
The tibia and fibula are connected throughout their length by an
interosseus membrane. This is broad and very thin in its proximal part,
narrower and thicker distad.
Distad the two malleoli forming the ends of the fibula and tibia are
closely and immovably united. The capsule of the joint is here an extension
proximad of the capsule of the articulation with the astragalus. On the
dorsal side a short broad band of strong fibres passes from the surface of the
tibia obliquely laterodistad to the border of the fibula; this forms the
anterior ligament of the lateral malleolus. On the ventral side a very
much weaker set of fibres forms the ventral wall of the articular capsule; it
is called the posterior ligament of the lateral malleolus. Tibia and fibula
are also connected on the dorsal side by the ligamentum transversum
cruris, or transverse ligament of the lower leg (Fig. 91, 5), which spans the
tendons of Mm. extensor longus digitorum and tibialis anterior. From the
middle of the distal margin of this a slender supporting ligament passes
distad and is inserted on the dorsal surface of the tarsus. The grooves in the
two malleoli for the passage of the tendons are spanned by ligamentous
fibres (retinacula) for holding the tendons in place.
Articulation between the Leg and the Foot.—At the distal end there is
formed between the two malleoli a deep irregular fossa, into which is
received the trochlea of the astragalus. The joint is covered by a large
articular capsule, which passes also, as above noted, between the tibia and
fibula. In addition to the capsule the following ligaments may be
distinguished: (a) On the lateral side, (1) a short ligament from the fibula to
the astragalus, directed toward the proximal end of the foot; (2) a ligament
from the fibula to the calcaneus, attached to the latter proximad of the
peroneal tubercle; (3) a stronger ligament from the fibula to the calcaneus,
lying beneath the last-mentioned and directed toward the proximal end of
the bone. (b) On the medial side may be distinguished (1) a strong ligament
from the tibia (medial malleolus) to the sustentaculum tali, and passing
thence onto the scaphoid; (2) a short ligament from the medial malleolus to
the astragalus.
The Tarsus.—The articulations between the separate bones of the tarsus
and between the tarsus and metatarsus have a considerable number of
variously communicating articular capsules. The separate bones are

connected by many ligaments. The ligaments of the ventral surface
(ligamenta plantaria) are especially well developed. Here may be noticed
particularly a very large calcaneocuboid ligament, and a large
calcaneocuneiform ligament which passes from the sustentaculum tali to
the medial cuneiform. Those on the dorsal surface (ligamenta dorsalia) are
less strong and numerous. Many ligaments, longitudinal, transverse, and
oblique, pass also between the separate bones (ligamenta interossea).
Ligamenta lateralia, on the lateral and medial borders of the foot, are also
distinguishable. Strauss-Durckheim enumerates ninety-four ligaments of the
tarsus; an account of each of these does not form part of the plan of the
present work.
The ligaments of the metatarsus and phalanges are of the same general
character as in the forelimb. Of these Strauss-Durckheim enumerates thirty-
six; they will not be described here.

THE MUSCLES.

I. THE MUSCLES OF THE SKIN. (Fig. 62.)

M. cutaneus maximus (Fig. 62, b).—This is a very large, thin muscle
which covers almost the whole side of the body. It arises from the outer
surface of the latissimus dorsi (Fig. 68, m) near its ventral end and from the
bicipital arch (Fig. 65, t′) in the axilla; from the linea alba for a considerable
distance (two or three inches) caudad of the base of the xiphoid process,
and from the thorax over a line joining the axilla and the base of the
xiphoid. Sometimes a few fibres take origin from the fascia which covers
the pectoantibrachialis on the ventral side of the arm.
From their origin the fibres diverge. The cranial ones curve about the
base of the forelimb and are inserted into the skin at or near the middle line
caudad of the first thoracic vertebra. The most cranial fibres of all are
inserted about one to one and a half centimeters from the middorsal line;
thence the line of insertion approaches the middorsal line to reach it at
about the eighth or ninth thoracic vertebra. The middle fibres run parallel to
the middorsal line in the lumbar and sacral regions as far as the root of the
tail, a small bundle passing onto the dorsal side of the tail, another onto the
ventral side. The fibres of the caudal portion pass onto the thigh, the ventral
ones running in the fold of skin which stretches from thigh to abdomen, and
are finally lost in the fascia along a line connecting the knee and the root of
the tail. A strong fascia connects the adjacent borders of the cutaneus and
platysma and lies over the scapular region.

Fig. 62.—Muscles of the Skin.

a, a′, a″, M. platysma; b, M. cutaneus maximus; c, M. orbicularis oris. Between the platysma and
the cutaneus maximus are seen the following deeper muscles: d, M. acromio-trapezius; e, M.
levator scapulæ ventralis; f, M. spino-deltoideus; g, M. acromio-deltoideus; h, M. clavobrachialis; i,
caput laterale of M. triceps brachii; j, caput longum of M. triceps brachii; k, M. xiphi-humeralis; l,
M. pectoralis minor. 1, external jugular vein.]

This muscle lies immediately beneath the integument. It covers the first
layer of body muscles.
Action.—Moves the skin.
M. platysma (Figs. 62 and 64, a, a′, a″).—This muscle forms a thin layer
of fibres covering the sides of the neck and face, in close relation with the
integument. Several more or less distinct portions may be distinguished.
(1) Most of the fibres (a) arise from the middorsal line, from the occiput
to the first thoracic vertebra, in a narrow fascia common to the muscles of
the two sides. The most cranial fibres of this region arise as a small bundle
from the external occipital crest, beneath the levator auris longus (Fig. 63,
g, g′).
From this origin in the middle line the fibres pass craniolaterad. The most
cranial fibres curve about the ventral side of the ear and pass toward the
caudal angle of the eye, where they unite with fibres of the zygomaticus
(Fig. 64, d) or corrugator supercilii lateralis (Fig. 64, k), or pass to the lower
eyelid. Caudad of these the fibres cover the side of the face and become lost

among the facial muscles, some passing to the lower eyelid, some to the
fibrous pad which supports the vibrissæ, some to the angle of the mouth,
some to the lower lip. The most ventral fibres meet the fibres of the
opposite muscle just ventrad of the symphysis of the mandible.
The ventral free border of the platysma is separated on the ventral side of
the neck from the border of the opposite muscle by a wedge-shaped area
having its point at the symphysis menti.
The fibres of this portion of the muscle are interrupted by an attachment
to the skin, along a line passing from the base of the ear to about the middle
of the coracoid border of the scapula, The dorsal (a) and ventral (a′)
portions of the muscle, separated by this line of attachment, are sometimes
described as separate muscles (the supercervicocutaneus and
cervicofacial, respectively, of Strauss-Durckheim).
(2) A band of fibres one or two centimeters across (a″) arises in the fascia
of the side of the neck just craniad of the middle of the coracoid border of
the scapula, and passes caudoventrad toward the manubrium, its fibres
crossing the fibres of the first part of the platysma at right angles. These
fibres become lost in the fascia ventrad of the manubrium, or pass across
the middle line to intermingle with the corresponding fibres of the opposite
side. This portion of the platysma is sometimes absent.
The platysma is everywhere subcutaneous, except at its dorsocranial
angle, where a small bundle of fibres is covered by the levator longus auris.
It covers the deeper muscles of the neck and head. Closely attached to its
inner surface are the submentalis and depressor conchæ, whose fibres
bridge over the ventral interval between the borders of the platysmas of
opposite sides.
Action.—Moves the skin of the face and neck.

II. THE MUSCLES OF THE HEAD.

A. Superficial Muscles.—The most superficial layer of muscles on the
face and head is formed by differentiation of the fibres of the platysma. The
muscles thus formed are not clearly distinct from each other; in this region
sets of fibres differing in direction and in origin or insertion receive separate
names even though the different sets of fibres are closely interwoven.
In the quadrangle on the dorsal surface of the head enclosed between the
two eyes and the two ears, a thin superficial sheet of fibres is found, in

which a number of different sets may be distinguished (Fig. 63). These have
received the following names.
M. intermedius scutulorum (Fig. 63, a).—This consists of a broad thin
sheet of transverse fibres between the two external ears. The fibres are
attached at either end to the scutiform cartilage (1) of the two ears, and pass
without interruption across the middle line. At its cranial edge this muscle is
continuous with the corrugator supercilii medialis (b); at its lateral edge
with the frontoscutularis; at its caudal edge with the levator auris longus (g).
Relations.—Outer surface with the integument. Inner surface with the
galea aponeurotica (to which the muscle is closely united), the epicranius
muscle (h) and the temporal muscle (n).
Action.—Draws the two ears dorsad, toward the middle line.

Fig. 63.—Muscles on the Dorsal Surface of the Head.
On the right side are shown the superficial muscles; on the left side the superficial muscles have
mostly been removed, exposing the deeper muscles and the bone. a, M. intermedius scutulorum; b,
M. corrugator supercilii medialis; c, M. orbicularis oculi; d, M. corrugator supercilii lateralis; e,
cranial end fibres of M. platysma; f, M. adductor auris superior; g, g′, M. levator auris longus (g,
cranial portion; g′, caudal portion); h, h′, M. epicranius (h, M. occipitalis; h′ M. frontalis); i, M.
transversus auriculæ; k, M. auricularis superior (cut on the left side); l, M. abductor auris brevis; m,
M. abductor auris longus; n, M. temporalis; o, cut origin of M. frontoscutularis; p, p′, M. levator
labii superioris alæque nasi (p′, the origin from the maxillary bone); q, angular head of M.
quadratus labii superioris. 1, scutiform cartilage; 2, external ear; 3, bones of the skull.

M. corrugator supercilii medialis (b).—This consists of a thin sheet of
scattered fibres lying craniad of the last and intermingling with it. The
fibres take origin near the middle line, pass laterad, then curve craniad,
converging, to be inserted into the whole extent of the upper eyelid,
especially near the caudal angle. Here the fibres unite with those of the
orbicularis oculi (c).
This muscle is continuous caudad with the intermedius scutulorum (a),
craniad with the orbicularis oculi (c); laterad with the corrugator supercilii
lateralis (d). Toward the medial side the fibres lose themselves in a
tendinous sheet that joins the galea aponeurotica.
Relations.—Outer surface with the integument. Inner surface with the
frontoscutularis and the skull.
Action.—Raises the upper eyelid.
M. orbicularis oculi (Fig. 63, c; Fig. 64, s).—This consists of two thin
bands of muscle-fibres which lie one in either eyelid parallel to its border
and unite at the angle of the eye.
Origin by short tendon-fibres from a tubercle on the surface of the frontal
process of the maxillary bone just dorsad of the orbital end of the lachrymal
canal and between the two parts of the quadratus labii superioris (Fig. 63, p
and q).
The muscle splits into two parts which pass into the two eyelids. At the
outer angle of the eye the two bands unite by the intervention of tendon-
fibres between the muscle-fibre bundles of the two.
Relations.—Outer surface with the integument. Inner surface with the
inner membrane of the eyelid.
Action.—Closes the eye.

M. corrugator supercilii lateralis (Fig. 63, d; Fig. 64, k).—This consists
of a number of scattered fibres which arise from among the fibres of the
frontoscutularis, and from the tendon lying just craniad of the external
opening of the ear, to which are united also parts of the zygomaticus (Fig.
64, d) and submentalis (Fig. 64, c). The fibres pass craniad, converging so
as to form a narrow band which is inserted at the caudolateral angle of the
eye, where it unites with the orbicularis oculi (Fig. 64, s). This muscle is
continuous on the medial side with the corrugator supercilii medialis (Fig.
64, j) and the frontoauricularis, on the lateral side with the platysma.
Relations.—Outer surface with the integument. Inner surface with the
frontal bone and the frontoscutularis.
Action.—Pulls the angle of the eye caudad; at the same time pulls the
external ear craniad.
M. frontoauricularis.—A few of the fibres which are attached along the
upper eyelid sometimes pass dorsocaudad, mingled with fibres of the
corrugatores supercilii medialis and lateralis and the frontoscutularis, to the
craniomedial angle of the auricular cartilage, where they unite with the
fibres of the adductor auris superior. These fibres are sometimes
distinguished as the frontoauricularis muscle.
M. levator auris longus (Fig. 63, g and g′). (Part of the auricularis
posterior of man.)—This lies on the caudal half of the dorsal surface of the
head, forming a laterocaudal continuation of the intermedius scutulorum
(a).
Origin from the middle line of the neck dorsad of the atlas, and from the
sagittal crest for about one centimeter craniad of the external occipital
tubercle. The fibres form a broad thin sheet which passes craniolaterad as
far as the caudal end of the scutiform cartilage (1). Here the muscle divides;
the major portion is attached to the scutiform cartilage (1), its fibres
intermingling with those of the intermedius scutulorum (a). The caudal
portion of the muscle (g′) passes onto the surface of the auricle, extending
one or two centimeters distad; here it is inserted on an oblique line which
lies directly craniad of the insertion of the transversus auriculæ (i).
The caudal portion of this muscle (g′) having origin above the atlas and
insertion on the auricle, is sometimes considered a separate muscle, the
supercervicoauricular or cervicoauricular. The cranial portion (g) with
origin on the sagittal crest and insertion on the scutiform cartilage might be
distinguished as the occipitoscutularis.

The levator auris longus is continuous at its cranial end medially with M.
epicranius (h); laterally with M. intermedius scutulorum (a).
Relations.—Outer surface with the integument. Inner surface with the
temporal muscle (n), the auricularis superior (k), the abductor longus auris
(m), a narrow strand of the platysma, and the clavotrapezius.
Action.—Pulls the external ear dorsocaudad.
The four following muscles lie partly or entirely beneath those already
described; they are doubtless formed as differentiations of the inner layers
of the platysma.
M. auricularis superior (or attollens auris) (Fig. 63, k).—This muscle
forms a band about one centimeter broad lying just beneath the levator
longus (g).
Origin on the sagittal crest for about one centimeter craniad of the
interparietal bone. The muscle passes laterad onto the surface of the auricle
and is inserted into the auricular cartilage a little caudad of the middle of its
convex surface. At its lateral end the cranial margin is closely united to the
under surface of the levator auris longus (g).
Relations.—Outer surface at the medial end with the epicranius (h), the
abductor auris longus (m), and levator auris longus (g); at the lateral end
with the skin. Inner surface with the temporal muscle (n) and the auricular
cartilage.
Action.—Pulls the external ear dorsad.
M. abductor auris longus (Fig. 63, m; Fig. 64, q). (Part of the
auricularis posterior of man.)
Origin on the sagittal crest dorsad of the interparietal bone, caudad of
that of the auricularis superior (k), which it partly covers.
The muscle passes laterad as a flat band 8 to 10 millimeters wide over the
caudal surface of the concha of the ear, and is inserted (Fig. 64, q) on the
lateral surface of the eminentia conchæ, caudad of the antitragus.
Relations.—Outer surface with the levator auris longus (g) and the
integument. Inner surface with the auricularis superior (k), the abductor
auris brevis (l), and the concha.
Action.—Pulls the external ear caudad.
M. abductor auris brevis (Fig. 63, l).
Origin by a tendon from the lambdoidal crest for one or two centimeters
laterad of the middle.

The muscle passes lateroventrad lying beneath the abductor longus (m) as
a flat band 6 to 8 millimeters wide which is inserted into the medial surface
of the most proximal portion of the concha, just distad of its junction with
the cartilaginous auditory meatus.
Relations.—Outer surface with the abductor longus (m), a small strand of
the platysma and the concha. Inner surface with the temporal muscle (n).
Action.—Pulls the concha caudad.
M. epicranius (or occipitofrontalis) (Fig. 63, h and h′).
Origin on the sagittal crest or suture, just craniad of the origin of the
levator longus auris, to the inner surface of which this muscle is closely
united. From the origin the fibres pass craniad forming a band (h) about 8 or
10 millimeters in width, the two muscles lying close to one another and
partly united in the middle line. About two centimeters craniad of their
origin the fibres of both muscles end in a tendinous sheet, the galea
aponeurotica, which covers the surface of the skull in the region between
the ears and eyes, and is formed by the inner surface of the intermedius
scutulorum (a) and other muscles of this region. The galea aponeurotica
passes craniad onto the surface of the nose, where it gives origin again to a
thin sheet of muscle-fibres (h′) which are inserted into the integument near
the cranial ends of the nasal bones.
M. epicranius is thus formed of two muscular portions (h and h′),
connected by a long tendinous sheet. The caudal portion is frequently
distinguished as the occipital muscle (M. occipitalis, h), the cranial portion,
on the nose, as the frontal muscle (M. frontalis, h′).
Relations.—Outer surface of the occipitalis (h) with the intermedius
scutulorum (a), the levator auris longus (g), and the integument; inner
surface with the auricularis superior (h), the abductor auris longus, and the
bone. Outer surface of the frontalis (h′) with the integument; inner surface
with the bones of the skull.
Action.—Moves the integument of the dorsal surface of the head and of
the nose.
Ventrad of the external ear the following three differentiated portions of
the platysma may be distinguished.
M. zygomaticus (major) (Fig. 64, d).—A slender band connecting the
angle of the mouth with the scutiform cartilage of the ear.

Fig. 64.—Superficial Muscles on the Lateral Surface of the Head and Neck.

a, a′, a″, M. platysma; b, M. depressor conchæ; c, M. submentalis; d, M. zygomaticus (b,
c, and d lie beneath the platysma and are seen through it); e, M. zygomaticus minor; f′, M.
caninus; f, g, parts of M. quadratus labii superioris (f, angular head; g, M. levator labii
superioris alæque nasi); h, M. myrtiformis; i, M. orbicularis oris; j, M. corrugator supercilii
medialis; k, M. corrugator supercilii lateralis; l, M. adductor auris superior; m, M. helicis;
n, M. antitragicus; o, M. adductor auris inferior; p, M. conchæus externus; q, M. abductor
auris longus; r, parts of M. auricularis externus; s, M. orbicularis oculi.

At the angle of the mouth the fibres arise from among those of the
orbicularis oris (i), from both the upper and the lower lip. They pass thence

dorsocaudad across the zygomatic arch as a band 8 or 10 millimeters wide
which is attached to a tendinous aponeurosis lying just craniad of the
external opening of the ear. To this aponeurosis are attached also, wholly or
partly, the corrugator supercilii lateralis (k) and the submentalis (c). The
aponeurosis is united with the caudoventral angle of the scutiform cartilage
and with the ventral edge of the cranial margin of the auricular cartilage.
This muscle is united at its cranial end with the orbicularis oris (i);
throughout its length more or less with the platysma (a, a′); at its
caudodorsal end with the corrugator supercilii lateralis (k) on its medial
side, and with the submentalis (c) on its lateral side.
Relations.—Outer surface with the integument and the platysma (a′).
Inner surface with the masseter, temporal, frontoscutularis, and adductor
auris inferior (o).
Action.—Draws the angle of the mouth dorsocaudad; the external ear
ventrocraniad.
M. submentalis (Fig. 64, c).—A flat band, similar to the last, and closely
connected for some distance to its caudal border.
It arises as scattered fibres near the ventral middle line at about the level
of the larynx, the fibres of the opposite muscles crossing the middle line
and intermingling. The fibres pass dorsad, converging so as to form a
narrower band, which unites dorsad with the zygomaticus (d), to be inserted
with it into the tendinous aponeurosis above described.
Relations.—Outer surface with the integument and platysma (a′). Inner
surface with the muscles of the hyoid, the digastricus, the parotid gland, the
masseter, the zygomatic arch and the temporal muscle.
Action.—Draws the external ear ventrad.
M. depressor conchæ (Fig. 64, b).—A thin band of fibres, caudad of the
last and parallel with it. The muscle arises as scattered fibres on the ventral
surface of the neck, one or two centimeters craniad of the manubrium, the
fibres of the muscles of opposite sides crossing the middle line and
interdigitating. They pass dorsad, gathering together to form a narrow band
which is inserted into the summit of the antitragus.
Relations.—Outer surface with the skin at the ventral end, and with the
platysma (a′) further dorsad. Inner surface with the deep muscles of the
neck and with the parotid gland.
Action.—Draws the external ear ventrad.

Lying deeper than the muscles thus far described, but closely connected
with a number of them, are the following:
M. frontoscutularis. Origin (Fig. 63, o) on the frontal bone, along the
supraorbital margin, from the craniomedial angle of the eye caudad to the
zygomatic process of the frontal.
The fibres form a large muscle which passes dorsocaudad to the
scutiform cartilage and is mostly attached along its ventrolateral border.
Some of the outer fibres, however, pass distad of the scutiform cartilage
toward the cartilage of the ear, thus joining the adductor auris superior (f).
The outer surface of this muscle is closely connected with fibres of the
intermedius scutulorum (a), the corrugatores supercilii medialis (b) and
lateralis (d), and the frontoauricularis, when this exists. The outer surface is
covered near the origin by the orbicularis oculi (c), farther dorsad by the
muscles just mentioned and the integument. The inner surface is in relation
with the frontal bone and the adductor auris inferior (Fig. 64, o).
Action.—Pulls the ear craniad.
M. adductor auris inferior. (Fig. 64, o.) (Part of the auricularis anterior
of man.)—A small muscle lying beneath the frontoscutularis.
Origin on the ligament which connects the zygomatic process of the
frontal with the frontal process of the malar. The fibres form a thin band
about 7 millimeters wide which passes craniad, closely united to the inner
surface of the frontoscutularis. At the caudal edge of the zygomaticus (d)
the muscle is interrupted by a short tendinous interval; the fibres then
continue to their insertion on the tip of the antitragus.
Relations.—Outer surface with the frontoscutularis, the zygomaticus (d),
and the integument. Inner surface with the temporal muscle and M.
antitragicus (n).
Action.—Pulls the ear craniodorsad.

The remainder of the muscles of the ear, which, with the exception of the
tragicus lateralis, merely interconnect the cartilages of the external ear or
parts of these cartilages, are described in connection with the account of the
Auditory Organ.

Owing to the presence of the fibrous pad to which the whiskers are
attached, the facial muscles between the eye and the mouth differ in the cat
in some respects from those of related animals. This fibrous pad interrupts

the muscles, frequently breaking muscles which are elsewhere single into
two.
M. zygomaticus minor, or malaris (Fig. 64, e).—This muscle is not
always present; when it exists it forms a very thin flat band of fibres passing
from the ventral side of the eye toward the angle of the mouth.
Origin among the fibres of the orbicularis oculi (s) in the lower eyelid.
The fibres pass ventrad; the insertion varies. In some specimens the
insertion is among the fibres of the orbicularis oris (i), at the angle of the
mouth, beneath the zygomaticus (d). In other cases this muscle is said to be
inserted into the pad on which the whiskers rest.
Relations.—Outer surface with the integument and near its insertion with
the zygomaticus major (d). Inner surface with the malar bone and the
masseter muscle.
Action.—Pulls the angle of the mouth (or the whiskers) dorsad.
M. orbicularis oris (Fig. 64, i).—This forms a very thin layer of
subcutaneous concentric fibres which surround the mouth, that of the upper
lip being thicker than that of the lower lip. The part of the muscle in the
lower lip has its fibres intermingled with those of the platysma (a′). In the
median line the fibres of the upper lip are interrupted by a raphe, and
caudad of this are intermingled with those of the caninus.
M. quadratus labii superioris (Fig. 63, p and q; Fig. 64, f and g).—This
is a complex of muscle-fibres attached chiefly to the fibrous pad on which
the whiskers rest. In it two parts can be distinguished more or less
completely.
(1) M. levator labii superioris alæque nasi (Fig. 63, p; Fig. 64, g) on
the sides of the nose. This arises (a) as a continuation of the frontal portion
of the epicranius, and (b) in a small bundle (Fig. 63, p) from near the dorsal
end of the frontal process of the maxillary bone, in common with the next.
The two slips thus formed unite craniad and are inserted partly into the
integument on the outer side of the wing of the nose, partly into the skin of
the upper lip, lateroventrad of the nose, and partly into the pad on which the
whiskers are located, in connection with the next.
(2) The angular head (caput angulare), or levator labii superioris
proprius (Fig. 63, q; Fig. 64, f) is much larger than the last. It takes origin
from a small tubercle at the cranial border of the orbit, close to the origin of
the orbicularis oculi. The fibres diverge from their origin to their insertion
among the whiskers and in the fibrous pad on which the whiskers rest.

Action.—Erects the whiskers and raises the upper lip.
M. caninus or levator anguli oris (Fig. 64, f′).
Origin in a depression on the lateral surface of the maxillary bone, just
craniad of the last premolar tooth. The fibres pass craniad, diverging,
toward the whiskers, and have their insertion into the pad of tissue on which
the whiskers rest.
Action.—Retracts the whiskers and raises the upper lip.
M. buccinator.—A thin muscle against the mucous membrane of the
upper lip, partly united with the orbicularis oris and lying beneath M.
caninus.
Origin on the outer surface of the superior maxillary bone in the
depression between the infraorbital foramen and the first premolar tooth.
The fibres pass ventrad, diverging, and mingle with those of the deep part
of the orbicularis oris.
Relations.—Outer surface with the caninus and with the orbicularis oris.
Inner surface with the mucous membrane of the upper lip.
Action.—Raises the upper lip.
M. myrtiformis (probably corresponds to a part of the human M.
nasalis) (Fig. 64, h).—A thin sheet of muscle-fibres lying craniad of the
levator labii superioris alæque nasi and passing from the whiskers to the
nose and upper lip. It is distinguishable from the alæque nasi by the
direction of the fibres.
Origin from the pad upon which the whiskers rest. The fibres diverge and
have their
Insertion upon the wing of the nose and into the skin of the upper lip near
the median line.
Action.—Dilator of the nares and elevator of the upper lip.
M. “moustachier” (Str.-D.) (probably corresponds to one of the Mm.
incisivi).—It lies on the upper lip near the median line.
Origin from the outer surface of the premaxilla near the suture along the
ventral border of the narial opening. The fibres diverge and pass caudad
into the upper lip within the superficial fibres of the orbicularis oris.
Insertion.—The skin of the upper lip just craniad of the whiskers. Some
of the fibres pass into the pad on which the whiskers rest.
Action.—It carries the lip craniad.
M. quadratus labii inferioris.—A thin flat band extending almost the
length of the lower lip.

Origin from the alveolar border of the mandible, between the molar tooth
and the canine. The fibres pass dorsad into the lower lip, where they
intermingle with those of the orbicularis oris. The muscle is perhaps not
constant.
Action.—Depressor of the lower lip.
Sometimes a few fibres arising from the cranial portion of the alveolar
border of the mandibula pass mediad, seeming to join corresponding fibres
from the opposite side. Such fibres would constitute a M. transversus menti.

B. Deep Muscles of the Head.

(a) Muscles of Mastication.
M. digastricus (Fig. 65, b).—The digastric is a thick prismatic muscle
lying mediad of the angle of the lower jaw, connecting it with the base of
the skull.
Origin by fleshy fibres from the outer surface of the jugular process of
the occipital bone, and by a thin tendon from the tip of the mastoid process
and from the ridge between the mastoid and the jugular processes. The
muscle passes craniad, becoming at the same time broader and more
voluminous.
Insertion.—The ventral border of the mandible craniad of the caudal
border of the molar tooth. The insertion area extends slightly onto both
surfaces of the bone and is triangular, with its apex craniad.
Relations.—Outer (ventral) surface with the following, beginning at the
caudal end: the rectus capitis lateralis, the cleidomastoid (h), the
submaxillary gland (2), the stylohyoid (d), a large lymph-gland (3), and the
integument. Inner (dorsal) surface with the jugulohyoid, the tympanic bulla,
the masseter (a), the hyoglossus, and the mylohyoid (c).
Action.—Depressor of the lower jaw.
M. masseter (Figs. 65 and 66, a).—The masseter forms the projecting
mass so prominent in the cat behind and below the eye. Its outer surface is
covered by a strong aponeurosis. The muscle is divided into three layers
which are distinct as to origin, insertion, and direction of fibres, but which
are otherwise not distinct.
The superficial layer takes

Origin by the superficial aponeurosis from the ridge which runs
lengthwise of the outer surface of the malar bone, and by fleshy fibres from
the surface of the malar bone ventrad of this ridge. The fibres pass obliquely
caudad to their insertion.
Insertion.—The caudal half of the lateral margin of the ventral border of
the mandible, by a sheet of fascia which lies on the inner surface of the
muscle. The superficial fibres curve ventrad of the mandible and are
inserted into a tendinous intersection between this muscle and the internal
pterygoid (Fig. 66, c).
The middle layer takes
Origin from the ventral border of the malar bone, from opposite the
molar tooth to within three millimeters of the mandibular fossa. The fibres
pass ventrad and have their
Insertion into the mandible at the ventral border of the external coronoid
fossa by means of the aponeurosis which covers the inner surface of the
muscle.

Fig. 65.—Muscles on the Ventral Surface of the Thorax, Neck and Head.

The left side shows the first layer of muscles beneath the skin and skin-muscles; the right side
shows the second layer, except in the head region. a, M. masseter; b, M. digastricus; c, M.
mylohyoideus; d, M. stylohyoideus; e, M. sternohyoideus; f, M. thyreohyoideus; g, M.
sternomastoideus; g′, M. sternothyreoideus; h, M. cleidomastoideus; i, M. levator scapulæ ventralis;
j, M. clavotrapezius; k, M. clavobrachialis; l, M. pectoralis major; m, M. pectoantibrachialis; n, part
of M. scalenus; o, M. pectoralis minor; p, M. xiphihumeralis; q, M. latissimus dorsi; r, M.
epitrochlearis; s, caput longum of M. triceps brachii; t, M. biceps brachii; t′, bicipital arch; u, M.
acromiodeltoideus; v, M. brachialis. 1, parotid gland; 2, submaxillary gland; 3, lymphatic glands; 4,
external ear; 5, external jugular vein; 6, manubrium; 7, first rib; 8, common carotid artery; 9, molar
gland.

The deep layer takes
Origin by a strong tendon from the ventral border of the zygoma just
craniad of the mandibular fossa. The fibres pass cranioventrad, diverge and
have their
Insertion into the external coronoid fossa.
Relations.—Outer surface with the following, beginning at the caudal
border: the external ear, the parotid gland (Fig. 65, 1), the platysma, the
submentalis, the zygomaticus (major), the zygomaticus minor. Ventral
border with a lymph gland caudad of the angle of the mouth (Fig. 65, 3),
and the digastric muscle (b). Inner surface with the bones.
Action.—A very powerful elevator of the lower jaw.
M. temporalis (Fig. 63, n).—The temporal muscle is the great mass
taking origin from the temporal fossa and having its insertion on both
surfaces and both borders of the coronoid process of the mandible. It may
be divided into two layers, deep and superficial.
The superficial layer. The temporal fascia stretches over the temporal
fossa, being attached to its borders; that is, to the sagittal and lambdoidal
crests, to the curved ridge which connects the sagittal crest with the
zygomatic process of the frontal bone, to the caudal border of this process,
to the caudal border of the malar bone, to the caudal border of the ligament
connecting the malar bone and the zygomatic process of the frontal, and to
the dorsal border of the zygomatic process of the temporal bone and its
dorsal root. The craniolateral part of this fascia is much stronger than the
remainder.
The muscle-fibres take origin from the strong craniolateral part of the
inner surface of the temporal fascia, from the groove on the temporal bone
dorsad of the dorsal root of its zygomatic process, from the whole inner
surface of this process and of the zygomatic process of the malar bone, and
sometimes also from that part of the frontal bone which lies within the
temporal fossa.
Insertion.--The outer surface of the coronoid process of the mandible
dorsad of the coronoid fossa, and both borders of the coronoid process. The
cranial fibres may be inserted craniad of the coronoid process onto the
aponeurosis covering the deep portion of the muscle. The caudal part of this
portion is more or less distinct and is sometimes described as a separate
head.
The deep portion.

Origin by fleshy fibres from the whole surface of the temporal fossa,
except in cases where the cranial part of the fossa is occupied by the
superficial portion. The fibres converge toward the coronoid process, and
the ventral third of the outer surface is covered by strong fascia.
Insertion.—The whole inner surface of the coronoid process of the
mandible.
Relations.—Outer surface with the external ear, the ear-muscles (Fig.
63), the epicranius (Fig. 63, h), the corrugatores supercilii lateralis (d) and
medialis (b). Inner surface with the skull, the pterygoideus externus (Fig.
66, b), and the structures within the orbit.
Action.—Elevator of the lower jaw.
M. pterygoideus externus (Fig. 66, b).—This lies on the medial side of
the mandible, ventrad of the ventral portion of the temporal.
Origin.—The external pterygoid fossa (Fig. 40, h), which lies on the
lateral surface of the perpendicular plate of the palatine bone, and on the
surface of the pterygoid process of the sphenoid bone dorsad of the internal
pterygoid fossa. The fossa extends from the foramen rotundum to the
sphenopalatine foramen. The muscle passes with parallel fibres laterad,
ventrad, and caudad and has its
Insertion by a strong flat tendon into the medial surface of the mandible
near its ventral border between the opening of the mandibular canal and the
base of the angular process.
Relations.—Ventral surface with the masseter (a), the digastric, and the
soft palate with its muscles. Dorsal surface with the temporal, and near its
origin with the muscles of the eye, and other structures in the orbit.
Action.—Elevator of the lower jaw.
M. pterygoideus internus (Fig. 66, c).—This lies caudad of the
pterygoideus externus, nearly parallel to it, and is connected with it at its
lateral end.
Origin from the whole surface of the internal pterygoid fossa (Fig. 40, s).
Insertion by fleshy fibres into the ventral surface of the external
pterygoid and its tendon, into the medial surface of the angular process of
the mandible and caudad of the angular process for about one centimeter
into a fascia common to it and the masseter muscle, and into the
stylomandibular ligament.

Fig. 66.—Obliquely Ventral View of the Deep Muscles of the Lower Jaw and
Palate.

The tongue and other structures forming the floor of the mouth have been
removed, showing the roof of the mouth. On the right side the masseter and
pterygoideus internus have been removed, a, a′, M. masseter; b, M. pterygoideus
externus; c, M. pterygoideus internus; d, d′, M. tensor veli palatini; e, e′, M. levator
veli palatini; f, M. constrictor pharyngis superior. 1, aponeurosis of the velum
palatinum; 2, ridges formed by the palatines and pterygoid portions of the
sphenoid; 3, hamular processes; 4, free caudal border of the velum palatinum; 5,
bulla tympani.

Relations.—Ventral surface with the styloglossus and the soft palate.
Dorsal surface with the bulla tympani (5) and base of the skull. Cranial
surface with the pterygoideus externus (b), with which it is partly united.
Action.—Assists the pterygoideus externus.

(b) Muscles of the Hyoid Bone.
M. stylohyoideus (Fig. 65, d).—The stylohyoid is a ribbon-like muscle
about three millimeters wide. It lies on the superficial surface of the
digastric, caudad and ventrad of the angle of the jaw.
Origin by fleshy fibres from the outer surface of the stylohyal bone near
its middle. The muscle curves over the outer surface of the digastric (b), and
ends about one centimeter from the middle line in a slender flat tendon.
Insertion into the middle of the ventral surface of the body of the hyoid
bone. Some of the fibres of the mylohyoid (c) are inserted into its tendon.
Relations.—Outer surface with the submaxillary gland (2) and the
submentalis muscle. Inner surface with the digastric (b), the hyoglossus
(Fig. 67, h), and the geniohyoid (Fig. 67, g).
Action.—Raises the hyoid.
M. geniohyoideus (Fig. 67, g).—The geniohyoid is a long slender
muscle which lies next to the median line between the symphysis menti and
the hyoid bone, closely applied to its fellow of the opposite side and within
(dorsad of) the mylohyoid (Fig. 65, c).
Origin from the ventral half of the inner surface of the mandibula for
about one millimeter from the symphysis.
Insertion by muscle-fibres into the lateral half of the ventral surface of
the body of the hyoid bone.
Relations.—Outer (ventral) surface with the stylohyoid (Fig. 65, d) and
the mylohyoid (Fig. 65, c); medial border with the muscle of the opposite
side. Lateral border with the hyoglossus (Fig. 67, h) and genioglossus (Fig.
67, f). Inner (dorsal) surface with the genioglossus.
Action.—Draws the hyoid forward.
M. jugulohyoideus (Fig. 67, b).—The jugulohyoid is a small flat
quadrangular muscle covering the outer part of the ventral surface of the
tympanic bulla.
Origin from the ventral border of the jugular process.
Insertion into the caudal side of the cartilaginous part of the stylohyoid
opposite the origin of the styloglossus.
Relations.—Ventral surface with the digastric. Dorsal surface with the
tympanic bulla (3).
Action.—Draws the hyoid backward and thus gives a firmer surface of
origin for the styloglossus.

M. mylohyoideus (Fig. 65, c).—The mylohyoid is a large thin muscle
seen after the reflection of the digastric, filling with its fellow of the
opposite side the whole angle between the rami of the lower jaw. Its fibres
are transverse.
Origin from the middle of the medial surface of the body of the mandible
between the caudal opening of the mandibular canal and the symphysis of
the jaw.

Fig. 67.—Muscles of Tongue, Hyoid Bone, and Pharynx.

a, M. tragicus lateralis; b, M. jugulohyoideus; c, M. pterygoideus externus; d,
partially cut surface of M. pterygoideus internus; e, M. styloglossus; f, M.
genioglossus; g, M. geniohyoideus; h, M. hyoglossus; i, M. glossopharyngeus; j,
M. constrictor pharyngis medius; k, M. constrictor pharyngis inferior; l, M.
stylopharyngeus; m, M. sternohyoideus (cut); n, M. cricothyreoideus; o, M.
sternothyreoideus (cut); p, M. thyreohyoideus. 1, mandible; 1′, angular process of
mandible; 2, stylomandibular ligament; 3, bulla tympani; 4, trachea; 5, œsophagus;
6, thyroid gland; 7, isthmus of the thyroid gland.

Insertion with the opposite muscle into a median raphe which extends
from the symphysis of the jaw to the hyoid bone and is closely united to the
external surface of the geniohyoid. Some of the fibres gain insertion into the
body of the hyoid bone through their insertion into the tendon of the
stylohyoid (d).
Relations.—Outer surface with the submentalis (Fig. 64, c) and the
digastric (Fig. 65, b). Lateral edge with the masseter (a), the digastric (b),
and the mandibula. Caudal border with the stylohyoid (d). Inner (dorsal)
surface with the geniohyoid (Fig. 67, g), the hyoglossus (Fig. 67, h), and the
genioglossus (Fig. 67, f).
Action.—Raises the floor of the mouth and thus brings the hyoid forward.
M. ceratohyoideus.
Origin, the two proximal pieces of the cranial horn of the hyoid. The
fibres pass caudad parallel to one another and within the middle constrictor
of the pharynx.
Insertion into the whole length of the caudal cornu of the hyoid bone.
Relations.—Outer surface with the middle constrictor of the pharynx.
Inner surface with the pharynx.
Action.—Draws craniad the body of the hyoid by bringing its cornua
together and bending the joint between the two pieces of the cranial cornua.
The muscles connecting the hyoid and the tongue are described in
connection with the description of the tongue.

III. MUSCLES OF THE BODY.

1. Muscles of the Back.

A. Muscles of the Shoulder (connecting the forelimb with the back)
(Fig. 68).
M. trapezius.—The trapezius muscle is divided in the cat into three
portions, the spinotrapezius, the acromiotrapezius, and the clavotrapezius.
M. spinotrapezius, or trapezius inferior (Fig. 68, j).—The spinotrapezius
(caudal part of the human trapezius) is a flat triangular muscle.
Origin from the tips of the spinous processes of all or nearly all the
thoracic vertebræ and from the intervening supraspinous ligament. The

origin may extend from a point anywhere between the first and fourth
spines to any point between the eleventh and thirteenth.
Insertion along an S-shaped line (Fig. 76, k-l) which crosses the
tuberosity of the scapular spine and forms an angle with the spine of about
forty-five degrees. The line extends on one side onto the fascia covering the
supraspinatus muscle, and on the other side onto the fascia covering the
infraspinatus, but does not reach the borders of the scapula. The cranial
two-thirds of the insertion is by a flat tendon which is broader craniad.
Relations.—Outer surface with the cutaneus maximus, and craniad with
the acromiotrapezius (h). Inner surface with the latissimus dorsi (m) caudad
and with the rhomboideus, supraspinatus, and infraspinatus craniad. Caudal
border free; cranial border in contact with the acromiotrapezius (h).
Action.—Draws the scapula dorsocaudad.
M. acromiotrapezius, or trapezius superior (Fig. 68, h).—The
acromiotrapezius (middle part of the human trapezius) is a flat four-sided
muscle just craniad of the spinotrapezius, from the median dorsal line to the
scapular spine.
Origin along the median dorsal line from the spinous process of the axis
to a point anywhere between the spinous processes of the first and fourth
thoracic vertebræ. Its caudal two-thirds is from a flat tendon which is
directly continuous with the muscle of the opposite side and thus bridges
the depression between the vertebral borders of the scapulæ. This tendon
narrows craniad, and its cranial fourth is attached by a fascia to the spinous
processes of the cervical vertebræ. At the cranial border of the muscle the
fibres sometimes reach the middle line. The fibres of the muscle run nearly
transversely.
Insertion (Fig. 76, h).—Into the outer surface of the metacromion, the
glenoid border of the scapular spine from the metacromion to the tuberosity,
and along a line continued for about one centimeter from the tuberosity
onto the surface of the spinotrapezius (j) at the junction of its muscular and
tendinous portions.

Fig. 68.—First Layer of Body-muscles, beneath the Skin and Skin-muscles.

a, M. frontoscutularis; b, M. masseter; c, M. sternomastoideus; d, M. clavotrapezius; e, M.
clavobrachialis; f, M. levator scapulæ ventralis; g, M. acromiodeltoideus; h, M. acromiotrapezius; i,
M. spinodeltoideus; j, M. spinotrapezius; k, caput longum of M. triceps brachii; l, caput laterale of
M. triceps brachii; m, M. latissimus dorsi; n, M. xiphihumeralis; o, M. pectoralis minor; p, M.
obliquus abdominis externus; q, M. sartorius; r, M. tensor fasciæ latæ; s, M. caudofemoralis; t, M.
biceps femoris; u, M. semitendinosus; v, M. extensor caudæ lateralis; w, M. abductor caudæ
externus; x, M. flexor caudæ longus; y, lumbodorsal fascia, superficial layer; z, fascia lata. 1,
parotid gland; 2, submaxillary gland.

Relations.—Outer surface with the cutaneus maximus, the integument
and platysma. Inner surface with a mass of fat partially covering the
rhomboideus; with the occipitoscapularis, spinotrapezius, supraspinatus,
levator scapulæ, and splenius. Near its origin its caudal border touches the
outer surface of the spinotrapezius (j). Its cranial border is overlaid near its
insertion by the levator scapulæ ventralis (f) and is closely related to the
caudal border of the clavotrapezius (d) near its origin.
Action.—The two muscles hold the scapulæ together.
M. clavotrapezius (Fig. 68, d).—The clavotrapezius (cranial part of the
human trapezius) is a flat muscle passing from the lambdoidal crest and
middorsal line to the clavicle and covering the side of the neck.
Origin.—The medial half of the lambdoidal crest and the middorsal line
between the crest and the caudal end of the spine of the axis. The fibres are

parallel and pass caudoventrad so that the muscle covers the ventral surface
of the neck caudally and fills the concavity at the front of the shoulder.
Insertion into the clavicle and into a raphe between the clavotrapezius
and the clavobrachial (e) muscles. This raphe extends along the clavicle and
for some distance laterad of it. The muscle is partly continuous with the
clavobrachial (e).
Relations.—Outer surface with the platysma, and at its craniomedial
angle with the levator auris longus. Inner surface with the rhomboideus,
splenius, occipitoscapularis, levator scapulæ, cleidomastoid, and
supraspinatus. The cranial edge touches the sternomastoid. The caudal
border touches the acromiotrapezius near the origin.
Action.—Draws the scapula craniodorsad.
This muscle and the clavobrachial (e) are sometimes considered as
forming a single muscle, the cephalohumeral, or cephalobrachial.
M. occipitoscapularis (or levator scapulæ dorsalis or rhomboideus
capitis) (Fig. 73, a).—The occipitoscapularis (equivalent to a part of the
human rhomboideus) is a slender flat muscle from the lambdoidal ridge to
the coracovertebral angle of the scapula.
Origin, the medial half of the lambdoidal ridge beneath the
clavotrapezius (Fig. 68, d). The origin does not extend quite to the middle
line. The muscle passes almost directly caudad. Its caudal end is thicker and
narrower than the cranial end and is wedged between the rhomboideus
dorsally and the levator scapulæ ventrally.
Insertion either into the inner surface of the levator scapulæ near its
dorsocranial border at its insertion or into the scapula near the
coracovertebral angle (Fig. 78, f) or into both. Its fibres are very closely
related to those of the rhomboideus.
Relations.—By its outer surface with the clavotrapezius (Fig. 68, d) and
acromiotrapezius (h). At its insertion it is often overlaid by either the
rhomboideus or the levator scapulæ or both. By its inner surface with the
splenius (Fig. 73, b). Its caudal third is wedged between the rhomboideus
and the levator scapulæ.
Action.—Draws forward and rotates the scapula.
M. rhomboideus (probably equivalent to the human rhomboideus major
and rhomboideus minor).—A rather thick trapezoid muscle connecting the
vertebral border of the scapula with the spinous processes of the adjacent
vertebræ.

Origin from the caudal two or three fifths of the cervical supraspinous
ligament and from the sides and tips of the first four thoracic vertebral
spines and the interspinous ligaments caudad of these four spines. It passes
lateroventrad, and the fibres converge somewhat so that the line of insertion
is shorter than the line of origin.
Insertion by a short tendon (1 millimeter long) into the vertebral border
of the scapula, the line of insertion passing gradually from the inner (Fig.
78, e) to the outer (Fig. 76, i) surface; and by fleshy fibres into the outer
surface of the glenovertebral angle of the scapula (Fig. 76, i) in close
connection with the origin of the teres major (j). A bundle of fibres at the
cranial border may be inserted into the cranial border of the levator scapulæ
at its insertion.
Relations.—By its outer surface with the spinotrapezius (Fig. 68, j),
acromiotrapezius (h), latissimus dorsi (m), and clavotrapezius (d); it is
usually partially separated from these muscles by a mass of fat. By its inner
surface near its insertion with the serratus anterior (Fig. 73, i) and levator
scapulæ (Fig. 73, h), and craniad with the splenius (Fig. 73, b), and the
tendon of the serratus posterior superior (Fig. 73, l). At its lateral end it
touches the occipitoscapularis (Fig. 73, a), serratus anterior (i), levator
scapulæ (h), supraspinatus (Fig. 75, a), and infraspinatus (Fig. 75, c), and
the teres major (Fig. 75, d).
Action.—Draws the scapula toward the vertebral column.
M. cleidomastoideus (clavicular portion of the human
sternocleidomastoid) (Fig. 65, h).—A narrow flat muscle between the
mastoid process and the clavicle.
Origin from the apex and caudal margin of the mastoid process of the
temporal bone, by tendon and muscle fibres. The muscle passes caudad,
becoming broader and thinner.
Insertion into the lateral four-fifths of the clavicle within the insertion of
the clavotrapezius, and into the raphe which continues laterad of the
clavicle.
Relations.—Outer or lateral surface at the caudal end with the
clavotrapezius (Fig. 65, j); further craniad with the depressor conchæ (Fig.
64, b), the platysma, and the sternomastoid (Fig. 65, g). Inner or medial
surface with the supraspinatus (Fig. 75, a) caudad, with the mass of fat in
the axilla at its middle, with the levator claviculæ ventralis (Fig. 65, i) and
obliquus capitis superior (Fig. 71, e) craniad.

Action.—Pulls the clavicle craniad when the head is fixed. Turns the head
and depresses the snout when the clavicle is fixed.
M. levator scapulæ ventralis, or levator claviculæ (Fig. 68, f; Fig. 65, i;
Fig. 72, c, c′, c″) (not usually found in man).
Origin (Fig. 72, c′, c″) in two parts. (1) By fleshy fibres from the ventral
surface of the atlantal transverse process near its caudal border (c′). (2) By a
small tendon from the ventral surface of the basioccipital opposite the
middle of the length of the bulla tympani (c″) in common with the longus
capitis (a). The two heads unite to form a flat band which passes
caudoventrad and is inserted (Fig. 76, f) by a flat short tendon, about eight
millimeters broad, into the outer surface of the metacromion along its
ventral border, and into the infraspinatus fossa for one or two millimeters
distad of that border.
Relations.—Near the insertion the dorsal border overlaps the border of
the acromiotrapezius (Fig. 68, h), and the ventral border is attached by
strong fascia to the border of the clavotrapezius (Fig. 68, d). The outer
surface is in relation with the longissimus capitis (Fig. 73, g),
clavotrapezius (Fig. 68, d), cleidomastoid (Fig. 73, d), platysma, and the
skin. The inner surface is in relation caudad with the supraspinatus and with
a mass of fat and a lymphatic gland which occupy the hollow of the
shoulder. Craniad it is in relation with the cleidomastoid (Fig. 73, d), the
scalenus (Fig. 73, f), the longus capitis (Fig. 73, e), and the obliquus
superior (Fig. 71, e).
Action.—Pulls the scapula craniad.
M. latissimus dorsi (Fig. 68, m; Fig. 65, q; Fig. 77, e).—A large
triangular sheet covering rather more than the dorsocranial half of the
abdomen and thorax. It arises from the middorsal line, from the pelvis to the
fifth thoracic spine, and is inserted into the humerus.
Origin from the tips of the neural spines of the vertebræ from the fourth
or fifth thoracic to about the sixth lumbar. As far as the tenth or eleventh
thoracic vertebra the origin is directly by muscle-fibres. Caudad of this is a
broad triangular tendon which may be so closely united to the tendons of
the underlying muscles that it cannot be separated. The muscle passes
cranioventrad, the fibres converging to the axilla. In the axilla a part of the
cutaneus maximus and the epitrochlearis (Fig. 65, r) take origin from the
outer surface.

Insertion.—The muscle then ends in a flat tendon, to the cranial surface
of which the fibres of the teres major (Fig. 77, c) are attached. Five to ten
millimeters from the humerus the muscle-fibres of the teres give place to
the tendon-fibres, and the conjoined tendon of the teres and latissimus
which is thus formed (Fig. 79, d′) is inserted into a rough elongated area
(Fig. 82, f) which lies parallel with the pectoral ridge on the medial surface
of the shaft of the humerus (Fig. 48, g). The teres tendon forms the
proximal part of the conjoined tendon. A part of the tendon of the latissimus
may join the pectoralis minor at its distal or caudal border (Fig. 65), and
thus it may contribute to the formation of both pillars of the bicipital arch
(Fig. 65, t′).
Relations.—Its outer surface is covered caudad by the cutaneus maximus,
and craniad by the spinotrapezius (Fig. 68, j) and the long head of the
triceps (Fig. 68, k). The cranial border comes into relation with the
spinotrapezius (j) and teres major (Fig. 77, c). The caudal border is in
contact at the ventral end with the xiphihumeralis (Fig. 65, p) and pectoralis
minor (Fig. 65, o). The inner surface of the latissimus covers near its
cranioventral end parts of the xiphihumeralis (Fig. 68, n), pectoralis minor
(Fig. 68, o), teres major (Fig. 77, c), and serratus anterior (Fig. 73, i). The
caudal border covers a portion of the obliquus externus abdominis (Fig. 68,
p); the dorsal and middle portions cover parts of the longissimus dorsi (Fig.
69, f″), the spinalis dorsi (Fig. 69, g), the serratus posterior superior (Fig.
73, l), and serratus posterior inferior (Fig. 73, n).
Action.—Pulls the arm caudodorsad.
M. serratus anterior and levator scapulæ (Fig. 73, i and h) in the cat
are continuous at both origin and insertion, and it is barely possible to
separate their contiguous borders without cutting the fibres. The muscle
extends from the transverse processes of the last five cervical vertebræ and
from the first nine or ten ribs to the medial surface of the scapula near its
vertebral margin (Fig. 78, c and d).
M. serratus anterior (or serratus magnus) (Fig. 73, i).
Origin.—From the first nine or ten ribs in as many subdivisions. The first
subdivision arises from the whole or nearly the whole of the caudal border
of the first rib. The next four or five arise either from the ribs or from the
costal cartilages near or at their junction with the ribs. The last four
subdivisions arise from the ribs at increasing distances from the cartilages.
The fibres converge and the subdivisions join one another.

Insertion (Fig. 78, c) into a narrow area on the medial surface of the
scapula near the vertebral border. The glenoid half of the insertion is by a
short tendon, the remainder by muscle-fibres.
Relations.—Outer (lateral) surface with the latissimus dorsi (Fig. 68, m),
teres major (Fig. 77, c), subscapularis (Fig. 77, a), and near the origin with
the rectus abdominis (Fig. 73, k), the scalenus (Fig. 73, f-f‴), and the
obliquus externus (Fig. 68, p). Inner (medial) surface with the serratus
posterior superior (Fig. 73, l) and its tendon, and with the intercostales
externi (Fig. 73, m). At its insertion the muscle touches the rhomboideus.
The cranial edge is united to the caudal edge of the levator scapulæ (Fig.
73, h).
Action.—Depressor of the scapula.
M. levator scapulæ (Fig. 73, h).
Origin.—From the dorsal tubercles of the transverse processes of the last
five cervical vertebræ and from the ligaments between the tubercles. A slip
sometimes arises from the atlas.
Insertion (Fig. 78, d) into a triangular area on the medial surface of the
scapula near its vertebral border. It is continuous with the insertion of the
serratus anterior.
Relations.—Outer (lateral) surface with a mass of fat separating it from
the clavotrapezius (Fig. 68, d) and cleidomastoid (Fig. 65, h), and with the
subscapularis (Fig. 77, a). Inner (medial) surface with the splenius (Fig. 73,
b), the tendon of the serratus posterior superior (Fig. 73, l), and the cervical
portion of the longissimus dorsi (Fig. 69, f″). Near the insertion the muscle
touches the occipitoscapularis (Fig. 73, a) and rhomboideus. Caudal border
united with the serratus anterior (Fig. 73, i).
Action.—Draws the scapula cranioventrad.
B. Muscles of the Back (interconnecting parts of the vertebral column)
(Fig. 69).—The muscles connected with the vertebral column form a mass
which is less markedly differentiated into distinct muscles than is the case
in the limbs. A great longitudinal mass of fibres begins in the sacral region
and extends along the vertebral column to the head. This mass contains
fibres running in various directions and attached at one or both ends to the
sacrum, the innominate bones, the spinous, transverse, and articular
processes, and to the arches, of the vertebræ; to the ribs and to the head, and
having in general the function of moving the vertebræ in various ways, or
of moving parts connected with the vertebræ. In some regions, especially

the cervical, it is possible to distinguish clearly distinct muscles which have
been differentiated from this mass. In the greater part of its extent, however,
it is possible to distinguish only more or less closely interconnected
bundles,—the more clearly marked of which have received special names.
The great dorsal mass running along each side of the vertebral column,
occupying the space between the spinous processes and the transverse
processes, receives the general name of M. extensor dorsi communis; the
separate muscles are to be considered as parts or differentiations of this.
The largest part of the mass is in the lumbar region (first portion of the
longissimus dorsi, Fig. 69, f). At the caudal end of the thorax a lateral
mass, parts of which become connected with the ribs, is separated off from
the main part of the muscle; this extends craniad into the cervical region as
M. iliocostalis (h). The main portion of the longissimus dorsi (f′) continues
craniad on the medial side of the iliocostal into the neck region. At about
the level of the eighth or ninth thoracic vertebra a strip begins to become
separated off on the medial side of the longissimus; further forward it
becomes clearly distinct, forming the spinalis dorsi (g). The separate
muscles connecting the cervical vertebræ with each other and with the head
are differentiations of the extensor dorsi communis.
A still deeper set of fibres, interconnecting the vertebræ, forms the
multifidus spinæ and a number of other small muscles.
A description of the different bundles of fibres, under the names usually
given, follows. Certain general principles are observed in some of the
names used. Muscles which interconnect the spinous processes of the
vertebræ receive the name spinalis. Those interconnecting contiguous
spinous processes are called interspinalis. Muscles attached at one end to
transverse processes, at the other to the spinous processes, receive the name
transversospinalis. Semispinalis has the same signification as
transversospinalis, but is a name usually applied to subdivisions of the
transversospinalis group. The intertransversarii are muscles
interconnecting the transverse processes.

Fig. 69.—Deep Muscles of Body, Exposed after Removal of the Muscles shown in Fig. 73.

a, M. biventer cervicis; b, M. complexus; c, M. obliquus capitis superior; d, M. longus atlantis; e,
cut end of M. longissimus capitis; f, f′, f″, M. longissimus dorsi; g, M. spinalis dorsi; h, M.
iliocostalis; i, Mm. intercostales externi; k, Mm. intercostales interni; l, M. transversus abdominis.

(a) Muscles of the Lumbar and Thoracic Regions.—The muscles of the
lumbar and thoracic regions are mostly covered by a strong fascia, known
as the lumbodorsal fascia (Fig. 68, y). This consists of two sheets, the
superficial sheet being applied directly to the outer surface of the inner
sheet, or separated from it by a mass of fat.
The superficial sheet (Fig. 68, y) overlies the lumbar region and the
caudal half of the thoracic region. On the medial side it is attached to the
spinous processes of the vertebræ and is united closely to the deeper layer.
Laterally this fascia is continuous with the latissimus dorsi (m) and obliquus
abdominis externus (p). Caudad it is attached to the spine of the ilium and
becomes continuous with the fascia covering the gluteus muscles.
The deeper sheet (Fig. 70, c) is of a tendinous character, forming the
external tendinous layer of the longissimus dorsi, many of whose fibres take
origin from its under surface. It is described more fully in the account of
this muscle.
M. longissimus dorsi (Fig. 69, f, f′, f″; Fig. 70, a and b).—A very large
muscle, filling most of the region between the spinous processes and
transverse processes of the lumbar and thoracic vertebræ, and extending
into the cervical region.

The muscle is largest in the lumbar region (Fig. 69, f; Fig. 70), where it is
divided into a narrow medial (Fig. 70, a) and a thick lateral portion (Fig. 70,
b), the latter being again partially subdivided by the fascia. The two parts
unite farther craniad.
The medial division (Fig. 70, a) consists of muscular bundles connecting
the spinous processes of the vertebræ with the accessory and mammillary
processes of other vertebræ; it is continuous caudad with the extensor
caudæ lateralis (Fig. 70, f). The muscle-fibres take origin in the sacral
region by small round tendons from the spinous processes of the last two
sacral and the caudal vertebræ. They curve cranioventrad, forming a large
belly, and are inserted into the accessory and mammillary processes of the
lumbar vertebræ. In the thoracic region this division unites with that portion
of the lateral division in which the fibres coming from the fascia of origin
are inserted into the laminæ and transverse processes of the thoracic
vertebræ.
The lateral division (Fig. 70, b) is much larger than the medial one,
forming in the lumbar region a nearly cylindrical mass.

Fig. 70.—Muscles on the Dorsal Side of the Vertebral Column in the
Lumbar, Sacral, and Caudal Regions.

Both sheets of the lumbodorsal fascia have been removed, the deep layer (c)
being cut where it passes into the longissimus dorsi. 1, crest of ilium; 4-7, tips of
spinous processes of the fourth to seventh lumbar vertebræ. I, II, tips of spinous
processes of first two sacral vertebræ. a, b, M. longissimi dorsi (a, medial portion;
b, lateral portion; b′, portion taking origin from the lumbodorsal fascia); c, cut edge
of deep layer of lumbodorsal fascia; d, M. multifidus spinæ; e, M. extensor caudæ
medialis; f, M. extensor caudæ lateralis, g, M. abductor caudæ externus.

Origin from the crest of the ilium (Fig. 70, 1) and the medial surface of
the ilium as far caudad as the auricular impression; also from the deep layer
of the lumbodorsal fascia (c). This fascia is connected with the crest of the

ilium and with the tips of the spinous processes of the vertebræ in the
lumbar and thoracic regions, and from it a large proportion of the fibres of
the longissimus take origin. In the lumbar region it dips into the muscle as
an intermediate longitudinal sheet (c), partially dividing it lengthwise into
two parts. Fibres taking origin from the lateral surface of this intermediate
sheet curve cranioventrad, and are inserted on the transverse processes of
the lumbar vertebræ. Fibres taking origin from the medial surface of the
sheet pass mediocraniad and are inserted into the accessory processes and
the surfaces of the vertebral arches. In the thoracic region (Fig. 69, f′) most
of the fibres are inserted in separate bundles by small tendons on the
transverse processes of the vertebræ, while some of the medial fibres unite
with tendinous strands which become attached to the laminæ and articular
processes of the vertebræ. At the region of the eighth or ninth thoracic
vertebra the spinalis dorsi (Fig. 69, g) begins to be separated off on the
medial side, the separation becoming complete only some distance farther
craniad; the longissimus dorsi then continues into the cervical region (f″).
Bundles of fibres become attached in the manner above described to
transverse processes of all the thoracic vertebræ. In the cervical region (f″)
the muscle spreads out and becomes thinner, and bundles of fibres become
attached to the transverse processes of the cervical vertebræ as far forward
as the second. In the more cranial portion of its extent the muscle receives
fibres having origin on the articular processes and laminæ of the cervical
and a few of the more cranial thoracic vertebræ.
The portion of the muscle which is inserted on the cervical transverse
processes (f″) is sometimes distinguished as the longissimus cervicis; it is
not well separated from the rest of the muscle in the cat. The longissimus
capitis (Fig. 69, c; Fig. 73, g) is to be considered a differentiated cranial
portion of this muscle.
Relations.—Outer surface with the following, beginning with the caudal
end: the sartorius (Fig. 68, q), the latissimus dorsi (Fig. 68, m), the
lumbodorsal fascia (Fig. 68, y), the serratus posterior inferior (Fig. 73, n)
and superior (Fig. 73, l), and the levator scapulæ (Fig. 73, h). Lateral
margin with the abdominal muscles, the iliocostal (Fig. 69, h), and the
levator scapulæ (Fig. 73, h). Medial side with the multifidus spinæ (Fig. 70,
d), the spinous processes of the thoracic vertebræ, the spinalis dorsi (Fig.
69, g), the complexus (Fig. 69, b), the biventer cervicis (Fig. 69, a), and the
longissimus capitis (Fig. 69, e).

Action.—Extends the vertebral column.
M. iliocostalis (Fig. 69, h).—This is a muscle about 1½ to 2 centimeters
wide, lying on the dorsal portion of the ribs, laterad of the longissimus dorsi
(f′). It is composed of many partly separated bundles, each with an oblique
tendon. The muscle begins at the last or next to the last rib, where it is
connected with the longissimus by a rather small bundle of fibres. The rest
of the muscle-fibres take origin in bundles from the lateral surface of the
ribs, at about the angles, or from thin tendons connecting the angles, of the
ribs; they pass obliquely craniad and are inserted, usually by tendons, on the
lateral surface of the third or fourth rib craniad of the one on which the
given bundle has origin. The insertions on any given rib lie ventrad of the
origins on the same rib. In the cat this muscle is confined to the thoracic
region.
Relations.—Outer surface with the serratus posterior inferior (Fig. 73, n)
and superior (Fig. 73, l), and the levator scapulæ (Fig. 73, h). Inner surface
with the dorsal surface of the ribs, the external intercostals (Fig. 69, i), and
craniad with the levatores costarum. Medial edge in contact with the
longissimus dorsi (Fig. 69, f′).
Action.—Draws the ribs together.
M. spinalis dorsi (Fig. 69, g).—A muscle interconnecting the spinous
processes of vertebræ some distance apart, in the thoracic and cervical
regions. It lies on the medial side of the longissimus dorsi (f′).
Origin by strong tendons from the tips of the spinous processes of the
tenth to the thirteenth thoracic vertebræ. These tendons represent the cranial
portion of the deep layer of the lumbodorsal fascia, and give origin also to
many fibres of the longissimus dorsi, so that the two muscles are
completely united at the origin of the spinalis. They become separated at
about the level of the sixth thoracic vertebra, the spinalis forming a strong
separate bundle passing into the neck region close against the sides of the
spinous processes. The insertion is by fleshy bundles into the sides of the
spinous processes of the first nine or ten thoracic vertebræ and of the
cervical vertebræ as far forward as the second. Some of the fibres of this
muscle pass craniad into the biventer cervicis (Fig. 69, a).
Relations.—Outer surface with the tendons of the serratus posterior
inferior (Fig. 73, n) and serratus posterior superior (Fig. 73, l), and with the
splenius (Fig. 73, b), biventer cervicis (Fig. 69, a), and complexus (Fig. 69,

b). Lateral and ventral surface with the longissimus dorsi (f′); medial
surface with the spinous processes and the multifidus spinæ.
Action.—Extensor of the vertebral column.
M. multifidus spinæ.—This consists of bundles of fibres which have
origin on the transverse processes or neighboring parts, pass craniodorsad
across one or more vertebræ, and are inserted into the spinous processes of
vertebræ lying some distance craniad of the origin. They lie deeper than the
muscles previously described. The muscle is most strongly developed in the
lumbar region (Fig. 70, d), where it forms a thick interwoven mass in which
it is difficult to distinguish separate bundles. The fibres in this region have
origin on the accessory or mammillary processes and usually pass over
more than one vertebra between origin and insertion; their insertions reach
the dorsal ends of the spinous processes, so that part of the muscle lies
immediately beneath the lumbar fascia. In other regions the multifidus is
covered by other muscles. In the thoracic region the separate bands are
more distinct, and usually pass in their course over but one intervening
vertebra. In the cervical region the bands are interconnected, forming a
fairly distinct single muscle, which is described separately below as the
semispinalis cervicis (Fig. 71, c). The portion of this muscle attached to the
head (semispinalis capitis) forms the biventer cervicis (Fig. 69, a) and
complexus (b). Caudad this muscle passes onto the tail as the extensor
caudæ medialis (Fig. 70, c).
Relations.—Outer and lateral surface in the lumbar region with the
longissimus dorsi (Fig. 69, f) and the lumbodorsal fascia (Fig. 68, y); in the
thoracic region with the longissimus dorsi (Fig. 69, f′) and spinalis dorsi (g).
Inner surface with the arches, articular processes, and spinous processes of
the vertebræ.
Action.—Extends the back when the muscles of both sides work together.
Turns the vertebral column obliquely sideways when one set acts alone.
The deepest layer of the multifidus forms what is sometimes
distinguished as the Mm. rotatores; no separate layer of this sort is to be
made out in the cat.
Mm. interspinales.—Muscle-bundles passing from the spinous process
of one vertebra to that of the vertebra immediately craniad or caudad of it.
They are best developed in the lumbar region.
Mm. intertransversarii.—Muscle-fibres interconnecting the transverse
processes. In the lumbar region the intertransversarii mediales connect

the accessory and mammillary processes; the intertransversarii laterales
lying between the transverse processes. In other regions only one set of the
intertransversarii is to be distinguished.
(b) Dorsal Muscles of the Cervical Region.—The clavotrapezius (Fig. 68,
d) and occipitoscapularis (Fig. 73, a) have been described in connection
with the muscles of the shoulder. The remaining muscles of this region may
be considered as differentiations of the general vertebral musculature (M.
extensor dorsi communis).
M. splenius (Fig. 73, b.)—A large sheet of muscle covering the dorsal
part of the side of the neck, beneath the trapezii.
Origin from the whole cervical ligament and from the fascia covering the
deeper muscles along a line which extends from the first thoracic spinous
process caudolaterad for about two centimeters.
Insertion by a thin tendon into the whole lambdoidal ridge. Laterad the
tendon may be fused with that of the longissimus capitis (Fig. 73, g).
Relations.—Outer surface with the sternomastoid (Fig. 68, c),
occipitoscapularis (Fig. 73, a), clavotrapezius (Fig. 68, d), rhomboideus,
tendon of the serratus posterior superior (Fig. 73, l), and the levator scapulæ
(Fig. 73, h). Lateral edge closely united with the longissimus capitis (Fig.
73, g). Inner surface with the longissimus capitis, complexus (Fig. 69, b),
and biventer cervicis (Fig. 69, a).
Action.—Lateral flexor of the head. The two together elevate the head.
M. longissimus capitis (trachelomastoideus) (Fig. 73, g; Fig. 69, e).—
This is a slender muscle lying close against the lateral border of the splenius
(Fig. 73, b), and sometimes fused with the splenius at its craniad end. It is a
cranial continuation of the longissimus dorsi (Fig. 69, f″).
Origin by five slips which are attached by strong tendons to the anterior
articular processes of the last four cervical vertebræ. The tendons are
common to this muscle and the complexus. The five slips unite to form a
flat belly which has its
Insertion by a strong rounded tendon into the mastoid process of the
temporal bone. The tendon may be closely united to that of the splenius.
Relations.—Lateral surface with the sternomastoid (Fig. 68, c), the
levator scapulæ (Fig. 73, h), and longissimus dorsi (Fig. 69, f″). Medial
surface with the splenius (Fig. 73, b) (to which it is partly united), the
complexus (Fig. 69, b), and the longus atlantis (Fig. 69, d).
Action.—Lateral flexor of the head.

M. biventer cervicis (Fig. 69, a) (medial portion of M. semispinalis
cervicis et capitis).—The biventer cervicis is a flat muscle which lies
beneath the splenius (Fig. 73, b), next the median line of the neck, with its
fibres longitudinal.
Origin in three or four slips from the surface of the three or four
aponeurotic arches which take origin from the tips of the spinous processes
of the last cervical and the first three thoracic vertebræ and pass laterad and
caudad to the anterior processes of the second, third, fourth, and fifth
thoracic vertebræ. These arches are deviated from their straight course by
four aponeurotic bands which pass from them obliquely caudad and dorsad
to the sides of the spinous processes of the vertebræ into which the arches
are inserted. The arches form the beginning of the sheet of fascia which
passes outside of the longitudinal supraspinous muscles, and the anchoring
bands form the beginning of a similar sheet which passes within the
longitudinal supraspinous muscles. An additional slip may take origin from
the cervical ligament between the last cervical and the first thoracic
vertebræ. The fibres form a flat band divided by two or three oblique
tendinous intersections. It adheres closely to the cervical supraspinous
ligament.
Insertion by a strong tendon into the medial part of the lambdoidal crest.
Relations.—Outer surface with the splenius (Fig. 73, b) and at the caudal
end with the longissimus dorsi (Fig. 69, f″). Inner surface with the spinalis
dorsi (Fig. 69, g), the semispinalis cervicis (Fig. 71, c), and the rectus
capitis posterior major (Fig. 71, a). Medial edge with the muscle of the
opposite side; lateral edge with the complexus (Fig. 69, b).
Action.—Raises the snout.
M. complexus (Fig. 69, b) (lateral portion of M. semispinalis cervicis
et capitis).—The complexus is closely associated with the biventer cervicis
(a) and lies on its lateral side beneath the splenius (Fig. 73, b).
Origin by tendinous bands from the anterior articular processes of the last
five or six cervical and the first one, two, or three thoracic vertebræ. The
same bands give origin externally to the fibres of the longissimus capitis
(Fig. 69, e), and internally to those of deeper muscles of the neck. The six
or more muscular slips continued from these tendons unite to form a flat
band, the
Insertion of which is by a flat tendon into the medial third of the
lambdoidal crest some distance ventrad of the free edge of the crest. Near

the insertion the lateral border of the muscle is connected by an aponeurotic
band to the lateral border of the transverse process of the atlas.
Relations.—Outer surface at the dorsal border with the biventer cervicis
(Fig. 69, a); at the middle with the splenius (Fig. 73, b); at the ventral
border with the longissimus capitis (Fig. 69, e) and the longissimus dorsi
(Fig. 69, f″). Inner surface with the cervical portion of the spinalis dorsi,
with the semispinalis cervicis (Fig. 71, c), the obliquus capitis inferior (Fig.
71, b), the rectus capitis posterior major (Fig. 71, a), and the obliquus
superior (Fig. 71, e).
Action.—Raises the head.
M. spinalis dorsi extends into the cervical region; it has been described.
M. semispinalis cervicis (Fig. 71, c).—This represents that portion of
the multifidus spinæ which extends into the cervical region. It is not
composed of distinct bundles, like the multifidus of the thoracic region, but
all the fibres are united into a fairly well-defined muscle.
Origin from the articular processes of the last five cervical vertebræ.
Insertion into the spinous processes of the cervical vertebræ up to the
second, the largest part of the muscle being inserted into the caudal end of
the spine of the atlas.
Relations.—Outer surface with the spinalis dorsi (Fig. 69, g) and the
complexus (Fig. 69, b). Inner surface with the vertebræ.
Action.—Extends the neck.
M. longissimus dorsi extends into the cervical region, where it is often
distinguished as the longissimus cervicis (Fig. 69, f″). It has been
described.
M. longus atlantis (Fig. 71, f; Fig. 69, d).—This represents a
differentiated portion of the longissimus dorsi.
Origin from the transverse process and the side of the vertebral arch of
the third cervical vertebra.
Insertion into the caudolateral angle of the wing of the atlas.
Relations.—Dorsal surface with the complexus (Fig. 69, b), the
longissimus capitis (Fig. 69, e), and the obliquus inferior (Fig. 71, b).
Ventral surface with the scalenus (Fig. 71, g), longissimus dorsi (Fig. 69,
f″), and levator scapulæ (Fig. 71, h).
Action.—Extends the neck and turns the head sideways.
M. rectus capitis posterior major (Fig. 71, a).

Origin.—The whole length of the spinous process (or crest) of the axis,
or its caudal part only. It is united by a raphe to the opposite muscle. The
muscle passes craniad and laterad to its
Insertion into an area ventrad of the medial part of the lambdoidal crest
beneath the insertion of the complexus (Fig. 69, b) and the biventer cervicis
(Fig. 69, a).
Relations.—Dorsal surface with the biventer cervicis (Fig. 69, a). Ventral
surface with the rectus capitis posterior medius (Fig. 71, d) and the obliquus
capitis inferior.
Action.—Raises the snout.
M. rectus capitis posterior medius (Fig. 71, d). (This is in man a part of
the rectus capitis posterior major.)—It lies beneath the rectus capitis
posterior major (Fig. 71, a).

Fig. 71.—Deep Muscles of the Neck, after the Removal of Mm. Biventer
Cervicis and Complexus.

a, M. rectus capitis posterior major; b, M. obliquus capitis inferior; c, M.
semispinalis cervicis; d, M. rectus capitis posterior medius; e, M. obliquus capitis
superior; f, M. longus atlantis; g, M. scalenus (part of cervical portion); h, cut end
of M. levator scapulæ.

Origin from the cranial end of the axial spine. It forms a triangular
prismatic mass which passes craniad and has its

Insertion into an elongated area on the occipital bone, ventrad of the
median half of the lambdoidal crest.
Relations.—Dorsal surface with the rectus capitis posterior major (Fig.
71, a). Ventral surface with the atlas and the rectus capitis posterior minor.
Action.—Assists the rectus capitis posterior major.
M. rectus capitis posterior minor.—A small triangular muscle beneath
the rectus capitis posterior medius (Fig. 71, d).
Origin by the apex of the triangle from the cranial border of the dorsal
arch of the atlas for about two millimeters laterad of the median line. The
muscle passes over the ligament which connects the atlas to the occiput and
adheres to it.
Insertion into an elongated area on the occipital bone, ventrad of the
insertion of the rectus capitis posterior medius for about five millimeters
next to the median line.
Relations.—Dorsal surface with the rectus capitis posterior medius.
Ventral surface with the posterior atlanto-occipital membrane.
Action.—Assists the rectus capitis posterior major.
M. obliquus inferior (Fig. 71, b).
Origin from the whole lateral surface of the spine of the axis. The parallel
fibres form a thick mass which passes laterad and craniad.
Insertion into the dorsal surface of the transverse process of the atlas
along a narrow area near its lateral margin.
Relations.—Outer surface with the rectus capitis posterior major (Fig. 71,
a), the complexus (Fig. 69, b), and the obliquus superior (Fig. 71, e). Inner
surface with the axis.
Action.—Rotates the head.
M. obliquus capitis superior (Fig. 71, e; Fig. 72, e).—This is a
triangular muscle passing from the outer border of the atlas laterad of the
recti capitis posteriores to the occiput.
Origin from the lateral border of the transverse process of the atlas on its
ventral margin. The fibres pass craniad and diverge.
Insertion into the caudal side of the mastoid process of the temporal bone
and into a line parallel with the lambdoidal ridge and ventrad of it, from the
mastoid process to within one centimeter of the median line.
Relations.—Outer surface with the splenius (Fig. 73, b), complexus (Fig.
69, b), and longissimus capitis (Fig. 73, g). Inner surface with the obliquus
inferior (Fig. 71, b), the wing of the atlas, and the rectus lateralis (Fig. 72,

d). Ventral border with the cleidomastoid (Fig. 73, d) and one head of the
levator scapulæ ventralis (Fig. 72, c′).
Action.—Flexes the head laterally.
Mm. interspinales and intertransversarii are found in the neck region
also; they are described with the muscles of the back.
C. Muscles of the Tail.—M. extensor caudæ medialis (Fig. 70, e).—
This is a continuation caudad of the multifidus spinæ (Fig. 70, d); it lies
next to the dorsal median line, the muscles of right and left side touching
one another in the middle line.
Origin by numerous fleshy bundles from the spinous processes of the
sacral and first caudal vertebræ. The fibres pass caudad and are inserted by
tendons into the articular processes and the dorsal surface of the caudal
vertebræ.
Action.—Extends (raises) the tail.
M. extensor caudæ lateralis (Fig. 70, f).—This is a continuation caudad
of the medial portion of the longissimus dorsi (Fig. 70, a); it lies just laterad
of the extensor caudæ medialis (Fig. 70, e).
Origin in many fleshy bundles from the articular processes of the sacral
vertebræ, and the transverse processes of the caudal vertebræ. The fibres
curve dorsocaudad and are inserted by many long slender tendons on the
dorsal surfaces of the caudal vertebræ. The muscle grows continually
smaller as it passes caudad.
Action.—Raises the tail.
M. abductor caudæ (coccygis) externus (Fig. 68, w; Fig. 70, g).—A
rounded muscle on the lateral surface of the cranial part of the tail.
Origin from the medial side of the dorsal border of the ilium, and from
the dorsal surface of the sacrum. The muscle passes caudad, lying just
ventrad of the extensor lateralis, and is inserted into the transverse
processes and lateral surfaces of the caudal vertebræ, as far back as the
eighth or ninth.
Action.—Bends the tail sideways.
M. abductor caudæ internus (or M. coccygeus).—A large flat muscle,
having origin on the spine of the ischium. The muscle passes dorsomediad,
spreading out, and is inserted into the transverse processes of the second to
the fourth caudal vertebræ.
Relations.—Lateral surface with the caudofemoralis (Fig. 68, s), gluteus
maximus, and pyriformis. Medial surface with the iliocaudalis and the

flexor caudæ longus (Fig. 68, x).
M. iliocaudalis (Str.-D.) (Fig. 162, 11′, page 398).—This represents a
portion of the levator ani of man, and in some specimens is united with that
muscle (Fig. 162, 11) in the cat.
Origin along the ventral half of the medial surface of the ilium, caudad of
the sacrum. The fibres pass caudad and are inserted by a flat tendon into the
ventral surface of the caudal vertebræ, from the second or third to about the
seventh.
Relations.—Lateral surface with the gluteus maximus and abductor
caudæ internus (Fig. 68, w). Medial surface with the levator ani (Fig. 162,
11), with which this muscle may be partly united.
Action.—The two muscles together flex the tail.
M. flexor caudæ longus (Fig. 162, 12; Fig. 113, c, page 270).
Origin on the ventral surface of the last lumbar vertebra, of the sacrum,
and of the transverse processes of the caudal vertebræ. Caudad the muscle
forms long, strong tendons which are inserted on the ventral surface of the
tail.
Relations.—Lateral surface with the ilium, the gluteus maximus, the
abductor caudæ internus, the iliocaudalis, and the skin of the tail. Dorsally it
touches in the caudal region the abductor caudæ externus (Fig. 68, w),
medially the flexor caudæ brevis (Fig. 162, 13).
Action.—Flexes the tail.
M. flexor caudæ brevis (Fig. 162, 13).
Origin on the ventral surface of the caudal vertebræ, from the first to the
seventh or eighth. The principal head comes from the first vertebra. The
bundles thus formed pass caudad and are inserted each into the ventral
surface of a vertebra some distance caudad of the origin. The muscle
extends to about the tenth caudal vertebra, and its most caudal parts are
closely interconnected with the flexor caudæ longus.
Relations.—Lateral edge with the flexor caudæ longus. Medial edge in
the sacral region with the levator ani (Fig. 162, 11) and the iliocaudalis (Fig.
162, 11′); in the caudal region with the muscle of the opposite side.
Action.—Flexes the tail.

2. Muscles on the Ventral Side of the Vertebral Column.

A. Lumbar and Thoracic Regions.—The iliopsoas (Fig. 162, 8) belongs
in this group, but since it moves the leg it is described with the muscles of
the pelvic limbs.
M. psoas minor (Fig. 162, 9, page 398).—This muscle lies along the
ventral surface of the vertebral column, next to the peritoneum, and extends
from the thoracic vertebræ to the ilium.
Origin usually by five heads, from the caudal border of the centra of the
last two (or one) thoracic and first three (or four) lumbar vertebræ. These
heads also serve as origin for a part of the iliopsoas, and are closely united
at their origin with the quadratus lumborum. They unite to form an, at first,
rather large flat muscle, which rapidly becomes smaller caudad, finally
forming a slender tendon which is inserted on the iliopectineal line, just
craniad of the acetabulum.
Relations.—Dorsolateral surface with the quadratus lumborum and
iliopsoas (Fig. 162, 8). Ventral surface with the pleura and diaphragm near
the origin; with the peritoneum caudad.
Action.—Flexes the back in the lumbar region.
M. quadratus lumborum.—A flat muscle lying on the ventral surface of
the transverse processes of the lumbar vertebræ. Craniad it has origin on the
ventral surface of the last two thoracic vertebræ, and by a few fibres from
the last rib. The muscle passes caudad, lying on the lateral side of the psoas
minor (Fig. 162, 9), and becomes attached to each of the transverse
processes of the lumbar vertebræ. Caudad the muscle passes into a strong
flat tendon which is inserted into the anterior inferior spine of the ilium.
Relations.—Dorsal surface with the transverse processes and the
intertransverse muscles. Ventral and medial surfaces with the psoas minor
(Fig. 162, 9) and iliopsoas (Fig. 162, 8).
Action.—Bends the vertebral column sideways.
B. Muscles on the Ventral Side of the Neck (Fig. 65, page 109).—M.
sternomastoideus (Fig. 65, g; Fig. 68, c).—The sternomastoid (sternal
portion of the human sternocleidomastoid) is a flat band one to three
centimeters wide extending from the cranial end of the manubrium and the
midventral line craniad of it to the lambdoidal ridge.
The origin extends from the cranial end of the manubrium along the
midventral line as far as the caudal border of the cricoid cartilage, and is in

two parts. The caudal portion arises from the lateral surface of the
manubrium along the dorsal half of its cranial end, and from the median
raphe for about one centimeter craniad of the manubrium. Its fibres are
parallel and tend to diverge into two layers. The cranial portion arises by
means of fibres which cover the median line and interdigitate with the
fibres of the opposite muscle between the cricoid cartilage and a point a few
millimeters craniad of the manubrium. Its caudal border is thus overlaid by
the caudal portion. Its fibres converge and join those of the caudal portion.
The muscle passes dorsocraniad and is
Inserted by means of a flat tendon into the lateral half of the lambdoidal
ridge and into a continuation of the ridge onto the mastoid portion of the
temporal bone as far as the mastoid process. The thickest part of the tendon
is inserted into the mastoid process.
Relations.—Outer surface at the caudal end with the pectoralis major
(Fig. 65, l); in the middle part with the platysma, the depressor conchæ (Fig.
64, b), and with the external jugular vein (Fig. 65, 5), which crosses it
obliquely; at the cranial end with the submaxillary (Fig. 65, 2) and parotid
(1) glands. Inner surface with the sternohyoid (Fig. 65, e), sternothyroid (g′),
internal jugular vein, longus capitis muscle, the cleidomastoid (h), levator
scapulæ ventralis (i), a large lymphatic gland ventrad of the ear, and the
splenius (Fig. 73, b).
Action.—One muscle turns the head and depresses the snout. Both
together depress the snout.
M. sternohyoideus (Fig. 65, e).—A slender muscle on the midventral
line of the neck close to the opposite muscle.
Origin from the cranial border of the first costal cartilage. The muscle
passes craniad closely united near its caudal end to the sternothyroid (g′).
Insertion (Fig. 67, m) into the outer half of the ventral surface of the body
of the hyoid bone caudad of the origin of the geniohyoid (Fig. 67, g).
Relations.—Outer surface with the sternomastoid (Fig. 65, g). Inner
surface with the thyrohyoid (Fig. 65, f; Fig. 67, p), the trachea (Fig. 67, 4),
and the larynx.
Action.—Draws the hyoid caudad. Raises the ribs and sternum when the
hyoid is fixed.
M. sternothyreoideus (Fig. 65, g′).—The sternothyroid lies beneath the
sternohyoid and is connected with it at its caudal end.
Origin from the first costal cartilage beneath the sternohyoid.

Insertion (Fig. 67, o) into the lateral part of the caudal border of the
thyroid cartilage of the larynx.
Relations.—Outer surface with the sternohyoid (Fig. 65, e) and laterally
with the sternomastoid (Fig. 65, g). Inner surface with the trachea (Fig. 67,
4), and at the lateral edge with the thyroid gland (Fig. 67, 6).
Action.—Pulls the larynx caudad.
M. scalenus (Fig. 73, f-f‴).—This is a large and complex muscle lying on
the ventral side of the neck and the lateral surface of the thorax. It might
equally well be classified with the muscles of the thorax. It is divisible into
a considerable number of interconnected bundles which are sometimes
described as separate muscles.
The largest, middle portion (scalenus medius) (f′) takes origin by thin
tendons from the sixth, seventh, eighth, and ninth ribs, just dorsad of their
junction with the cartilages; these tendons unite near their origins to form a
flat band which becomes fleshy at about the fifth rib, passes craniad, and
unites just craniad of the first rib with the other parts of the muscle. The
dorsal portion (scalenus posterior) (f″) has origin by a very slender tendon
from about the middle of the outer surface of the third or fourth rib; it
extends craniad as a narrow band which passes laterad between the heads of
the serratus anterior (i) that are attached to the second and third (or third
and fourth) ribs, and unites with the other heads. The ventral head (part of
scalenus anterior) (f‴) arises by one or two minute tendons from the
cartilages of the second and third ribs; they are partly united with the
transversus costarum (j). This ventral head passes craniad and unites with
the other heads.
These three divisions unite just craniad of the first rib with each other and
with the cervical portion of the muscle (f) (part of scalenus anterior). This
consists of a number of small bundles of fibres which arise from the first rib
and the transverse processes of the first thoracic and the last six cervical
vertebræ.
The insertion is onto the transverse processes of all the cervical vertebræ,
including the axis and atlas. According to Strauss-Durckheim the fibres
from any given transverse process are inserted into the transverse processes
of all the vertebræ craniad of it.
The muscle is partly continuous craniad with the longus capitis (e). The
cervical nerves pass out between the bundles of the cervical portion.

Relations.—Outer (lateral) surface in the thoracic region with the
external oblique (Fig. 68, p), the pectoralis minor (Fig. 65, o), and in part
with the serratus anterior (Fig. 73, i); in the cervical region with the
sternomastoid (Fig. 65, g). Inner (medial) surface with the serratus anterior
(Fig. 73, i), the levator scapulæ (Fig. 73, h), the longus atlantis, the
transverse processes of the cervical vertebræ, and the longus capitis (Fig.
73, e).
Action.—Flexes the neck and draws the ribs craniad.
M. longus capitis (or rectus capitis anterior major) (Fig. 72, a; Fig. 73,
e).—This is a long muscle lying on the ventral aspect of the cervical
vertebræ. With the muscle of the opposite side and the underlying longus
colli (Fig. 72, g′) it forms a trough in which lie the œsophagus, pharynx,
and trachea.
Origin by five (or six) heads from the ventral margins of the transverse
processes of the cervical vertebræ from the second to the sixth inclusive.
The heads unite into a common belly, the lateral border of which is united
with the levator scapulæ ventralis (Fig. 72, c) near its insertion.
Insertion into the body of the sphenoid bone between the bulla and the
middle line. The insertion extends craniad onto the basisphenoid.
Relations.—Ventral surface with the sternomastoid (Fig. 65, g) and the
large lymphatic gland ventrad of the external ear. Lateral surface with the
scalenus (Fig. 72, h) and craniad with the levator scapulæ ventralis (Fig. 72,
c-c″). Medial surface with the carotid artery, the trachea, œsophagus, and
pharynx. Dorsal edge with the vertebræ, the longus colli (Fig. 72, g′), and
the rectus capitis anterior minor (Fig. 72, b).
Action.—Lowers the snout.
M. rectus capitis anterior minor (Fig. 72, b).—This is a flat band
beneath (dorsad of) the longus capitis (a).
Origin from the ventral surface of the inferior arch (body) of the atlas (3)
for about five millimeters laterad of the middle line.
Insertion into a deep depression on the basioccipital caudad of the
insertion of the longus capitis (a) and between the caudal end of the bulla
(1) and the median line.
Relations.—Ventral surface with the longus capitis (a). Dorsal surface
with the anterior (ventral) atlanto-occipital membrane (2).
Action.—Depresses the snout.

Fig. 72.—Muscles on the Ventral Surface of the Cervical Vertebræ.

On the left side the longus capitis and one head of the levator scapulæ ventralis
have been cut, in order to show the rectus capitis anterior minor. a, M. longus
capitis; b, M. rectus capitis anterior minor; c, M. levator scapulæ ventralis (c′, its
atlantal head; c″, its occipital head); d, M. rectus capitis lateralis; e, M. obliquus
capitis superior; f, M. longissimus capitis; g, M. longus colli (g′, its cervical
portion; g″, its thoracic portion); h, part of M. scalenus. 1, bulla tympani; 2, ventral
atlanto-occipital membrane; 3, ventral arch of atlas; 4, first rib.

M. rectus capitis lateralis (Fig. 72, d).—This lies ventrad of the
obliquus superior (e) on the ventral face of the transverse process of the
atlas and at first appears to be a part of the obliquus superior.

Origin from the median half of the ventral surface of the transverse
process of the atlas. The fibres form a cylindrical mass which passes
craniad and slightly laterad.
Insertion into the fossa laterad of the condyle of the occipital bone.
Relations.—Ventral surface with the digastric (Fig. 65, b) and the
lymphatic gland ventrad of the ear. Dorsal surface with the wing of the
atlas.
Action.—Flexes the head laterally.
M. longus colli (Fig. 65, g′, g″).—A long, rather slender muscle lying on
the ventral surface of the cervical and first six thoracic vertebræ. It consists
of many separate bundles, and is divisible into a thoracic and a cervical
portion.
The thoracic portion (g″) has origin by six heads from the ventral
surface of the first six thoracic vertebræ. The separate heads join to form a
band which passes craniad and is inserted for the most part into the
processus costarius of the sixth cervical vertebra; a portion of it joins the
cervical division of the muscle.
The cervical portion (g′) is a continuation craniad of the thoracic
portion. It arises in small bundles from the transverse processes and sides of
the ventral surfaces of the centra of the cervical vertebræ. These bundles
pass craniomediad, so that those from the muscles of opposite sides meet
and are inserted on the centra of the vertebræ in the middle line, each pair
of bundles forming a V opening caudad. The most cranial insertion is into
the tubercle on the middle of the ventral surface of the ventral arch of the
atlas (3).
Relations.—Dorsal surface with the centra of the vertebræ. Ventral
surface in the thorax with the trachea; in the neck with the œsophagus.
Medial edge with the muscle of the opposite side. Lateral margin in the
cervical region with the longus capitis (a).
Action.—Bends the neck.

3. Muscles of the Thorax.

A. Breast-muscles (connecting the arm and thorax) (Fig. 65, page 109).
The muscles connecting the arm with the sternum, corresponding to the
pectoralis muscles of man, fall into a considerable number of not always

clearly separated bundles in the cat. We shall distinguish by name four such
bundles; these might be, and frequently are, further subdivided.
M. pectoantibrachialis (Fig. 65, m).—This is a small flat bundle about
one or two centimeters wide, forming the most superficial portion of the
pectoralis group.
Origin on the lateral surface of the manubrium. The muscle passes
laterad onto the arm and is inserted by a flat tendon into the superficial
fascia of the dorsal border of the forearm, near the elbow-joint. The tendon
is continuous craniad with the border of the clavobrachial (k), so that a
bundle of fibres may pass from this muscle to be inserted with the
clavobrachial, or a bundle from the clavobrachial to be inserted with this.
The tendon is continuous caudad with that of the epitrochlearis (r). The
fascia of insertion may be traced to an attachment into the dorsal border of
the ulna. This muscle usually receives near its insertion a slip, sometimes
called its caudal division, from the deep layer of the pectoralis major.
Relations.—Outer surface with the integument. Inner surface with both
divisions of the pectoralis major (l) on its medial two-thirds, and with the
biceps (t) and bicipital arch (t′) in its lateral one-third. The cranial border is
closely applied to that of the clavobrachial (k), except at the two ends.
Action.—Draws the arm mediad.
M. pectoralis major, or ectopectoralis (Fig. 65, l, l′).—In this it is
usually possible to distinguish a superficial and a deep layer.
The superficial (l′) layer is a flat band of fibres one or two centimeters
wide.
Origin from a raphe in the midventral line, along the cranial half of the
manubrium and for five to ten millimeters craniad of it.
Insertion (Fig. 81, f).—The pectoral ridge of the middle third of the shaft
of the humerus, slightly dorsad of the line of insertion of the deep portion.
Relations.—Outer surface with the clavobrachial (Fig. 65, k) and
integument, the medial end caudally with the pectoantibrachialis (m), and
the distal end with the brachialis (v). Inner surface with the deep portion (l),
the fibres of which it crosses obliquely.
The deep portion (l) is a flat band of parallel fibres about three times as
broad as the superficial portion.
Origin.—The ventral surface of the manubrium and of the first three
divisions of the sternum, and the median raphe for about one centimeter
craniad of the manubrium. It passes directly laterad.

Insertion (Fig. 81, e) along a line which begins at the infraspinatus fossa
of the great tuberosity, and runs parallel to the deltoid ridge until it reaches
the pectoral ridge at the junction of the second and third fourths of the
humerus and then continues in the direction of the pectoral ridge as far as
the junction of the third and fourth fourths of the humerus. Some of its
fibres may pass caudad of the biceps and be inserted with the epitrochlearis.
Into the part of the line which is parallel to the deltoid ridge the muscle is
inserted by a flat tendon; into the remainder of the line it is usually inserted
directly by muscle-fibres, though at its caudal end its insertion may again be
tendinous.
Relations.—Outer surface with the cutaneus maximus, the outer layer of
the pectoralis major (Fig. 65, l′), the pectoantibrachialis (m), and the
clavobrachial (k). Inner surface with the pectoralis minor (o), the proximal
end of the humerus, the coracobrachialis (Fig. 77, f), and the supraspinatus
(Fig. 77, d) at the insertion of the latter. At the cranial part of its origin it
touches the sternomastoid (Fig. 65, g) and sternohyoid (Fig. 65, e).
Action.—Draws the arm mediad and turns the foot forward.
M. pectoralis minor, or entopectoralis (Fig. 65, o).—This is a fan-
shaped mass of fibres, flat but thicker than the pectoralis major.
Origin from the lateral half of the first six divisions of the body of the
sternum and sometimes from the xiphoid process. The fibres are divisible
into several bundles which vary in extent and distinctness and are
sometimes described as separate muscles. They pass craniolaterad and
converge so that the line of insertion is about one-half as long as that of the
origin.
Insertion (Fig. 81, d) into the humerus along a line which forms the
ventral border of the bicipital groove at the proximal end of the bone,
passes thence onto the pectoral ridge and continues in the direction of the
pectoral ridge nearly as far as the middle of the length of the humerus. The
cranial and caudal fibres are inserted by means of a thin tendon; the middle
fibres directly. The cranial border of the tendon of insertion is continued as
a thin tendon to the coracoid process; it is closely united with the insertion
of the supraspinatus.
Relations.—By its outer surface with the pectoralis major (Fig. 65, l)
over its cranial half; with the cutaneus maximus, latissimus dorsi (Fig. 65,
q), and integument over its caudal half. By its inner surface with the
xiphihumeralis (Fig. 65, p), rectus abdominis (Fig. 73, k), and a mass of fat

in the axilla. The tendon of the xiphihumeralis is also connected with its
inner surface near its insertion. Its cranial border is free. Its caudal border is
in relation at its medial end with the xiphihumeralis, at its lateral end with
the tendon of the latissimus dorsi (Fig. 65, q).
Action.—Draws the arm toward the middle line.
M. xiphihumeralis (Fig. 65, q).—A long, thin, narrow muscle which
may be considered as part of the pectoralis minor.
Origin a median raphe along the xiphoid process or at an angle to the
median line on the rectus abdominis muscle. It passes craniad, becoming
gradually smaller, and about two centimeters from its insertion ends in a
thin tendon.
Insertion.—It ends in a flat tendon which in passing is connected by a
strong fascia with the tendon of the latissimus (Fig. 65, q). It passes along
the inner surface of the pectoralis minor (o) to be inserted with its cranial
fibres near the ventral border of the bicipital groove.
Relations.—Outer surface with the cutaneus maximus at its medial end,
with the pectoralis minor (o) at its distal end. Inner surface with the external
oblique (Fig. 68, p), the rectus abdominis (Fig. 73, k), and a mass of fat in
the axilla. Borders free. Some of the fibres of the cutaneus maximus are
attached to its outer surface.
Action.—Assists the pectoralis minor.
B. Muscles of the Wall of the Thorax.—M. serratus posterior
superior (Fig. 73, l).—A thin sheet of muscle and tendon beneath the
serratus anterior (i) on the dorsal part of the thorax and neck.
Origin by fleshy slips from the outer surfaces of the first nine ribs just
ventrad of their angles. The origin may extend as far as the tenth or eleventh
ribs. The first slip is usually delicate. The fibres are directed dorsad and
craniad and unite to form a continuous sheet. This ends along a longitudinal
line opposite the vertebral transverse processes in the aponeurosis which
covers the longissimus dorsi and other muscles in this region. Its insertion is
into the median dorsal raphe between the axial spinous process and the
tenth thoracic spinous process.
Relations.—Outer surface with the serratus anterior (i), the latissimus
dorsi (Fig. 68, m), and the rhomboideus. Inner surface with the external
intercostals (Fig. 73, m), the iliocostal (Fig. 69, h), the longissimus dorsi
(Fig. 69, f), the spinalis dorsi (Fig. 69, g), and the splenius (Fig. 73, b).
Action.—Draws the ribs craniad.

M. serratus posterior inferior (Fig. 73, n).—The serratus posterior
inferior is a thin muscle lying caudad of the serratus posterior superior (l)
and sometimes overlying the caudal end of the latter.
Origin by four or five heads from the last four or five ribs. In some
specimens only three heads may be present. The separate bundles pass
dorsocaudad and unite to form a continuous sheet which ends in a
continuation of the aponeurosis of the serratus posterior superior (l).
Insertion into the lumbar spinous processes and the intervening
interspinous ligaments.
Relations.—Outer surface with the latissimus dorsi (Fig. 68, p), and at
the origins with the intercostales externi (Fig. 73, m). Inner surface with the
intercostales interni (Fig. 69, k) at the origin and with the intercostales
externi (Fig. 69, i), iliocostal (Fig. 69, h), longissimus dorsi (Fig. 69, f), and
the caudal end of the spinalis dorsi (Fig. 69, g).

Fig. 73.—Body Muscles exposed after Removal of the Forelimb and the Muscles shown in
Fig. 68.

a, M. occipitoscapularis (cut); b, M. splenius; c, M. levator scapulæ ventralis (cut); d, M.
cleidomastoideus (cut); e, M. longus capitis; f, M. scalenus (f′, middle division; f″, dorsal division;
f‴, ventral division; f, cervical portion); g, M. longissimus capitis; h, M. levator scapulæ (cut); i, M.
serratus anterior (cut); j, M. transversus costarum; k, M. rectus abdominis (k′, its tendon); l, M.
serratus posterior superior; m, M. intercostales externi; n, M. serratus posterior inferior; o, M.
obliquus abdominis internus; p, lumbodorsal fascia.

Action.—Assists the serratus posterior superior.
M. transversus costarum, or sternocostalis externus (Fig. 73, j).—This
is a thin muscle applied to the cranial part of the side of the thorax, covering
the cranial end of the rectus abdominis (k).

Origin by tendon from the side of the sternum between the attachments
of the third and sixth ribs. The muscle passes dorsocraniad to its
Insertion on the first rib and the lateral portion of its costal cartilage.
Relations.—Outer surface with the pectoralis minor (Fig. 65, o). Inner
surface with the scalenus (Fig. 73, f‴), the rectus abdominis (Fig. 73, k), and
the intercostales externi (Fig. 73, m). At its insertion it is united with a
portion of the scalenus (Fig. 73, f‴).
Action.—Draws the sternum forward.
Mm. levatores costarum.—Small muscles having origin on the
transverse processes of the thoracic vertebræ, passing caudoventrad, and
becoming inserted on the angle of the rib lying immediately caudad of the
origin. They are continuous with the external intercostals.
Relations.—Outer surface with the longissimus dorsi (Fig. 69, f), and
craniad with the iliocostal (Fig. 69, h). Inner surface with the internal
intercostals (Fig. 69, k).
Action.—Pull the ribs dorsocraniad.
Mm. intercostales externi (Fig. 73, m; Fig. 69, i).—The external
intercostals are placed in the outer portion of the intercostal spaces. They
are composed of bundles of fibres attached by their ends to the adjacent
borders of the ribs and having in general the direction of the external
oblique muscle, i.e., they pass from their cranial ends caudoventrad. They
occupy the intercostal spaces between the true ribs and extend even caudad
into the spaces between the false ribs. They are lacking between the ventral
ends of the costal cartilages of the first six to eight ribs, so that the internal
intercostals (Fig. 69, k) are here exposed. The more caudal external
intercostals are more nearly craniocaudal in direction.
Relations.—Outer surface with obliquus abdominis externus (Fig. 68, p),
latissimus dorsi (Fig. 68, m), serratus posterior inferior (Fig. 73, n) and
superior (Fig. 73, l), serratus anterior (Fig. 73, i), scalenus (Fig. 73, f), and
iliocostal (Fig. 69, h). Inner surface with the internal intercostals (Fig. 69,
k).
Action.—Protractors of the ribs.
Mm. intercostales interni (Fig. 69, k).—The internal intercostals are
similar to the external intercostals, beneath which they lie. Their fibres pass
between the ribs at nearly right angles to those of the external intercostals
and have nearly the direction of the fibres of the internal oblique. They
occupy all the intercostal spaces from the first to the thirteenth ribs.

Relations.—Outer surface with the external intercostals (Fig. 69, i), and
ventrad with the scalenus (Fig. 73, f), transversus costarum (Fig. 73, j), and
rectus abdominis (Fig. 73, k). Inner surface with the pleura and the
transversus thoracis.
Action.—Retractors of the ribs.
M. transversus thoracis (triangularis sterni; sternocostalis internus).—
This represents a thoracic portion of the transversus abdominis. It consists
of five or six flat muscular bands lying on the inner surface of the thoracic
wall.
Origin on the lateral borders of the dorsal face of the sternum, opposite
the attachments of the cartilages of the third to the eighth ribs. The six
bands thus formed, each about one centimeter wide, pass laterad and are
inserted into the cartilages of the ribs near their junction with the ribs, and
into the fascia which covers the inner surface of the internal intercostals in
this region.
Relations.—Outer surface with the internal intercostals and the cartilages
of the ribs. Inner surface with the pleura.
Diaphragma (Fig. 74).—The diaphragm consists of a central so-called
semilunar tendon (e) and of muscular fibres which pass radially from the
body wall to the tendon. It forms a complete oblique partition between the
abdominal and thoracic cavities. The dorsal end is farther caudad than the
ventral.
The central tendon (e) is thin and irregularly crescent-shaped, with the
convexity ventrad and the horns of the crescent prolonged as two tendinous
bands (e′) which end in two triangular membranous portions (d) of the
diaphragm, one on each side of the spinal column. It is pierced by an
opening for the vena cava (f).

Fig. 74.—Diaphragm, Caudal Surface seen Obliquely from the Right.

a, right crus; b, left crus; c, c′, sternocostal part of diaphragm; d, d′, membranous
portions of the diaphragm; e, central tendon; e′, prolongations of central tendon; f,
opening for posterior vena cava; g, œsophagus; h, aorta; i, M. transversus
abdominis.

The muscular portion is in two parts: (a) The vertebral portion (a, b)
arises by a single tendon from the ventral surface of the second, third, and
fourth lumbar centra. The tendon diverges into two, the right one (a) of
which is much stronger, and from each of the two arise muscle-fibres. Each
mass of fibres is one of the two crura (sing. crus) of the diaphragm. The
aorta (h) enters the abdomen between the crura dorsally. The fibres of each
crus diverge to be inserted into the central tendon and the dorsal
continuation of its horn. The two sets of fibres unite ventrad of the opening
of the aorta. Between this opening and the central tendon is another opening
for the œsophagus (g); this lies entirely in that part of the diaphragm which

arises from the right crus (a). The fibres are again united ventrad of the
œsophageal opening.
(b) The sternocostal part (c, c′) takes origin from the xiphoid process
and the last five ribs, by fleshy bundles which interdigitate with those of the
transversus abdominis (i). The fibres converge to the central tendon (e).
Between the crus of each side and the most dorsal of the costal fibres is the
membranous interval (d) mentioned above.

4. Abdominal Muscles.

M. obliquus abdominis externus (Fig. 68, p).—A large, thin sheet of
muscle covering the whole abdomen and part of the thorax ventrally.
Origin.—(a) From the last nine or ten ribs by means of as many tendons,
which are interconnected to form arches that span the slips of the serratus
anterior. The muscle-fibres arise from these tendons and from their
intervening arches. (b) From the lumbodorsal aponeurosis common to it and
the internal oblique. The cranial fibres pass nearly ventrad, the caudal fibres
caudad, and the intervening fibres take an intermediate course. The fibres
end in a thin aponeurosis of insertion along a curved line which passes at
first caudad and then laterodorsad. The aponeurosis fibres continue in the
direction of the muscle-fibres to the
Insertion into the median raphe ventrad of the sternum from the insertion
of the seventh costal cartilage to the xiphoid process, into the linea alba
from the sternum to the pubic tubercle, and into the tubercle and the cranial
border of the pubis. Caudad of the xiphoid process the aponeurosis is
closely united to the superficial layer of the internal oblique, where it forms
the outer layer of the sheath of the rectus abdominis. Laterad of the pubic
tubercle the tendon is perforated by the inguinal canal. In the cat neither the
caudal part of the muscle nor its tendon is attached to the ilium, as it is in
man and the dog, so that no Poupart’s ligament, or inguinal ligament, is
formed.
Relations.—Outer surface with the cutaneus maximus, the integument,
and near the origin with the latissimus dorsi (Fig. 68, m). Inner surface with
the obliquus internus (Fig. 73, o), the rectus abdominis (Fig. 73, k), the
intercostales externi (Fig. 73, m), a small part of the serratus posterior

inferior (Fig. 73, n), and by its dorsal tendon with the longissimus dorsi
(Fig. 69, f).
Action.—Constrictor of the abdomen.
M. obliquus abdominis internus (Fig. 73, o).—A thin sheet similar to
the preceding but of less extent. Its fibres cross those of the external oblique
nearly at right angles and lie beneath them.
Origin.—(1) Between the fourth and seventh lumbar vertebræ from the
lumbar aponeurosis which is common to it and the external oblique. The
lumbar aponeurosis takes origin from the lumbar spinous processes and the
interspinous ligaments, and is continuous craniad with the aponeurosis of
the serratus posterior inferior. Laterad it splits into three sheets, two for the
above-named muscles and a third which passes to the vertebral transverse
processes and forms the fascia covering the supraspinous muscles of the
lumbar region. (2) By a similar aponeurosis from the ventral half of the iliac
crest. (3) By fleshy fibres from the three crural arches. These are three
delicate ligamentous arches which stretch from the crest of the ilium to the
pubic spine. The dorsal one gives exit to the iliopsoas muscle, the middle to
the femoral vessels, and the ventral to the spermatic cord. In the female the
middle and ventral arches may fuse. The pillar between the dorsal and
middle arches is attached to the iliopectineal eminence.
Insertion.—The fibres pass cranioventrad and end along a longitudinal
line in a thin aponeurosis of insertion, which is united in the linea alba to
those of the external oblique and transversus. At the caudal end of the
aponeurosis all its fibres pass outside of the rectus abdominis (Fig. 73, k).
At its cranial end the fibres divide into two sheets or laminæ, one of which
passes outside of the rectus and the other inside. The outer lamina unites
with the aponeurosis of the external oblique, while the inner lamina unites
with that of the transversus. There is thus formed a sheath for the cranial
part of the rectus muscle.
Relations.—Outer surface with the obliquus externus (Fig. 68, p). Inner
surface with the transversus abdominis (Fig. 69, l), and by its ventral tendon
with the rectus.
Action.—Compressor of the abdomen.
M. transversus abdominis (Fig. 69, l).—A thin sheet covering the
whole surface of the abdomen and lying beneath the internal oblique. Its
fibres are nearly transverse.

Origin.—(1) By fleshy fibres or by a thin aponeurosis from the cartilages
of all the false and floating ribs, by interdigitation with the fibres of the
diaphragm. (2) From the tips of all the lumbar transverse processes. (3)
From the ventral border of the ilium. (4) From the dorsal and middle of the
three crural arches, where it may blend partly with the internal oblique. The
muscle is continuous craniad with the transversus thoracis muscle. Near the
lateral border of the rectus abdominis the muscle ends in a thin aponeurosis
of insertion which is continued (its fibres having the direction of the
muscle-fibres) to the
Insertion in the linea alba.
Relations.—Outer surface with the internal oblique (Fig. 73, o) and the
rectus abdominis (Fig. 73, k), dorsad also with the longissimus dorsi (Fig.
69, f). Inner surface with a thin fascia covering the peritoneum and
ventrocaudad with the rectus (Fig. 73, k). The dorsal edge of the muscle
touches the iliopsoas and longissimus dorsi; the ventral edge touches the
muscle of the opposite side.
Action.—Constrictor of the abdomen.
M. rectus abdominis (Fig. 73, k).—A rather thick, flat muscle which lies
near the median ventral line separated by the linea alba from its fellow of
the opposite side and stretching from the pubis to the first costal cartilage.
Opposite the first lumbar vertebra it is approximately four centimeters wide.
It narrows at both ends.
Origin by a strong tendon from the tubercle of the pubis. The muscle
passes craniad at first between the peritoneal fascia and the transversus
aponeurosis, then in the sheath formed by the internal and external oblique
and the transversus aponeurosis. It emerges from the sheath opposite the
xiphoid process and passes ventrad of the costal cartilages. Between the
third and fourth costal cartilages it ends in a thin tendon which passes
beneath the transversus costarum and is
Inserted into the first costal cartilage near its middle, into the second
costal cartilage near its sternal end, and into the sternum between the first
and fourth cartilages.
Relations.—Outer surface of the cranial part of the muscle and its tendon
with the pectoralis minor (Fig. 68, o) and the transversus costarum (Fig. 73,
j); caudad the muscle is covered by the outer layer of the rectus sheath.
Lateral edge with the obliquus externus (Fig. 68, p), obliquus internus (Fig.
73, o), and transversus abdominis (Fig. 69, l). Medial edge with the muscle

of the opposite side. Inner surface with the internal intercostals (Fig. 69, k)
and the rib cartilages; the inner layer of the rectus sheath and the
peritoneum.
Action.—Retracts the ribs and sternum and compresses the abdomen.

IV. MUSCLES OF THE THORACIC LIMBS.

The muscles connecting the thoracic limbs with the rest of the body have
been described.

1. Muscles of the Shoulder.

A. Muscles on the Lateral Surface of the Shoulder.
M. deltoideus.—The deltoid muscle of the cat is divided into two (or
three) portions which are together equivalent to the human deltoid. These
are the spinodeltoid, the acromiodeltoid, and possibly the clavobrachial,
which is frequently called clavodeltoid.
M. spinodeltoideus (Fig. 75, e; Fig. 68, i).—A rather thick, flat muscle
between the scapular spine and the deltoid ridge of the humerus. It forms a
chord of the angle between the glenoid border of the scapula and the
humerus.
Origin by short tendon-fibres from the glenoid border of somewhat more
than the middle third of the spine of the scapula (Fig. 76, g), and from a
tendinous raphe between the spinotrapezius (Fig. 68, j), acromiotrapezius
(Fig. 68, h), and infraspinatus (Fig. 75, c). The origin may pass toward the
vertebral border of the scapula onto the infraspinatus muscle (Fig. 75, c).
Insertion (Fig. 81, h) by a flat tendon upon the deltoid ridge of the
humerus, nearly parallel to that of the pectoralis major.
Relations.—Outer surface with the integument and at the insertion with
the acromiodeltoideus (Fig. 75, f). Inner surface with the infraspinatus (c),
teres minor (Fig. 80, c), caput laterale (Fig. 75, h), and caput longum (Fig.
75, g) of the triceps muscle.
Action.—Flexes the humerus and rotates it outward.
M. acromiodeltoideus (Fig. 75, f; Fig. 68, g).—A flat muscle which
overlies the distal end of the spinodeltoideus (Fig. 75, c). It connects the
acromion with the humerus.

Origin (Fig. 76, d).—From the glenoid border of the acromion, and
sometimes the adjacent metacromion as far as the tip.
Insertion.—Mostly upon the outer surface of the spinodeltoideus (Fig.
75, c). The outer fibres are continued to the bone, especially at the lateral
border of the muscle, and are inserted along a line ventrad of the line of
insertion of the spinodeltoideus, and extending farther distally (Fig. 81, g).
Some of the outer fibres pass into the brachialis (Fig. 80, h).
Relations.—Outer surface with the integument and the clavobrachial
(Fig. 68, e). Inner surface with the infraspinatus (Fig. 75, c), teres minor
(Fig. 80, c), spinodeltoid (Fig. 75, e), and caput laterale of the triceps (Fig.
75, h).
Action.—Like that of the spinodeltoid.
M. clavobrachialis (Fig. 65, k; Fig. 68, e).—A flat, triangular muscle on
the cranial surface of the shoulder, forming a direct continuation of the
clavotrapezius (Fig. 68, d). These two are frequently described as
constituting a single muscle, the cephalohumeral or cephalobrachial. (The
clavobrachial is frequently given the name clavodeltoid; as its homology
with the human clavodeltoid appears doubtful, it seems well to use the
name clavobrachial, as proposed by Clasen.)

Fig. 75.—Muscles on the Lateral Surface of the Arm.
a, M. supraspinatus; b, part of insertion of M.
rhomboideus; c, M. infraspinatus; d, M. teres
major; e, M. spinodeltoideus; f, M.
acromiodeltoideus; g, caput longum of M. triceps
brachii; h, caput laterale of M. triceps brachii; i,
M. brachialis; j, M. biceps; k, M. brachioradialis;
l, M. extensor carpi radialis longus; m, M.
extensor communis digitorum (m′, tendon of
same); n, M. extensor lateralis digitorum; (n′,
tendon of same); o, M. extensor carpi ulnaris (o′,
tendon of same); p, M. extensor indicis proprius;
q, fifth head of M. flexor profundus digitorum; r,
M. flexor carpi ulnaris. 1, vertebral border of the
scapula; 2, spine of the scapula; 3, greater
tuberosity of the humerus; 4, olecranon; 5,
transverse ligament of the wrist.

Origin.—Its superficial fibres are continuations of the clavotrapezius
(Fig. 68, d); other fibres have origin from the clavicle and from a raphe
laterad of the clavicle which is common to this muscle and the
clavotrapezius. It passes distad along the cranial surface of the arm,
growing narrower as it approaches the convexity of the elbow.

Insertion.—Eight to ten millimeters from the ulna it joins the brachialis
muscle (Fig. 79, i) to be inserted with it by a flat tendon (Fig. 79, i; Fig. 87,
c) upon a rough area on the medial surface of the ulna just distad of the
semilunar notch, and about midway between the dorsal and ventral borders.
Relations.—Outer surface with the integument. Inner surface with the
pectoralis major (Fig. 65, l), biceps (Fig. 77, g), lateral head of the triceps
(Fig. 75, h), acromiodeltoid (Fig. 75, f), and brachialis (Fig. 80, h). Medial
border with the pectoantibrachialis (Fig. 65, m). Lateral border free except
near the insertion, where it is in relation with the brachialis.
Action.—Flexor of the antibrachium.
M. supraspinatus (Fig. 75, a) occupies the whole of the supraspinatus
fossa of the scapula. It is covered by strong fascia which stretches from the
free edge of the spine to the coracoid border of the scapula and to the
coracoid half of its vertebral border.
Origin (Fig. 76, b) by fleshy fibres from the whole surface of the
supraspinatus fossa, from the above-mentioned fascia, and from the
subscapularis (Fig. 77, a) craniad of the coracoid border of the scapula.
Insertion (Fig. 83, a).—It passes over the capsule of the shoulder-joint, to
which it is closely attached, and is inserted into the free border of the great
tuberosity ventrad (or proximad) of the fossa for the infraspinatus (Fig. 83,
c).
Relations.—Outer surface with the spinotrapezius (Fig. 68, j),
acromiotrapezius (Fig. 68, h), levator scapulæ ventralis (Fig. 68, f),
clavotrapezius (Fig. 68, d), and cleidomastoid (Fig. 65, h). Inner surface
with the scapula. The distal end of the coracoid border is closely related to
the pectoralis minor (Fig. 79, f). The glenoid border is related to the origin
of the deltoidei.
Action.—Extends the humerus after it has been flexed on the scapula.
M. infraspinatus (Fig. 75, c).—This fills the infraspinatus fossa, its
fibres converging to the insertion on the great tuberosity of the humerus.

Fig. 76.—Lateral Surface of the Scapula, with the Areas of
Attachment of Muscles.

a, M. infraspinatus; b, M. supraspinatus; c, origin of M. biceps;
d, M. acromiodeltoideus; e, M. teres minor; f, M. levator scapulæ
ventralis; g, M. spinodeltoideus; h, M. acromiotrapezius; i, M.
rhomboideus; j, M. teres major; k-l, line of insertion of M.
spinotrapezius.

Origin (Fig. 76, a).—By fleshy fibres from the whole infraspinatus fossa,
and by a raphe between it and the teres major (Fig. 75, d), and sometimes
by fibres from the teres minor (Fig. 80, c), triceps, spinodeltoideus (Fig. 75,
e), spinotrapezius (Fig. 68, j), and subscapularis (Fig. 77, a).
Insertion (Fig. 83, c).—By a flat tendon which passes over the capsule of
the joint, into the ventral half of the infraspinatus fossa on the great
tuberosity of the humerus. (The dorsal half of the fossa is covered by a
synovial bursa.)

Relations.—Outer surface with the spinotrapezius (Fig. 68, j),
spinodeltoid (Fig. 68, i), acromiodeltoid (Fig. 68, g), teres major (Fig. 75,
d), and levator scapulæ ventralis (Fig. 68, f). Inner surface with the scapula.
Glenoid border with the teres minor (Fig. 80, c), the teres major (Fig. 75, d),
and the long head of the triceps (Fig. 75, g).
Action.—Rotates the humerus outward.
M. teres minor (Fig. 80, c).—A small muscle from the glenoid border of
the scapula to the proximal end of the humerus.
Origin (Fig. 76, e) by a sheet of tendinous fibres from the glenoid border
of the scapula beginning about one-fifth the length of the border from the
glenoid fossa and extending to its middle. It is often attached to the
infraspinatus (Fig. 80, b) and the caput longum of the triceps (Fig. 75, g).
Insertion (Fig. 83, d) by a short tendon into the tubercle just distad of the
infraspinatus fossa on the great tuberosity of the humerus.
Relations.—Outer surface with the spinodeltoideus (Fig. 75, e),
acromiodeltoideus (Fig. 75, f), and the infraspinatus (Fig. 80, b). Inner
surface with the lateral (Fig. 75, h) and long (Fig. 75, g) heads of the triceps
and the capsule of the joint.
Action.—Assists the infraspinatus to rotate the humerus outward.
B. Muscles on the Medial Surface of the Shoulder.
(Fig. 77.)
M. subscapularis (Fig. 77, a).—A triangular mass from the subscapular
fossa to the lesser tuberosity of the humerus.
Origin (Fig. 78, a).—From the whole subscapular fossa except along the
fusiform area for the attachment of the levator scapulæ and the serratus
anterior near the vertebral border, and except over a quadrangular area
about one centimeter long near the glenoid angle. The origin is by fleshy
fibres directly from the periosteum except along two or three lines marked
by oblique ridges. To these lines are attached tendinous fibres. At the
glenoid border the area of origin sometimes occupies part or the whole of
the surface of the fossa for the origin of the teres major, so that the teres
arises from the fascia on the surface of the subscapularis. At the coracoid
border some of the fibres may take origin from the adjacent fascia of the
supraspinatus (Fig. 77, d).
Insertion (Fig. 82, b).—The fibres converge to the glenoid border, and
the insertion is by a strong, flat tendon into the dorsal border of the lesser

tuberosity of the humerus.

Fig. 77.—Muscles on the Medial Side of the Arm.
M. epitrochlearis, M. clavobrachialis,
and the breast-muscles have been
removed. a, M. subscapularis; b,
insertion of M. levator scapulæ and of M.
serratus anterior; c, M. teres major; d, M.
supraspinatus; e, M. latissimus dorsi (e′,
cut edge of that part which becomes
united with the bicipital arch); f, M.
coracobrachialis; g, M. biceps brachii
(the capsule of the joint has been laid
open to show its tendon); h, cut
insertions of pectoralis muscles; i, caput
longum of M. triceps brachii; j, long
portion of caput mediale of M. triceps
brachii; k, intermediate portion of caput
mediale of M. triceps brachii; l, short
portion of caput mediale of M. triceps
brachii; m, cut end of M. clavobrachialis;
n, M. brachioradialis; o, M. extensor
carpi radialis longus; p, M. extensor carpi
radialis brevis; q, M. pronator teres; r, M.
flexor carpi radialis; s, M. palmaris
longus (s′, its tendons); t, M. flexor carpi
ulnaris (t, ulnar head; t′, humeral head);
u, third head of M. flexor profundus
digitorum; u′, fifth head of M. flexor
profundus digitorum; u″, one of the
tendons of M. flexor profundus
digitorum; v, M. pronator quadratus; w,
M. abductor brevis pollicis; x, ulnar part
of M. flexor sublimis digitorum. 1,
transverse ligament of the wrist.

Relations.—Lateral surface with the scapula and the capsule of the
shoulder-joint. Medial surface with the levator scapulæ (Fig. 73, h), serratus
anterior (Fig. 73, i), part of the scalenus (Fig. 73, f), the transversus

costarum (Fig. 73, j), and the coracobrachialis (Fig. 77, f). Cranial border
with the supraspinatus (Fig. 77, d). Caudal border with the teres major (Fig.
77, c) and infraspinatus (Fig. 75, c).
Action.—Pulls the humerus inward (mediad).
M. teres major (Fig. 75, d; Fig. 77, c).—A thick muscle, triangular in
cross-section, lying parallel with the glenoid border of the scapula.
Origin (Fig. 76, j; Fig. 78, b) from the vertebral one-third of the glenoid
border of the scapula, and from fascia covering the subscapularis (Fig. 77,
a) and the infraspinatus (Fig. 75, c) over a small area near the
glenovertebral angle of the scapula. It may touch the insertion of the
rhomboideus.
Insertion (Fig. 82, f) by a tendon common to it and the latissimus dorsi
(Fig. 79, d′), as already described.
Relations.—Outer surface with the caput longum (Fig. 75, g) and the
long portion (Fig. 80, f) of the caput mediale of the triceps, the latissimus
dorsi (Fig. 77, e), and the cutaneus maximus. Inner surface with the serratus
anterior (Fig. 73, i), the scalenus (Fig. 73, f), the transversus costarum (Fig.
73, j), and the biceps (Fig. 77, g). Dorsal border with the subscapularis (Fig.
77, a) and infraspinatus (Fig. 75, c).
Action.—Rotates the humerus inward and flexes it in opposition to the
infraspinatus, teres minor, and the deltoidei.

Fig. 78.—Medial Surface of the Scapula with the Areas of
Attachment of Muscles.

a, M. subscapularis; b, M. teres major; c, M. serratus anterior;
d, M. levator scapulæ; e, M. rhomboideus; f, M.
occipitoscapularis; g, M. biceps; h, M. coracobrachialis; i, caput
longum of M. triceps.

2. Muscles of the Brachium or Upper Arm.

M. clavobrachialis and the pectoralis group (Fig. 65, page 109) lie partly
in this region; they have been described.
M. coracobrachialis (Fig. 77, f; Fig. 79, c).—A very short muscle
covering the inner (medial) surface of the capsule of the shoulder-joint. It
extends from the coracoid process to the proximal end of the humerus.

Origin (Fig. 78, h).—By a round tendon from the tip of the coracoid
process.
Insertion (Fig. 82, e) usually by fleshy fibres on an area five to eight
millimeters long and about half as wide, which lies on the medial side of the
humerus parallel with the ridge which runs from the dorsal end of the lesser
tuberosity to the shaft and close to it. The proximal end of the area is about
one centimeter from the proximal end of the head of the humerus.
Relations.—Medial surface with the biceps (Fig. 77, g), pectoralis minor
(Fig. 65, o), and teres major (Fig. 77, c). Lateral surface with the capsule of
the shoulder-joint. Dorsal border with the subscapularis (Fig. 77, a) and the
long portion of the caput mediale of the triceps (Fig. 77, j).
Action.—Adducts the humerus.
The part of the coracobrachialis just described is known as the short
head. A long head is sometimes found. It is a conical bundle of fibres of
varying size, which arises from the tendon of origin of the short head. It
passes distad into a long and extremely slender tendon, the insertion of
which varies greatly in different individuals. It is commonly on the humerus
in the region of the supracondyloid foramen.
M. epitrochlearis or extensor antibrachii longus (Fig. 65, r).—A thin,
flat muscle on the inner or medial side of the brachium, from the lateral
surface of the latissimus dorsi (Fig. 65, q) to the olecranon process of the
ulna.
Origin from the lateral or outer surface of the ventral border of the
latissimus dorsi (Fig. 65, q) near the insertion of the cutaneus maximus.
Fibres are often attached to the teres major and the pectoralis minor.
Insertion by a flat tendon which is closely connected with that of the
pectoantibrachialis (Fig. 65, m) and is continuous with the general
antibrachial fascia, into the caudal border of the cutaneous (dorsal) surface
of the olecranon process of the ulna.
Relations.—Outer (medial) surface with the integument, the latissimus
dorsi (Fig. 65, q), and the cutaneus maximus. Inner (lateral) surface with the
biceps (Fig. 65, t), caput longum (Fig. 65, s), and caput mediale (Fig. 77, j,
k) of the triceps.
Action.—Extends the antibrachium and tends to supinate the hand by
rotating the ulna.
M. biceps brachii (Fig. 77, g; Fig. 65, t).—A thick, fusiform muscle
lying on the front (ventral) surface of the humerus.

Origin (Fig. 76, c) by a strong, round tendon from the bicipital tubercle
of the glenoid angle of the scapula, at its coracoid margin. (In man there is a
second head—coracoid head—from the coracoid process.) The tendon
passes through the capsule of the joint and then along the bicipital groove,
which is converted into a canal by a strong ligament.
Insertion by a rounded tendon (Fig. 87, b) on the bicipital tuberosity of
the radius (Fig. 86, k).
Relations.—The tendon of origin passes through the capsule of the joint,
which is covered by a part of the pectoralis minor. The muscle is then
spanned for the middle part of its course by the bicipital arch (Fig. 65, t′), a
description of which is given below. Farther distad it is covered by the
clavobrachial (Fig. 65, k) and epitrochlearis (Fig. 65, r). At its distal end
(Fig. 79, l′) the muscle passes between the pronator teres on the radial side
and the conjoined tendon of the brachialis and clavobrachial (Fig. 79, i′) on
the other. The biceps lies throughout most of its length on the ventral
surface of the humerus, and touches along the medial border of its inner
surface the coracobrachialis (Fig. 77, f), the teres major, (Fig. 77, c), the
intermediate portion of the caput mediale of the triceps (Fig. 77, k), and the
short portion (Fig. 77, l) of the same. Its lateral border touches the
pectoralis minor (Fig. 65, o) and the brachialis (Fig. 79, i).
Action.—Flexes the forearm, and tends to supinate the hand.
The bicipital arch (Fig. 65, t′) is a tendinous arch formed over the biceps
muscle. Its outer or lateral pillar is formed by the tendon of the pectoralis
minor (o), to which may be added part of the latissimus (q) tendon. Its inner
or medial pillar is formed by the conjoined tendon of the teres major and
latissimus dorsi (Fig. 79, d′), while the xiphihumeralis (Fig. 65, p), cutaneus
maximus (Fig. 62, b), and epitrochlearis (Fig. 65, r) are connected with one
or the other pillar or with the muscles composing them. The caudal portion
of the deep layer of the pectoralis major (Fig. 65, l) may be connected with
the inner pillar.
M. brachialis (Fig. 79, i; Fig. 75, i).—From the lateral surface of the
humerus to the ulna.
Origin (Fig. 83, g, g′) from a long V-shaped line two to four millimeters
wide on the lateral surface of the humerus. The apex of the V is just distad
of the teres minor tubercle (d). Its dorsal limb (g′) extends along the lateral
supracondyloid ridge to a point opposite the proximal margin of the
supracondyloid foramen; its ventral limb (g) extends in the direction of the

deltoid ridge to the middle of the bone. No muscle-fibres take origin
between the two limbs. The fibres converge and end in a flat tendon which
joins the tendon of the clavobrachial (Fig. 79, k).
Insertion (Fig. 87, c).—The dorsal portion of the depressed rough area on
the lateral surface of the ulna just distad of the semilunar notch.
Relations.—Outer surface with the acromiodeltoid (Fig. 75, f), the caput
laterale of the triceps (Fig. 75, h), the brachioradialis (Fig. 75, k), and the
proximal end of the extensor carpi radialis longus (Fig. 75, l). Inner surface
with the humerus. Medial edge with the pectoralis major (Fig. 65, l) and the
biceps (Fig. 77, g).
Action.—Flexor of the antibrachium.
M. triceps brachii.—The triceps muscle of the cat, like that of man, is
divisible (as its name indicates) into three main portions. These are a lateral
portion (caput laterale), an intermediate or long portion (caput longum), and
a medial portion (caput mediale). The first two correspond to the similarly
named heads in man; the medial portion falls into a number of subdivisions
whose homologues are uncertain.

Fig. 79.—Deep Muscles on the Medial Side of the Humerus.

a, M. supraspinatus; b, M. subscapularis; c, M. coracobrachialis; d, M. teres
major (d′, its tendon); e, part of M. latissimus dorsi joining the teres major; f, cut
end of M. pectoralis minor; g, long part of caput mediale of M. triceps brachii; h,
intermediate part of caput mediale of M. triceps; i, M. brachialis (i′, its tendon); j,
short part of caput mediale of M. triceps; k, cut end of M. clavobrachialis; l, l′, cut
ends of M. biceps; m, M. brachioradialis; n, M. extensor carpi radialis longus; o,
M. extensor carpi radialis brevis; p, fifth head of M. flexor profundus digitorum; q,
first head of M. flexor profundus digitorum. 1, humerus; 2, olecranon; 3, medial
epicondyle of humerus.

Caput laterale (anconeus lateralis) (Fig. 75, h; Fig. 68, l).—The lateral
portion is a flat muscle (most of it subcutaneous) on the lateral side of the

brachium, connecting the proximal end of the humerus with the olecranon
process of the ulna.
Origin (Fig. 81, h′).—By a flat tendon from the proximal portion of the
deltoid ridge and the distal border of the teres minor tubercle.
Insertion (Fig. 86, c) by a thin, flat tendon into the lateral border of the
dorsal surface of the ulna between a point opposite the distal margin of the
semilunar notch and the proximal end of the olecranon.
Relations.—Lateral surface with the integument, and at the proximal end
with the spinodeltoid and acromiodeltoid (Fig. 75, e and f). Medial surface
with the brachialis (Fig. 75, i), the caput longum (g), the caput mediale, the
brachioradialis (k), the anconeus (Fig. 80, l), and the origins of the extensor
carpi radialis longus (Fig. 75, l), the extensor communis digitorum (m), and
the extensor digitorum lateralis (n).
Caput longum (anconeus longus) (Fig. 75, g; Fig. 68, k; Fig. 77, i).—A
prismatic, fusiform mass connecting the scapula with the olecranon.
Origin (Fig. 78, i) by a thick, flat tendon from a triangular area one or
two centimeters long at the glenoid end of the scapula on the glenoid
border. The base of the area is about one millimeter from the margin of the
glenoid fossa.
Insertion (Fig. 86, b).—The muscle ends in a thick tendon which passes
over the bifurcated ventral end of the olecranon and is inserted upon the
rounded tuberosity which forms the dorsal angle of the olecranon.
Relations.—Lateral surface with the caput laterale (Fig. 75, h), a portion
of the caput mediale (Fig. 77, j and k), the spinodeltoid (Fig. 75, e), the
infraspinatus (Fig. 75, c), and the integument. Medial surface with the
epitrochlearis (Fig. 65, r) and the conjoined portions of the latissimus dorsi
and teres major (Fig. 79, d′). Ventral border with the caput mediale (Fig. 77,
j and k).
Caput mediale.—The medial head consists of three portions (Fig. 79, g,
h, j).
(1) The long portion (anconeus posterior) (Fig. 77, j; Fig. 79, g; Fig. 80,
f).
Origin (Fig. 83, e) from a triangular area on the dorsal surface of the
humeral shaft. The base of the area is against the articular head, and its apex
about one-sixth the length of the humerus from the head. It is between the
coracobrachialis and the lateral head of the triceps.

Fig. 80.—Deep Muscles on the Lateral Surface of the Humerus.
a, part of M. supraspinatus; b, part of M.
infraspinatus; c, M. teres minor; d, M. teres
major; e, part of M. latissimus dorsi joining M.
teres major; f, long part of caput mediale of M.
triceps brachii; g, cut insertion of M.
acromiodeltoideus; h, M. brachialis; i, M.
brachioradialis; j, intermediate part of caput
mediale of M. triceps brachii; k, M. extensor
carpi radialis longus; l, M. anconeus; m, M.
extensor communis digitorum. 1, great
tuberosity of humerus; 2, 3, superficial radial
and dorsal interosseous branches, respectively,
of the radial nerve.

Insertion (Fig. 86, a).—The muscle ends in a long, slender tendon which
passes through the furrow on the ventral angle of the olecranon and is
inserted into an oblique ridge which forms the dorsal limit of the furrow.
The tendon is separated from the floor of the furrow by a synovial bursa.
(2) The intermediate portion (anconeus internus) (Fig. 77, k; Fig. 79, h;
Fig. 80, j).

Origin (Fig. 82, g) by fleshy fibres from a triangular area proximad of the
middle of the dorsomedial surface of the humerus. The length of the area
equals about one-fourth the length of the bone. Its apex points proximad
and is almost continuous with the apex of the area of origin of the long
portion.
Insertion (Fig. 87, i) by short tendon-fibres into the medial border of the
ventral and proximal surfaces of the olecranon. It is connected with the
tendon of the long portion.
(3) Short portion (Fig. 79, j; Fig. 77, l).
Origin (Fig. 82, h) from the outer surface of the bony bar which encloses
the supracondyloid foramen of the humerus, as far as the medial
epicondyle.
Insertion (Fig. 87, e) by fleshy fibres into the medial border of the
olecranon distad of the tuberosity for the insertion of the caput longum.
Relations of the caput mediale.—Lateral surface with the caput laterale
(Fig. 75, h), the humerus, and the anconeus (Fig. 80, l). Dorsal surface with
the caput longum (Fig. 77, i), the epitrochlearis (Fig. 65, r), and the teres
major (Fig. 79, d). Ventral surface with the biceps (Fig. 77, g).
Action of the Triceps.—The entire triceps group forms a powerful
extensor of the forearm. The short portion of the medial head tends also to
rotate the arm outward, so as to supinate the hand.
M. anconeus (Fig. 80, l).—A triangular muscle on the outside of the
elbow-joint from the humerus to the ulna.
Origin (Fig. 83, i).—An irregularly triangular area at the distal end of the
dorsal surface of the humerus. The area of origin is limited laterally by the
sharp lateral supracondyloid ridge. It sometimes extends onto the lateral
epicondyle.

Fig. 81.—Ventral Surface of Fig. 82.—Medial Side of Fig. 83.—Dorsal Surface of
Humerus, with the Areas Humerus, with the Areas of the Left Humerus, with the
of Attachment of Muscles. Attachment of Muscles. Areas of Attachment of
Muscles.

Fig. 81.—a, M. subscapularis; b, M. supraspinatus; c, Mm. teres major and latissimus dorsi; d,
M. pectoralis minor; e, deep layer of M. pectoralis major; f, superficial layer of M. pectoralis major;
g, M. acromiodeltoideus; h, M. spinodeltoideus; h′, caput laterale of M. triceps; i, M. brachialis; j,
second portion of M. brachialis; k, M. extensor carpi radialis longus; l, M. extensor carpi radialis
brevis; m. M. extensor communis digitorum; n, M. extensor lateralis digitorum; o, M. extensor
carpi ulnaris; p, short portion of caput mediale of M. triceps; q, M. pronator teres; r, M. palmaris
longus; s, third and fourth parts of M. flexor profundus digitorum; t, M. flexor carpi radialis; u,
second head of M. flexor profundus digitorum.
Fig. 82.—a, M. supraspinatus; b, M. subscapularis; c, M. pectoralis minor; d, long portion of
caput mediale of M. triceps; e, M. coracobrachialis; f, Mm. teres major and latissimus dorsi; g,

intermediate portion of caput mediale of M. triceps; h, deep layer of M. pectoralis major; i,
superficial layer of M. pectoralis major; j, M. anconeus; k, short portion of caput mediale of M.
triceps; l, M. pronator teres; m, M. flexor carpi radialis; n, second head of M. flexor profundus
digitorum; o, third and fourth heads of M. flexor profundus digitorum; p, M. palmaris longus; q, M.
flexor carpi ulnaris.
Fig. 83.—a, M. supraspinatus; b, M. subscapularis; c, M. infraspinatus; d, M. teres minor; e, long
portion of caput mediale of M. triceps; f, M. coracobrachialis; g, g′, M. brachialis; h, intermediate
portion of caput mediale of M. triceps; i, M. anconeus; j, short portion of medial head of M. triceps;
k, M. pronator teres; l, second and third heads of M. flexor profundus digitorum; m, M. palmaris
longus; n, M. extensor carpi ulnaris.

Insertion (Fig. 86, d).—The lateral surface of the ulna from the distal
margin of the semilunar notch to the proximal end of the olecranon. The
muscle covers the capsule of the joint and is closely adherent to it.
Relations.—Outer (dorsal) surface with the caput laterale (Fig. 75, h) and
the intermediate portion (Fig. 80, j) of the caput mediale. Inner surface with
the bones and the capsule of the joint.
Action.—Keeps the capsule tense and probably rotates the ulna slightly
so as to pronate the hand.

3. Muscles of the Antibrachium or Forearm.

Fascia of the Forearm.—The muscles of the forearm are not in contact
with the skin, but are covered by the strong antibrachial fascia. This
consists of two layers. The superficial one is a continuation of the general
subcutaneous fascia of the arm; it covers the forearm as a continuous sheet
which becomes thinner distad, and is finally lost near the wrist. The deep
layer forms a dense, tendinous sheet which is closely applied to the
muscles. It begins partly as a continuation of the general fascia of the arm,
partly from the tendons of the triceps and epitrochlearis muscles. The sheet
is attached to the dorsal surface of the ulna, between the extensor carpi
ulnaris and the first head of the flexor profundus digitorum. It surrounds the
forearm as a continuous sheath. On the lateral surface it dips between the
extensor muscles, becoming closely attached to them and forming a partial
sheath for each; it is attached with special firmness to their tendons. On the
medial side of the arm the fascia passes smoothly over the flexors without
dipping between them; it is continuous, however, with the border of the
pronator teres, and distad of this muscle it is firmly attached to the radius.

At the wrist the fascia becomes attached to the longitudinal ridges on the
dorsal surface of the head of the radius, bridging thus the intervening
grooves and holding the tendons in place between the ridges. The fascia
then continues to form the dorsal fascia of the hand. On the ventral side of
the wrist the fascia becomes thickened to form a strong transverse
ligament (Fig. 77, 1), which is attached at its radial and ulnar ends to the
carpus, and which holds in place the tendons of the flexor muscles. Distad
of the transverse ligament the fascia spreads out in the palm of the hand,
and becomes united with the fibrous pad which is situated here. On the
fingers the fascia becomes attached to the phalanges, forming tendinous
sheaths, the so-called vaginal ligaments, for the flexor muscles. Near the
base and the head of the first phalanx strong, narrow, ring-like bands, the
annular ligaments (Fig. 88, 2), are formed in these sheaths; these surround
and bind down the tendons of the flexor muscles.
A. Muscles on the Ulnar and Dorsal Side of the Forearm (extensors
and supinators)
(Fig. 75, p. 158).
M. brachioradialis or supinator longus (Fig. 75, k; Fig. 77, n).—This is
a ribbon-like muscle lying on the lateral side of the brachium and the
ventrolateral border of the antibrachium just beneath the superficial fascia.
It connects the humerus and the radius.
Origin.—By a thin tendon from about the middle fifth of the dorsal
border of the humerus, or sometimes proximad of the middle. The muscle
curves over the outer surface of the brachialis (Fig. 75, i), to which it is
closely applied, and runs along the lateral border of the antibrachium to its
insertion.
Insertion by a short tendon into the ridge which forms the ventral limit of
the groove on the outer surface of the styloid process of the radius and upon
the adjacent ligaments.
Relations.—Outer surface with the integument, and at the proximal end
with the caput laterale of the triceps (Fig. 75, h). Inner surface with the
brachialis (i), the extensor carpi radialis longus (l) and brevis, and the
extensor communis digitorum (m).
Action.—Supinator of the hand.
M. extensor carpi radialis longus (Fig. 75, l; Fig. 77, o).—This lies
along the radial side of the forearm, and connects the humerus and the
second metacarpal.

Origin (Fig. 81, k) from the middle portion of the lateral supracondyloid
ridge between the origin of the brachialis (j) and the anconeus. About the
middle of the forearm the muscle ends in a slender tendon (Fig. 84, e)
which passes through the groove on the radial side of the dorsal surface of
the distal end of the radius.
Insertion (Fig. 84, c).—The tendon passes across the carpus and is
inserted onto the dorsal surface of the base of the second metacarpal on the
radial side just distad of the groove for the radial artery.
Relations.—Outer surface at the proximal end with the caput laterale of
the triceps (Fig. 75, h), farther distad with the integument and the
brachioradialis (k); the distal tendon with the extensor pollicis brevis (Fig.
84, d). Radial surface with the brachialis (Fig. 75, i) and the integument.
Ulnar surface with the extensor carpi radialis brevis (Fig. 77, p), and near
the proximal end with the extensor communis digitorum (Fig. 75, m).
Action.—Extensor of the hand.
M. extensor carpi radialis brevis (Fig. 77, p).—A slender muscle from
the humerus to the third metacarpal.
Origin (Fig. 81, l) from the distal part of the lateral supracondyloid ridge
distad of the extensor longus. Near the carpus the muscle ends in a slender
tendon which passes through the groove with the extensor longus tendon.
The tendon then diverges from the extensor longus and has its
Insertion (Fig. 84, f) into the radial side of the dorsal surface of the base
of the third metacarpal.
Relations.—Outer surface with the extensor longus (Fig. 77, o), the
integument, and distad with the extensor pollicis brevis (Fig. 84, d). Radial
surface with the extensor longus. Ulnar surface with the extensor communis
digitorum (Fig. 75, m) and the extensor brevis pollicis. Inner surface with
the pronator teres (Fig. 77, q), supinator (Fig. 85, b), and extensor brevis
pollicis (Fig. 85, a).
Action.—Extensor of the hand.

Fig. 84.—Arrangement of the Tendons on the Back of the
Hand.

a, M. extensor communis digitorum; b, M. extensor lateralis
digitorum; c, M. extensor indicis; d, M. extensor brevis pollicis; e,
M. extensor carpi radialis longus; f, M. extensor carpi radialis
brevis; g, M. extensor carpi ulnaris; h, tendons of the interossei. 1,
transverse ligament of the wrist.

M. extensor digitorum communis (Fig. 75, m).—A slender muscle from
the lateral supracondyloid ridge of the humerus to the phalanges of the
second, third, fourth, and fifth digits.

Origin (Fig. 81, m).—The distal surface of the lateral supracondyloid
ridge dorsad of the origin of the extensor carpi radialis brevis.
At the junction of the middle and distal thirds of the radius the muscle
passes into a large, flat tendon (Fig. 75, m′) which passes through the
groove on the middle of the dorsal surface of the distal end of the radius.
The groove is converted into a canal by a strong transverse ligament. The
tendon divides near the groove into four portions (Fig. 84, a) which diverge
and pass to the four ulnar digits.
Insertions.—Each division of the tendon as it passes over the dorsal
surface of the first phalanx has its border connected by strong fascia to the
dorsal surface of the phalanx. It finally passes through the groove at the
distal end of the first phalanx and is inserted mostly into the base of the
second phalanx; a portion continues distad to be inserted into the third
phalanx.
Relations.—Outer surface with the integument and at the origin with the
caput laterale (Fig. 75, h) of the triceps. Radial surface with the extensor
longus (l) and extensor brevis. Ulnar surface with the extensor digitorum
lateralis (n). Inner surface with the supinator (Fig. 85, b) and the extensor
pollicis brevis (Fig. 85, a).
Action.—Extensor of the four ulnar digits.
M. extensor digitorum lateralis (Fig. 75, n). (This corresponds in
position to the extensor digiti quinti proprius of man.)
Origin (Fig. 81, n) from the lateral supracondyloid ridge of the humerus
distad of the origin of the extensor communis.
The muscle passes along the ulnar border and dorsal surface of the
forearm between the extensor communis (Fig. 75, m) and the extensor carpi
ulnaris (o). Near the carpus it ends in a tendon (n′), which divides
immediately into three or four (Fig. 84, b). These pass through the groove
on the ulnar side of the dorsal surface of the radius and diverge to the digits
lying beneath the extensor communis tendon.
Insertion (Fig. 84, b).—The three tendons on the ulnar side join the ulnar
sides of the tendons of the extensor communis (a) at their insertions. The
radial of the four tendons (not always present) joins the tendon of the
extensor indicis (c) and may also give a branch to the radial side of the base
of the first phalanx of the third digit.
Relations.—Outer surface with the integument. Radial border with the
extensor communis digitorum (m); ulnar border with the extensor carpi

ulnaris (o). Inner surface with the supinator (Fig. 85, b) and the extensor
brevis pollicis (Fig. 85, a); distad with the extensor indicis (Fig. 85, c).
Action.—Extensor of the four ulnar digits.
M. extensor carpi ulnaris (Fig. 75, o).
Origin.—(1) By a short, broad tendon from the distal portion of the
lateral epicondyle of the humerus (Fig. 81, o) distad of the origin of the
extensor lateralis, and (2) by a smaller tendon from the ulna at the dorsal tip
of the semilunar notch (Fig. 86, e).
The muscle passes along the ulnar side of the forearm dorsad of the
extensor digitorum lateralis (n). It ends near the junction of the middle and
distal thirds of the forearm in a large, flat tendon (o′) which is closely
adherent to the ligaments of the wrist and which passes over the distal end
of the ulna to its
Insertion into the tubercle on the ulnar side of the base of the fifth
metacarpal (Fig. 84, g).
Relations.—Outer surface with the integument. Radial (or ventral) border
with the extensor digitorum lateralis (Fig. 75, n); ulnar (or dorsal) border
with the flexor profundus digitorum (q). Inner surface with the radius, the
extensor indicis (Fig. 85, c), and the extensor pollicis brevis (Fig. 85, a).
Action.—Indicated by its name.
M. extensor indicis (proprius) (Fig. 85, c; Fig. 75, p) (includes extensor
pollicis longus also).
Origin (Fig. 86, f) by short, fleshy fibres from the lateral surface of the
ulna between the semilunar notch and the junction of the third and fourth
(distal) fourths.
The muscle-fibres pass obliquely distad and toward the radial side and
join the tendon (Fig. 85, c′), which runs nearly the whole length of the
radial surface.
Insertion (Fig. 84, c).—The tendon passes through the groove on the
ulnar side of the dorsal surface of the base of the radius and divides into
two. Both of these usually go to the base of the second phalanx of the
second digit, but one may pass to the pollex, or there may be three divisions
going to the first three digits.

Fig. 85.—Deep Muscles on the Extensor Surface of the Radius and Ulna.

a, M. extensor brevis pollicis (a′, its tendon); b, M. supinator; c, M. extensor indicis (c′, its
tendon); d, tendon of M. extensor carpi radialis brevis; e, tendon of M. extensor carpi radialis
longus. 1, humerus; 2, olecranon; 3, styloid process of ulna; 4, distal end of radius; 5, head of
radius.

Relations.—Outer surface with the integument, the extensor carpi ulnaris
(Fig. 75, o), and the extensor digitorum lateralis (Fig. 75, n). Dorsal border
with the flexor profundus digitorum (Fig. 75, q). Inner surface with the
extensor brevis pollicis (Fig. 85, a).
Action as indicated by the name.
M. supinator (Fig. 85, b).—A flat muscle wrapped spirally about the
proximal end of the radius.
Origin by a short, strong tendon from the lateral side of the annular
ligament of the radius and by tendinous fibres from the radial collateral
ligament passing from the humerus to the radius. From the tendon of origin
the fibres diverge, passing toward the radial side and distad.
Insertion (Fig. 86, g).—The dorsal and part of the ventral surface of the
proximal two-fifths of the radius to within five millimeters of the articular
face of the head.
Relations.—Outer surface with the extensor carpi radialis brevis,
extensor communis digitorum (Fig. 75, m), and extensor lateralis digitorum
(Fig. 75, n). Radial border with the pronator teres (Fig. 77, q). Inner surface
with the radius.
Action.—Supinator of the hand.

Fig. 86.—Lateral or Extensor Surface of Radius and Ulna,
with the Areas of Attachment of Muscles.

a, long portion of caput mediale of M. triceps; b, caput longum
of M. triceps; c, caput laterale of M. triceps; d, M. anconeus; e, M.
extensor carpi ulnaris; f, M. extensor indicis; g, M. supinator; h,
M. extensor brevis pollicis; i, M. pronator teres; j, M. flexor
profundus digitorum; k, M. biceps.

M. extensor brevis pollicis or extensor ossis metacarpi pollicis (Fig. 85,
a) (includes M. abductor longus pollicis of man).
Origin (Fig. 86, h) by fleshy fibres from the ventral half of the lateral
surface of the shaft of the ulna from the semilunar notch to the styloid

process; from the ulnar half of the dorsal surface of the radius from the
bicipital tubercle to a short distance distad of the middle of the bone; and
from the interosseous membrane between these two areas. The fibres
converge to form a strong, flat tendon (Fig. 84, d) which passes obliquely
over the tendons of the extensor carpi radialis longus (e) and brevis (f) to its
Insertion into the radial side of the base of the first metacarpal. The radial
sesamoid bone of the wrist is imbedded in the tendon at its insertion.
Relations.—Outer surface with the extensor carpi radialis brevis, the
extensor communis digitorum (Fig. 75, m), extensor lateralis digitorum
(Fig. 75, n), and extensor indicis (Fig. 85, c). Inner surface with the radius
and ulna, and distad with the tendons of the two extensores carpi radiales
(Fig. 84, e and f).
Action.—Extends and abducts the pollex.
B. Muscles on the Radial and Ventral Side of the Forearm (flexors
and pronators).

M. pronator teres (Fig. 77, q).
Origin (Fig. 82, l) by a short strong tendon from the extremity of the
medial epicondyle of the humerus.
Insertion (Fig. 86, i) by fleshy fibres and short tendinous fibres along the
medial border of the radius, at its middle. The radial edge of the muscle is
continuous with the strong deep layer of the antibrachial fascia.
Relations.—Outer surface with the superficial fascia. Radial border with
the tendon of the biceps (Fig. 79, l′), with the extensor carpi radialis brevis
(Fig. 77, p), and the supinator (Fig. 85, b). Ulnar border with the flexor
carpi radialis (Fig. 77, r) and part of the flexor profundus digitorum (Fig.
77, u).
Action.—Pronates the hand by rotating the radius.
M. flexor carpi radialis (Fig. 77, r).—A slender fusiform muscle.
Origin (Fig. 82, m) from the tip of the medial epicondyle of the humerus.
Insertion.—The slender tendon passes through a deep groove between
the os magnum and the first metacarpal. The groove is converted into a
canal by the overlying tendons and muscles. The tendon is finally inserted
into the bases of the second and third metacarpals.
Relations.—Outer surface with the pronator teres (Fig. 77, q), the
superficial fascia, and the third head of the flexor profundus (u). Radial
border with the pronator teres (q). Ulnar border with the third and fourth

heads of the flexor profundus. Inner surface with the ulna proximad and the
fifth head of the flexor profundus (u′) distad.
Action indicated by the name.
M. palmaris longus (Fig. 77, s).—A flat fusiform muscle beneath the
fascia on the medial border of the forearm.
Origin (Fig. 82, p) by a short flat tendon from the distal part of the
medial surface of the medial epicondyle of the humerus.
About one centimeter from the wrist the muscle ends in a flat tendon
which passes through the transverse ligament and divides on the hand into
four or five (or sometimes only three) tendons (Fig. 77, s′) which diverge to
the insertions. The ulnar portion of the flexor sublimis digitorum (Fig. 77,
x) takes origin from the common tendon before its division.
Insertion.—Each tendon except the first gives off a branch which spreads
out in the trilobed pad in the palm. The middle two of these may be traced
to the integument covering the pad. The tendon is then inserted (Fig. 88, a)
near the base of the first phalanx onto the outer surface of the perforated
portion of the flexor sublimis tendon (b, b′) at its side, except that to the
thumb, which divides near its distal end into two which are inserted into the
sesamoid bones at the base of the first phalanx. The tendons of insertion are
closely united to the fibrous pulley-ring at the base of the first phalanx, and
each may send a slip to the base of the phalanx at either side of the ring.
Relations.—Outer surface with the superficial fascia and one head of the
flexor sublimis (Fig. 77, x). Radial border with the flexor carpi radialis.
Ulnar border with the flexor carpi ulnaris and a part of the flexor profundus
digitorum. Inner surface with the flexor carpi radialis (r), the flexor carpi
ulnaris (t), the flexor profundus digitorum (u), and the radial head of the
flexor sublimis digitorum.
Action.—Flexor of the first phalanx of each of the digits.
M. flexor carpi ulnaris (Fig. 77, t, t′).
Origin.—There are two heads. The first or humeral head (t′) takes origin
in common with the second part of the flexor profundus from the median
surface of the distal end of the humerus just distad of the medial epicondyle
(Fig. 82, q). The second or ulnar head (t) takes origin by fleshy fibres from
the lateral surface of the olecranon and from the dorsal border of the ulna
from the olecranon to a point distad of the semilunar notch (Fig. 87, f). The
two heads join proximad of the middle of the forearm. The muscle passes
obliquely across the ventral surface of the forearm to its

Insertion by fleshy and tendinous fibres into the proximal surface of the
pisiform bone.
Relations.—Outer surface with the integument and the palmaris longus
(Fig. 77, s). Inner surface and ulnar border with the flexor profundus
digitorum.
Action indicated by the name.
M. flexor sublimis digitorum (or perforatus).—This muscle is in two
parts, which are given a common name only because of the similar structure
and insertions of their tendons.
The ulnar part (Fig. 77, x) is a conical muscle taking origin from the
outer surface of the tendon and muscle of the palmaris longus and from the
adjacent ligament. It gives rise to two or three tendons (Fig. 88, b) which
arise from distinct slips of the muscle; these pass to the ulnar two or three
digits. That passing to the fourth or fifth digit receives an accessory slip
from a small mass of fibres attached to the transverse ligament on the radial
side of the palmaris tendon.
The radial part is a small flat triangular muscle which takes origin from
the outer surface of the tendon formed by the junction of the tendons of the
first and second parts of the flexor profundus. It divides into two slips, each
giving rise to a tendon. These tendons (Fig. 88, b′) pass to the second and
third digits. That to the third digit may divide into two, one of which goes to
the fourth digit.
Each of the four tendons (Fig. 88, b and b′) is perforated by a tendon of
the flexor profundus (Fig. 88, c) as it passes through the fibrous pulley-ring
at the base of the first phalanx. It then continues beneath the flexor
profundus tendon through the second pulley-ring (2) and is inserted into the
base of the second phalanx.
Relations.—Outer surface of the ulnar part with the integument; inner
surface with the palmaris longus (Fig. 77, s). Outer surface of the radial part
with the palmaris longus; inner surface with the flexor profundus.
Action.—Flexor of the second phalanx of digits 2-5.
M. flexor profundus digitorum (or perforans).—This arises by five
heads, the tendons of which join one another at the wrist to make the
strongest and deepest of the flexor tendons.
The first or ulnar head has origin (Fig. 87, g) from the dorsal half of the
medial (radial) surface of the ulna from the proximal lip of the semilunar
notch to within a centimeter of the styloid process. Its fibres converge to a

large flat tendon which forms the lateral (ulnar) and superficial part of the
common tendon.

Fig. 87.—Radius and Ulna, Medial or Flexor Side, with M. pronator
quadratus and the Areas of Attachment of Other Muscles.

a, M. pronator quadratus; b, tendon of M. biceps; c, conjoined tendon of
M. brachialis and M. clavobrachialis; d, insertion of caput longum of M.
triceps; e, insertion of short portion of caput mediale of M. triceps; f,
origin of M. flexor carpi ulnaris; g, origin of first head of M. flexor
profundus digitorum; h, origin of fifth head of M. flexor profundus
digitorum; i, intermediate portion of caput mediale of M. triceps.

The second head has origin (Fig. 82, n) from the distal end of the medial
epicondyle of the humerus between the flexor ulnaris and the third and
fourth heads of the profundus. It may be very closely attached to these
muscles at their origins. Its tendon joins the radial border of the tendon of
the first head. From this junction the radial part of the flexor sublimis arises.
The third head (Fig. 77, u) has origin (Fig. 82, o) by a strong tendon
from the medial epicondyle of the humerus, between the palmaris (p) and
flexor radialis (m). Its tendon forms the radial part of the common tendon.
The fourth head has origin by a strong tendon from the medial
epicondyle of the humerus just ventrad of the origin of the second head and
the flexor ulnaris, to which many of its fibres are attached. Its tendon forms
the middle and superficial part of the common tendon.
The fifth or radial head (Fig. 75, q; Fig. 77, u′) has origin (Fig. 87, h)
from the middle third of the ventral surface of the shaft of the radius over an
area limited by two oblique bony ridges; from the adjacent parts of the
interosseous membrane; and from the ventral part of the medial surface of
the shaft of the ulna between a point about two centimeters distad of the
semilunar notch and the junction of the middle and distal thirds of the shaft.
Its very thick tendon forms the middle and deep part of the common tendon.
The common tendon (Fig. 88, c′) covers the carpus and metacarpus
ventrally. It divides into five tendons (c) which pass to the five digits and
are inserted into the bases of the terminal phalanges. Those of the first four
digits perforate the tendon of the flexor sublimis (b) at the base of the first
phalanx of each digit. At the same place each passes through a fibrous
pulley-ring attached to the base of the phalanx. Each then passes through a
second pulley-ring (2) near the head of the phalanx and is finally inserted
into the base of the terminal phalanx.
Relations.—Outer surface with the pronator teres (Fig. 77, q), flexor
carpi radialis (Fig. 77, r), palmaris longus (s), flexor carpi ulnaris (t),
integument, and extensor carpi ulnaris (Fig. 75, o). Inner surface with the
radius, ulna, interosseous membrane and pronator quadratus (Fig. 87, a).
Action.—Flexor of all the digits.

Fig. 88.—Arrangement of the Tendons of M. palmaris longus, M. flexor
sublimis digitorum, and M. flexor profundus digitorum, with Mm.
lumbricales.

The integument, fibrous pads, and the palmaris longus (except the ends
of its tendons) have been removed; the flexor sublimis has been cut. a, cut
ends of tendons of M. palmaris longus; b, tendons of M. flexor sublimis
digitorum, ulnar division; b′, radial part of M. flexor sublimis digitorum; c,
tendons of M. flexor profundus digitorum (c′, the common tendon); d, M.
abductor digiti quinti; e, M. flexor brevis digiti quinti; f, Mm. lumbricales
(f′, their tendons). 1, transverse ligament of wrist; 2, annular ligaments.

M. pronator quadratus (Fig. 87, a).—A thick quadrangular muscle
whose fibres run obliquely between the distal ends of the ulna and radius.
Origin by fleshy fibres from about the distal half of the ventral (flexor)
surface or border of the ulna and from the interosseous membrane adjacent
to the area. The fibres pass obliquely distad toward the radial side to their

Insertion by fleshy fibres into the ventral (flexor) surface of the radius
distad of the area of origin of the fifth head of the profundus.
Relations.—Outer surface with the flexor profundus. Inner surface with
the radius, ulna, and interosseous membrane.
Action as indicated by the name.

4. Muscles of the Hand.

A. Between the Tendons.—Mm. lumbricales (Fig. 88, f, f′).—Four
small muscles in the palm of the hand.
Origin by fleshy fibres from the outer (palmar) surface of the tendon
common to the ulnar four parts of the profundus (c′).
Insertion (f′).—The four slips are flat at their origin. Each becomes
cylindrical and curves about the base of one of the four ulnar digits and is
inserted into the radial side of the base of the first phalanx close to its
ventral border.

Fig. 89.—Deep Muscles of the Palm of the Hand.
a, M. flexor brevis pollicis; b, M. adductor pollicis; c, M. interosseus of
second digit (M. flexor brevis digiti secundi); d, M. adductor digiti
secundi; e, M. interosseus of third digit; f, M. interosseus of fourth digit; g,
M. opponens digiti quinti; h, M. interosseus of fifth digit (M. flexor brevis
digiti quinti); i, M. abductor digiti quinti. 1-5, the digits in order.

Action.—Bend the digits toward the radial side.
B. Muscles of the Thumb.—M. abductor brevis pollicis (Fig. 77, w)
(includes also the opponens pollicis of man).—A very minute, probably
rudimentary muscle.
Origin from the transverse ligament (1) which connects the prominent
fibrous, hairless projection that lies over the pisiform bone with the radial
border of the head of the radius. The muscle passes radiodistad and ends in
a very slender tendon, the insertion of which is into the base of the first
phalanx of the thumb.
M. flexor brevis pollicis (Fig. 89, a).
Origin by fleshy fibres from the adjacent borders of the os magnum and
scapholunar bones and from the fascia which bridges the intervening
groove for the flexor carpi radialis.
Insertion by a short tendon into the base of the first phalanx of the pollex.
Action.—Flexor of the thumb.
M. adductor pollicis (Fig. 89, b).
Origin by fleshy fibres from the ventral border of the os magnum. It
curves about the base of the first metacarpal on its ulnar side to its insertion.
Insertion by fleshy fibres into the base of the first phalanx of the pollex
on its ulnar side.
C. Muscles Lying between the Metacarpals.—Mm. interossei (Fig.
89).—Small stout muscles lying on the palmar surfaces of the metacarpals
of the second, third, fourth, and fifth digits.
Origin by fleshy fibres from the ventral or lateral surfaces of the bases of
the metacarpals. Near the distal end of the metacarpal each divides into two
masses which pass onto the lateral surfaces of the metacarpal, so as to leave
the ventral surface of the distal end exposed.
Insertion partly onto the lateral surfaces of the base of the first phalanx
and its sesamoids, and partly by a slender tendon (Fig. 84, h) which is
continued dorsad to join the extensor tendon of the digit.
D. Special Muscles of the Second Digit (the Index).

—M. flexor brevis digiti secundi (or indicis).—This name may be applied
to M. interosseus of the second digit (Fig. 89, c).
M. abductor digiti secundi.—This name might be applied to a portion
of the interosseus of the second digit which is sometimes differentiated
from the remainder.
Origin from the radial and ventral surfaces of the base of the second
metacarpal, and from the ventral surface of the trapezium.
Insertion into the radial side of the base of the first phalanx of the second
digit and into its sesamoid.
M. adductor digiti secundi (Fig. 89, d).
Origin from the ventral surface of the os magnum.
Insertion into the ulnar side of the base of the first phalanx of the second
digit.
E. Special Muscles of the Fifth Digit.—M. abductor digiti quinti (Fig.
89, i).—A thick, small, conical bundle.
Origin from the distal surface of the pisiform bone and from the
transverse ligament on the ulnar side of the pisiform. It ends in a slender
tendon which runs along the ulnar side of the fifth metacarpal to its
Insertion into the ulnar side of the base of the first phalanx of the fifth
digit.
M. flexor brevis digiti quinti (Fig. 89, h; Fig. 88, e).—This covers the
ventral surface of the fifth metacarpal, and is really the interosseus of this
digit.
Origin by fleshy fibres from the ventral surface of the base of the fifth
metacarpal; from the ventral process of the unciform bone, and from the
transverse ligament proximad of the fifth metacarpal.
Insertion by fleshy fibres into the ventral border of the proximal end of
the first phalanx of the fifth digit.
M. opponens (adductor) digiti quinti (Fig. 89, g).
Origin by a flat tendon from the ventral surface of the os magnum on the
ulnar side of the adductor pollicis (b). It passes toward the ulnar side and
distad, the fibres diverging to their
Insertion (1) into nearly the whole of the radial surface of the fifth
metacarpal, (2) into the base of its first phalanx.

V. MUSCLES OF THE PELVIC LIMBS.

1. Muscles of the Hip.

A. On the Lateral Surface of the Hip.

Fascia of the Thigh.—After the removal of the superficial fascia with its
fat and blood-vessels, there is seen a strong glistening fascia, the fascia lata
(Fig. 68, z, page 117), covering the vastus lateralis muscle over the dorsal
half of the thigh. Ventrally it dips between the vastus lateralis and the biceps
femoris and, becoming gradually thinner, is lost on the surface of the former
muscle. Passing over the dorsal border of the thigh, it extends beneath the
sartorius and is attached to the dorsal border of the vastus medialis. Toward
its distal end the fascia is continuous with the tendon of the biceps femoris
and dorsad with the border of the sartorius muscle, while between these
points it is united with the tendon of the vastus lateralis; it thus gains
insertion into the patella. At its proximal end the fascia receives the
insertion of the tensor fasciæ latæ (Fig. 68, r).
M. tensor fasciæ latæ (Fig. 68, r, page 117; Fig. 92, a).—The tensor
fasciæ latæ is a thick triangular muscle which may be recognized by its
insertion into the proximal end of the fascia lata (Fig. 68, z; Fig. 92, a′).
Origin by fleshy fibres as a thick triangular prism from the outer margin
of the ventral border of the ilium craniad of the auricular impression and
from the fascia covering the ventral border of the gluteus medius (Fig. 90,
b) over its cranial half. The caudal border of the muscle may be continuous
with the cranial border of the gluteus maximus. The muscle spreads out in a
fan-like manner, covering the proximal third of the dorsal surface of the
thigh. The cranial fibres pass farther distad than the others.
Insertion into the fascia lata (Fig. 68, z) along an irregular line which
begins caudad at the base of the great trochanter and ends on the cranial
side of the thigh at the junction of the first and second thirds.
Relations.—Outer surface with the cutaneus maximus (Fig. 62, b, page
94) and craniad with the sartorius (Fig. 68, q). Cranial border with the
sartorius (q); caudodorsal border with the gluteus medius (Fig. 90, b). Inner
surface with the gluteus medius, the rectus femoris (Fig. 92, b), and the
vastus lateralis (Fig. 90, d).

Action indicated by the name. It also assists the quadriceps femoris in
extending the leg.
M. gluteus maximus.—The gluteus maximus is a rather small
quadrangular muscle in the angle between the gluteus medius (Fig. 90, b)
and the caudal vertebræ.
Origin (Fig. 163, 3, page 401) by fleshy fibres from the tips of the
transverse processes of the last sacral and the first caudal vertebræ, from the
fascia covering the spinous muscles dorsad of the transverse processes of
these vertebræ, and from the fascia covering the gluteus medius. The
muscle passes laterad and slightly caudad to its
Insertion by tendon and muscle-fibres into a tubercle on the caudal side
of the great trochanter at the middle of its distal end, and for a few
millimeters into the ridge which continues distad from this tubercle.
Relations.—Outer surface with the caudofemoralis (Fig. 68, s, page 117),
the superficial fascia, and a few fibres of the cutaneus maximus. Inner
surface with the abductor caudæ internus, the tenuissimus (Fig. 90, g), the
great sciatic nerve (Fig. 163, a), the obturator internus (Fig. 90, e), the
gluteus medius (Fig. 90, b), the gemellus superior, and the pyriformis (Fig.
163, 7). Cranial border with the gluteus medius and the tensor fasciæ latæ.
Caudal border with the caudofemoralis (Fig. 68, s).
Action.—Abducts the thigh.
M. gluteus medius (Fig. 90, b).—The gluteus medius is a very large
triangular muscle which connects the ilium and the sacrum with the great
trochanter (1).
Origin by fleshy fibres (1) from the superficial sacral fascia; (2) from the
lateral surface of the fascia which covers the surface of the supraspinous
extensor muscles of the tail; (3) from the fascia intervening between it and
the tensor fasciæ latæ; (4) by tendon fibres from the dorsal half of the crest
of the ilium and its dorsal border, and the dorsal half of the lateral surface
craniad of the auricular impression; and (5) from the tips of the transverse
processes of the last sacral and the first caudal vertebræ. The fibres
converge to a strong internal tendon.
Insertion into the proximal end of the great trochanter.
Relations.—Outer surface with the gluteus maximus and tensor fasciæ
latæ, and between these with the strong fascia lying beneath the cutaneus
maximus muscle. Inner surface with the gluteus minimus, the pyriformis,

and the gemellus superior. Cranial border with the tensor fasciæ latæ.
Caudal border with the gluteus maximus.
Action.—Abducts the thigh.
M. pyriformis (Fig. 163, 7).—The pyriformis is a triangular muscle
covered by the gluteus maximus and the gluteus medius (Fig. 90, b) and
overlying the gemellus superior (Fig. 163, 6).
Origin by fleshy fibres from the tips of the transverse processes of the
last two sacral and the first caudal vertebræ. The muscle passes laterad
through the great sciatic notch to its
Insertion by a flat tendon into an elongated area on the proximal border
of the great trochanter just outside (caudad) of the insertion of the gemellus
superior.
Relations.—Outer surface with the gluteus medius (Fig. 90, b) and the
gluteus maximus. Inner surface with the gemellus superior (Fig. 163, 6), the
great sciatic nerve (Fig. 163, a), and the flexor caudæ longus (Fig. 68, x).
Action.—Abductor of the thigh.
M. gemellus superior (Fig. 163, 6).—The gemellus superior is a
triangular muscle lying beneath the pyriformis (Fig. 163, 7). It is broader
than the pyriformis, so that it projects beyond its borders both caudad and
craniad. It is closely united craniad with the gluteus minimus, so that the
limits of the two are definable only with difficulty. Its caudal border is
closely united to the gemellus inferior.
Origin by fleshy fibres from an elongated area on the dorsal border of the
ilium and ischium. The area is narrowed craniad. It does not quite reach the
posterior inferior iliac spine in the one direction nor the spine of the ischium
in the other direction. The fibres converge to a strong tendon the
Insertion of which is into a triangular area dorsad of the tip of the great
trochanter.
Relations.—Outer surface with the gluteus medius (Fig. 90, b), the
pyriformis (Fig. 163, 7), the great sciatic nerve (Fig. 163, a), and the gluteus
maximus. Inner surface with the ilium, ischium, the capsularis, the caudal
edge of the gluteus minimus (Fig. 163, 5), and the cranial edge of the
obturator internus (Fig. 90, e).
Action.—Rotates the femur and abducts it so as to carry the foot outward.
M. gluteus minimus (Fig. 163, 5).—The gluteus minimus is a long
triangular muscle beneath the middle of the gluteus medius (Fig. 90, b) and

with its caudal border against or covering the cranial border of the gemellus
superior (Fig. 163, 6), to which it is frequently closely united.
Origin from the ventral half of the ilium, from near its cranial end to a
point midway between the posterior iliac spine and the spine of the ischium.
The muscle ends in a strong flat tendon.
Insertion into an oval facet at the base of the dorsal surface of the great
trochanter on its lateral side.
Relations.—Outer surface with the gluteus medius (Fig. 90, b) and at the
caudal border with the gemellus superior (Fig. 163, 6). Inner surface with
the capsularis and rectus femoris (Fig. 92, b).
Action.—Rotates the femur so as to carry the foot out.
M. capsularis (gluteus quartus, or epimeralis).—The capsularis is a
small flat bundle of muscle-fibres which lies obliquely beneath the gluteus
minimus (Fig. 163, 5) and gemellus superior (6) on the lateral or outer
surface of the ilium.
Origin by fleshy fibres from the surface of the ilium over a triangular
area between the origin of the rectus femoris (Fig. 92, b) ventrad, the
gemellus superior (Fig. 163, 6) dorsad, and of the gluteus minimus (Fig.
163, 5) craniad and the acetabulum caudad. The muscle passes over the
smooth surface of the ilium and the pubis ventrad of the acetabulum and
then over the capsule of the joint.
Insertion by fleshy fibres for about one centimeter in the middle line on
the dorsal surface of the femur distad of the great trochanter.
Relations.—Outer surface with the gluteus minimus (Fig. 163, 5), the
gemellus superior (6), and the vastus lateralis (Fig. 90, d). Inner surface with
the ilium, the rectus femoris (Fig. 92, b), the capsule of the joint, and the
vastus medialis (Fig. 92, c).
Action.—Rotates the thigh so as to carry the foot inward, hence
antagonizes the iliopsoas.
M. gemellus inferior.—The gemellus inferior is a flat triangular muscle
situated just caudad of the gemellus superior and beneath the obturator
internus (Fig. 90, e), so that it is seen on reflecting the latter
Origin from the dorsal one-half of the whole lateral surface of the
ischium between the ischial spine and the ischial tuberosity. The fibres
converge toward its insertion. The inner surface of the muscle is covered by
a strong tendon.

Insertion into the inner surface of the tendon of the obturator internus
(Fig. 90, e) by tendon- and muscle-fibres. Some of the muscle-fibres are
inserted into the capsule of the joint.
Relations.—Outer surface with the obturator internus (Fig. 90, e). Medial
surface with the ischium. Caudal border with the quadratus femoris (Fig.
90, f). Cranial border with the gemellus superior.
Action.—Abductor of the thigh. The muscle may be considered as a
separate head of the obturator internus (Fig. 90, e).
M. quadratus femoris (Fig. 90, f).—The quadratus femoris is a short
thick muscle connecting the ischial tuberosity (2) and the proximal end of
the femur. It lies just caudad of the obturator internus (e) beneath the
proximal end of the biceps femoris (Fig. 68, t).
The origin is by fleshy fibres from a considerable triangular area on the
lateral surface of the ischium near the tuberosity. The area lies between the
origin areas of the gemellus inferior, biceps, semimembranosus, and the
obturator externus.
Insertion into the distal two-thirds of the ventral border of the great
trochanter and about half the adjacent surface of the lesser trochanter.
Relations.—Outer surface with the tenuissimus (Fig. 90, g), the biceps
(Fig. 68, t), the semitendinosus (Fig. 90, j), and the great sciatic nerve (Fig.
163, a). Caudal border with the semimembranosus (Fig. 90, i). Ventral
border with the adductor femoris (Fig. 90, h); dorsal border with the
obturator internus (Fig. 90, e) and gemellus inferior.
Action.—Extensor of the thigh and rotator of the femur so as to carry the
foot inward.
M. obturator externus.—The obturator externus is a flat triangular
muscle beneath the adductor femoris (Fig. 92, g).
Origin by fleshy fibres from the median lip of the obturator foramen and
from both dorsal and ventral surfaces of the rami of the pubis and ischium
adjacent to the lip. Also from the outer surface of the ramus of the ischium
as far as the area for the quadratus femoris (Fig. 90, f). The fibres converge
to a strong flat tendon.

Fig. 90.—Muscles on the Lateral Side of the Leg, after Removal of the Muscles
shown in Fig. 68 (Biceps, Tensor fasciæ latæ, Caudofemoralis, and Gluteus
maximus).

a, M. sartorius; b, M. gluteus medius; c, M. rectus femoris; d, M. vastus lateralis; e, M.
obturator internus; f, M. quadratus femoris; g, M. tenuissimus; h, M. adductor femoris; i,
M. semimembranosus; j, M. semitendinosus; k, M. vastus intermedius; l, M. plantaris; m,
m′, m″, M. gastrocnemius, outer head (m, part from the external sesamoid bone; m′, from
the plantaris; m″, from the superficial fascia); n, M. tibialis anterior; o, M. soleus; p, M.
extensor longus digitorum; q, M. peroneus longus; r, M. peroneus tertius (r′, its tendon); s,
M. peroneus brevis; t, tendon of Achilles; u, M. extensor brevis digitorum. 1, great
trochanter of femur; 2, tuberosity of ischium, with cut origin of M. biceps femoris; 3,
patella; 4, calcaneus; 5, transverse ligaments; 6, lateral malleolus.

Insertion into the proximal portion of the bottom of the trochanteric
fossa.
Relations.—Ventral surface with the adductor femoris (Fig. 92, g). Dorsal
surface with the pubis and ischium. Caudal border with the quadratus
femoris (Fig. 90, f).
Action.—Assists the iliopsoas.
B. Muscles on the Medial Surface of the Hip.—M. obturator internus
(Fig. 90, e).—The obturator internus appears as a triangular muscle caudad
of the gemellus superior.
Origin by numerous small separate heads from the dorsal surface of the
ramus of the ischium along its symphysis and following its medial border
from the symphysis nearly to the tuberosity. The fibres form a flat muscle
which narrows and passes through the lesser sciatic notch, turns ventrad and
ends in a strong flat tendon whose
Insertion is into the bottom of the trochanteric fossa of the femur. The
tendon is continued proximad on the inner surface of the muscle and forms
a smooth firm surface by which the muscle glides over the dorsal border of
the ischium. Into the inner surface of this tendon near its insertion the
tendon of the gemellus inferior is inserted.
Relations.—Medial surface within the pelvis with a mass of fat
separating it from the pelvic organs. Dorsal or outer surface with the biceps
femoris, the tenuissimus, the caudofemoralis, and the great sciatic nerve.
Inner surface with the ischium and the great sciatic nerve. Caudal (or
ventral) border with the quadratus femoris.
Action.—Abductor of the thigh.
M. iliopsoas (Fig. 162, 8; Fig. 91, c).—The iliopsoas (equivalent to the
human psoas and iliacus) is a conical muscle emerging from the abdominal
cavity onto the medial surface of the femur.
Origin.—(a) The portion corresponding to the human psoas (Fig. 162, 8)
arises by ten vertebral heads. The first five of these come from the five
cranial tendons of origin of the psoas minor (Fig. 162, 9); the sixth from a
tendinous expansion which passes from the tendon of the first head over the
ventral longitudinal muscles to the transverse process of the fifth lumbar
vertebra. The seventh, eighth, ninth, and tenth heads arise by fleshy fibres
from the ventral surfaces of the centra of the last four lumbar vertebræ.
(b) The portion corresponding to the human iliacus arises by fleshy fibres
from the ventral border of the ilium, from opposite the auricular impression

to the iliopectineal eminence. The portions of the muscle all converge to
form a conical mass which ends in a strong tendon lying on its outer
surface.
Insertion by tendon and fleshy fibres into the apex of the lesser
trochanter of the femur.
Relations.—Dorsal surface with the quadratus lumborum (with which
this muscle is partly united), the rectus femoris (Fig. 91, d), and, by the iliac
head, with the gluteus minimus. Ventral and medial surface with the psoas
minor (Fig. 162, 9) and the peritoneum. Lateral edge with the transversus
abdominis (Fig. 162, 4).
Action.—Rotates the thigh so as to carry the foot out; also flexes the
thigh.

2. Muscles of the Thigh.

M. biceps femoris (Fig. 68, t, page 117).—A very large flat muscle
covering about two-thirds of the lateral side of the thigh.
Origin (Fig. 90, 2).—From the ventral surface of the tuberosity of the
ischium by tendon- and muscle-fibres. The fibres diverge, and near the knee
the mass has spread out, ending in a fascia. The dorsal border of the muscle
and the common fascia are continuous dorsad with the superficial fascia of
the thigh and with the tendon of the caudofemoralis (Fig. 68, s). Ventrad it
is continuous with the superficial fascia of the shank.
Insertion into rather more than the proximal one-third of the dorsal
border of the tibia along its lateral margin and into the lateral margin of the
patella. In passing over the knee-joint it is closely united to the underlying
ligaments and tendons.
Relations.—Outer surface with the superficial fascia and with a few of
the most caudal fibres of the cutaneus maximus (Fig. 62, b, page 94).
Cranial (or dorsal) edge with the caudofemoralis (Fig. 68, s) and the vastus
lateralis (Fig. 90, d). Caudal border with the semitendinosus (Fig. 68, u) and
a mass of fat. Inner surface with the caudofemoralis (Fig. 68, s), the
tenuissimus (Fig. 90, g), the obturator internus (Fig. 90, e), the quadratus
femoris (Fig. 90, f), the semitendinosus (Fig. 68, u), the semimembranosus
(Fig. 90, i), the adductor femoris (Fig. 90, h), the great sciatic nerve (Fig.
163, a), and distad with the following muscles of the lower leg: the tibialis

anterior (Fig. 90, n), the extensor longus digitorum (Fig. 90, p), the
peroneus longus (Fig. 90, q), and the lateral head of the gastrocnemius (Fig.
90, m).
Action.—Abductor of the thigh, and flexor of the shank.
M. tenuissimus or M. abductor cruris (Fig. 90, g).—A very slender
muscle, only three or four millimeters wide.
Origin from the tip of the transverse process of the second caudal
vertebra, in common with the caudofemoralis (Fig. 68, s) or gluteus
maximus. It passes obliquely beneath the biceps femoris (Fig. 68, t) distad
and ventrad, to the distal end of the ventral border of that muscle. Here it
becomes continuous with the ventral border of the biceps, ending in a
continuation of the same fascia into which the biceps is inserted.
Relations.—Outer surface with the caudofemoralis (Fig. 68, s) and the
biceps femoris (Fig. 68, t); distad with the integument. Inner surface with
the obturator internus (Fig. 90, e), quadratus femoris (f), semitendinosus (j),
adductor femoris (h), semimembranosus (i), and distad with the muscles of
the lower leg.
M. caudofemoralis (parameralis, Strauss-Durckheim) (Fig. 68, s, page
117).
Origin by a flat tendon from the transverse processes of the second and
third caudal vertebræ. The muscle forms a flat band which passes distad
along the middle of the lateral side of the thigh over the pelvis and caudad
of the great trochanter. At the middle of the thigh it ends in a very thin
tendon. The tendon passes distad along the medial surface of the biceps
femoris (Fig. 68, t), pierces the fascia lata near the knee, and passes to its
Insertion into the middle of the lateral border of the patella.
Relations.—Outer surface with the superficial fascia and a few fibres of
the cutaneus maximus; distad with the biceps femoris (Fig. 68, t). Cranial
border with the gluteus maximus; caudal border with the biceps femoris.
Inner surface with the tenuissimus (Fig. 90, g), the gluteus maximus, the
abductor caudæ internus, and with the obturator internus (Fig. 90, e); distad
with the vastus lateralis.
Action.—Abducts the thigh and helps to extend the shank.
M. semitendinosus (Fig. 90, j).—A long slender muscle on the ventral
(caudal) border of the thigh, between the semimembranosus (i) and the
biceps femoris (Fig. 68, t).

Origin from the apex of the tuberosity of the ischium beneath the origin
of the biceps femoris. The muscle passes to the medial side of the shank and
ends in a thin but strong tendon (Fig. 92, i′) about five millimeters broad.
The tendon curves proximad and passes beneath the gracilis tendon (Fig.
91, b) to its
Insertion into the crest (dorsal border) of the tibia one or two centimeters
from its proximal end.
Relations.—Lateral surface with the biceps femoris (Fig. 68, t), the
integument, a mass of fat, and distad with the gastrocnemius (Fig. 92, j) and
popliteus (Fig. 92, k). Caudal surface with the integument. Medial surface
with the semimembranosus (Fig. 90, i) and distad with the integument of
the lower leg.
Action.—Flexor of the shank.
M. semimembranosus (Figs. 90 and 91, i; Fig. 92, h).—A thick
prismatic muscle lying along the ventral (or caudal) side of the thigh
between the semitendinosus (j) and the gracilis (Fig. 91, b).
Origin by short tendon-fibres from the caudal border of the tuberosity
and the ramus of the ischium. The muscle mass is divided throughout most
of its length into two portions (Fig. 92, h and h′), one of which (h′) lies
laterad and caudad of the other. The two portions pass to the medial side of
the knee. The caudal portion (h′) ends in a strong flat tendon five
millimeters broad, the
Insertion of which is into the medial surface of the femur on the medial
epicondyle, at the middle of its distal border and into the adjacent medial
surface of the tibia behind the lateral ligament.
The dorsal part has its insertion into the distal one and one-half to two
centimeters of the ridge which is continued from the medial epicondyle of
the femur onto the shaft; and into the sesamoid bone of the medial
epicondyle.
Relations.—Lateral surface with the semitendinosus (Fig. 90, j), the
biceps femoris (Fig. 68, t), and distad with a small part of the adductor
femoris (Fig. 92, g), and with the gastrocnemius (Fig. 92, j). Medial surface
with the gracilis (Fig. 91, b) and distad with the sartorius (Fig. 91, a).
Cranial (or dorsal) border at the origin with the quadratus femoris (Fig. 90,
f); for the remainder of its length with the adductor femoris (Fig. 90, h).
Caudal border with the integument proximad.
Action.—Extensor of the thigh.

Fig. 91.—Muscles on the Medial Side of the Leg.

a, M. sartorius; b, M. gracilis; c, M. iliopsoas; d, M. rectus femoris; e, M. vastus
medialis; f, M. pectineus; g, M. adductor longus; h, M. adductor femoris; i, M.
semimembranosus; j, M. semitendinosus; k, medial head of M. gastrocnemius; l, M.
plantaris; m, M. flexor longus hallucis (m′, its tendon); n, M. flexor longus digitorum; (n′,
its tendon); o, M. tibialis posterior; p, M. tibialis anterior; q, M. interosseus of second digit.
1, patella; 2, calcaneus; 3, medial malleolus; 4, second metatarsal; 5, transverse ligament of
the lower leg.

M. sartorius (Fig. 91, a; Fig. 68, q).—A large flat muscle along the
medial side of the thigh near its cranial (dorsal) border.

Origin from the ventral half of the crest of the ilium and from the medial
half of its ventral border craniad of the auricular impression. The caudal
third of the origin is by a thin tendon, the rest by fleshy fibres.
Insertion on a long S-shaped line which begins on the dorsal border of
the tibial shaft about two centimeters from its proximal end, passes thence
to the middle of the proximal end of the medial surface of the tibia, thence
across the ligaments of the knee-joint and the medial surface of the medial
epicondyle to the patella, crosses the patella obliquely to the middle of its
proximal end, and may be continued for some distance proximad along the
middle line on the fascia.
Relations.—Medial surface with the integument and proximad with the
internal oblique muscle (Fig. 68, p). Lateral (inner) surface with the tensor
fasciæ latæ (Fig. 68, r), the vastus lateralis (Fig. 90, d), the superficial
fascia, the vastus medialis (Fig. 92, c), the rectus femoris (Fig. 92, b), and
the distal end of the semimembranosus (Fig. 92, h′).
Action.—Adducts and rotates the femur and extends the tibia.
M. gracilis (Fig. 91, b).—The gracilis is a flat, thin, subcutaneous muscle
occupying the ventral half of the medial surface of the thigh.
Origin by a strong tendon from the caudal three-fourths of the symphysis
of the ischium and pubis. The tendon may extend caudad of the symphysis
in the middle line to the level of the tuberosity of the ischium. For about its
first centimeter the tendon is common to the two muscles of opposite sides
and gives origin on two sides to the fibres of the adductor femoris. The
common tendon divides into two which pass laterad, each ending in a
convex border from which the muscle-fibres spring.
Insertion.—It ends in a thin aponeurosis, part of which is continuous with
that of the sartorius. The aponeurosis is finally inserted into the medial
surface of the tibia near its proximal end, while distally it is continuous with
the fascia.
Relations.—Outer (medial) surface with the integument. Inner (lateral)
surface with the semimembranosus (Fig. 91, i) and the adductor femoris
(Fig. 91, h).
Action.—Adducts the leg and draws it caudad.
M. adductor femoris (magnus et brevis) (Fig. 92, g; Fig. 90, h).—The
adductor femoris lies between the semimembranosus (Fig. 92, h) and the
femur. Its proximal part is covered by the semimembranosus, while its
distal part lies outside of it.

Origin by muscle-fibres from the rami of the pubis and the ischium along
the whole of the length of the symphysis; from the ramus of the ischium
between the symphysis and the tuberosity, and from the tendon of origin
common to the two gracilis muscles.
Insertion into nearly the whole of the ventral surface of the shaft of the
femur. The area begins at the base of the great trochanter opposite the
proximal end and the insertion area of the gluteus maximus. It extends
thence distad along the caudal border of the surface as an area about one
millimeter wide. At the junction of the first and second thirds of the shaft
the area expands and occupies the whole of the ventral surface of the bone,
ending at the intercondyloid fossa.
Relations.—Lateral surface with the biceps (Fig. 68, t), the great sciatic
nerve (Fig. 163, a), the tenuissimus (Fig. 90, g), and the semimembranosus
(Fig. 92, h); dorsolateral border in contact with the vastus lateralis (Fig. 92,
c). Dorsal surface with the quadratus femoris (Fig. 90, f) and obturator
externus (Fig. 90, e). Caudal surface with the semimembranosus (Fig. 92,
h). Medial surface with the gracilis (Fig. 91, b), adductor longus (Fig. 92, f),
pectineus (Fig. 92, e), vastus medialis (Fig. 92, c), and distad with the
medial head of the gastrocnemius (Fig. 92, j).
Action.—An extensor of the thigh.
M. adductor longus (Fig. 91, g; Fig. 92, f).—A thin muscle which
covers the dorsal half of the medial surface of the adductor femoris (Fig. 92,
g).
Origin by muscle-fibres from the median three-fourths of the cranial
border of the pubis, the line of origin forming a medial continuation of that
of the pectineus (Fig. 92, e).
Insertion by a thin aponeurosis into the external linea aspera of the femur
along the second and third fifths of the bone.
Relations.—With its medial or cranial surface the adductor longus forms
part of the boundary of a depression among the muscles at the proximal end
of the medial side of the leg. This depression is called the iliopectineal
fossa; it contains the femoral vein and artery and saphenous nerve
imbedded in fat (Fig. 127). The medial edge of the adductor longus is in
relation with the integument; the lateral edge with the pectineus (Fig. 92, e).
Inner or caudal surface with the adductor femoris (Fig. 92, g).
Action.—Adductor of the thigh.

Fig. 92.—Second Layer of Muscles on the Medial Side of the Thigh.

a, M. tensor fasciæ latæ; a′, fascia lata; b, M. rectus femoris; c, M.
vastus medialis; d, M. iliopsoas (cut); e, M. pectineus; f, M. adductor
longus; g, M. adductor femoris; h, h′, M. semimembranosus; i, M.
semitendinosus (i′, its tendon); j, medial head of M. gastrocnemius; k, M.
popliteus; l, M. flexor longus digitorum. 1, patellar ligament; 2,
ligamentum collaterale tibiale.

M. pectineus (Fig. 92, e).—A flat band of fibres closely united with the
adductor longus (f), of which it appears to be a lateral continuation.
Origin by fleshy fibres from the lateral one-fourth of the cranial border of
the pubis. The muscle passes over the smooth outer surface of the pubis
between its origin area and the acetabulum, crosses the iliopsoas (d)
obliquely and has its
Insertion by muscle-fibres into an elongated area (five millimeters in
length) on the shaft of the femur just distad of the lesser trochanter and

between the insertion of the adductor femoris (g) and that of the vastus
medialis (c).
Relations.—The cranial edge forms part of the floor of the iliopectineal
fossa. Lateral surface in relation with the iliopsoas (d) and vastus medialis
(c); medial surface with the adductor longus (f) and adductor femoris (g).
Action.—Adductor of the thigh.
M. quadriceps femoris.—The quadriceps femoris is a very powerful
extensor muscle on the front of the thigh. It consists of four muscles which
unite to form the great extensor of the shank. It is inserted into the patella
and through it, by the ligamentum patellæ, into the tibia. It may be
compared to the triceps brachii. The parts are:
(1) M. rectus femoris (Fig. 92, b; Fig. 90, c).
Origin by strong tendon from an elongated triangular area which has its
base at the acetabulum and its apex about five to seven millimeters craniad
of the acetabulum, along the ventral border of the ilium. The area is
between that for the capsularis and that for the iliopsoas. The muscle is flat
near its origin, but soon becomes a triangular prismatic mass which is
united to the dorsal border of the vastus lateralis (Fig. 90, d) at the junction
of the middle and last thirds of the thigh.
Insertion into the oblique area on the outer surface of the patella near its
proximal border in connection with the vastus lateralis.
Relations.—Outer or lateral surface at the origin with the gluteus
minimus, the edge of the capsularis, the gluteus medius (Fig. 90, b), and
farther distad with the vastus lateralis (Fig. 90, d). Medial surface with the
tensor fasciæ latæ (Fig. 92, a), sartorius (Fig. 90, a), and vastus medialis
(Fig. 92, c). Inner (caudal) surface with the vastus intermedius.
(2) M. vastus lateralis (Fig. 90, d).—A flat triangular prismatic mass
joined distally to the preceding. It covers the dorsal part of the lateral
surface of the thigh.
Origin from a triangular area on the dorsal and lateral surfaces of the
shaft and the great trochanter of the femur. The base of the area is at the
great trochanter, and its apex is at the junction of the second and third fifths
of the shaft on the linea aspera. The linea aspera forms the ventral boundary
of the triangle, while its dorsal boundary is formed by a line drawn from its
apex to the dorsomedial angle of the great trochanter. The mass unites with
the rectus femoris (c) by its dorsal border at the junction of the middle and
distal thirds of the thigh.

Insertion into the oblique area on the outer surface of the patella near its
lateral border in connection with the rectus femoris.
(3) M. vastus medialis (Fig. 92, c) lies on the medial side of the thigh.
Origin by fleshy fibres over a diamond-shaped area on the shaft of the
femur lying between the medial branch of the linea aspera and the area for
the vastus lateralis. Proximad the area is bounded by the spiral line, and
distad it is bounded by a line parallel to the spiral line and having its
proximal end at about the junction of the first and second thirds of the bone.
The muscle forms a triangular, prismatic mass. It ends in a thin aponeurosis
which is continuous dorsad with the border of the rectus femoris (Fig. 92,
b), and ventrad sometimes with the tendon of the gracilis (Fig. 91, b).
Insertion into the medial border of the patella and the ligamentum
patellæ. The insertion may extend onto the head of the tibia.
The adjacent surfaces of the vastus lateralis and the vastus medialis are
connected over their distal thirds by an aponeurosis which passes
transversely beneath the rectus femoris. The distal end of the aponeurosis is
inserted into the proximal border of the patella. Its proximal end receives
the insertion of some muscle-fibres which form a part of the vastus medialis
as here described. This mass of fibres is described by Strauss-Durckheim as
the crural muscle. Sometimes the transverse aponeurosis is continuous
with only one of the two vasti and sometimes with neither, so that the
insertion of the crural of Strauss-Durckheim becomes more or less
independent.
Relations of the vastus medialis.—Outer (medial) surface with the
sartorius (Fig. 91, a) and the structures in the iliopectineal fossa. Cranial (or
dorsal) surface with the rectus femoris (Fig. 92, b) and vastus intermedius.
Caudal (ventral) surface with the pectineus (Fig. 92, e), adductor longus
(Fig. 92, f), adductor femoris (Fig. 92, g), and semimembranosus (Fig. 92,
h).
(4) M. vastus intermedius.—A flat mass of muscle which lies beneath
the rectus femoris.
Origin from nearly the whole of the dorsal surface of the shaft of the
femur between the areas for the vastus medialis and vastus lateralis. The
area of origin extends distad to an oblique line the middle of which is about
one and one-half centimeters from the patellar surface, the lateral border of
the area being longer than the medial border.

Insertion by muscle-fibres into the capsule of the joint. The central fibres
are inserted about one centimeter proximad of the patella, while the lateral
mass passes to the level of the proximal end.
Relations.—Outer surface with the rectus femoris (Fig. 92, b); borders
with the vastus medialis (Fig. 92, c) and vastus lateralis (Fig. 90, d); inner
surface with the femur.
Action.—The quadriceps extensor is an extensor of the shank. The vastus
intermedius acting separately is a tensor of the capsule of the knee-joint.

3. Muscles of the Lower Leg (Crus).

A. On the Ventral Side.—M. gastrocnemius.—This is the great
muscular mass of the calf. It arises by two heads, the caput laterale or
lateral head (Fig. 90, m), and the caput mediale or medial head (Fig. 91, k),
of the gastrocnemius.
Caput laterale (Fig. 90, m, m′, m″).—The origin of the lateral head is in
four portions:
(1) From the tendon of origin of the plantaris which comes from the
middle of the lateral border of the patella. The tendon ends in a small
conical mass of fibres (m′) which joins the ventral part of the common head.
(2) By a slender flat tendon, distad of the first, from the superficial fascia
of the shank (m″). The tendon ends in a conical mass which joins the dorsal
border of the common head.
(3) By a strong tendon and by muscle-fibres from the distal border of the
lateral sesamoid bone (Fig. 61, 3) of the femur. These fibres (m) form the
middle and outer part of the common head.
(4) By muscle-fibres from the middle of the outer surface of the
aponeurosis covering the plantaris (Fig. 90, l) along rather more than the
proximal half of the tibia. The lateral head thus formed is flat and fusiform
in section.
Caput mediale (Fig. 91, k; Fig. 92, j).—The medial head resembles the
lateral head closely.
Origin by a strong tendon from the medial sesamoid bone of the femur
(Fig. 61, 4) and by muscle-fibres from the surface of the shaft for a short
distance proximad of this.

The two heads unite by their contiguous borders at the junction of the
first and second thirds of the tibia. The common muscle narrows rapidly
and ends in a flat tendon which joins the tendon of the soleus to form the
so-called tendon of Achilles (tendo calcaneus) (Fig. 90, t). This has its
Insertion into the proximal end of the calcaneus (Fig. 90, 4) near its
ventral border. This tendon together with that of the soleus (Fig. 90, o) and
the fascia of the shank forms a tubular sheath for the tendon of the plantaris.
Relations.—(1) Of the lateral head. Lateral (outer) surface with the
biceps femoris (Fig. 68, t) and the superficial fascia. Medial (inner) surface
with the popliteus (Fig. 92, k), the plantaris (Fig. 90, l) (to which it is
closely united), the medial head of the gastrocnemius (Fig. 91, k), the soleus
(Fig. 90, o), and the peroneus longus (Fig. 90, q). (2) Of the medial head.
Medial (outer) surface with the superficial fascia and the tendons of the
gracilis (Fig. 91, b), semimembranosus (Fig. 92, h′), and semitendinosus
(Fig. 92, i). Lateral (inner) surface at the origin with the adductor femoris
(Fig. 92, g), then with the plantaris (Fig. 91, l), the popliteus (Fig. 92, k),
flexor longus digitorum (Fig. 91, n), and the lateral head of the
gastrocnemius (Fig. 90, m).
Action.—Extensor of the foot. (It is to be noted that what is called
extension in the foot is analogous to what is called flexion in the hand, so
that the extensors of the foot are most readily to be compared with the
flexors of the hand.)
M. plantaris (Fig. 90, l; Fig. 91, l).—A fusiform muscle covered distally
by the gastrocnemius, but appearing between the two heads of the
gastrocnemius at their proximal ends (Fig. 90, l).
Origin by a strong tendon from the middle of the lateral border of the
patella and by fleshy fibres from the ventral border of the lateral sesamoid.
The patellar tendon ends in a flattened head which passes ventrad over
the lateral epicondyle of the femur and then curves distad; it is closely
united with the lateral head of the gastrocnemius. The muscle ends in a
thick tendon which passes through a sheath formed by the tendons of the
gastrocnemius and soleus, and the fascia of the shank. The tendon passes
over the grooved proximal end of the calcaneus onto its ventral surface. It is
held in place against the groove by two sheets of aponeurosis, which leave
the tendon on either side for a distance of more than a centimeter and are
attached to the lateral surfaces of the calcaneus at its proximal end. Lateral
motion is thus hindered, while longitudinal motion is permitted.

Between this tendon and the tendon of Achilles is a synovial bursa which
aids the gliding movement of the tendon. In the sole of the foot opposite the
distal end of the calcaneus the tendon broadens and ends in the flexor brevis
digitorum (pedis perforatus) muscle, which might also be considered as a
second part of the plantaris. In man the plantaris is inserted into the
calcaneus along with the gastrocnemius.
Relations.—The muscle is covered throughout by the two heads of the
gastrocnemius (Fig. 90, m; Fig. 91, k), except at the proximal end (Fig. 90,
l), where it is in contact with the integument. Inner surface in relation with
the popliteus (Fig. 92, k), the soleus (Fig. 90, o), the flexor longus digitorum
(Fig. 91, n), and flexor longus hallucis (Fig. 91, m).
M. soleus (Fig. 90, o).—A flat fusiform muscle lying beneath the
plantaris.
Origin by muscle-fibres from the lateral surface of the head of the fibula,
and by tendon-fibres from the proximal two-fifths of its ventral border.
Insertion.—The muscle ends in a slender tendon which joins the lateral
border of the gastrocnemius tendon to form the tendon of Achilles (Fig. 90,
t), which forms the sheath of the plantaris tendon.
Relations.—Outer surface with the gastrocnemius (Fig. 90, m) and
plantaris (Fig. 90, l). Inner surface with the peroneus longus (Fig. 90, q),
peroneus tertius (Fig. 90, r), and flexor hallucis (Fig. 91, m).
Action.—Assists the gastrocnemius to extend the foot.
M. triceps suræ.—The gastrocnemius and the soleus are sometimes
considered as forming a single muscle, with three heads, under the name
triceps suræ.
M. popliteus (Fig. 92, k).—A triangular muscle passing from the femur
obliquely toward the medial side over the ventral surface of the proximal
end of the tibia.
Origin by a strong tendon from the popliteal groove on the surface of the
lateral epicondyle of the femur. In the tendon is a sesamoid bone, the
popliteal bone (Fig. 61, 5, page 89), which glides over the ventral part of the
lateral articular facet on the proximal end of the tibia. As the muscle passes
over the joint it is closely attached to the joint capsule. From the popliteal
bone, which with the tendon lies within the capsule of the knee-joint, the
muscle-fibres diverge to their
Insertion into the proximal end of the ventral surface of the tibial shaft on
the medial side of the medial oblique ridge. The area of insertion extends

slightly onto the medial surface of the bone.
Relations.—Outer surface with the gastrocnemius (Fig. 92, j) and
plantaris (Fig. 91, l), and with the tendon of the semitendinosus (Fig. 92, i).
Distal border with the origins of the soleus and flexor longus digitorum.
Inner surface with the capsule of the knee-joint and the tibia.
Action.—Rotates the thigh so as to turn the toes inward.

The three following deep muscles on the ventral surface of the shank are
covered by a deep fascia (the deep crural fascia) which separates them from
the overlying muscles. This fascia stretches from the dorsal border of the
tibia about the ventral side of the shank to the medial border of the tibia. It
sends a slip beneath the border of the fibula.
M. flexor longus digitorum (Fig. 91, m and n).—Owing to the reduction
of the first digit in the cat the tendon of the flexor longus hallucis (m) has
become united to that of the flexor longus digitorum (n), so that the two
might be considered separate heads of a single muscle. The head
corresponding to the flexor longus hallucis (m) is much larger than that
corresponding to the flexor longus digitorum (n). The two heads will be
described separately.
(1) M. flexor longus hallucis (Fig. 91, m).—This lies against the ventral
surface of the tibia and fibula beneath the popliteus (Fig. 92, k) and soleus
(Fig. 90, o).
Origin by fleshy fibres, (1) from the sheet of deep crural fascia which
dips between it and the tibialis posterior (Fig. 91, o) and the flexor longus
digitorum (n). (2) From the ventral surface of the tibia distad of the lateral
oblique line to within one to three centimeters of the distal end of the shaft.
(3) From the medial surface of the shaft and head of the fibula and from the
whole interosseous ligament. On the fibular side the origin may extend onto
the tendon of the popliteus and the fascia of the peroneus longus. The fibres
form a flat fusiform mass ending one centimeter from the heel in a strong
flat tendon (m′) which passes over the groove on the distal surface of the
astragalus and over the groove on the sustentaculum tali. The two grooves
are converted into a continuous canal by strong transverse ligaments, and
the canal is lined by an extension of the synovial bursa of the ankle-joint.
Emerging from the canal the tendon broadens and receives on its medial
side the insertion of the tendon of the flexor longus digitorum (n). The
tendon gives origin on its outer surface to the lumbricales and to the

common plantar ligament. The tendon continues to broaden until it reaches
the middle of the length of the metacarpals; here it divides into four tendons
which pass to the terminal phalanges of the digits.
Insertion.—The relations of the four tendons and their insertions are
identical with those of the flexor profundus digitorum of the hand.
Relations.—Outer surface with the soleus (Fig. 90, o) and plantaris (Fig.
91, l). Lateral border with the soleus, the peroneus tertius (Fig. 90, r), and
peroneus brevis (Fig. 90, s). Medial border with the tibialis posterior (Fig.
91, o) and flexor longus digitorum (Fig. 91, n).
Action.—Flexor of the phalanges.
(2) M. flexor longus digitorum (Fig. 91, n).
Origin by muscle- and tendon-fibres from the ventral surface of the tibia
over its proximal half between the oblique ridges; by fleshy fibres from an
aponeurosis between it and the tibialis posterior (Fig. 91, o), and by tendon
from the medial surface of the head of the fibula. At the junction of the
middle and distal thirds of the bone the muscle ends in a slender tendon
which passes through the ventral groove on the medial surface of the tibia
and, curving onto the sole of the foot, becomes attached to the medial
border of the common tendon described under the last.
Relations.—Outer surface with the medial head of the gastrocnemius
(Fig. 91, k) and with the superficial fascia. Inner surface with the tibialis
posterior (Fig. 91, o). Medial border at the proximal end with the popliteus
(Fig. 92, k), lateral border with the tibialis posterior (Fig. 91, o), and flexor
longus hallucis (Fig. 91, m).
Action.—Flexor of the phalanges.
M. tibialis posterior (Fig. 91, o).—A slender flat fusiform muscle
beneath the flexor longus digitorum and between it and the flexor longus
hallucis.
Origin by fleshy fibres from nearly the whole medial surface of the head
of the fibula, from the inner surface of the aponeurosis between it and the
flexor longus digitorum (n), and by a few fleshy fibres from the ventral
surface of the tibia between the oblique ridges. Some fibres may also arise
from the outer surface of the aponeurosis covering the flexor longus
hallucis (m). The muscle ends at about the middle of the tibia in a slender
flat tendon which passes parallel to the tendon of the flexor longus
digitorum (n) through the dorsal groove on the medial surface of the distal
end of the tibia. This groove is converted into a canal by a transverse

ligament. Beyond the canal the tendon turns onto the plantar surface of the
foot and passes through a groove on the ventral surface of the scaphoid
bone. It then divides.
Insertion into the outer tuberosity on the surface of the scaphoid, and
onto the proximal end of the ventral surface of the medial cuneiform.
Relations.—Outer and medial surface with the flexor longus digitorum
(n). Lateral surface with the flexor longus hallucis (m).
Action.—Extensor of the foot.
B. Muscles on the Dorsal and Lateral Surfaces of the Lower Leg.—
M. peroneus longus (Fig. 90, q).—A slender, fusiform muscle lying
superficially on the lateral side of the leg, dorsad of the soleus.
Origin by tendon-fibres from the lateral surface of the head of the fibula
and from the proximal half of the lateral surface of its shaft.
At the junction of the middle and distal thirds of the lower leg the muscle
ends in a slender tendon which passes through the groove on the lateral
surface of the lateral malleolus. This groove is converted into a canal by a
transverse ligament. The tendon passes through the groove on the peroneal
tubercle of the calcaneus, then turns onto the sole of the foot and passes
through the peroneal groove on the cuboid bone. It then turns mediad and
passes through the groove between the ventral processes of the lateral
cuneiform and the metatarsal until it reaches the first metatarsal. The entire
groove is converted into a canal by the overlying ligaments.
Insertion into (1) the base of the fifth metatarsal, and (2) the outer side of
the base of the first metatarsal, and (3) by slender branches into the bases of
the other metatarsals.
Relations.—Outer (lateral) surface with the superficial fascia and the
tendon of the biceps femoris. Inner surface with the peroneus tertius (r) and
peroneus brevis (s), and with the extensor longus digitorum (p). At the
proximal end the dorsal border touches the tibialis anterior (n).
Action.—Flexor of the foot.
M. peroneus tertius (Fig. 90, r).—A slender fusiform muscle beneath
the peroneus longus (q).
Origin by fleshy fibres from about the second quarter of the lateral
surface of the fibula. The muscle ends in a slender tendon (r′), which passes
with that of the peroneus brevis (s) through the groove on the ventral border
of the lateral malleolus. The groove is converted into a canal by a transverse
ligament. Emerging from it, the tendon turns and passes along the outer

margin of the foot. In passing the sesamoid at the base of the first phalanx
of the fifth digit it is united to it by a band which passes from the sesamoid
to the tendon.
The insertion is finally into the lateral border of the extensor tendon of
the fifth digit as it passes from the first to the second phalanx.
Relations.—Outer surface with the peroneus longus (q), the soleus (o),
and the superficial fascia. Ventral border with the soleus (o) and flexor
longus hallucis (Fig. 91, m). Inner surface with the peroneus brevis (Fig. 90,
s).
Action.—Extensor and abductor of the fifth digit and flexor of the foot.
M. peroneus brevis (Fig. 90, s) lies beneath the other peronei.
Origin by fleshy fibres from the distal half of the surface of the fibula,
which it embraces. At the lateral malleolus the muscle ends in a thick
tendon which passes through the canal on the ventral surface of the
malleolus. In the canal it is enlarged and surrounded by a synovial bursa. It
then turns onto the foot and passes over the dorsal surface of the calcaneus
on its lateral side and has its
Insertion into the tubercle on the lateral side of the base of the fifth
metatarsal.
Relations.—Outer surface with the peronei longus (q) and tertius (r).
Inner surface with the bone.
Action.—Extensor of the foot.
M. extensor digitorum longus (Fig. 90, p).—A fusiform muscle which
lies beneath the tibialis anterior (n), against the interosseous membrane, and
between the tibialis anterior and the peronei.
Origin by a thin flat tendon from the lateral surface of the lateral
epicondyle of the femur just dorsad of the origin of the popliteus. The
tendon becomes narrower and thicker and passes through the capsule of the
knee-joint and over a slight groove on the tibia just dorsad of the head of
the fibula. The belly of the muscle extends the entire length of the tibia,
passing beneath the transverse ligament (5) along with the tendon of the
tibialis anterior (n). At the ankle it runs through a fibrous loop which is
attached to the dorsal surface of the calcaneus (the annular ligament of the
calcaneus); it then turns and passes onto the dorsum of the foot. The muscle
ends in four slender tendons, the two middle of which begin at the
transverse ligament, while the others begin at the fibrous loop. The tendons
diverge to the four digits. Each tendon is connected with the fibrous sheath

surrounding the base of the first phalanx, and each has a synovial bursa
beneath it at this point. Near the distal end of the first phalanx the tendon is
united on the lateral side to the conjoined tendon of the extensor brevis
digitorum and an interosseus muscle, and on the medial side to the tendon
of the interosseus. The lateral side of the most lateral tendon is not thus
united, but is joined on the outer side by the tendon of the peroneus tertius.
Insertion.—The tendon thus formed on the dorsum of each phalanx by
the junction of the two or three tendons above mentioned is firmly attached
to the base of the second phalanx at its proximal end in the middle of its
dorsal surface. In crossing the joint between the first and second phalanges
the tendon forms a fibrous pad which protects the dorsum of the joint and
glides over it. It then continues to be inserted into the base of the terminal
phalanx.
Relations.—Outer surface with the tibialis anterior (n) and the superficial
fascia. Inner surface with a part of the tibialis anterior, with the bones, the
interosseous membrane, and the peroneus brevis (s).
Action.—Extensor of the phalanges.
M. tibialis anterior (Fig. 90, n).—This is the superficial muscle
covering the lateral side of the tibia.
Origin by fleshy fibres from the proximal one-sixth of the lateral surface
of the shaft of the tibia, from the proximal third of the medial border of the
shaft and head of the fibula, and from the intervening interosseous ligament.
The triangular body of the muscle covers the lateral surface of the tibia and
the outer surface of the extensor longus digitorum (p). Near the malleolus it
ends in a strong tendon which passes beneath the transverse ligament along
with the tendon of the extensor longus (p). The tendon crosses the dorsal
surface of the foot obliquely toward its medial side.
Insertion into the outer surface of the first metatarsal.
Relations.—Outer surface with the superficial fascia and the tendon of
the biceps femoris. Inner surface with the extensor longus (p), the tibia, and
the interosseous membrane.
Action.—Flexor of the foot.

4. Muscles of the Foot.

A. Muscles on the Dorsum of the Foot.—M. extensor brevis
digitorum (Fig. 90, u).—A broad thin muscle covering the tarsus and part
of the metatarsus on the lateral side of the dorsum of the foot. It may be
divided into three slips.
Origin from the distal border of nearly the whole calcaneal annular
ligament (5), and from the proximal end of the dorsal surface of the three
lateral metatarsals. At the middle of the metatarsals the muscle ends in three
flat tendons which pass into the three interspaces between the four tendons
of the extensor longus. Each tendon is divided into two branches.
Insertion.—The lateral branch of each tendon is inserted into the
cartilaginous plate which lies in the metatarsophalangeal articulation of the
digit on the outer side. The medial branch joins the lateral side of the
extensor longus tendon on the dorsum of the first phalanx.
Action.—Extensor of the digits.
B. Muscles of the Sole of the Foot.—M. flexor brevis digitorum
(pedis perforatus).—This is the direct continuation of the tendon of the
plantaris. It lies immediately beneath the superficial plantar fascia. The flat
belly of the muscle has its medial border attached by an oblique tendinous
band to the medial surface of the scaphoid and the medial cuneiform. It
divides into four slips which diverge to the four toes, each ending in a flat
tendon. The slips decrease in size from the lateral to the medial side. The
three lateral ones overlap one another proximally.
Insertion.—Each tendon expands at the distal end of the metatarsal and is
wrapped about the tendon of the deep flexor which perforates it. The two
halves unite beneath the perforating tendon and pass together with the
perforating tendon through fibrous rings, the annular ligaments. One of
these is attached to the sesamoids at the base of the phalanx. The other is
attached to the head of the first phalanx. The tendons are finally inserted
into the bases of the second phalanges.
The two annular ligaments are connected by fascia so as to form a
continuous canal for the tendons. This canal is lined by a synovial
membrane. Covering this canal is a more superficial layer of fascia. Before
passing into the proximal annular ligament the two middle tendons unite
each with the tendon of the corresponding lumbrical muscle. Each also
gives off a branch, the lateral one on its lateral side and the medial one on

its medial side. These branches, like those of the two middle ones, are
inserted into the common phalangeal fascia.
Action.—Flexor of the second phalanges of the digits.
M. quadratus plantæ (called also the plantar head of the flexor longus
digitorum) is a thin flat muscle which takes origin from the dorsal part of
the lateral surface of the calcaneus and the cuboid. Its fibres converge to a
flat tendon which passes transversely across the flexor longus digitorum
and beneath the flexor brevis digitorum and calcaneometatarsal.
Insertion.—Into the medial part of the outer surface of the tendon of the
flexor longus digitorum.
Action.—It holds the flexor longus tendon in place.
Mm. lumbricales.—These are six.
Origin.—The three larger ones have origin from the outer surface of the
expanded portion of the flexor longus digitorum on its distal half. Each ends
in a slender tendon.
Insertions.—The tendons unite with the divisions of the tendon of the
flexor brevis which pass to the three lateral digits, at their entrance to the
first annular ligament. The one to the fifth digit is sometimes absent.
The other three have origin from the tendon of the flexor longus
digitorum at the point where it divides. Each occupies one of the three
intervals between the four divisions, and its fibres originate from the
proximal ends of the two tendons which bound its interval.
Insertion by a very slender tendon into the medial side of the first
phalanges of the third, fourth, and fifth digits near their bases.
Action.—Move the third, fourth, and fifth digits toward the medial side.
Mm. interossei.—The interosseus of the second digit forms five
portions, which cover the ventral surface of the digit.
Origin.—(1) By two tendons from the ventral process of the lateral
cuneiform. The muscle divides into four parts, three of which pass to the
medial side of the digit and act as abductors. They are called the long, short,
and middle abductors (abductor longus, brevis, and intermedius digiti
secundi).
Insertions.—The short head into the medial sesamoid of the
metatarsophalangeal joint, the middle into the medial side of the base of the
first phalanx, and the long into the extensor communis tendon near the
distal end of the first phalanx. The names long, short, and middle refer to
the lengths of the tendons as determined by their points of insertion.

The fourth portion which comes from the lateral cuneiform has its
insertion into the lateral side of the extensor tendon near the distal end of
the first phalanx. It is therefore an adductor longus digiti secundi. In some
cases there is an adductor brevis from this same head.
(2) The fifth part of the interosseus of the second digit has origin from
the middle of the ligament covering the peroneal canal, along with the
middle adductor of the fifth digit. The two muscles diverge. Insertion into
the outer side of the base of the first phalanx of the second digit. It is an
adductor medius digiti secundi.
The interossei of the third and fourth digits are alike.
Origin from the ventral surface of the base of the metatarsal. The muscles
cover the ventral surface of the shaft. At the head each divides and passes
onto the sides of the metatarsal.
Insertion.—Each half of the muscle shows a tendency to divide into two
parts. One of these, the more superficial and ventral, ends in a tendon which
joins the extensor tendon near the distal end of the first phalanx. The other
part is inserted by short tendon- and muscle-fibres into the side of the base
of the first phalanx; one of the parts is therefore a middle, and the other a
long, adductor or abductor, the adductores and abductores digiti tertii and
quarti.
The fifth digit has five short muscles.
M. abductor medius digiti quinti.
Origin from the ventral surface of the calcaneus and from the fifth
metatarsal.
Insertion by a slender tendon into the lateral side of the base of the first
phalanx of the fifth digit.
M. adductor medius digiti quinti.
Origin with the adductor medius digiti secundi.
Insertion on the inner side of the base of the phalanx of the fifth digit.
M. opponens digiti quinti.
Origin by a flat tendon from the middle of the ligament which covers the
peroneal canal. It passes obliquely outward parallel to the last.
Insertion on the inner side of the shaft of the fifth metatarsal.
The two remaining muscles of the fifth digit take origin from the outer
part of the ligament covering the peroneal canal. They cover the ventral
surface of the shaft.

Insertion.—The lateral one is inserted into the lateral sesamoid and is
therefore an abductor brevis. The medial one is inserted into the extensor
tendon and is therefore an adductor longus.
C. Muscles of the Tarsus.—M. calcaneometatarsalis (part of M.
adductor minimi digiti?).—A weak muscle made up largely of tendon-
fibres, some of which pass directly from origin to insertion. It may be
regarded as a ligament.
Origin, the lateral and ventral surface of the calcaneus near the proximal
end. It passes distad and slightly laterad outside of the quadratus plantæ.
Insertion, the lateral side of the base of the fifth metatarsal, and the
adjacent surfaces of the cuboid and calcaneus.
Action.—Probably causes slight motion of the cuboid on the head of the
calcaneus.
M. scaphocuneiformis.—A small muscle lying on the sole of the foot in
the depression between the lateral cuneiform, medial cuneiform, and the
lateral tubercle of the scaphoid. It is hidden by the overlying ligaments.
Origin, the lateral tubercle of the scaphoid bone. It passes distad and
laterad.
Insertion, the lateral surface of the medial cuneiform.
Action.—Rotates the medial cuneiform on the scaphoid and would thus
act as an opponens of the great toe if the great toe were present.

THE VISCERA.

I. THE BODY CAVITY.

The greater part of the viscera are situated in the body cavity or cœlom.
This is divided by the diaphragm into two parts, the thoracic cavity and the
abdominal cavity. Each is lined by a serous membrane, in which the part
covering the outer wall of the cavity is distinguished as the parietal layer
from the part covering the viscera, which is known as the visceral layer.
The thoracic cavity is bounded by the thoracic vertebræ, the ribs, the
sternum, and the diaphragm. The cranial opening of the cavity is filled by
the trachea and œsophagus as they enter from the neck region. The thoracic
cavity is lined by two thin layers of tissue, the outer one of which is the
fascia endothoracica, while the inner is the pleura. The fascia
endothoracica is a sheet of connective tissue which lines the entire inner
surface of the thoracic cavity, descending from the dorsal median line to the
heart, and passing into the fibrous layer of the pericardium. The pleura is a
thin membrane covering the fascia endothoracica and corresponding to the
peritoneum of the abdominal cavity. It forms two sacs, the pleuræ, lining
respectively the right and left halves of the thoracic cavity. Each of these
two sacs is closed, the viscera being suspended within them by folds of the
membrane, so that the cavity is everywhere separated from the viscera by a
sheet of the pleura. That portion of the pleura which lines the thoracic wall
is known as the parietal layer; it may be divided into that covering the ribs
(costal pleura), and that covering the diaphragm. That portion which covers
the viscera is the visceral layer, or, since it covers chiefly the lungs, it may
be distinguished as the pulmonary pleura. The medial walls of the two
pleural sacs come in contact in the median plane, forming a median vertical
partition passing lengthwise of the thoracic cavity. This partition is known
as the mediastinal septum. The space between the two layers which make
up the mediastinal septum is known as the mediastinum, or mediastinal
cavity; it contains numerous organs of the thorax. Three parts are usually
distinguished in this cavity: a ventral mediastinal cavity, containing chiefly

blood-vessels and the thymus gland; a middle mediastinal cavity, enclosing
the heart and the anterior and posterior venæ cavæ; and a dorsal
mediastinal cavity, containing the trachea, the œsophagus, and the aorta.
The abdominal cavity lies caudad of the diaphragm; in it are sometimes
distinguished the abdominal cavity proper, extending as far caudad as the
cranial edge of the pubis, and the pelvic cavity, lying caudad of this, in the
region surrounded by the innominate bones and the sacrum. The two
cavities are not distinctly marked off, so that it is convenient to consider the
abdominal cavity as undivided. Both parts are lined by the peritoneum.
The peritoneum is a thin transparent sheet of connective tissue
supporting on its surface a layer of flattened epithelial cells, the peritoneal
epithelium. It forms a sac which lines the entire abdominal cavity. This sac
is closed in the male; in the female, however, it communicates with the
exterior through the uterine (or Fallopian) tubes and uteri. All the organs of
the abdominal cavity are outside the sac. In the course of their development
these organs have encroached on the peritoneal sac. Each has grown against
the outer wall of the sac to a greater or less extent and has forced a part of
this wall ahead of it into the cavity. In some cases the encroachment has
gone so far that the organ in question lies apparently within the peritoneal
cavity, suspended from the wall of the sac by a fold of that wall. The wall
may thus be divided into three portions. One of these, the parietal layer,
lines the wall of the body cavity. The second (the mesentery in case of the
alimentary canal, or a ligament in the case of another organ) suspends the
organ from the body wall. Between the layers of each mesentery or
ligament blood-vessels may pass to the organs. The third portion or visceral
layer covers the organ in question, forming its serous covering.
The reflections of the peritoneum to form the mesenteries and ligaments
may be thus described:
Caudally the peritoneum covers the whole surface of the bladder and is
reflected from its ventral wall to the linea alba as the suspensory ligament
of the bladder. Farther craniad the peritoneum suspends the rectum and
colon from the middorsal line, forming the mesorectum and mesocolon.
The mesocolon continues craniad to the level of the caudal end of the right
kidney and is broadest at its cranial end. At this end the mesocolon passes
into the mesentery proper, which suspends the small intestine and is very
broad and much folded. Its dorsal border is attached to the median line
opposite the caudal end of the kidneys and is very short compared to its

very long ventral or intestinal border. Toward the cranial end the mesentery
of the jejunum passes gradually into the very much shorter duodenal
mesentery. This is drawn out at the caudal end of the duodenum into a fold,
the duodenorenal ligament which attaches the duodenum to the kidney.
The mesogastrium or peritoneal fold for the stomach passes from that
part of the median dorsal line lying between the kidneys and the diaphragm,
to the greater curvature of the stomach. It does not pass directly to the
stomach, but passes first ventrad of the small intestine as far as the pelvis.
Thence it turns craniad to reach the greater curvature of the stomach. The
fold thus formed is called the great omentum. It forms the dorsal and
ventral walls of a sac, the omental sac, the cavity of which is called the
lesser peritoneal cavity. The descending limb of the fold forms the dorsal
wall of the sac, and its ascending limb forms the ventral wall. Each of these
walls is double like a mesentery, so that the great omentum consists of four
sheets of peritoneum. Between the two sheets forming the descending limb
lies the left half of the pancreas, which passes thence to the right into the
duodenal mesentery. A transverse fold passes from the descending limb of
the omentum along the cranial border of the pancreas to the duodenal
mesentery. Farther to the right the descending limb of the omentum, which
is here shorter, encloses the spleen and holds it in position parallel to the
greater curvature of the stomach and about one centimeter from it. This part
of the great omentum is sometimes called the gastrosplenic or gastrolienal
omentum.
The great omental sac communicates with the peritoneal sac by an
opening, the foramen epiploicum or foramen of Winslow. This opening
lies caudad and dextrad of the caudate lobe of the liver. This lobe itself lies
within the sac. Along the ventral border of the foramen epiploicum pass the
common bile-duct from the liver and the portal vein to the liver.
The size of the great omental sac is increased by the lesser omentum.
This is a double sheet of peritoneum which stretches horizontally from the
liver to the duodenum and the lesser curvature of the stomach. It covers
ventrad the caudate lobe of the liver. Its right border is at the foramen
epiploicum. The part of it which stretches to the duodenum is called the
duodenohepatic ligament and contains the bile-ducts and the portal vein.
The part that stretches to the stomach is called the gastrohepatic ligament.
The peritoneum covers the caudal and cranial surfaces of the liver and is
reflected to the adjacent parts to form the ligaments of the liver.

The suspensory ligament of the liver passes from the caudal surface of
the diaphragm and the median ventral line for about one or two centimeters
caudad of the diaphragm, to the liver, and extends between its two halves.
The ligamentum teres or round ligament is the thickened free caudal
border of the suspensory ligament. It is the remains of the fœtal umbilical
vein. From the dorsal border of the liver the peritoneum which covers its
cranial surface turns ventrad onto the caudal surface of the diaphragm,
while that which covers its caudal surface turns dorsad onto the caudal
surface of the diaphragm to reach the dorsal body wall. Between these two
sheets a small linear part of the surface of the liver is closely applied to the
diaphragm without intervening peritoneum. The two sheets which bound
this area constitute the coronary ligament of the liver. This ligament is
broader where it passes from the left lateral lobe to the diaphragm and is
called the triangular ligament. (There is perhaps a corresponding right
triangular ligament, from the cranial division of the right lateral lobe.) The
caudal division of the right lateral lobe is held to the kidney of that side by
the hepatorenal ligament.

II. THE ALIMENTARY CANAL. APPARATUS DIGESTORIUS.

The alimentary canal may be divided into mouth, pharynx, œsophagus,
stomach, small intestine, and large intestine. With these are associated
certain accessory structures,—the salivary glands, the liver, and the
pancreas. The spleen, though not belonging to the digestive system, is
usually described in connection with it. The respiratory organs are almost
throughout in close relation with the organs of the digestive system.
1. The Mouth. Cavum oris.—The mouth cavity extends from the lips to
the pharynx. It is narrower toward the lips, broadens caudad as far back as
the last teeth, then becomes narrowed to form the isthmus faucium, by
which it communicates with the pharynx. The mouth cavity is divisible into
the vestibule of the mouth (vestibulum oris), which comprises that part
outside the jaws proper, bounded externally by the lips and cheeks, and the
mouth cavity proper (cavum oris proprium), which lies within the teeth.
That portion of the vestibule which is bounded by the cheeks is sometimes
farther distinguished as the buccal cavity. The entire mouth cavity (except
the teeth) is lined by the mucous membrane or mucosa.

The lips (labia oris) are thick folds of skin bounding the entrance to the
mouth cavity. The outer surface is covered with hair; the inner surface is
covered with the mucous membrane. The upper lip is marked in the median
line by a deep external groove which extends upward to the septum of the
nose. Along the inner surface of this groove the lip is closely united to the
jaw by a thick fold, the frenulum of the upper lip. For some distance on
each side of the frenulum the inner surface of the lip bears numerous large
papillæ. The lower lip is also united to the jaw by a frenulum in the median
line; it is again united to the jaw just caudad of the canine tooth, in the
space between the latter and the first premolar. Caudad the two lips pass
into each other (forming the commissura labiorum), and unite with the
cheek. The muscles of the lips have been described (page 105).
The cheeks (buccæ) in the cat are comparatively thin and small,
extending from the lips caudad to the ramus of the mandible. The outer
surface is covered with hair; the inner surface is smooth and somewhat
folded. The buccal cavity is rather small. On the inner surface of the cheek
open the duct of the parotid (Steno’s duct), the ducts of the molar gland, and
that of the infraorbital gland.
The roof of the mouth cavity is formed by the hard and soft palates. The
hard palate (palatum durum) forms the cranial part of the roof; it is
supported by the palatal plates of the maxillary and palatine bones. The
mucosa of the hard palate is elevated to form seven or eight curved
transverse ridges, which are concave caudad. Between the ridges are rows
of papillæ. In front of the most cranial ridge is a papilla in the middle line,
and at each side of the papilla is the opening of a small duct (the incisive
duct or Stenson’s duct), which leads dorsad through the incisive foramen
to the vomeronasal organ (or organ of Jacobson), which lies on the floor
of the nasal cavity. Caudad of the hard palate the roof of the mouth is
formed by the soft palate or velum palatinum, described below.
The floor of the mouth cavity is formed chiefly by the tongue, which
extends as far caudad as the isthmus faucium. Ventrad of the free edge of
the tongue the mucosa forms a prominent median vertical fold which unites
the tongue with the floor of the mouth beneath it; this fold is the frenulum
linguæ. On each side of the median line at the cranial border of the floor of
the mouth is a prominent papilla, at the apex of which open the ducts of the
submaxillary and sublingual glands, the former on the lateral side of the
apex, the latter on the medial side.

The sides of the mouth cavity are formed by the teeth and the gums,
covering the alveolar borders of the mandible, maxillaries, and
premaxillaries.
The mouth cavity presents further for examination the glands, the teeth,
the tongue, and the soft palate.
The Glands of the Mouth (Glandulæ oris).—There are five pairs of
salivary glands which open into the mouth cavity.
1. The parotid gland (glandula parotis) (Fig. 65, 1; Fig. 131, 10) is
flattened, rather finely lobulated, and lies ventrad of the external auditory
meatus and beneath the dermal muscles. Its cranial border follows the
caudal border of the masseter muscle and overlies it somewhat; its caudal
border is about three centimeters caudad of the border of the masseter. Its
borders are unevenly lobed. The parotid duct (ductus parotideus:
frequently called Stenon’s or Steno’s duct) is formed by the union of
several smaller ducts near the ventral end of the cranial border of the gland.
It passes craniad imbedded in the fascia covering the masseter. At the
cranial border of the masseter it turns inward and lies close against the
mucous membrane of the mouth, so that from the inside of the mouth it
appears as a white ridge on the mucosa. It opens on the inside of the cheek
opposite the most prominent cusp of the last premolar tooth. Along the
course of the parotid duct in some cases one or more small accessory
parotid glands are found.
2. The submaxillary gland (glandula submaxillaris) (Fig. 65, 2, page
109, and Fig. 131, 11) is approximately kidney-shaped. Its surface is nearly
smooth, the lobulations not being apparent externally. It lies ventrad of the
parotid, at the caudal edge of the masseter muscle, just caudad of the
angular process of the mandible. The posterior facial vein (Fig. 131, b)
crosses its outer surface, and its cranioventral border is hidden by two
lymphatic glands (Fig. 131, 12) lying at the sides of the anterior facial vein.
The submaxillary duct (ductus submaxillaris, frequently called
Wharton’s duct) leaves the inner surface of the gland and passes beneath
the digastric and mylohyoid muscles and against the outer surface of the
styloglossus. From the point where the styloglossus passes into the tongue
the duct continues craniad close against the oral mucosa and parallel to the
mandibula. It is accompanied by the duct of the sublingual, which lies at
first dorsad of it and then mediad. It opens at the apex of the prominent

papilla which lies at the side of the middle line at the cranial end of the
floor of the mouth.
3. The sublingual gland is elongated and conical in form, with its base
against the submaxillary, of which it appears to be a continuation. It
stretches along the submaxillary duct for about one and one-half
centimeters, lying between the masseter and digastric muscles. The
sublingual duct leaves its ventral side, passes close to the submaxillary
duct, at first dorsad and then mediad of it, and opens on the medial side of
the apex of the same papilla with the submaxillary duct.
4. The molar gland (glandula molaris) (Fig. 65, 9) lies between the
orbicularis oris and the mucosa of the lower lip. It stretches from the cranial
border of the masseter to a point between the first premolar and the canine.
It is flat, broad caudad, and ends in a point craniad. It has several ducts
which pass straight through the cheek and open on the mucous surface of
the mouth.
5. The infraorbital (or orbital) gland lies in the lateral part of the orbit
on its ventral floor. It is ovoid and about one and one-half centimeters long
and one-third as thick. Its ventral end rests against the mucosa of the mouth
just caudad of the molar tooth. Its duct leaves the ventral end and opens into
the mouth at a point about three millimeters caudad of the molar tooth.
The Teeth. Dentes.—The adult cat has thirty teeth, fourteen in the lower
jaw and sixteen in the upper jaw. There are twelve incisors, four canines,
ten premolars, and four molars. The tooth formula for the cat is then
3—3 1—1 3—3 1—1
i , c , pm , m .
3—3 1—1 2—2 1—1
The teeth are implanted in the alveolar borders of the premaxillaries,
maxillaries, and mandible. In each tooth can be distinguished the root,
imbedded in the socket of the bone, the crown, which projects above the
gums, and a narrow neck connecting the two. The root is composed of one
or more separate fangs; the crown bears one or more points or cusps.
At the cranial end of each jaw are six incisor teeth (Figs. 93 and 94, a).
These are imbedded in the alveolar borders of the premaxillaries and the
mandible. The incisor teeth are small, with a crown bearing a sharp edge
which is notched so as to form three minute cusps. The root of each has a
single fang. The lateral incisors are the largest in each jaw, and those of the
upper jaw are larger than those of the lower.

Fig. 93.—Upper Jaw, with Roots of the Teeth Laid Bare.

a, incisors; b, canine; c, first premolar; d, second premolar; e, third
premolar; f, molar.

Caudad of the incisors, and in the upper jaw separated from them by a
slight interval, are the canines (b), two in each jaw. These are long, strong,
pointed teeth, deeply imbedded in the mandible and maxillaries, their large
sockets causing a rounded swelling on the external surface of the bones.
Each has a single fang and a single cusp. When the mouth is closed the
upper canines lie laterocaudad of the lower ones.
Caudad of the canines there is in each jaw a considerable interval free
from teeth: this is called the diastema. Caudad of the diastema are the
premolar teeth, three pairs (c, d, e) in the upper jaw and two pairs (c, d) in
the lower jaw. These teeth are compressed sideways, and those of the lower
jaw fit inside of those of the upper jaw. In the upper jaw (Fig. 93) the first
premolar (c) is small and usually has but a single cusp and a single fang,
though occasionally there is a small supplementary cusp and fang. The
second premolar is larger (d); it has a large central cusp, with a single
smaller cranial cusp and two small caudal cusps, making four in all. This
tooth has two fangs. The third premolar (e) is the largest tooth in the jaws; it
has three large cusps in longitudinal series and a small cusp lying on the
medial side of the first one in the row. Its root has three fangs. The molar

tooth (f) of the upper jaw is small and lies caudomediad of the last premolar.
It has two small cusps and two fangs.

Fig. 94.—Mandible, with Roots of the Teeth Laid Bare.

a, incisors; b, canine; c, first premolar; d, second premolar; f, molar.

In the lower jaw (Fig. 94) the two premolars (c and d) are similar, the
caudal one being a little larger. Each has four cusps; a single large one, a
small one craniad of this, and two small ones caudad of it. Each has two
fangs. The single molar (f) is the largest tooth of the lower jaw; it has two
large cusps and two fangs.
The Deciduous Teeth.—At birth the cat has no teeth. There appears later
a set of twenty-six teeth: twelve incisors, four canines, and ten molars (six
in the upper jaw and four in the lower). These teeth are later replaced by the
permanent ones above described. The deciduous teeth of the cat are fully
described by Jayne (“Mammalian Anatomy,” vol. 1. p. 319), where also an
account is given of the order of appearance of the teeth.
The Tongue. Lingua (Fig. 95).—The tongue is a muscular organ covered
with mucous membrane; in life it is very mobile. It is an elongated organ,
flat above, broadest in the middle, and very slightly narrowed at each end. It
extends from the incisor teeth to the isthmus faucium and nearly fills the
mouth cavity. The caudal third of the tongue forms the floor of the mouth
cavity, so that the tongue has here no ventral surface, but is directly
continuous with underlying organs. It is in this region that the extrinsic
muscles of the tongue (except the genioglossus) enter it. The cranial two-
thirds of the tongue is partly or entirely free from the floor of the mouth, the
cranial one-third being completely free and movable. In about the middle

third the ventral surface of the tongue is held to the floor of the mouth by
the fold known as the frenulum linguæ. The frenulum contains parts of the
two genioglossus muscles, which enter the tongue through it. The ventral
surface and lateral borders of the tongue are smooth, soft, and free from
papillæ. The dorsal surface is raised into papillæ of various kinds, and has a
slight median longitudinal furrow. The caudal part of the dorsal surface is
softer, redder, and marked with papillæ of a different kind from those of the
rest of the tongue. From the caudal end a small median vertical fold, the
frenulum (or plica) glossoepiglottica passes from the dorsal surface of the
tongue to the cranial surface of the epiglottis.

Fig. 95.—Tongue, Epiglottis, and Opening of Larynx.
a, filiform papillæ; b, fungiform papillæ; b′, very large papillæ
at the sides of the tongue; c, circumvallate papillæ; d, tonsils; e,
epiglottis; f, plica aryepiglottica; g, arytenoid cartilages (covered
with mucosa); h, glottis; i, false vocal cords; j, true vocal cords.

The papillæ of the tongue are of three kinds. 1. The very numerous
filiform papillæ (a) (papillæ filiformes); many of them are horny and
tooth-like, with points turned caudad. These are most numerous at the
middle of the free end of the tongue. 2. The fungiform papillæ (b)
(papillæ fungiformes) are found scattered over the surface of the middle of
the tongue caudad of the large filiform papillæ. They are enlarged at their
free ends. There is a prominent row of very large ones (b′) opposite the
circumvallate papillæ at the borders of the tongue. 3. The circumvallate
papillæ (c) (papillæ vallatæ) are blunt and each is surrounded by a trench
which is bounded in turn by a raised wall. They are in two rows of two or
three each, which converge near the base of the tongue so as to form a V
with the apex directed caudad.
Muscles of the Tongue (Fig. 96).—M. genioglossus (f) passes from the
symphysis of the lower jaw into the tongue and lies beneath (dorsad of) the
geniohyoid (g).
Origin from the medial surface of the mandible near the symphysis and
dorsad of the origin of the geniohyoid.
Insertion.—The fibres pass dorsad, diverging in a fan-like manner and
forming a flat vertical plate closely applied to the muscle of the opposite
side. This plate extends along the caudal three-fourths of the tongue, i.e. as
far as it is attached. The cranial fibres arch craniad to the tip of the tongue,
the caudal fibres arch caudad to the root of the tongue. Dorsad the muscle is
confounded with the muscle of the opposite side.
Action.—Draws the root of the tongue forward and the tip backward.
M. hyoglossus (h).—From the body of the hyoid bone to the tongue.
Origin.—(1) From the ventral surface of the body of the hyoid laterad of
the geniohyoid (g), and (2) by a second head from the ceratohyal.
Insertion.—Both heads penetrate into the tongue between the
styloglossus (e) and the genioglossus (f). The fibres intermingle with those
of the styloglossus (e) and thus help to form the lateral parts of the tongue.
They finally end in the integument on the dorsum of the tongue at the sides.

Action.—Retracts the tongue and depresses it.
M. styloglossus (e).—From the stylohyal bone to the tongue.
Origin from the mastoid process of the temporal bone, from the
stylomandibular ligament (2) (which connects the border of the external
auditory meatus with the angular process of the mandible) and from the
proximal cartilaginous portion of the cranial cornu of the hyoid bone. The
fibres pass mediad, diverging between those of the digastric and hyoglossus
(h) into the lateral part of the tongue.
Insertion.—The fibres pass toward the tip of the tongue, where the mass
finally ends in a point, the superficial ones gaining insertion into the
integument at the sides of the tongue.
Relations.—Outer surface with the digastric (Fig. 65, b) and mylohyoid
(Fig. 65, c). Inner surface with the pterygoideus internus (Fig. 96, d), the
cranial cornu of the hyoid, and the tympanic bulla.
Action.—Retracts the tongue and raises it.

Fig. 96.—Muscles of Tongue, Hyoid Bone, and Pharynx.

a, M. tragicus lateralis; b, M. jugulohyoideus; c, M. pterygoideus externus; d, partially
cut surface of M. pterygoideus internus; e, M. styloglossus; f, M. genioglossus; g, M.
geniohyoideus; h, M. hyoglossus; i, M. glossopharyngeus; j, M. constrictor pharyngis
medius; k, M. constrictor pharyngis inferior; l, M. stylopharyngeus; m, M. sternohyoideus
(cut); n, M. cricothyreoideus; o, M. sternothyreoideus (cut); p, M. thyreohyoideus. 1,
mandible; 1′, angular process of mandible; 2, stylomandibular ligament; 3, bulla tympani;
4, trachea; 5, œsophagus; 6, thyroid gland; 7, isthmus of the thyroid gland.

The intrinsic muscles of the tongue (those entirely within it) are attached
to its integument at both their ends. There are three sets of fibres: a
longitudinal, a transverse, and a vertical one. These are seen most readily in
cross-sections.
The Soft Palate. Velum Palatinum (Fig. 66, page 112).—The soft palate
is the free curtain-like structure which forms the caudal part of the roof of
the mouth. It is attached to the caudal border of the palatal plates and the
ventral border of the perpendicular plates, of the palatine, and to the
pterygoid processes and hamuli of the sphenoid, and extends some distance
caudad of the hamuli. It thus forms a rather long and narrow curtain
separating the caudal part of the nasal cavity from the mouth. Caudad it
ends in a free arched border (Fig. 66, 4) which is at about the level of the
epiglottis, and may lie against the cranial or the caudal surface of the latter.
The narrowed passage bounded by the margin of the velum palatinum
dorsad and the tongue ventrad is the isthmus faucium. From the sides of
the velum a short distance from the caudal border a fold of mucosa passes
ventrad to the side of the tongue; a short distance caudad of this a similar
fold passes to the floor of the pharynx. These folds form the cranial and
caudal pillars of the fauces. Between these folds is a shallow pocket, from
the bottom of which there arises a prominent projection or swelling which
is one of the two tonsils (Fig. 95, d). Each tonsil is a reddish, lobulated
gland, lymphoid in the adult, nearly a centimeter in length, and about one-
third as long as broad, with its long axis craniocaudad.
The velum palatinum consists of two layers of mucous membrane, oral
and nasal, with intervening muscular and connective tissue. The muscles of
the soft palate in the cat are as follows:
M. tensor veli palatini (Fig. 66, d, d′, page 112).
Origin from the ventral surface of the body of the sphenoid between the
foramen ovale and the groove for the Eustachian tube. The muscle ends in a
flat tendon which passes over the hamular process (3) of the pterygoid bone.

Insertion by spreading out in the soft palate into an aponeurosis which
joins the aponeurosis of the opposite muscle and lies between the mucous
membrane of the mouth and that of the nose.
Action.—Stretches the palate.
M. levator veli palatini (Fig. 66, e, e′).—A flat triangular muscle which
lies within the tensor.
Origin from the surface of the body of the sphenoid mediad of the groove
for the Eustachian tube, from the styliform process of the bulla tympani,
and in part from the Eustachian tube. The muscle passes caudad, and its
fibres then diverge into the velum palatinum.
Insertion into the velum palatinum, some of the fibres meeting in the
middle line.
Action indicated by the name.
A number of other muscles have been described in the soft palate of the
cat; they are, however, poorly developed and not easily distinguished. For
an account of these, see Stowell, Proceedings of the Am. Soc. of
Microscopists, 1889.
2. The Pharynx.—At the caudal end of the mouth cavity the passage for
the food and that for the air cross; at the cranial end the food-passage
(mouth) is ventral, the respiratory passage (nasal cavity) dorsal. Farther
caudad the food-passage (œsophagus) is dorsal, while the respiratory
passage (larynx and trachea) is ventral. In the region of crossing there is
therefore for a certain distance a common passageway for food and air, and
this is known as the pharynx. It extends from the isthmus faucium, at the
free caudal margin of the soft palate, to the beginning of the œsophagus, at
the dorsal or caudal margin of the opening of the larynx. The dorsal wall of
the pharynx is separated from the base of the skull and the centra of the
cervical vertebræ only by intervening muscles (longus capitis, levator
scapulæ ventralis, and longus colli, Fig. 72, page 143). Its lateral and
ventral walls are supported by the hyoid bone and the cartilages of the
larynx.
Craniad the pharynx continues, usually, without break into the cavity
lying dorsad of the soft palate. But at the time of swallowing the free edge
of the soft palate is pushed dorsad against the dorsal wall of the pharynx,
while the caudal part of the pharynx is drawn craniad, so as to form a cavity
continuous with that of the mouth. In this way the cavity above the soft
palate is completely separated at the time of swallowing from the rest of the