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Full text of "The anatomy of the domestic animals"

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THE ANATOMY 



OF THE 



DOMESTIC ANIMALS 



SEPTIMUS SISSON, S.B., V.S. 

PROFESSOR OF COMPARATIVE ANATOMY IN THE OHIO STATE UNIVERSITY, COLUMBUS, OHIO 

MEMBER OF THE AMERICAN ASSOCIATION OF ANATOMISTS 

FELLOW OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE 



WITH 725 ILLUSTRATIONS 
MANY IN COLORS 



SECOND EDITION, ENTIRELY RESET 



PHILADELPHIA AND LONDON 

W. B. SAUNDERS COMPANY 



Copyright, 1910, by W. B. Saunders Company 



Reprinted June, 1911 



Revised, Entirely Reset, Reprinted 

AND ReCOPYRIGHTED SEPTEMBER, 1914 



Copyright. 1914, by W. B. Saunders Company 



Reprinted September, 1917 



Reprinted March, 1921 



Reprinted October, 1927 



Reprinted September, 1930 



PRESS OF 

W. B. SAUNDERS COMPANY 

PHILADELPHIA 



TO 
MY WIFE 

KATHERINE OLDHAM SISSON 

IN GRATEFUL RECOGNITION OF CONSTANT INSPIRATION 
AND ENCOURAGEMENT 



PREFACE 

This book supersedes the author's Text-book of Veterinary Anatomy. A 
comparison of the two will show the new title to be justified by the extent and 
character of the changes which have been made. 

The number of illustrations has been increased from 588 to 725. More than 
three hundred new and original figures have been prepared. Nearly all of these 
are reproductions of photographs, most of which were taken by the author. The 
preparation of the prints for reproduction has been executed by Mr. W. J. Norris 
with unusual care and skill. 

Continued observations of well-hardened material and frozen sections have led 
to a considerable number of modifications of statement. It is scarcely necessary 
to say that the recent literature, so far as available, has been utilized. 

Many changes in nomenclature have been made. Most of the synonyms have 
been dropped or relegated to foot-notes. Exceedingly few new names have been 
introduced. Nearly all eponyms have been eliminated, on the ground that they 
are not designative and are usually incorrect historically. The changes made in 
this respect are in conformity with the report of the Committee on Revision of 
Anatomical Nomenclature which was adopted by the American Veterinary Med- 
ical Association two years ago. Progress in the direction of a simplified and uni- 
form nomenclature is much impeded by the archaic terminology which persists to 
a large extent in clinical literature and instruction. 

The author is under special obligation to Professors EUenberger, Baum, and 
Schmaltz, and to their publishers, for permission to use or to copy figures from 
their excellent works. Their generosity in this matter has been of great value to 
those who are unable to use the German literature. A few illustrations have been 
taken from other sources and credit has been given in each case. 

For helpful suggestions and for assistance in the reading of the proof-sheets 
the author is much indebted to his colleague, Dr. F. A. Lambert. 

Great credit is due the publishers for their determination to spare neither 
pains nor expense in attaining a high degree of typographical excellence. 

Septimus Sisson 
The Ohio State University, Columbus, Ohio. 



PREFACE TO THE FIRST EDITION 

The lack of a modern and well-illustrated book on the structure of the princi- 
pal domestic animals has been acutely felt for a long time by teachers, students, 
and practitioners of veterinary medicine. The work here offered is the expression 
of a desire to close this gap in our literature. 

The study of frozen sections and of material which has been hardened by intra- 
vascular injection of formalin has profoundly modified our views concerning the 
natural shape of many of the viscera and has rendered possible much greater pre- 
cision in topographic statements. The experience of the author during the last 
ten years, in which almost all of the material used for dissection and for frozen 
sections in the anatomical laboratory of this University has been hardened with 
formalin, has demonstrated that many of the current descriptions of the organs in 
animals contain the same sort of errors as those which prevailed in regard to similar 
structures in man previous to the adoption of modern methods of preparation. 

While the method of treatment of the subject is essentially systematic, topog- 
raphy is not by any means neglected either in text or illustrations; it is hoped that 
this will render the book of value to the student in his chnical courses and to 
the practitioner. Embryological and histological data have been almost entirely 
excluded, since it was desired to offer a text-book of convenient size for the student 
and a work of ready reference for the practitioner. It is believed that the use of 
black type for the names of important structures and of small print for certain 
details or matter of secondary importance will prove useful in this respect. 

Veterinary anatomical nomenclature is at present quite chaotic in EngUsh- 
speaking countries. In this work an attempt is made to eliminate some terms 
which do not appear to the author to fulfil any useful purpose, and others which are 
clearly erroneous or otherwise undesirable. In many cases the terms agreed upon 
by the Congresses at Baden and Stuttgart are adopted either in the original Latin 
or in anglicized form; otherwise these terms are added in parenthesis. The 
author favors the substantial adoption of this terminology, but considered it 
desirable to offer a sort of transitional stage at present. 

The original illustrations are chiefly reproductions of photographs, many of 
which were taken by Mr. F. H. Haskett. The preparation of the pictures for 
reproduction was carried out by Messrs. J. V. Alteneder and W. J. Norris. The 
author takes pleasure in expressing his appreciation of the care and skill exercised 
by these gentlemen in this often difficult task. 

The author is under great obligation to Professors Ellenberger and Baum in 
Dresden, to Professor Schmaltz in Berlin, and to their pubUshers for permission to 
use or to copy figures from their most excellent works. Their generosity in this 
matter has made it possible to supply this text with a larger number of high-class 
illustrations than is to be found in any other. A few figures have been taken from 
other sources, and proper credit has been given in each case. 

For checking over certain data and for assistance in the correction of the proofs 
the author is much indebted to his associate, Dr. F. B. Hadley. 

The author desires to express his high appreciation of the determination and 
constant effort of the publishers to do all in their power to render the book worthy 
of favorable reception by the profession for whom it is intended. 

Ohio State University, Columbus, Ohio Septimus Sisson. 



CONTENTS 



INTRODUCTION 

OSTEOLOGY p^ob 

The Skeleton 20 

Structure of Bones 21 

Development and Growth of Bone 23 

Composition and Physical Properties of Bone 24 

Descriptive Terms 25 

The Vertebral Column 25 

The Ribs and Costal Cartilages 27 

Costal Cartilages 27 

The Sterjium 28 

The Thorax 28 

The Skull 28 

Bones of the Thoracic Limb 29 

Bones of the Pelvic Limb 30 

Skeleton of the Horse 32 

Vertebral Column 33 

Ribs 45 

Sternum 48 

Bones of the Skull 49 

Cranium 49 

Face 63 

The Skull as a Whole 73 

The Cranial Cavity 81 

The Nasal Cavity 82 

The Paranasal Sinuses 84 

Bones of the Thoracic Limb 86 

Bones of the Pelvic Limb 105 

Skeleton of the Ox 125 

Vertebral Column 125 

Ribs 130 

Sternum 131 

Bones of the Skull 131 

The Skull as a Whole 140 

Bones of the Thoracic Limb 145 

Bones of the Pelvic Limb 151 

Skeleton of the Sheep 156 

Vertebral Column 156 

Ribs 156 

Sternum 157 

Skull 157 

Bones of the Thoracic Limb 160 

Bones of the Pelvic Limb 160 

Skeleton of the Pig 161 

Vertebral Column 161 

Ribs 165 

Sternum 166 

Bones of the Skull 166 

The Skull as a Whole 173 

11 



12 CONTENTS 

PAGE 

Bones of the Thoracic Limb 176 

Bones of the Pelvic Limb 180 

Skeleton of the Dog 184 

Vertebral Column 184 

Ribs 188 

Sternum 188 

Bones of the Skull 188 

The Skull as a Whole 195 

Bones of the Thoracic Limb 197 

Bones of the Pelvic Limb 202 

ARTHROLOGY 
Synarthroses 207 

DiARTHROSES 208 

Amphiarthroses 210 

Articulations of the Horse 211 

Joints and Ligaments of the Vertebrae 211 

Atlanto-occipital Articulation 214 

Costo-vertebral Articulations 215 

Costo-chondral Articulations 216 

Chondro-sternal Ailiculations 216 

Sternal Joints and Ligaments 217 

Articulations of the Skull 217 

Articulations of the Thoracic Limb 218 

Articulations of the Pelvic Limb 229 

Articulations of the Ox, Pig, and Dog 244 

MYOLOGY 

The Muscles and Accessory Structures 252 

Fascl« and Muscles of the Horse 254 

Fasciae and Muscles of the Head 255 

Fascia? and Muscles of the Neck 266 

Fascite and Muscles of the Back and Loins 276 

Fasciae and Muscles of the Tail 279 

Muscles of the Thorax 281 

Abdominal Fasciae and Muscles 287 

Muscles of the Thoracic Limb 293 

Fasciae and Muscles of the Pelvic Limb 317 

Muscles of the Ox 343 

Muscles of the Pig 359 

Muscles of the Dog 368 

SPLANCHNOLOGY 

Digestive System of the Horse 385 

The Mouth 385 

The Tongue 390 

The Teeth 394 

The SaHvary Glands 404 

The Pharynx 405 

The CEsophagus 409 

The Abdominal Cavity 410 

The Peritoneum 411 

The Pelvic Cavity 412 

The Stomach 415 

The Small Intestine 419 

The Large Intestine 422 

The Pancreas 432 

The Liver 434 



CONTENTS 13 

PAGE 

The Spleen 439 

The Peritoneum 441 

Digestive System of the Ox 444 

Digestive System of the Sheep 470 

Digestive System of the Pig 477 

Digestive System of the Dog 491 

THE RESPIRATORY SYSTEM 

Respiratory System of the Horse 508 

The Nasal Cavity 508 

The Larynx 514 

The Trachea 523 

The Bronchi 525 

The Thoracic Cavity 525 

The Pleuraj 526 

The Lungs 530 

The Thyroid Gland of the IIorse 535 

The Thymus of the Horse 536 

Respiratory System of the Ox 537 

Respiratory System of the Pig 545 

Respiratory System of the Dog 548 

THE UROGENITAL SYSTEM 

Urinary Organs of the Horse 554 

The Kidneys 554 

The Ureters 561 

The Urinary Bladder 561 

The Adrenal Bodies 563 

LTrinary Organs of the Ox 564 

Urinary Organs of the Pig 567 

Urinary Organs of the Dog 569 

THE MALE GENITAL ORGANS 

Genital Organs of the Stallion 571 

The Testicles 571 

The Scrotum 574 

The Ductus Deferens 575 

The Spermatic Cord 575 

The Tunica VaginaUs 576 

Descent of the Testicles 577 

The Vesiculse Seminales 578 

The Prostate 578 

The Uterus MascuUnus 579 

The Bulbo-urethral Glands 579 

The Penis 580 

The Prepuce 582 

Genital Organs of the Bull 586 

Genital Organs of the Boar 591 

Genital Organs of the Dog 593 

THE FEMALE GENITAL ORGANS 

Genital Organs of the Mare 596 

The Ovaries 596 

The Uterine or Fallopian Tubes 599 

The Uterus 599 

The Vagina 602 



14 CONTENTS 

PAGB 

The Vulva 603 

The Urethra 604 

The Mammary Glands 604 

Genital Organs of the Cow 605 

Genital Organs of the Ewe 609 

Genital Organs of the Sow 610 

Genital Organs of the Bitch 612 

ANGIOLOGY 

General Considerations 614 

The Organs of Circulation 614 

Blood-vasct'lar System of the Horse 617 

The Pericardium 617 

The Heart 617 

The Pulmonary Artery 629 

The Systemic Ai-teries 629 

The Coronary Arteries 630 

Common Brachiocephalic Trunk 631 

Arteries of the Thoracic Limb 650 

Branches of the Thoracic Aorta 660 

Branches of the Abdominal Aorta 661 

Arteries of the Pelvic Limb 673 

The Veins 681 

The Pulmonary Veins 681 

Cardiac Veins 681 

The Anterior Vena Cava and its Tributaries 682 

The Posterior Vena Cava and its Tributaries 692 

The Lymphatic System 697 

The Thoracic Duct 697 

The Right Lymphatic Duct 698 

The Lymph Glands and Vessels of the Head and Neck 698 

The Lymph Glands and Vessels of the Thorax 700 

The Lymph Glands and Vessels of the Abdomen and Pelvis 701 

The Lymph Glands and Vessels of the Thoracic Limb 703 

The Lymph Glands and Vessels of the Pelvic Limb 703 

The P'cetal Circulation 704 

Blood-vascular System op the Ox 705 

The Pericardium and Heart 705 

The Arteries 706 

The Veins 719 

Lymphatic System of the Ox and Sheep 722 

Circulatory System of the Pig 734 

The Pericardium and Heart 734 

The Arteries 736 

The Veins 740 

Lymphatic System 740 

Circulatory System of the Dog 742 

The Pericardium and Heart 742 

The Arteries 744 

The Veins 754 

Lymphatic System 756 

NEUROLOGY.— THE NERVOUS SYSTEM 

General Considerations 760 

Nervous System of the Horse 764 

The Spinal Cord 764 

The Brain 768 



CONTENTS 15 

PAGE 

The Cranial Nerves 793 

The Spinal Nerves 810 

Sympathetic Nervous System of the Horse 829 

Nervous System of the Ox 834 

Nervous System of the Pig 843 

Nervous System of the Dog 847 

^STHESIOLOGY 

The Sense Organs and Common Integument of the Horse 857 

The Eye 857 

The Ear 870 

The Common Integument 884 

The Ergot and Chestnut 895 

The OKactory and Gustatory Apparatus 895 

The Sense Organs and Common Integument of the Ox 896 

The Sense Organs and Common Integument of the Pig 900 

The Sense Organs and Common Integument of the Dog 902 



Index 907 



THE ANATOMY OF THE DOMESTIC ANIMALS 



INTRODUCTION 

Anatomy is the branch of biological science which deals with the form and 
structure of organisms, both animal and vegetal. It is therefore in close correlation 
with physiology, which treats of the functions of the body. 

Etymologically the word "anatomy" signifies the cutting apart or disassociat- 
ing of parts of the body. In the earlier phases of its development anatomy was 
necessarily a purely descriptive science, based on such observations as were possible 
with the unaided eye and simple dissecting instruments — the scalpel, forceps, and 
the like. At this time, therefore, the term adequately expressed the nature of the 
subject. But as the scope of the science extended and the body of anatomical 
knowledge grew, subdivisions became necessary and new terms were introduced to 
designate special fields and methods of work. With the introduction of the mi- 
croscope and its accessories it became possible to study the finer details of structure 
and minute organisms hitherto unknown, and this field of inquiry rapidly developed 
into the science of microscopic anatomy or histology as conventionally distinguished 
from macroscopic or gross anatomy. In the same way the study of the changes 
which organisms undergo during their development soon attained sufficient im- 
portance to be regarded on practical grounds as a separate branch known as 
embryology.^ 

Comparative anatomy is the description and comparison of the structure of 
animals, and forms the basis for their classification. By this means — including 
extinct forms in the scope of inquiry — it has been possible to show the genetic 
relationship of various groups of animals and to elucidate the significance of many 
facts of structure which are otherwise quite obscure. The deductions concerning 
the general laws of form and structure derived from comparative anatomical 
studies constitute the science of morphology or philosophical anatomy. The 
morphologist, however, deals only with such anatomical data as are necessary to 
form a basis for his generalizations. The anatomical knowledge required in the 
practice of medicine and surgery is evidently of a different character and must 
include many details which are of no particular interest to the morphologist. 

Special anatomy is the description of the structure of a single type or species, 
e. g., anthropotomy, hippotomy. 

Veterinary anatomy is the branch which deals with the form and structure of 
the principal domesticated animals. It is usually pursued with regard to pro- 
fessional requirements, and is therefore largely descriptive in character. As a 
matter of convenience, the horse is generally selected as the type to be studied in 
detail and to form a basis for comparison of the more essential differential characters 
in the other animals. 

Two chief methods of study are employed — the systematic and the topo- 
graphic. In the former the body is regarded as consisting of systems of organs or 

1 Tliis term is usually limited in its application to the earlier phases of development during 
which the tissues and organs are formed. The term ontogeny is used to designate the entire 
development of the individual. The ancestral history or phylogeny of the species is constituted 
by the evolutionary changes which it has undergone as disclosed by the geological record. 
2 17 



X8 INTRODUCTION 

apparatus which are similar in origin and structure and are associated in the per- 
formance of certain functions. The divisions of systematic anatomy are : 

1. Osteology, the description of the Skeleton. 

2. Arthrology, the description of the Joints. 

3. Myology, the description of the Muscles and accessory structures. 

4. Splanchnology, the description of the Viscera. This includes the following 
subdivisions : 

(1) Digestive System 

(2) Respiratory System 

(3) Urogenital System 

(a) Urinary Organs 
(h) Genital Organs 

5. Angiology, the description of the Organs of Circulation 

6. Neurology, the description of the Nervous System 

7. ^sthesiology, the description of the Sense Organs and Common Integu- 

ment 

The term topographic anatomy designates the methods by which the relative 
positions of the various parts of the body are accurately determined. It presup- 
poses a fair working knowledge of systematic anatomy. 

Descriptive Terms. — In order to indicate precisely the position and direction 
of parts of the body, certain descriptive terms are employed, and must be under- 
stood at the outset. In the explanation of these terms it is assumed here that 
they apply to a quadruped such as the horse in the ordinary standing position. 
The surface directed toward the plane of support (the ground) is termed ventral 
(or inferior), and the opposite surface is dorsal (or superior) ; the relations of parts in 
this direction are named accordingly. The longitudinal median plane divides the 
body into similar halves. A structure or surface which is nearer than another to the 
meclian plane is medial (or internal) to it, and an object or surface which is further 
than another from the median plane is lateral (or external) to it. Planes parallel 
to the median plane are sagittal. Transverse or segmental planes cut the long axis 
of the body perpendicular to the median plane, or an organ or limb at right angles 
to its long axis. A frontal plane is perpendicular to the median and transverse 
planes. The term is also used with reference to parts of the limbs or various organs 
in a similar sense. The head end of the body is termed anterior or cranial; and the 
tail end posterior or caudal ; relations of structures with regard to the longitudinal 
axis of the body are designated accordingly. With respect to parts of the head, 
the corresponding terms are oral and aboral. Certain terms are used in a special 
sense as applied to the limbs. Proximal and distal express relative distances of 
parts from the long axis of the body. The anterior face of the thoracic limb from 
the elbow downward is termed dorsal, and the opposite face volar. In the corre- 
sponding part of the pelvic limb the terms are dorsal and plantar respectively. In 
the same regions radial and ulnar (thoracic limb), tibial and fibular (pelvic limb), 
may be used to designate that side of the extremity on which the corresponding 
bone is situated; they are therefore equivalent respectively to medial and lateral 
in the animals with which we are concerned. The terras superficial (superficialis) 
and deep (profundus) are useful to indicate relative distances of i);irts from the 
surface of the body. 

It is evidently advantageous to employ terms which are as far as possible independent of 
the position of the body in space and capable of general application, e. g., dorsal, ventral, proximal, 
etc. It is also desirable that the terms internal and external be reserved to indicate relations of 
depth in cavities or organs, and medial and lateral to designate relations to the median plane. 
Such terms are coming into more extensive use in human and veterinary anatomy, but the older 
nomenclature is very firmly established and cannot well be discarded at once and entirely. To 
facilitate the transition, a table of the older and more recent terms is given below; the recent 
terms are in the first column and the older equivalents in the second. 



INTRODUCTION 

A. Relating to Head, Neck, and Trunk: 

Dorsalis Superior 

Ventralis Inferior 

MediaUs I?tf™^\ 

LateraUs External 

Cranialis 1 Anterior 

Oralis / 

Caudalis 1 Posterior 

Aboralis J 

B. Relating to Limbs: 

Proximalis Superior 

Distalis Mf"?^ 

DorsaUs Anterior 

Volaris \ , . Posterior 

Plantaris f 

Radialis ] Internal 

Tibialis f 

Ulnaris \ External 

Fibularis f 



19 



OSTEOLOGY 

THE SKELETON 
The term skeleton is applied to the framework of hard structures which sup- 
ports and protects the soft tissues of animals. In the descriptive anatomy of the 
higher animals it is usually restricted to the bones and cartilages, although the 
ligaments Avhich bind these together might well be included. 

In zoology the term is used in a much more comprehensive sense, and includes all the harder 
supporting and protecting structures. When the latter are situated externally, they form an 
exoskeleton, derived from the ectoderm. Examples of this are the shells and cliitinous coverings 
of many invertebrates, the scales of fishes, the shields of turtles, and the feathers, hair, and hoofs 
of the higher vertebrates. The endoskeleton (with which we have to deal at present) is embedded 
in the soft tissues. It is derived from the mesoderm, but includes the notochord or primitive 
axial skeleton, which is of entodermal origin. 

The skeleton may be divided primarily into three parts: (1) axial; (2) appen- 
dicular; (3) splanchnic. 

The axial skeleton comprises the vertebral column, ribs, sternum, and skull. 

The appendicular skeleton includes the bones of the limbs. 

The splanchnic or visceral skeleton consists of certain bones developed in the 
substance of some of the viscera or soft organs, e. g., the os penis of the dog and the 
OS cordis of the ox. 

The number of the bones of the skeleton of an animal varies with age, owing 
to the fusion during growth of skeletal elements which are separate in the fostus 
or the young subject. Even in adults of the same species numerical variations 
occur, e. g., the tarsus of the horse may consist of six or seven bones, and the carpus 
of seven or eight; in all the domestic mammals the number of coccygeal vertebrae 
varies considerably. 

The bones are commonly divided into four classes according to their shape 
and function.^ 

(1) Long bones (Ossa longa) are typically of elongated cylindrical form with 
enlarged extremities. They occur in the limbs, where they act as supporting 
columns and as levers. The cylindrical part, termed the shaft or body (Corpus), 
is tubular, and incloses the medullary cavity, which contains the medulla or marrow. 

(2) Flat bones (Ossa plana) are expanded in two directions. They furnish 
sufficient area for the attachment of muscles and afford protection to the organs 
which they cover. 

(3) Short bones (Ossa brevia), such as those of the carpus and tarsus, present 
somewhat similar dimensions in length, breadth, and thickness. Their chief func- 
tion appears to be that of diffusing concussion. Sesamoid bones, which are de- 
veloped in the capsules of some joints or in tendons, may be included in this group. 
They diminish friction or change the direction of tendons. 

(4) Irregular bones (Ossa irregularia) . This group would include bones of 
irregular shape, such as the vertebrae and the bones of the cranial base; they are 
median and unpaired. Their functions are various and not so clearly specialized 
as those of the preceding classes. 

^ This classification is not entirely satisfactory; some bones, e. g., the ribs, are not clearly 
provided for, and others might be variously placed. 

20 



STRUCTURE OF BONES 



21 



STRUCTURE OF BONES i 
Bones consist chiefly of bone tissue, but considered as organs they present 
also an enveloping membrane, termed the periosteum, the marrow, vessels, and 
nerves. 

The architecture of bone can be studied best by means of longitudinal and 
transverse sections of specimens which have been macerated so as to remove most 
of the organic matter. These show that the bone 
consists of an external shell of dense compact sub- 
stance, within which is the more loosely arranged 
spongy substance. In tyjDical long bones the shaft 
is hollowed to form the medullary cavity (Cavum 
medullare) . 

The compact substance (Substantia compacta) 
differs greatly in thickness in various situations, in 
conformity with the stresses and strains to which 
the bone is subjected. In the long bones it is 
thickest in or near the middle part of the shaft and 
thins out toward the extremities. On the latter the 
layer is very thin, and is especially dense and smooth 
on joint surfaces. 

The spongy substance (Substantia spongiosa) 
consists of delicate bony plates and spicules which 
run in various directions and intercross. These are 
definitely arranged with regard to mechanical re- 
quirements, so that systems of pressure and tension 
plates can be recognized, in conformity with the 
lines of pressure and the pull of tendons and liga- 
ments respectively. The intervals between the 
plates are occupied by marrow, and are termed 
marrow spaces (Cellulse meduUares). The spongy 
substance forms the bulk of short bones and of the 
extremities of long bones; in the latter it is not con- 
fined to the ends, but extends a variable distance 
along the shaft also. Some bones contain air-spaces 
within the compact substance instead of spongy 
bone and marrow, and hence are called pneimiatic 
bones (Ossa pneumatica) . These cavities are termed 
sinuses, and are lined with mucous membrane; 
they communicate indirectly with the external air. 
In certain situations the two compact layers of flat 
bones are not separated by spongy bone, but fuse 
with each other; in some cases of this kind the bone 
is so thin as to be translucent, or may undergo 
absorption, producing an actual deficiency. 

The flat bones of the cranial vault and sides 
are composed of an outer layer of orchnary compact 
substance, the lamina externa, an inner layer of 
very dense bone, the lamina interna or tabula vitrea, and between these a variable 
amount of spongy bone, here termed diploe. 

The periostetun is the membrane which invests the outer surface of bone, 
except where it is covered with cartilage. It consists of an outer protective fibrous 

1 Only the gross structure is discussed here. For the microscopic structure reference is to 
be made to histological works. 




Fig. 1. — Sagittal Section op Large 
Metatarsal Bone of Horse 
(Right). 

S.c, Compact substance; S.s., 
spongy substance; Cm., medullary 
cavity; F.n., nutrient foramen. Note 
the greater thickness of the compact 
substance of the anterior part of the 
shaft. 



22 



OSTEOLOGY 



layer, and an inner cellular osteogenic layer. During active gro^vth the osteogenic 
layer is well developed, but later it becomes much reduced. The fibrous layer 
varies much in thickness, being in general thickest in exposed situations. The 
adhesion of the periosteum to the bone also differs greatly in various places; it 
is usually very thin and easily detached where it is thickly covered with muscular 
tissue which has little or no attachment. The degree of vascularity conforms to 
the activit}^ of the periosteum. 

The endosteum is a thin fibrous membrane which lines the medullary cavity 
and the larger Haversian canals. 

The marrow (Medulla ossium) occupies the interstices of the spongj^ bone and 
the medullary cavity of the long bones. There are two varieties in the adult — 
red and yellow. In the young subject there is only red marrow (Medulla ossium 
mbra), but later this is replaced in the medullary cavity by yellow marrow (Medulla 
ossium flava). The red marrow contains several types of characteristic cells and 
is a blood-forming suV)stance, Avhile the yellow is practically ordinary adipose tissue.^ 

Vessels and Nerves. — It is customary to recognize two sets of arteries — the 
periosteal and the medullary. The former ramify in the periosteum and give off 





Fig. 2. — Cross-section of Proximal Third of Shaft 
OF Right Humerus of Horse. 



Fig. 



Cross-section of Distal Third of Shaft op 
Left Humerus of Horse. 
Section passes through nutrient foramen and canal. 



innumerable small branches which enter minute openings (Volkmann's canals) on 
the surface and reach the Haversian canals of the compact substance. Other 
branches enter the extremities of the long l^ones and supply the spongy bone and 
marrow in them. In the case of the larger bones — and especially the long bones — 
the large nutrient or medullary artery (Arteria nutricia) enters at the so-called nu- 
trient foramen (Foramen nutricium), passes in a canal (Canalis nutricius) through 
the compact substance, and ramifies in the marrow; its branches anastomose -with 
the central branches of the periosteal set. The larger veins of the spongy bone do 
not, as a rule, accompany the arteries, but emerge chiefly near the articular surfaces. 
Within the bone thej^ are destitute of valves. The l5anph-vessels exist as peri- 
vascular channels in the periosteum and the Haversian canals of the compact sub- 
stance. They also form a fine subperiosteal network, froxn which the larger vessels 
proceed, usually in company with veins. Lymph-spaces exist at the periphery of 
the marrow. 

The nerves appear to be distributed chiefly to the blood-vessels. Special nerve- 

1 Since yellow marrow is formed by regressive changes in red marrow, including fatty infiltra- 
tion and degeneration of the characteristic cells, we find transitional forms or stages in the process. 
In aged or badly nourished subjects the marrow may undergo gelatinous degeneration, resulting 
in the formation of gelatinous marrow. 



DEVELOPMENT AND GROWTH OF BONE 



23 



endings (Vater-Pacini corpuscles) in the periosteum are to be regarded as sensory, 
and probably are concerned in mediating the muscle sense (kinesthesia) 



DEVELOPMENT AND GROWTH OF BONEi 

The primitive embryonal skeleton consists of cartilage and fibrous tissue, in 
which the bones develop. The process is termed ossification or osteogenesis, and 
is effected essentially by bone-producing cells, called osteoblasts. It is customary, 
therefore, to designate as membrane bones those which are developed in fibrous 
tissue, and as cartilage bones those which are preformed in cartilage. The princi- 
pal membrane bones are those of the roof and sides of the cranium and most of the 
bones of the face. The cartilage bones comprise, 
therefore, most of the skeleton. Correspondingly 
we distinguish intramembranous and endochondral 
ossification. 

In intramembranous ossification the process 
begins at a definite center of ossification (Punctum 
ossificationis) , where the osteoblasts surround them- 
selves with a deposit of bone. The process extends 
from this center to the periphery of the future bone, 
thus producing a network of bony trabeculae. The 
trabeculae rapidly thicken and coalesce, forming a 
bony plate which is separated from the adjacent 
bones by persistent fibrous tissue. The superficial 
part of the original tissue becomes periosteum, and 
on the deep face of this successive layers of perios- 
teal bone are formed by osteoblasts until the bone 
attains its definitive thickness. Increase in circum- 
ference takes place by ossification of the surround- 
ing fibrous tissue, which continues to grow until 
the bone has reached its definitive size. 

In endochondral ossification the process is 
fundamentally the same, but not quite so simple. 
Osteoblasts emigrate from the deep face of the peri- 
chondrium or primitive periosteum into the cartilage 
and cause calcification of the matrix or ground- 
substance of the latter. Vessels extend into the cal- 
cifying area, the cartilage cells shrink and disappear, 
forming primary marrow cavities which are occupied 
by processes of the osteogenic tissue. There is thus 
formed a sort of scaffolding of calcareous trabeculae 
on which the bone is constructed by the osteoblasts. 
At the same time perichondral bone is formed by 

the osteoblasts of the primitive periosteum. The calcified cartilage is broken down 
and absorbed through the agency of large cells called osteoclasts, and is replaced 
by bone deposited by the osteoblasts. The osteoclasts also cause absorption of the 
primitive bone, producing the marrow cavities; thus in the case of the long bones 
the primitive central spongy bone is largely absorbed to form the medullary cavity 
of the shaft, and persists chiefly in the extremities. Destruction of the central 
part and formation of subperiosteal bone continue until the shaft of the bone has 
completed its growth. 

A typical long bone is developed from three primary centers of ossification, 

1 Only a brief general statement of osteogenesis can be made here; details must be sought 
in embryological literature. 




Fig. 4. — Left Femur of Young Piq, 
Lateral View, to Show Di- 
VI8IOX OF A Long Bone into 
Shaft (s) and Extremities. 
Proximal extremity consists of 
two parts, head (h) and trochanter 
major (t.m.), which have separate 
centers of ossification. Distal extrem- 
ity consists of trochlea (0 and condyles 
(c); e.L, epiphyseal cartilages; s.f., 
supracondyloid fossa. 



24 OSTEOLOGY 

one, which appears first, for the diaphysis or shaft and one for each epiphysis oi 
extremity. Many bones have secondary centers from which processes or apophyses 
develop. 

The foregoing outhne accounts for the gro^Hh of bones except in regard to 
length. Increase in length may be explained briefly as follows : Provision for con- 
tinued ossification at either end of the diaphysis is made by a layer of actively 
groAving cartilage — the epiphyseal cartilage — which intervenes between the diaph- 
ysis and the epiphysis. It is evident that so long as this cartilage persists and 
grows, new bone may continue to be formed at its expense, and increase of length 
is possible. When the epiphyseal cartilage ceases to grow, it undergoes ossification, 
the bone is consolidated, and no further increase in length is possible. This fusion 
takes place at fairly definite periods in the various bones, and it is of value to know 
the usual times at which it occurs in the larger bones of the limbs at least. In the 
case of membrane bones, increase in circumference is provided for by the ossification 
and new formation of the surrounding fibrous tissue. 

After the bones have reached their full size, the periosteum becomes relatively reduced and 
inactive so far as its osteogenic layer is concerned; the bone-forming function may be stimulated 
by various causes, as is well seen in the heaUng of fractures and the occurrence of bony enlarge- 
ments. 

Profound changes occur in the skeleton after birth, and during the period of growth the bones 
are much more plastic than might be supposed. In the new-])orn foal, for example, it is evident 
that the rnetacarpal and metatarsal bones are relatively long and the scapula and humerus short; 
also that in general the shafts of the long bones are slender in comparison with the extremities. 
The various prominences are much less pronounced than in the adult, and most of the minor 
surface markings are absent, so that the bones have a relatively smooth appearance. The period 
of gro^v-th may be regarded as terminating with the union of the extremities and shafts of the long 
bones and the fusion of the parts of other bones. During adult life the skeletal changes proceed 
more slowly; they comprise accentuation of the larger prominences and depressions and the ap- 
pearance of smaller ones. These secondary markings are chiefly correlated with the attachments 
of muscles, tendons, and hgaments, or are produced by pressure exerted by various structures on 
the bones. Later in hfe ossification invades more or less extensively the cartilages and the at- 
tachments of tendons and ligaments. Senile changes in the bones, consisting of decrease of the 
organic matter and rarefaction of the bone tissue, render them brittle and liable to fracture. 



CHEMICAL COMPOSITION OF BONE 
Dried bone consists of organic and inorganic matter in the ratio of 1 : 2 ap- 
proximately. The animal matter gives toughness and elasticity, the mineral 
matter hardness, to the bone tissue. Removal of the organic matter by heat does 
not change the general form of a bone, but reduces the weight by about one-third, 
and makes it very fragile. Conversely, decalcification, while not affecting the form 
and size of the bone, renders it soft and pliable. The organic matter (ossein) when 
boiled yields gelatin. The following table represents the composition in 100 parts 
of ox bone of average quality : 

Gelatin 33.30 

Phosphate of Ume 57.35 

Carbonate of lime 3.85 

Phosphate of magnesia 2.05 

Carbonate and chlorid of sodium 3.45 

100.00 
PHYSICAL PROPERTIES OF BONE 
Fresh dead bone has a yellowish-white color; when macerated or boiled and 
bleached, it is white. The specific gravity of fresh compact bone is a little over 
1.93. It is very hard and resistant to pressure; a 5-millimeter cube of compact 
bone of the ox will resist pressure up to 852 pounds, if the pressure be applied in 
the line of the lamellae (Rauber). Its tensile strength is estimated to be nearly 
twice that of oak. 



THE VERTEBRAL COLUMN 25 



DESCRIPTIVE TERMS 

The surfaces of the bones present a great variety of eminences and depressions, 
as well as perforations. The prominences and cavities may be articular, or non- 
articular, furnishing attachment to muscles, tendons, ligaments, or fascia. A 
number of descriptive terms are used to designate these features, and the following 
are some of those in general use: 

Process (Processus) is a general term for a prominence. 

A tuberosity (Tuber, Tuberositas) is a large, rounded projection; a tubercle 
(Tuberculum) is a smaller one. 

The term trochanter is applied to a few prominences, e. g., the trochanters of 
the femur. 

A spine (Spina) or spinous process (Processus spinosus) is a pointed projection. 

A crest (Crista) is a sharp ridge. 

A line (Linea) is a very small ridge. 

A head (Caput) is a rounded articular enlargement at the end of a bone; it 
may be joined to the shaft by a constricted part, the neck (Collum). 

A condyle (Condylus) is an articular eminence which is somewhat cylindrical; 
a non-articular projection in connection with a condyle may be termed an epi- 
condyle (Epicondylus). 

A trochlea is a pulley-like articular mass. 

A glenoid cavity (Cavitas glenoidalis) is a shallow articular depression, and a 
cotyloid cavity or acetabulum is a deeper one. 

The term facet is commonly applied to articular surfaces of small extent, 
especially when they are not strongly concave or convex. 

The terms fossa, fovea, groove or sulcus, and impression are applied to various 
forms of depressions. 

A foramen is a perforation for the transmission of vessels, nerves, etc. 

A sinus is an air-cavity within a bone or bones; it is lined with mucous mem- 
brane and communicates with the exterior. 

Other terms, such as canal, fissure, notch, etc., require no explanation.^ 



THE VERTEBRAL COLUMN 

The vertebral coliram (Columna vertebralis) is the fundamental part of the 
skeleton. It consists of a chain of median, unpaired, irregular bones which 
extends from the skull to the end of the tail. In the adult certain vertebrae have 
become fused to form a single bony mass with which the pelvic girdle articulates. 
Vertebrae so fused are termed fixed (or ''false") vertebrae (Vertebrae immobiles), as 
distinguished from the movable (or 'Hrue") vertebrae (Vertebrae mobiles). 

The column is subdivided for description into five regions, which are named 
according to the part of the body in which the vertebrae are situated. Thus the 
vertebrae are designated as cervical, thoracic, lumbar, sacral, coccygeal (Vertebrae 
cervicales, thoracales, lumbales, sacrales, coccygeae). The number of vertebrae in 
a given species is fairly constant in each region except the last, so that the verte- 
bral formula may be expressed (for the horse, for example) as follows: 

C7Ti8L6S5Cyi5.21. 

The vertebrae in a given region have characters by which they may be dis- 
tinguished from those of other regions, and individual vertebrae have special 
characters which are more or less clearly recognizable. All typical vertebrae have 

1 As might be expected from the history of anatomy, a good many of these terms are more or 
less interchangeable; furthermore, a given skeletal feature may differ greatly in various species. 



26 



OSTEOLOGY 



a common plan of structure, which must first be understood. The parts of which 
a vertebra consists are the body, the arch, and the processes. 

The body (Corpus vertebrae) is the more or less cylindrical mass on which the 
other parts are constructed. The anterior and posterior extremities of the body 
are attached to the adjacent vertebrse by intervertebral fibro-cartilages, and are 
usually convex and concave respectively. The dorsal surface is flattened and enters 
into the formation of the vertebral canal, while the ventral aspect is rounded later- 
ally, and is in relation to various muscles and viscera. In the thoracic region the 
body presents two pairs of facets (Foveae costales) at the extremities for articula- 
tion with part of the heads of two pairs of ribs. 

The arch (Arcus vertebrae) is constructed on the dorsal aspect of the body. 
It consists originally of two lateral halves, each of which is considered to consist 
of a pedicle and a lamina. The pedicle (Radix arcus vertebrge) forms the lateral 
part of the arch, and is cut into in front and behind by the vertebral notches (In- 
cisura vertebralis cranialis, caudalis). The notches of two adjacent vertebrae form 
intervertebral foramina (Foramina intervertebralia) for the passage of the spinal 

nerves and vessels; in some vertebrae, how- 
ever, there are complete foramina instead 
of notches. The laminae are plates which 
complete the arch dorsally, uniting with each 
other medially at the root of the spinous 
process. 

The body and the arch form a bony 
ring which incloses the vertebral foramen 
(Foramen vertebrale); the series of verte- 
bral rings, together with the ligaments which 
unite them, inclose the vertebral canal 
(Canalis vertebralis), Avhich contains the 
spinal cord and its coverings and vessels. 

The articular processes, two anterior 
and two posterior (Processus articulares 
craniales, caudales), project from the bor- 
ders of the arch. They present articular 
surfaces adapted to those of adjacent verte- 
brae, and the remaining surface is roughened 
for muscular and ligamentous attachment. 
The spinous process or spine (Processus 
spinosus) is single, and projects dorsally from the middle of the arch. It varies 
greatly in form, size, and direction in different vertebrae. It furnishes attachment 
to muscles and ligaments. 

The transverse processes (Processus transversi) are two in number and project 
laterally from the sides of the arch or from the junction of the arch and body. 
In the thoracic region each has a facet for articulation with the tubercle of a rib 
(Fovea costalis transversalis) . They also give attachment to muscles and liga- 
ments. 

Some vertebrae have also a ventral spine or a haemal arch. 
Mammillary processes (Processus mamillares) are found in most animals on 
the last thoracic and anterior lumbar vertebrse, between the transverse and an- 
terior articular processes or on the latter. 

Accessory processes (Processus accessorii), when present, are situated between 
the transverse and posterior articular processes. 

Development. — The vertebrae are developed by ossification in the cartilage 
Avhich surrounds the notochord and forms the sides of the neural canal. There are 
three primary centers of ossification, one for the body and one for each side of the 




Cosraijkcef 



Fig. 5. — First Thoracic Vertebra of Horse. 
To illustrate plan of structure of vertebrae. 



THE COSTAL CARTILAGES 27 

arch. Secondary centers appear later for the summit of the spinous process 
(except in the cervical region), the extremities of the transverse processes, and the 
thin epiphyseal plates at the extremities of the body. 

Sometimes there are at first two centers for the body, which soon fuse. The process of ossifi- 
cation extends from the lateral centers to form, not only the corresponding part of the arch, but 
also the processes and a part of the body next to the root of the arch (Radix arcus) . In the horse 
and ox the body and arch are fused at birth or unite very soon after, but the epiphyses do not 
fuse till growth is complete. In the pig, sheep, and dog the body and arch are united at l)irth 
by cartilage (neurocentral synchondrosis), but fuse in the first few months. 

THE RIBS 

The ribs (Costae) are elongated curved bones which form the skeleton of the 
lateral thoracic walls. They are arranged serially in pairs which correspond in 
number to the thoracic vertebrae. Each articulates dorsally with two vertebrae 
and is continued ventrally by a costal cartilage. Those which articulate with the 
sternum by means of their cartilages are termed sternal ribs (Costae sternales); 
the remainder are asternal ribs (Costae asternales). Ribs at the end of the series 
which have their ventral ends free in the abdominal wall are named floating ribs 
(Costae fiuctuantes). The intervals between the ribs are termed intercostal spaces 
(Spatia intercostalia) . 

A typical rib^ consists of a shaft and two extremities. The shaft (Corpus 
costae) is band-like and varies much in length, breadth, and curvature in different 
ribs. In the case of some ribs the curvature is not uniform, but is accentuated at a 
certain point, termed the angle of the rib (Angulus costae) ; this occurs at a variable 
distance from the vertebral end, and is usually marked by a rough ridge. The 
direction also varies; the first rib is usually almost vertical, while the remainder 
slope backward in increasing degree. The lateral surface (Facies lateralis) is con- 
vex, and the medial surface (Facies medialis) flattened from edge to edge; on the 
latter, close to the posterior border, is the costal groove (Sulcus costae), which fades 
out ventrally. It contains the intercostal vein. The anterior and posterior 
borders (Margo cranialis, caudalis) are thin and sharp on some ribs, rounded on 
others. 

The vertebral extremity (Extremitas vertebralis) consists of the head, neck, 
and tubercle. The head (Capitulum costae) is the actual end of the rib, and is 
rounded and somewhat enlarged. It presents two facets (Facies articularis capituli 
costae) for articulation with the bodies of two adjacent thoracic vertebrae; these 
surfaces are separated by a groove in which the conjugal ligament is attached. 
The neck (CoUum costae) joins the head to the shaft. It varies in length and 
diameter. Its lateral surface is rough, its medial smooth. The tubercle (Tuber- 
culum costae) projects backward at the junction of the neck and shaft. It has a 
facet (Facies articularis tuberculi costae) for articulation with the transverse process 
of the posterior vertebra of the two with which the head articulates. The tubercle 
gradually approaches the head in the posterior ribs, and eventually fuses with it. 

The sternal extremity (Extremitas sternalis) is commonly slightly enlarged, 
and is roughened at the junction with the costal cartilage. 

Development. — The ribs are ossified in cartilage from three centers — one each 
for the shaft (and sternal end), head, and tubercle; the third center is absent in 
some ribs at the terminal part of the series. 

THE COSTAL CARTILAGES 

These (Cartilagines costales) are bars of hyaline cartilage which continue the 
ribs. Those of the sternal ribs articulate with the sternum, while those of the 

1 The term is employed here, as is usual in descriptive anatomy, to designate only the bony 
part of the rib (Os costale) ; morphologically it includes the cartilaginous part also. 



28 OSTEOLOGY 

asternal ribs overlap and are attached to each other to form the costal arch (Arcus 
costalis). The cartilages of floating ribs are not attached to those adjacent. 



THE STERNUM 

The stemxun (or breast-bone) is a median segmental bone -which completes the 
skeleton of the thorax ventrally, and articulates Avith the cartilages of the sternal 
ribs laterally. It consists of six to eight bony segments (Sternebra^) connected by 
intervening cartilage in the yoimg subject. Its form varies with that of the thorax 
in general anil with the development of the clavicles in animals in which these bones 
are present. Its anterior extremity, the manubrium stemi or presternum, is 
specially affected by the latter factor, being broad and strong when the clavicles 
are well ileveloped and articulate with it (as in man), relatively small and laterally 
compressed Avhen they are absent (as in the horse) or rudimentary (as in the dog). 
The cartilages of the first pair of ribs articulate with it. The body or mesostemimi 
(Corpus sterni) presents laterally, at the junction of the segments, concave facets 
(Incisura^ costales) for articulation Avith the cartilages of the sternal ribs. The 
posterior extremity or metastemiun presents the xiphoid cartilage (Processus 
xiphoideus) ; this is thin and wide, as in the horse and ox, or narroAv and short, as 
in the dog. 

Development. — The cartilaginous sternmn is formed by the fusion medially 
of two lateral bars which unite the ventral ends of the first eight or nine costal 
cartilages, and is primitively imsegmented. The manubrium ossifies from a single 
center, but the centers for the other segments appear to be primitively paired. 
The sternum never becomes completely ossified; details in regard to persisting 
cartilage will be given in the special descriptions. The layer of compact tissue is 
for the greater part very thin and the spongy substance is open-meshed and ver^' 
vascular. 

THE THORAX 

The skeleton of the thorax comprises the thoracic vertebnp dorsally. the ribs 
and costal cartilages laterally', and the sternmn ventrally. The thoracic cavity 
(CaAinn thoracis) resembles in shape an irregular truncated cone; it is compressed 
laterally, especially in front, and the dorsal wall or roof is much longer than the 
ventral wall or floor. The anterior apertvire or inlet (Apertura thoracis cranialis) is 
bc^unded by the first thoracic vertebra dorsally, the first pair of ribs and costal 
cartilages laterally, and the manubrium sterni ventrally. The posterior aperture 
(Apertura thoracis caudalis) is bounded by the last thoracic vertebra, the last 
pair of ribs, the costal arches, and the anterior part of the xiphoid cartilage. 

It may be noted here that the diaphragm (which forms the partition hetween the thoracic 
and abdominal caA-ities) does not follow the costal arches in its posterior attachment, so that the 
posterior ribs enter also into the formation of the abdominal wall. 



THE SKULL 

The term skull is usually imderstood to include all of the bones of the head. 
The head consists of the cranium and the face, and it is therefore convenient to 
diAnde the bones into cranial antl facial groups. 

The cranial bones (Ossa cranii) inclose the brain AA-ith its membranes and 
vessels and the essential organs of hearing. They concur with the facial bones in 
forming the orbital and nasal caA'ities, in AA-hich the peripheral organs of sight ami 
of smell are situated. 

The facial bones (Ossa faciei) form the skeleton of the oral and nasal caA'ities, 
and also support the pharA'nx, the larynx, and the root of the tongue. 



THE BONES OF THE THORACIC LIMB 29 

Most of the bones of the skull are flat bones, developed in membrane; those 
of the cranial base may be classed as irregular, and are developed in cartilage. Only 
two form permanent movable joints with other parts of the skull. The mandible 
(or lower jaw-Vjone) forms diarthrodial joints with the temporal bones, and the 
hyoid bone is attached to the latter Vjy bars of cartilage. The other bones form 
immovable joints, most of which disappear with age. 

In order to study the separate bones, skulls of young subjects are necessary, since later most 
of the hnes of demarcation become effaced. The relations of each bone to its surroundings should 
be specially noted, since the final object is to understand the skull as a whole. In the descriptions 
which follow the skull is considered with its long axis horizontal, and that of the horse will serve 
as a type. 

THE BONES OF THE THORACIC LIMB 

The thoracic limb (Extremitas thoracalis) consists of four chief segments, viz., 
the shoulder girdle, the arm, the forearm, and the manus. 

The shoulder girdle (Cingulum extremitatis thoracalis) , when fully developed, 
consists of three bones — the scapula (or shoulder-blade), the coracoid, and the 
clavicle (or collar-bone). In the domesticated mammals only the scapula, a large, 
flat bone, is well developed, and the small coracoid element has fused with it, while 
the clavicle is either absent or is a small rudiment embedded in the brachiocephali- 
cus muscle. There is therefore no articulation of the shoulder with the axial 
skeleton. 

The shoulder girdle is fully developed in birds and the lower mammals (monotremata) . In 
the higher manmials the coracoid is reduced to the coracoid process of the scapula, and the develop- 
ment of the clavicle is in conformity with the function of the hmb. Thus in typical quadrupeds, 
such as the horse and ox, in which the foreUmbs are used only for support and locomotion, the 
clavicle is absent. Other animals which use these hmbs for grasping, burrowing, chmbing, etc. 
(e. g., man, apes, moles), have well-developed cla\'icles which connect the scapula with the stemiun. 

The arm (Brachium) contains a single long bone, the humerus (or arm bone). 

In the forearm (Antibrachium) are two bones, the radius and ulna. These 
vary in relative size and mobility. In the horse and ox the two bones are fu.sed, 
and the distal part of the limb is fixed in the position of pronation. The radius is 
placed in front and supports the weight. The ulna is well developed only in its 
proximal part, which forms a lever for the extensor muscles of the elbow. In the 
pig the ulna is the larger and longer of the two bones, but is closely attached to 
the back of the radius. In the dog the ulna is also well developed and a small 
amount of movement is possible between the two bones. 

The manus,! the homologue of the hand in man, consists of three subdivi- 
sions, viz., the carpus, metacarpus, and digit or digits. 

The carpus, popularly termed the "knee" in animals, and homologous with 
the wrist of man, contains a group of short bones, the ossa carpi.^ These are typic- 
ally eight in number and are arranged in two transverse rows — a proximal or anti- 
brachial, and a distal or metacarpal. The bones of the proximal row, named from 
the radial to the ulnar side {i. e., from within outward), are the radial, intermediate, 
ulnar, and accessory carpal bones. The bones of the distal row are designated 
numerically, in the same direction, as first, second, third, and fourth carpal bones. 

This nomenclature, introduced by Gegenbaur, and now used largely by comparative anat- 
omists, seems decidedly preferable to the ^'ariety of terms borrowed from human anatomy and 
based on the form of the bones in man. The follo^vang table of synonyms in cornmon use is ap- 
pended for comparison. The Latin terms and abbreviated notations are given in parentheses. 

1 It is unfortunate that there is no popular name for this part of the limb. The term "fore- 
foot" is sometimes appUed to it, but this leads to confusion, since the word "foot" has long been 
used in a different sense. 

2 The term "knee" as applied to this region is unfortunate, but the usage is very firmly 
established and there is no other popular name. 



30 OSTEOLOGY 

The central carpal bone (Os carpi centrale) is omitted, since it is not a separate element in the 
animals under consideration here. 

Radial (Os carpi radiale, Cr) Scaphoid 

Intermediate (Os carpi intermedium, Ci) Semilunar 

Ulnar (Os carpi ulnare, Cu) Cuneiform 

Accessory (Os carpi accessorium, Ca) Pisiform 

First carpal (Os carpale primum, CI) Trapezium 

Second carpal (Os carpale secundum, C2j Trapezoid 

Third carpal (Os carpale tertium, C3) Os magnum 

Fourth carpal (Os carpale quartum, C4) Unciform 

The metacarpus contains typically five metacarpal bones (Ossa metacarpalia 
I-V), one for each digit; they are long bones and are designated numerically from 
the radial to the ulnar side (i. e., from within outward). This arrangement occurs 
in the dog, although the first metacarpal is much smaller than the others, and the 
second and fifth are somewhat reduced. Further reduction has taken place in the 
other animals, resulting in the perissodactyl and artiodactyl forms. In the horse 
the first and fifth metacarpals are absent, the third is the large supporting meta- 
carpal bone and carries the single digit, while the second and fourth are much re- 
duced. In artiodactyls (e. g., ox, sheep, pig) the third and fourth are the chief 
metacarpals and carry the well developed digits; they are fused in the ox and sheep. 
The others are variously reduced or absent, as noted in the special descriptions to 
follow. 

The fossil remains of the ancestors of the existing Equidse illustrate in a most complete man- 
ner the reduction which has occurred in this respect. The earliest known ancestor of the horse, 
Eohippus of the Lower Eocene, had four well developed metacarpal bones, each of which carried 
a digit; the first metacarpal bone was small. Intermediate forms show the gradual evolution of 
the race from this primitive animal, which was about the size of the domestic cat. There is reason 
to believe that earlier forms had five digits. 

The digits (Digiti manus) are homologous with the fingers of man, and are 
typically five in number. They are designated numerically from the radial to 
the ulnar side, in correspondence with the metacarpus. The full number is present 
in the dog. In the ox and pig the third and fourth are well developed and support 
the weight, while the second and fifth are reduced. The existing horse has a single 
digit, the third of his pentadactyl ancestors. The skeleton of each fully developed 
digit consists of three phalanges and certain sesamoid bones. The first phalanx 
(Phalanx prima) articulates with the corresponding metacarpal bone above and 
with the second phalanx (Phalanx secunda) below. The third phalanx (Phalanx 
tertia) is inclosed in the hoof or claw, and is modified to conform to the latter. The 
sesamoid bones (Ossa sesamoidea) are developed along the course of tendons or in 
the joint capsules at points where there is increased pressure. Two proximal 
sesamoids (Ossa sesamoidea phalangis primse) occur at the flexor side of the meta- 
carpo-phalangeal joint and form a pulley for the flexor tendon. The distal sesa- 
moid (Os sesamoideum phalangis tertise) is similarly placed between the deep 
flexor tendon and the joint between the second and third phalanx; it is absent in 
the dog, which has a small sesamoid on the extensor side of the metacarpo-phalan- 
geal joint, and often at the proximal interphalangeal joint also. 

Numerous cases are recorded of the occurrence of supernumerary digits (hyperdactylism) 
in the horse and other animals. In some pigs, on the other hand, the two chief digits are fused,, 
and the condition (syndactylism) appears to be inherited. 



THE BONES OF THE PELVIC LIMB 

The pelvic limb (Extremitas pelvina), like the thoracic, consists of four seg- 
ments, viz., the pelvic girdle, thigh, leg, and the pes; the last is subdivided into 
tarsus, metatarsus, and digits. 

The pelvic girdle (Cingulum extremitatis pelvinse) consists of the os coxae (or 



THE BONES OF THE PELVIC LIMB 31 

hip bone), which joins its fellow of the opposite side ventrally at the symphysis 
pelvis, and articulates very finnlj^ with the sacrum dorsally. The two coxal bones, 
together with the sacrum and the first three or more coccygeal vertebrae, constitute 
the bony pelvis. The os coxae consists originally of three flat bones, the ilium, 
ischium, and pubis, which meet at the acetabulum, a large cotyloid cavity with 
which the head of the femur articulates. These three parts are fused before growth 
is complete, but are considered separately for convenience of description. The 
iliimi (Os ilium) is situated in the lateral wall of the pelvis, the pubis (Os pubis) in 
the anterior part, and the ischium (Os ischii) in the posterior part of the ventral 
wall. 

The thigh (Femur), like the arm, contains a single long bone, the femur (or 
thigh bone) (Os femoris). This articulates with the acetabulum above and the 
tibia and patella below. 

The skeleton of the leg (Crus) comprises three bones (Ossa cruris), viz., the 
tibia, fibula, and patella. The tibia is a large, prismatic long bone which supports 
the weight, and articulates distally with the tibial tarsal bone. The fibula is 
situated along the lateral border of the tibia, from which it is separated by the 
interosseous space of the leg. It is much more slender than the tibia and does not 
articulate with the femur. In the pig and dog it has a complete shaft and two 
extremities, but in the horse and ox it is much reduced and otherwise modified. 
The patella (or "knee-cap") is a short bone which articulates with the trochlea of 
the distal end of the femur; it is to be regarded as a large sesamoid bone intercalated 
in the tendon of the quadriceps femoris muscle. 

The tarsus (or "hock") consists of a group of short bones, the ossa tarsi, 
numbering five to seven in the different animals. The proximal or crural row con- 
sists of two bones, the tibial and fibular tarsals ; the former is situated at the tibial 
side, and has a trochlea for articulation with the distal end of the tibia; the latter, 
situated at the fibular side, has a process, the tuber calcis, which projects upward 
and backward and constitutes a lever for the muscles which extend the hock joint. 
The distal or metatarsal row consists of four bones when seven tarsal elements are 
present, as in the pig and dog. They are best designated numerically as first tarsal, 
second tarsal, etc. The central tarsal is interposed between the rows. 

The preceding terms are anglicized abbreviations of those introduced by Gegenbaur into 
comparative anatomy. The Latin names and synonyms are given in the following table: 

Tibial (Os tarsi tibiale, Tt.) Astragalus or Talus 

Fibular (Os tarsi fibulare, Tf.) Calcaneus or Os calcis 

Central (Os tarsi centrale, Tc.) Scaphoid or Navicular 

First Tarsal (Os tarsale primum, Tl) First or internal cuneiform 

Second Tarsal (Os tarsale secundum, T2) Second or middle cuneiform 

Third Tarsal (Os tarsale tertium, T3) Third or external cuneiform 

Fourth Tarsal (Os tarsale quartum, T4) Cuboid 

The metatarsal and digital bones resemble in general those of the corresponding 
regions of the thoracic limb; the differential features will be noted in the special 
descriptions. 



32 



THE SKELETON OF THE HORSE 



THE SKELETON OF THE HORSE 

The skeleton of the horse consists of 205 bones, as shown in the following table: 

Vertebral column 54 

Ribs 36 

Sternum 1 

Skull (including auditory ossicles) 34 

Thoracic limbs 40 

Pelvic limbs 40 

205 

In this enumeration the average number of coccygeal vertebrae is taken to be 18, the tem- 
poral and OS coxae are not divided into parts, the usual number of carpal and tarsal elements is 
taken, and the sesamoids are included. 

t 




Fig. 6. — Skeleton of Horse, with Outune of Contour of Body. 
I.H., Atlas; 7.H., seventh cervical vertebra; I.R., first thoracic vertebra; 17. R., seventeenth thoracic vertebra; 
I.L., first lumbar vertebra; O.L., sixth lumbar vertebra; K, sacrum; I.S., first coccygeal vertebra; 16.S., sixteenth 
coccygeal vertebra; ^.i?., sixth rib; e. A'., costal cartilage; 18. R., lust rih; 1, scapula; 1', cartilage of scapula; 2, spine 
of scapula; 4, humerus; 4' lateral epicondyle of humerus; 5, lateral tuberosity of humerus; 6, deltoid tuberosity; 
7, shaft of ulna; 8, olecranon; 9, radius; 10, carpus; 11, accessory carpal bone; 12, metacarpus; 13, digit; 14, sternum, 
14", xiphoid cartilage; 15, ilium; 16, 16', angles of ilium; 17, ischium; 18, femur (shaft) ; 19, trochanter major; 20, 
patella; 21, tibia (shaft); 21', lateral condyle of tibia; 2.3, fibula; 22, tarsus; 24, tuber calcis; 25, metatarsus; 
26, digit; 27, trochanter minor of femur; 28, trochanter tertius of femur. (After EUenberger-Baum, Anat. fiir 
Kiinstler.) 



THE VERTEBRAL COLUMN 



33 



The Vertebral Column 

The vertebral formula of the horse is C7Ti8L6S5Cyi5-2i. 



Anterior artic- 
ular process 
of axis 
Spinous proc- 
ess of axis 



Transverse 
process of axis 




Fig. 7. — Cervical Vertebrae of Horse; Dorsal View. 
a, Articular processes; b, transverse processes; 1, 
dorsal arch of atlas; 2, w-ing of atlas; 3, intervertebral 
foramen of atlas; 4, alar foramen of atlas; 6, foramen 
transversarium of atlas; 6, dens of axis; 7, intervertebral 
foramen of axis; 8, foramen transversarium of axis; 9, 
spinous processes. 

3 



Fig. 8. — Cervical Vertebr.e of Horse; Ventral 
View. 
a. Transverse processes; 1, ventral tubercle of atlas; 

3, anterior articular cavities of atlas; S, fossa atlantis; 

4, alar foramen; 6, foramen transversarium; 6, ventral 



34 



THE SKELETON OF THE HORSE 




Head 

Fig. 9. — Sixth Cervical Vertebra of Horse; Anterior View. 



THE CERVICAL VERTEBRA 

The cervical vertebrae (Vertebrae cervicales) are seven in number. 
The first and second cervical vertebrae are highly modified in conformity with 

the special functions of support 
and movements of the head. 
The sixth and seventh present 
special characters, but do not 
differ greatly from the tj'pe. 
With the exception of the first, 
they are quadrangular, mass- 
ive, and longer than the ver- 
tebrae of other regions; they 
decrease in length from the 
second to the last. The third, 
fourth, and fifth have the fol- 
lowing characters: 

1. The body is long as 
compared with those of other 
vertebrae. The ventral surface 
presents a median ventral 
spine, which becomes more 
prominent as it is traced back- 
ward, and is tuberculate at its 
posterior end ; it separates two 
concave areas. The dorsal sur- 
face has a flat central area which is narrow in the middle of the vertebrae, and ^\^de 
at either end ; it gives attachment to the dorsal longitudinal ligament. On either 
side of this area there is a groove which lodges the longitudinal spinal vein. These 
lateral grooves are connected about the middle of the surface by a transverse furrow, 
in which there are several for- 
amina through which veins 
emerge from the spongy sub- 
stance of the body. The an- 
terior extremity or head (Ca- 
put vertebrae) has an oval 
articular surface which faces 
forward and downward; it is 
strongly convex, and wider 
above than below. The pos- 
terior extremity is larger and 
has a nearly circular cotyloid 
cavity (Fossa vertebrae). 

2. The arch is large and 
strong. It is perforated on 
either side by a foramen which 
communicates with the for- 
amen trans versarium. The 
vertebral notches are large. 

3. The articular processes 
are large. Their articular sur- 
faces are extensive, oval in outline, and slightl}^ concave; the anterior ones are 
directed dorso-medially; the posterior, ventro-laterally. The remaining surface is 
mainly roughened for ligamentous and muscular attachment. A crest connects 



— Spinous process 

Vertebral 

foramen Articular 

I process 



PlBff^ — ' f 


jii iri, 


fW>-— -^ A 




/ 1 m \ 




L|^jL^ 


^-' Trans- 
H^ perse 

process 


^^^^^^^ 




Ventral spine 
Seventh Cervical Vertebra of Horse; 


Anterior View 



THE ATLAS 



35 



the articular processes of the same side on the fourth and fifth; on the third it does 
not reach the anterior process. 

4. The transverse processes are large and plate-like. Each arises by two 
roots, one from the arch and one from the body; between these is the foramen 
transversariiun, through which the vertebral vessels and a nerve pass. The aggre- 
gate of these foramina constitutes the canalis transversarius. The process divides 
laterally into anterior and posterior branches, which are thickened and rough for 
muscular attachment. 

5. The spinous process has the form of a low crest (Crista spinosa), which 
widens behind, and is connected by ridges with the posterior articular processes. 

The sixth cervical vertebra has the following distinctive features: It is shorter 
and wider than the fifth. The arch is large, especially posteriorly. The posterior 
articular processes are shorter, thicker, and further apart; each is connected with 
the corresponding anterior one by a thick ridge. The spinous process is less rudi- 
mentary; it is half an inch or more (ca. 1.5 cm.) in height. The transverse proc- 
esses have three branches; the third part is a thick, almost sagittal plate, which 
forms with its fellow and the body a wide ventral groove; the other branches 
correspond to those of the typical vertebrae, but are short and thicker.^ The fora- 
men transversarium is large; below its posterior end there is a fossa. The 
ventral spine is small and is less prominent posteriorly. 

The seventh cervical vertebra is readily distinguished by the following charac- 
ters : It is shorter and wider than the others. The body is flattened dorso-ventrally 
and wide, especially behind; here it has a facet on each side for articulation with 
part of the head of the first rib. The arch and its notches are large. The anterior 
articular processes are wider and longer than the posterior pair. The spinous 
process is an inch or more (ca. 3 cm.) 
in height. The transverse process is 
undivided, and has no foramen trans- 
versarium.2 The ventral crest is re- 
placed by a pair of tubercles. 



The Atlas 

This vertebra is decidedly atypi- 
cal in form and structure. The body 
and spinous process are absent. It 
has the form of a strong ring, from 
which two curved plates, the wings, 
project laterally. The ring incloses a 
very large vertebral foramen, and con- 
sists of two lateral masses connected 
by dorsal and ventral arches. 

The lateral masses (Massse later- 
ales) present two deep oval anterior 
articular cavities (Foveas articulares 

craniales) which receive the occipital condyles; they are separated by a wide notch 
above and a narrow one below. The lateral margin is also notched, and a trian- 
gular non-articular depression cuts into the medial part of each cavity. The pos- 
terior articular surfaces (Facies articulares caudales) are somewhat saddle-shaped; 
they are confluent on the ventral arch, but are widely separated dorsally, and do 
not conform in shape to the corresponding surfaces of the axis. 

1 The third branch of the transverse process and the fossa are sometimes absent or reduced 
on one side. 

2 In some specimens a large foramen transversarium is present on one side or (rarely) on 
both sides. 




Fig. 



Atlas of Horse, Dorsal, View after Removal 
OF Dorsal Arch. 
1, Anterior articular cavities; 2, 2', posterior articular 
surfaces; 3, articular surface of ventral arch for dens of 
axis; 4, transverse ridge; 5, 5', alar foramina; 6, 6', foram- 
ina transversaria. 



'36 THE SKELETON OF THE HORSE 

The dorsal arch (Arcus dorsalis) presents a median dorsal tubercle (Tuber- 
culum dorsale) and is concave ventrally. It is perforated on either side near its 
anterior margin by the intervertebral foramen (Foramen invertebrate). The an- 
terior border is deeply notched, and the posterior is thin and concave. 

The ventral arch (Arcus ventrahs) is thicker, narrower, and less curved than 
the dorsal. On its lower surface is the ventral tubercle (Tuberculum ventrale), 
into which the terminal tendon of the longus colli muscle is inserted. The upper 
face has posteriorly a transversely concave articular surface, the fovea dentis, on 
which the dens or odontoid process of the axis rests. In front of this is a transverse 
rough excavation and a ridge for the attachment of the ligamentum dentis. 

The wings or alae are modified transverse processes. They are extensive 
curved plates which project ventro-laterally and backward from the lateral masses. 
The dorsal surface is concave. Between the ventral aspect of the wing and the 
lateral mass is a cavity, the fossa atlantis; in this there is a foramen which opens 
into the vertebral canal. The border is thick and rough; its position can be recog- 
nized in the living animal. Two foramina perforate each Aving. The anterior one, 
the foramen alare, is connected with the intervertebral foramen by a short groove. 
The posterior one is the foramen transversariimi. 

Development. — The atlas ossifies from four centers, two for the ventral arch, 
and one on either side for each lateral mass, wing, and half of the dorsal arch. At 
birth the bone consists of three pieces — the ventral arch and two lateral parts, 
which are separated by a layer of cartilage in the dorsal median line and by two 
ventro-lateral layers. These parts are usually fused at about six months. 

The Axis 

The axis (Axis s. Epistropheus) is the longest of the vertebrae, and is character- 
ized by the presence of the dens or odontoid process, which projects from the an- 
terior part of the body. 

The anterior extremity of the body presents centrally the dens or odontoid 



Spinous process 



Dens 



Anterior articular process 




Posterior articular process 

\ 

Trajisverse process 



Body 

Fig. 12. — Axis of Horse, Left View. 
1, Arch; 2, intervertebral foramen; 3, notch; 4. foramen transversarium. 

process (Dens axis) ; this has a convex articular surface ventrally for articulation 
with the ventral arch of the atlas, and two rough depressions for the attachment of 
the ligamentum dentis dorsally. Flanking this on either side are the modified 
anterioi articular processes, which have saddle-shaped articular surfaces confluent 



THE THORACIC VERTEBRA 



37 



ventrally with that of the dens. The posterior extremity has the usual cavity. 
The ventral spine resembles that of the typical vertebrae. 

The arch presents in the young subject a notch on each side of its anterior 
border; this is converted into a foramen by a ligament which ossifies later. The 
posterior border has the usual notches. 

The posterior articular processes are typical. 

The transverse processes are small, single, and project backward. The 
foramen transversariiun is small. 

The spinous process is very large and strong. Its free border is rough, thickens 
posteriorly, and is continued to the articular processes by two ridges. The lateral 
surfaces are concave and rough for muscular attachment. 

Development. — The axis has six or seven centers of ossification. In addition 
to the usual five, one or two appear for the dens, which is regarded as the displaced 
body of the atlas. A nucleus behind the dens, which remains distinct to three or 
four years of age, is considered to be the head of the axis. 



Spinous 
process 



THE THORACIC VERTEBRA 
The thoracic vertebrae (Vertebrae thoracales) are usually eighteen in number in 
the horse, but there are sometimes nineteen, rarely seventeen. As regional char- 
acters we note the surfaces for articulation with the ribs and the length and form of 
the spinous processes. Those in the 
middle of the series are the most 
typical and present the following fea- 
tures: 

1. The bodies are short and con- 
stricted in the middle. The ends are 
expanded and have articular surfaces 
which are not strongly curved; the an- 
terior surface is convex, the posterior 
concave. On the upper part of each 
side are anterior and posterior costal 
facets (Fovea costalis cranialis, cau- 
dalis), which, with those of adjacent 
vertebrae and the intervening fibro-car- 
tilages, form sockets for the heads of 
the ribs. 

2. The arches are small. Their 
posterior notches are relatively large 
and are often converted into foram- 
ina. 

3. The articular processes are 
small. The anterior processes are in 
fact represented only by two oval facets 
on the anterior part of the arch which 
face almost directly upward. The pos- 
terior processes spring from the base of the spinous process; their facets face 
almost directly downward. 

4. The transverse processes are short, thick, and tuberous at the free end. 
Each has a facet (Fovea transversaria) for articulation with the tubercle of the 
rib which has the same serial number. 

5. The spinous process is large, narrow, and slopes upward and backward. 
The anterior border is thin, the posterior wider and furrowed. The summit is 
expanded and rough. 



Facet for tubercle 
of rib 

Facet for 
head 
of rib 




Body 



Fig. 13. — Seventh Thoracic Vertebra of Horse, An- 
terior View. 



38 



THE SKELETON OF THE HORSE 



The first thoracic vertebra has the following specific characters: The body is 
wide and flattened dorso-ventrally. In front it has a head like the cervical verte- 



Spinnus process 
Articular processes 

Arch 



Facet for tubercle of first rib A^ ~-^__^ Transverse process 

Facet for head of second rib ""'^fl^'^ Body 
Fig. 14. — First Thoracic Vertebra of Horse, Posterior View. 




brae, and behind a cavity somewhat deeper than any other thoracic vertebra. Two 
large costal facets are found on either side, and a well-marked spine ventrallj". 




Fir., l.'i. — T,\sT Three THORArir ^■ERTEBR.E of Horse, [.eft \'iew. 

1, Body; 2, 2, facets for head of rib; S, facet for tubercle of rib; 4, J/ , articular processes; 5, intervertebral foramen; 

6, mammillary process; 7, spinous process. 

The arch is large and strong, and has large notches. The articular processes are 
much larger than those of other thoracic vertebrae, and resemble a good deal those 
of the seventh cervical. The transverse processes are short and thick, and each 



THE LUMBAR VERTEBRA 39 

has on its ventral aspect a large concave facet for articulation with the tubercle of 
the first rib. The spinous process is curved backward and tapers to a point. Its 
length is usually about three or four inches (ca. 8 to 10 cm.). This vertebra may be 
mistaken at first glance for the last cervical, but is promptly identified by the three 
costal facets on each side and the length of the spine. 

The last thoracic vertebra is distinguished by the absence of the posterior pair 
of costal facets, and the confluence of the anterior pair with those on the transverse 
processes. 

The serial position of others may be determined at least approximately by the 
following data: (1) The bodies graduallj^ diminish in length and width to the 
middle of the region and then increase slightly. Their costal facets become smaller 
and less concave from first to last. The ventral crest is distinct on three or four 
vertebrae at either end of the region. (2) The transverse processes diminish in 
size and are placed lower down as they are traced backward. Their costal facets 
become smaller and lower in position; on the last (and sometimes on its predecessor 
also) it fuses with the costal facet of the body. The upper non-articular part of 
the process gradually becomes more sharply defined, and in the last four or five 
forms a distinct mammillary process. (3) The spinous processes increase in length 
to the third and fourth, and then gradually diminish to the fifteenth, beyond which 
they have about the same length. The backward inclination is most pronounced 
in the second, the sixteenth is vertical, and the last two are directed a little forward. 
The longest spines {i. e., those of the withers) are the thickest and have expanded 
summits which remain more or less cartilaginous; the others are more plate-like, 
and are surmounted by a thick lip. The second spine is more than twice as large 
as the first. The summits of the fourth and fifth usually form the highest point 
of the withers. 

Development. — There are six or seven centers of ossification, three for the 
body, two for the arch, and one for the spinous process; some of the latter have an 
additional center for the summit. 



THE LUMBAR VERTEBRJE 

The lumbar vertebrae (Vertebrae lumbales) are usually six in number in the 
horse. They are characterized by the size and form of their transverse processes. 

The bodies of the first three are semi-elliptical on cross-section, and present a 
distinct ventral crest. From the fourth backward they become wider and flatter 
and the ventral crest subsides. 

The arches of the first three are about equal in size and similar to that of the 
last thoracic; behind this they increase in breadth and height. The posterior 
notches are much deeper than the anterior ones. 

The anterior articular processes are fused with the mammillary processes, and 
present dorsally concave surfaces for articulation with the posterior pair of the 
preceding vertebra. The posterior articular processes project distinctly from the 
arch at the base of the spinous process, and have ventrally convex articular surfaces, 
which fit into the concave surfaces of the anterior pair of the next vertebra. 

The transverse processes are elongated plates, flattened dorso- ventrally, which 
project outward and usually curve slightly downward; their length increases to 
the third or fourth, and then diminishes to the last, which is the shortest. The 
first one or two usually curve somewhat backward, the last two decidedly forward. 
Those of the fifth have an oval concave facet on the medial part of the posterior 
border for articulation with the sixth process; the latter has a corresponding con- 
vex facet on the anterior border, and a larger concave surface on the posterior border 
for articulation with the wing of the sacrum. Sometimes the fifth process has a 
small surface for articulation with the fourth. The medial part of the sixth process 



40 



THE SKELETON OF THE HORSE 



is tliick, the lateral part thinner, narrower, and curved forward. The medial part 
of the fifth is also somewhat thickened. Medial to the articular surfaces the edges 
of the transverse processes are cut into by notches, which form foramina by apposi- 
tion with each other and the sacrum. 

The spinous processes resemble those of the last two thoracic vertebrae. 




Spinous process 

Mammilhinj process 
Articular process 



\r f ■} ■ Transverse process 



Ventral spine 
Fig. 16. — Second Lumbar Vektebra of Horse; Posterior View. 



They are usually about equal in height, but minor differences are common, and the 
width diminishes in the last three. 

Development. — This is similar to that of the thoracic vertebrae. The extremi- 
ties of the transverse processes remain cartilaginous for some time after ossification 
is otherwise complete. 

The transverse processes of this region are considered equivalent to the proper transverse 
process + the costal element, and hence the distinctive term processus lateralis (s. costarius) 



Spinous process 

Vertebral foramen 
> Articular processes 



Transverse process 




Notch 



Body 



Articular surface for 
wing of sacrum 
-Last Lumbar Vertebra op Horse; Posterior View. 



has been proposed. The occurrence of a rib in connection with the transverse process of the first 
lumbar vertebra is common. Reduction of the number to five has been observed frequently, and 
may or may not be compensated by an additional thoracic vertebra. Very few cases are recorded 
of seven lumbar vertebra^ — especially with the normal thoracic number. An anomalous vertebra 
with mixed thoracic and lumbar characters sometimes occurs at the junction of the two regions. 



THE SACRUM 



41 



THE SACRUM 

The sacrum (Os sacrum) is formed by the fusion of five vertebrae, and is con- 
veniently described as a single bone. It is triangular in form and is wedged in 
between the ilia, with which it articulates very firmly on each side. Its long axis 
is gently curved and slightly oblique, so that the posterior end is a little higher 
than the anterior. It presents two surfaces, two borders, a base, and an apex. 

The dorsal surface (Facies dorsalis) presents centrally the five sacral spines 
(Processus spinosi), which are directed upward and backward, and have (with the 
exception of the first) tuberous summits which are sometimes bifid. 



Wing 




Transverse process 



Fig. 18. — Sacrum of Horse; Dorso-lateral View. 
I-V, Spinous processes; I-4, dorsal sacral foramina; 5, 0', articular processes; 6, surfaces of wings for articulation 
with transverse processes of last lumbar vertebra; 7, body of first sacral vertebra. Arrows point into sacral 
canal. 



The first spine is relatively thin and narrow, and is not so high as the sacral angle of the 
ilium. The second is the longest and highest, and the length and height diminish to the last. 
The bases of the spines are often fused in old subjects. 

On either side of the spines there is a groove, in which are the four dorsal sacral 
foramina (Foramina sacralia dorsalia); the dorsal branches of the sacral nerves 
emerge through them. 

The pelvic surface (Facies pelvina) is concave in its length, wide in front, 
narrow behind. The curvature is variable and is more pronounced in the mare 
than in the stallion. It is marked by four more or less distinct transverse lines 
(Lineae transversse) , which indicate the demarcation of the bodies of the vertebrae. 
At the ends of these lines are the ventral sacral foramuia (Foramina sacralia ven- 



42 



THE SKELETON OF THE HORSE 



tralia), which are larger than the dorsal series and diminish in size from first to 
last; they transmit the ventral divisions of the sacral nerves. 

The dorsal and ventral foramina communicate with the sacral canal and are 
together equivalent to the usual intervertebral foramina. 

The lateral borders are rough, thick in front, thin behind. 

The base (Basis ossis sacri) is directed forward, and is relatively very wide. 
It presents centrally the body of the first sacral segment, which is wide transversely, 
flattened dorso-ventrally, and has a rounded surface which articulates with the 
last lumbar vertebra through the medium of an intervertebral fibro-cartilage. 
The ventral margin projects slightly, forming the promontory (Promontorium) . On 




Fig. 19. — Sacrum of Horse; Ventral View. 
J- F, Bodies of original five vertebrse, marked off by transverse lines; /-4, ventral sacral foramina; 5, articular 
surface of body of first vertebra; 6, 6, notches; 7, 7, surfaces of wings for articulation with transverse processes of last 
lumbar vertebra; S, S, wings; 9, auricular surface; 10, lateral border; 11, transverse process; 12, posterior orifice 
of sacral canal; 13, last spinous process. 



either side of the body there is a smooth notch, which, with one on the last lumbar 
vertebra, forms a large foramen for the passage of the ventral branch of the last 
lumbar nerve. Above the body is the entrance to the sacral canal, flanked by a 
pair of articular processes, which project upward and forward from the arch, and 
have concave surfaces medially for articulation with those of the last Imnbar 
vertebra. Lateral to each of these is a smooth notch which is converted into a 
foramen by apposition with the last lumbar vertebra. The lateral parts of the base, 
the alae or wings (Alae sacrales), are strong prismatic masses with pointed ends. 
Each has in front a large, oval, slightly convex surface for articulation with the 
transverse process of the last lumbar vertebra. Posteriorly there is an elongated 
oval area which faces dorso-laterally; this is the auricular surface (Facies auricu- 



THE COCCYGEAL VERTEBRA 43 

laris), which articulates with the ihum; it is slightly concave in its length, and 
somewhat rough and irregular. The rest of the dorsal surface of the wing is rough- 
ened for ligamentous attachment, while the ventral surface is smooth. 

The apex (Apex ossis sacri) is the posterior aspect of the last sacral vertebra 
and is quite small. It presents the elliptical flattened surface of the body, above 
which is the triangular posterior opening of the sacral canal, surmounted by the 
last sacral spine. There is a pair of narrow notches between the arch and body, 
above which rudiments of articular processes may occur. 

The name sacral canal (Canalis sacralis) is applied to that part of the vertebral 
canal which traverses the sacrum. Its anterior part is large and has the form of 
a triangle with the angles rounded off; its width is nearly tAvice its height. Traced 
backward it is seen to diminish in size rapidly, and the posterior opening is small 
and triangular. 

The term lateral part (Pars lateralis) designates the portion lateral to the 
foramina, which results from the fusion of the transverse processes. 

Development. — The several sacral vertebrae ossify in the typical manner. 
Separate centers for costal elements in the lateral parts have not yet been found in 
the domesticated animals. Fusion begins in front, and is usually not complete 
till adult age.i The lateral parts unite before the bodies. It is rather curious 
that the epiphyseal plates of adjacent segments unite with each other before they 
fuse with the main portion of the bodies. 



THE COCCYGEAL VERTEBRA 

The coccygeal vertebrae (Vertebrae coccygeae) vary considerably in number, but 
eighteen may be taken as an average. From first to last they become reduced 
in size and, with the exception of a few at the beginning of the series, consist of 



] 'crtebral foramen Vertebral foramen 

Arch 
A rch 

Transverse process 



Spinous process Spinous process 

Vertebra 

Transverse proc- 



Groove 
Body Body 

Fig. 20. — First CoccygEAL Vertebra of Horse; Fig. 21. — Second Coccygeal Vertebra of Horse; 

View. Posterior View. 





Leader to arch points to rudimentary articular 

bodies only. The first three have bodies which are somewhat flattened dorso- 
ventrally, constricted in the middle, and have at the ends convex, elliptical, artic- 
ular surfaces. The ventral surface has a median groove (Sulcus vasculosus) for 
the coccygeal artery. The arch is small and triangular; it is formed of two flat 
plates which are prolonged to form a short spinous process with a thickened and 
often double summit. The anterior notches are absent. Functional articular 
processes are not present, but small rudiments of the anterior pair commonly occur. 
The transverse processes are relatively large plates which project horizontally 
outward. Further back the arch becomes incomplete dorsally, and soon disap- 
pears; the transverse processes gradually fade out, and the vertebrae are reduced 
to cylindrical rods of diminishing size. The last one has a pointed end. 

^ It is not rare to find fusion of some of the bodies incomplete even in adult subjects. 



44 



THE SKELETON OF THE HORSE 



Variations. — The number is said by good observers to vary between fourteen and twenty- 
one. In old age the first is often fused with the sacrum, and sometimes with the second. The 
arch of the third may be open. 



THE VERTEBRAL COLUMN AS A WHOLE 

In the mid-dorsal line is the series of spinous processes, which are low ridges 
in the cervical region with the exception of the second and seventh, reach their 
maximum height at the fourth and fifth thoracic vertebrae, and diminish to the 
fifteenth or sixteenth thoracic. Behind this they are about equal in height as far 
as the last lumbar and first sacral, which are somewhat lower. The second sacral 
spine is about as high as the middle luml^ar; behind this they diminish rather 
rapidly in height and fade out about the third coccygeal. Their inclination back- 
ward is most decided at the second thoracic and diminishes from the sixth or seventh 
to the sixteenth thoracic, which is vertical and is termed the anticlinal or dia- 
phragmatic vertebra. Behind this they are inclined a little forward until the 
sacrum is reached; here there is an abrupt change to the backward inclination, so 
that a considerable interspinous angle is formed. 

On either side of the spinous processes is a vertebral groove which contains the 
deep muscles of the spine. The floor of the groove is formed by the arches and 
articular processes. It is wide in the neck and narrows progressively in the back. 

Viewed from the side, the column presents a series of curves. When the head 
and neck are in the ordinary neutral position, the anterior part of the cervical spine 
forms a gentle curve, concave ventrally. The posterior cervical and first thoracic 
vertebrae form a more pronounced curve in the opposite direction. At the junction 
of the cervical and thoracic regions there is a marked change of direction, forming a 
ventral projection or angle. At the second thoracic vertebra a gentle curve, con- 
cave ventrally, begins. This is continued to the lumbo-sacral junction, where 
there is a change of direction, and hence a promontory. The sacrum has a variable, 
but never very pronounced, ventral concave curvature, which is continued in a 
much accentuated form in the coccygeal region. It should be noted that a line 
through the summits of the spines does not correspond to these curves formed by 
the bodies. 

The vertebral canal corresponds in its curvature to that of the bodies. Its 
caliber varies greatly at different points. The greatest diameter is in the atlas, 
where it contains the dens of the axis in addition to the spinal cord, and provision 
must be made for extensive movement. It is very much smaller in the axis. It 
widens considerably at the junction of the cervical and thoracic regions to accom- 
modate the cervical enlargement of the spinal cord. Beyond this it diminishes, 
and is smaller in the middle of the back than at any preceding point ; this is corre- 
lated with the small size of the spinal cord and the very limited movement of the 
spine here. Beyond the middle of the lumbar region it again enlarges considerably 
to contain the lumbar enlargement of the spinal cord. The caliber diminishes very 
rapidly from the second sacral segment backward, and the canal ceases to be com- 
plete at the fourth coccygeal vertebra. 

The transverse and vertical diameters of the vertebral canal at various points are given 
in the annexed table. The measurements were made on a horse of medium size; they represent 
the maximum width and height in the middle of the vertebra and are expressed in centimeters. 



Vertebra 


CI 


C2 


C4 


C7 


TIO 


L3 


L6 


SI 


So 




5.2 
4.2 


2.6 
2.5 


2.6 
2.1 


3.5 
2.5 


2.3 
1.7 


2.4 
l.S 


4.0 
2.5 


4.0 
2.1 


1.8 


Vertical 


1.5 



The articular processes are very large and wide apart in the neck, greatly 



THE RIBS 45 

reduced and much closer together in the back, larger and interlocking in the lumbar 
region. 

The transverse processes are large and outstanding in the neck, where they 
form the lateral boundary of a ventral groove occupied by the longus colli muscle. 
In the back they are short and stout, and are characterized by the facets for the 
tubercles of the ribs. On the first thoracic vertebra this facet is large, deeply con- 
cave, and situated almost directly outward from the cavity for the head of the rib; 
traced backward it becomes smaller and flatter, and gradually comes to lie behind 
the cavity for the head of the rib, with which it is fused on the last and often also on 
the next to the last thoracic vertebra. The processes in the lumbar region have a 
characteristic elongated plate-like form. In the sacral region they are fused to 
form the wings and lateral parts of the sacrum. In the coccygeal region they are 
at first of considerable size relatively, but undergo rapid reduction, and disappear 
at the fifth or sixth vertebra. 

The cavities for the heads of the ribs diminish progressively in size and depth 
from first to last. 

The mammillary processes are usually distinct on the fourteenth to the seven- 
teenth thoracic vertebrae. In front of these they blend with the transverse, behind 
with the anterior articular, processes. 

The length of the vertebral column (including the intervertebral fibro-cartilages) in a horse 
of medium size is about nine feet (ca. 2.7 meters). The relative lengths of the various regions ap- 
pear to vary most in the neck and back. The following average lengths of the several regions 
were obtained by measurement of several subjects: Cervical, 70 cm.; thoracic, 86 cm.; lumbar, 
34 cm.; sacral, 20 cm.; coccygeal, 60 cm. The percentage values are approximately 26, 32, 12.5 
7.5, 22. 



The Ribs 

There are usually eighteen pairs of ribs in the horse, but a nineteenth rib on 
one side or both is not at all rare. Eight are sternal ribs, the remainder asternal. 
Ribs from different parts of the series vary much in length, curvature, and other 
characters. We will therefore consider as a type a rib from the middle of the series 
first, and afterward note the chief serial differences; such a rib has the following 
characters : 

The shaft or body (Corpus costae) is elongated, relatively very narrow, and 
strongly curved; the curvature is most pronounced in the dorsal third, and the 
ventral part is twisted and inclined inward, so that when a rib is laid with its lateral 
surface on the table, the sternal end is raised. The lateral surface is convex in 
its length and also transversely; its anterior part is, however, grooved longitudin- 
ally. A distinct angle, i. e., a point at which the curve of the rib changes rather 
suddenly, as in man, can scarcely be said to exist in the horse. The term is some- 
times applied, however, to a corresponding rough elevation which gives attachment 
to the longissimus muscle. The medial surface is smooth, concave in its length, 
and rounded from side to side; the costal groove (Sulcus costse), situated posteriorly, 
is very distinct above and fades out about the middle; it contains the intercostal 
vein. The anterior border is concave, the posterior convex. 

The vertebral extremity (Extremitas vertebralis) consists of the head, neck, 
and tubercle. The head (Capitulum costse) has an articular surface (Facies 
articularis capituli costse) which is composed of two convex facets, anterior and 
posterior, separated by a groove (Sulcus capituli) for the attachment of the con- 
jugal ligament. It articulates with the cavity formed by facets on the bodies of 
two adjacent thoracic vertebrae and the intervertebral fibro-cartilage. The neck 
(Collum costse) is roughened above and in front. The tubercle (Tuberculum costse) 
is placed above and behind the junction of neck and shaft; it has an oval surface 



46 



THE SKELETON OF THE HORSE 



(Facies articularis tuberculi costae) for articulation with the transverse process of 
the corresponding thoracic vertebra. 

The sternal extremity (Extremitas sternalis) is slightly enlarged, and is united 
with the costal cartilage. 

The first rib is easily distinguished. It is shortest and the shaft widens greatly 
toward the sternal end. At the lower part of the anterior border there is a smooth. 



Tubercle 



^ Costal groove 



Head Neck Tubercle 



Groove 




Head 




Anterior border 




Anterior border - 




Sternal extremity 
Fig. 22. — Left Eighth Rib of Horse; Lat- 



Costo- 
chondral 
junction 



Sternal extremity of costal cartilage 

Fig. 23. — Right Eighth Rib and Costal Cartilage of 
Horse; Medial View. 



impression where the brachial vein curves around it; above this there is commonly 
a small tubercle (Tuberculum scaleni) which indicates the lower limit of the in- 
sertion of the scalenus muscle. The costal groove is absent. The head is large and 
has two facets of unecjual extent, which meet at an acute angle in front ; the smaller 
one faces forward antl articulates with the last cervical vertebra; the larger one is 
directed medially and articulates with the first thoracic vertebra. The neck is 
thick and very short. The tubercle is larger than that of any other rib and has an 



THE COSTAL CARTILAGES 



47 



Tubercle 



extensive articular surface which is convex in its length. The sternal end is larger 
than that of any other rib; it is thick and very wide, and is turned a little forward. 

The last rib is the most slender and regularly curved. It is usually but little 
longer than the second. The facet on the tubercle is confluent with that of the head. 
(This feature, however, is common on the seventeenth also, and may occur on the 
sixteenth.) 

The serial position of the other ribs may be determined approximately by the fol- 
lowing considerations : The length increases from the first to the tenth and eleventh 
and then diminishes. The width increases somewhat to the sixth and then diminishes. 
The anterior border is thin and sharp from the 
second to the eighth, and behind this becomes thick 
and rounded. The groove of the lateral surface is 
distinct on the fourth to the eighth inclusive. The 
curvature increases in degree rapidly from the second 
to the seventh, remains a])Out the same to the six- 
teenth, and then decreases very noticeably. In re- 
gard to dorso-ventral direction, the first rib inclines 
a little forward, the second is about vertical, while 
behind this they slope l)ackward in increasing de- 
gree, so that a transverse plane tangent to the ventral 
ends of the last pair cuts the third lumbar vertebra. 
The head and tubercle diminish in size from first to 
last. Their relative positions change, in that the 
tubercle of the first rib is almost directly lateral to 
the head, while further back it gradually comes to 
lie behind it. The neck is longest on the longest 
ribs, and is absent on the last two or three. A 
costo-transverse foramen (Foramen costo-transver- 
sarium) is formed between the neck and the trans- 
verse process. 

Development. — The ribs ossify in cartilage from 
three centers, one each for the shaft, head, and 
tul)ercle; the third center is absent in some of the 
posterior ribs. 




Cartilage 



-Left First Rib of Horse; 
Medial View. 



Variations. — A nineteenth rib on one side or both is not 
at all rare. It is usually imperfectly developed and quite vari- j-j^ 24. 
able. In many cases it is a mere strip of cartilage connected 
by ligament with the first lumbar transverse process; in other 
cases it is well developed, and may be fused with the process; 

in others again it is connected with a vertebra which may be thoracic or lumbar or ambiguous 
in character. It is commonly floating, but may be attached to the eighteenth costal cartilage. 
Reduction in number is uncommon. In rare cases the first rib is imperfectly developed and does 
not reach to the sternum. Partial fusion of adjacent ribs and other anomalies occur. 



THE COSTAL CARTILAGES 

The first costal cartilage is an inch or more (2.5 to 3 cm.) in length. The 
dorsal end is very wide and thick. The sternal end is small. The two articulate 
with each other as well as with the sternum. The cartilages of the other sternal 
ribs increase progressively in length and become more rounded. The sternal end 
is enlarged and has an elliptical convex facet for articulation with the sternum. 
The cartilages of the asternal ribs are long, slender, and pointed. The ninth is 
very firmly attached to the eighth; it and the next two are the longest and behind 
this they diminish progressively in size. The cartilages of the asternal ribs overlap 
and are attached to each other by elastic tissue, forming the costal arch (Arcus 



48 



THE SKELETON OF THE HORSE 



costarum). Except in the case of the first, the cartilage does not continue the 
direction of the rib, but forms with the latter an angle which is open in front, and 
increases from second to last. More or less extensive ossification is to be regarded 
as a normal occurrence, especially in the cartilages of the sternal ribs. 



Costal 
carlilages"^^^^ 



Cariniform 
cartilage 



Ribs 



The Sternum 

The sternum of the horse is shaped somewhat like a canoe; it is compressed 

laterally, except in its posterior part, which is flattened dorso-ventrally. It is 

inclined obliquely so that the posterior end 
is about six to eight inches (15 to 20 cm.) 
lower than the anterior. 

The dorsal surface (Facies dorsalis) has 
the form of a very narrow isosceles triangle 
with the apex in front. It is concave longi- 
tudinally, flattened transversely. 

The lateral surfaces (Facies laterales) 
are convex above, slightly concave below, and 
diminish in extent behind. Each presents on 
its upper part seven costal cavities (Foveas 
costales), with which the sternal ends of the 
second to the eighth costal cartilages inclu- 
sive articulate. These cavities are situated 
in series at the intersternebral junctions. 
The first four are elliptical in outline with 
the long diameter vertical, and are sepa- 
rated by considerable regular intervals. 
The others are progressively smaller, more 
circular, and closer together. The area 

below these cavities gives attachment to the pectoral muscles. 

The dorso-lateral borders separate the dorsal and lateral surfaces. They give 

attachment to the lateral branches of the sternal ligament. 

The ventral border forms the prominent keel-like crest of the sternum (Crista 

sterni) which may be felt in the living animal; it fades out behind. 




Xiphoid cartilage 



Fig. 25. — Sternum and Costal Cartilages of 
Horse; Ventral View. (After Ellenberger- 
Baum, Anat. f. Kiinstler.) 




yi/rarinJfor"l 



r a. I 

Fig. 26. — Sternum of Horse; Lateral View. 
The sternebrae are designated by Roman numerals and the costal facets by ordinary figu 



The anterior extremity or manubrium sterni^ can be distinctly felt in the 
central furrow of the breast. It consists largely of a lal;erally compressed cartil- 
aginous prolongation, commonly called the cariniform cartilage. Its lateral sur- 
faces are flat and furnish attachment to muscles of the breast and neck. The 

^ The manubrium sterni of man is equivalent, strictly speaking, to the cariniform cartilage 
-h the first osseous segment of the horse. 



THE THORAX — THE OCCIPITAL BONE 



49 



ventral border is rounded, and is continued backward on the body of the bone. 
The dorsal border is concave and has an articular cavity for the first pair of costal 
cartilages. 

The posterior extremity is formed by the xiphoid cartilage (Processus xiphoideus). 
This is a thin plate, connected in front with the last bony segment by a relatively 
thick, narrow neck, and expanding in nearly circular form behind and laterally. 
Its dorsal surface is concave, and gives attachment to the diaphragm. The ventral 
surface is convex and furnishes attachment to the transversus abdominis and the 
linea alba. The free margin is very thin. 

Development. — At birth the sternum of the horse consists of seven bony seg- 
ments termed sternebrse, which are united by in- 
tersternebral cartilages. The last two sternebra} 
fuse in the second month, but the others do not 
usually unite completely even in old age. The 
sternebrse consist of very vascular spongy bone 
covered by a very thin layer of compact sub- 
stance. The adult sternum thus consists to a /v-^IP^ Jil ^ ^ - First 
very considerable extent of persisting cartilage, w .,« ^^"'^fc.^vl thoracic 

viz., the intersternebral cartilages, the ventral 
keel, and the extremities; in old age these under- 
go partial ossification. 



THE THORAX 



The bony thorax of the horse is remarkably 
compressed laterally in its anterior part, but 
widens greatly behind. The anterior aperture 
(Apertura thoracis cranialis) is oval and very 
narrow below; in a horse of medium size its 
greatest width is about 4 inches (10 cm.), and its 
height 7 to 8 inches (ca. 18-20 cm.). The ventral 
wall or floor is about 16 inches (40 cm.) long, and 
the dorsal wall or roof about 38 to 40 inches 
(95-100 cm.) long. The height from the last seg- 
ment of the sternum to the seventh or eighth 
thoracic vertebra is about twice that of the anterior 
aperture; this is due to the obliquity and diver- 
gence of the roof and floor. The greatest width of 
the posterior aperture is about 20 to 24 inches 

(50-60 cm.). The intercostal spaces (Spatia intercostalia) increase in width from 
the first to the seventh or eighth, and then diminish. Their average width is 
about I'j/i to 13^ inches (3-3.5 cm.). 




vertebra 



First rib 



Cariniform 
cartilage of 
sternum 



Fig. 27. — Anterior Aperture of Tho- 
rax OF Horse. (After Schmaltz, Atlas 
d. Anat. d. Pferdes.) 



The Skull 

(A) BONES OF THE CRANroM 
The bones of the cranium (Ossa cranii) are the occipital, sphenoid, ethmoid, 
interparietal, parietal, frontal, and temporal. The first three are single, the others 
paired. 

The Occipital Bone 

The occipital bone (Os occipitale) is situated at the posterior part of the era- 
oium, of which it forms the posterior wall and part of the ventral wall or base.^ 
1 The long axis of the skull is considered to be horizontal in these descriptions. 



50 



THE SKELETON OF THE HORSE 



Its lower part is perforated centrally by a large, almost circular opening, the 
foramen magnum (Foramen occipitale magnum), at which the cranial cavity and 
vertebral canal join. The foramen is bounded laterally and dorsally by the lateral 
parts of the bone, and ventrally by the basilar part. Above the lateral parts — 
but not entering into the formation of the foramen magnum — is the squamous' part. 

The lateral parts (Partes laterales)^ bear the occipital condyles (C'ondyli oc- 
cipitales), which articulate with the atlas. The condyles are obliquely placed, 
wide apart dorsally, and separated ventrally by a small interval (Incisura inter- 
condyloidea). The articular surface is curvecl so sharply in the dorso- ventral 

Occipital Parietal Squamous temporal 




Fig. 2S. — Skull of Horse, Right View. 
1, Occipital condyle; 2, paramastoid process; 3, mastoid process; 4> posterior process of squamous temporal bone; 
6, external acoustic process; 6, zygomatic process of temporal bone; 7, postglenoid process; 8, glenoid cavity of squamous 
temporal bone; 9, condyle of same; 10, supraorbital process of frontal bone; 11, temporal part of frontal bone; 12, 
orbital part of frontal bone; /5, fossa sacci lacrimalis; 74, orbital surface of lacrimal bone; 75, lacrimal tubercle; 16, 
zygomatic process of malar bone; 77, maxillary tuberosity; ZS, facial crest; 79, infraorbital foramen; ^0, naso-maxil- 
lary notch; 21, body of premaxilla; 21', nasal process of same; 22, body of mandible; 23, mental foramen; 24, 25^ 
horizontal and vertical parts of ramus of mandible; 26, condyle of mandible; 27, coronoid process of mandible; 2S, 
angle of mandible; 29, vascular impression; 30, interalveolar margin; 31, incisor teeth; 32, canine teeth; 33, hyoid 
bone (great cornu) . 



direction as to form a blunt ridge. The cranial surface is concave and smooth. 
Lateral to the condyle is the paramastoid process (Processus paramastoideus),^ a 
strong plate of bone which projects downward and backward; its lateral surface is 
convex and roughened for muscular attachment ; its medial surface is concave from 
end to end. Between the root of this process and the condyle is a smooth depres- 
sion, the condyloid fossa (Fossa condyloidea ventralis) ; in this is the h3rpoglossal 
foramen (Foramen hypoglossi), which transmits the nerve of like name. 

The basilar part (Pars basilaris)^ is a strong, somewhat prismatic bar, which 

1 Also known as the exoccipitals. ^ Also known as the styloid or jugular process. 

' Also termed the basi-occipital or basilar process. 



THE OCCIPITAL BONE 



51 



extends forward from the ventral margin of the foramen magnum. It is wide and 
flattened behind, narrower and thicker in front. The ventral surface is rounded. 
The cranial surface is concave and smooth ; its posterior part supports the medulla 
oblongata, and its anterior part has a shallow cavity on which the pons rests. The 
lateral borders are thin and sharp, and form the medial margin of the foramen 
lacerum. The anterior end has, in the young subject, a semicircular, flat, pitted 
surface which is attached to the body of the sphenoid bone by a layer of cartilage ; 
in the adult there is complete fusion. On the ventral aspect of the junction are the 
basilar tubercles (Tubercula basilaria) for the attachment of the ventral straight 
muscles of the head. 

The squamous part (Squama occipitalis)^ is the somewhat quadrilateral mass 




Fig. 20. — Occipital Bone of Colt; Front View. 
1, Depression of squamous part for cort'bclluin; 2, foramen magnum; 3, paramastoid process; 4, condyloid fossa; 
a, squamous part; 6, lateral part; c, basilar part; rf, junction with interparietal bone; e, junction with parietal bone; 
/, junction with petro-mastoid part of temporal bone. 



situated dorsal to the lateral parts, from which it remains distinct till the second 
year. The external surface is crossed by a very prominent ridge, the nuchal crest 
(Crista nuchalis) ; the middle part of this is thick, transverse in direction, and forms 
the highest point of the skull when the head is in the ordinary position; laterally it 
becomes thinner and runs downward and forward to join the temporal crest.- The 
crest divides the surface into two very unequal parts; the small dorsal area (Planum 
parietale) presents a median ridge which is the posterior part of the external parietal 
crest (Crista sagittahs externa) ; the large area ventral to the crest (Planum nu- 
chale) has a central eminence, the external occipital protuberance, on which the funic- 
ular part of the ligamentum nuchte is attached. The internal surface is concave 

^ Also known as the supraoccipital. 

^ The nuchal crest of this description is equivalent to the external occipital protuberance 
and superior nuchal line of man; it has been commonly termed the occipital crest, but is not the 
equivalent of that feature of the human skull. A curved line a httle lower down, which is con- 
tinued on the paramastoid process, represents the inferior nuchal line of man. 



52 THE SKELETON OF THE HORSE 

and presents a deep central depression and two shallower lateral ones which adapt 
it to the surface of the cerebellum. 

The parietal border (INIargo parietalis) is united by suture with the parietal 
and interparietal. The mastoid border (Margo mastoideus) joins the petro- 
mastoid part of the temporal bone. The basilar part is connected by cartilage (in 
the young subject) with the body of the sphenoid. The condyles articulate with 
the atlas. 

Development. — The occipital bone ossifies in cartilage from four centers, and 
consists at birth of four pieces as described above. The lateral parts unite with the 




11 10 

Fig. 30. — Cranium of New-born Fo.\l; Posterior View. 
A, B, C, Squamous, lateral, and basilar parts sf occipital bone; D, interparietal bone; E, parietal bone; F, squa- 
mous temporal bone; 6', petro-mastoid part of temporal bone; 1, external occipital protuberance; 2, 2, depressfons in 
which complexus tendons are attached; 3, sutural (preinterparietal?) bone; 4, supraorbital process; 5, zygomatic 
process of temporal bone; 6, postglenoid process; 7, posterior process of squamous temporal bone; 8, mastoid process; 
9, paramastoid process; 10, occipital condyle; 11, arrow in foramen magnum. 

basilar part at three to four months, and with the squama in the second year, when 
the bone is consolidated. 

The parieto-occipital suture and the spheno-occipital synchondrosis are ob- 
literated about the fifth year usually. The occipito-mastoid suture partially ossifies 
in old subjects. 

The Sphenoid Bone 

The sphenoid bone (Os sphenoidale) is situated in the base of the cranium, its 
central part lying in front of the basilar part of the occipital. It consists of the 
body, two pairs of wings, and two pterygoid processes. 

The body (Corpus) is situated medially; it is cylindrical, but flattened dorso- 
ventrall}', and wider in front than behind. Its ventral surface (Facies externa) is 
convex in the transverse direction, and its anterior part is concealed to a large extent 
by the vomer and pterygoid bones. The cerebral surface (Facies cerebralis) 
presents the following features: (1) In front there is a raised, flattened part (Jugum 
sphenoidale) which is partially subdivided by a median elevation into two slightly 
concave lateral areas; this part has a posterior, thin, free margin (Limbus sphe- 



THE SPHENOID BONE 



53 



noidalis), which overhes the entrance to the optic foramina. The median ridge is 
termed the ethmoidal spine, since it fits into a notch of the cribriform plate of the 
ethmoid bone and joins the crista galh. (2) Just behind this and at a lower level 
is a smooth transverse depression, the optic groove (Sulcus chiasmatis), on which 
the optic chiasma rests. (3) From each end of this groove the optic foramen 
(Foramen opticum) passes forward and outward to terminate in the posterior part 
of the orbital fossa. ^ (4) Near the posterior end is a central depression, the hypo- 
physeal or pituitary fossa (Fossa hypophyseos) , which lodges the hypophysis cerebri 
or pituitary body. On each side of this is a shallow groove for the internal carotid 
artery and the cavernous sinus. The anterior end is expanded, and joins the eth- 
moid and palatine bones; it is excavated to form the sphenoidal sinuses. These 
cavities extend back as far as the optic 
groove, and are usually continuous in front 
with the cavities in the vertical parts of the 
palate bones;- they are separated by a com- 
plete septum which is not always median. 
The posterior end is flat and is joined to 
the basilar part of the occipital ; at the line 
of junction there is dorsally a slight trans- 
verse elevation, the spheno-occipital crest 
(Crista spheno-occipitalis). 

The orbital wings (Alse orbitales) curve 
dorso-laterally from the sides of the body of 
the presphenoid. Their cerebral surface is 
concave, and is marked by digital impres- 
sions (Impressiones digitatse) for the gyri 
of the cerebrum. The lateral surface is con- 
vex and is largely concealed by the overlap- 
ping temporal wing and the squamous tem- 
poral and frontal bones ; a narrow part of it 
(Facies orbitalis) is uncovered on the medial 
wall of the orbital cavity at the sphenoidal 
notch of the frontal bone. The dorsal bor- 
der unites with the frontal bone at the 
spheno-frontal suture. The anterior border 
joins the ethmoid at the spheno-ethmoidal 
suture ; at its lower part it concurs with the 
ethmoid and frontal in the formation of the 
ethmoidal foramen (Foramen ethmoidale).^ 
The posterior border is overlapped by the 
temporal wing and the squamous temporal. 
The root of the wing is perforated by the 
optic foramen (Foramen opticum) . Immedi- 
ately below and behind the latter (i. e., beneath the root) is the foramen orbitale. 
Below this, and separated from it usually by a thin and often incomplete plate, is a 
larger opening, the foramen rotundum, which is bounded externally by the root of 
the pterygoid process. 

The temporal wings (Alse temporales) extend outward and somewhat upward 
from the body of the postsphenoid; they are smaller than the orbital wings and 




Fig. 31. — Sphenoid Bone and Basilar Part of 
Occipital Bone of New-born Foal; Dorsal 
View. 

C, Body of presphenoid; C, body of postsphe- 
noid; B.O., basilar part of occipital bone; A.o., orbital 
wing of sphenoid bone; A.t., temporal wing of sphe- 
noid bone; 1, 1, optic foramina; 2, optic groove; 3, 
hypophyseal fossa; 4, 5, grooves; 6, ethmoidal 
notch; 7, ethmoidal spine; 8, junction with crib- 
riform plate of ethmoid bone; 9, junction with 
frontal bone; 10, junction with squamous temporal 
bone; 11, margin of foramen lacerum anterius; 12, 
spheno-occipital crest; 13, junction of basilar part 
of occipital bone with lateral part. 



1 This foramen might well be called a canal, since it is an inch or more in length. 

2 The cavity so formed may be termed the sphenopalatine sinus. The sphenoidal sinus may 
be a separate cavdty which communicates only with the ventral ethmoidal meatuses; this arrange- 
ment exists in about a third of the cases according to Paulh. 

' Also called the internal orbital foramen. 



54 THE SKELETON OF THE HORSE 

are irregularly quadrilateral in outline. The temporal surface (Facies temporalis) 
enters into the formation of the infratemporal fossa, and bears the pterygoid process 
on its anterior part; at the junction with the body there is a small groove which 
leads forward to the pterygoid canal. The cerebral surface (Facies cerebralis) 
presents, at the junction with the body, two longitudinal grooves (Sulci nervorum). 
The lateral groove is the larger, and leads forward to the foramen rotundum; it 
contains the maxillary nerve. The medial groove conducts to the foramen orbitale, 
and contains the cavernous sinus of the dura mater. The outer groove is bounded 
laterally by a thin overhanging crest, on which is a small groove for the fourth nerve. 
The remainder of the surface is concave and supports the pyriform lobe of the brain. 
The dorsal border joins the squamous temporal at the spheno-squamous suture. 
The anterior border joins the orbital A\dng above; below this it is free and forms the 
pterygoid crest (Crista pterygoidea) . The crest is continued on the pterygoid 
process; on or under its upper part there is usually a small opening, the trochlear 
foramen (Foramen trochleare). Just behind the crest is the foramen alare parvimi,^ 
through which the anterior deep temporal artery emerges from the alar canal of 
the pterygoid process. The posterior border forms the anterior boundarj?- of the 
foramen lacerum; it presents three notches, which are, from within outward, the 
carotid, oval, and spinous (Incisura carotica, ovalis, spinosa). The angle of junc- 
tion of the dorsal and posterior borders articulates with the parietal bone. 

The pterygoid processes (Processus pterygoidei) arise from the temporal wings 
and the body. They project downward and forward, and curve outward at the 
lower part. The root is perforated by the alar canal (Canalis alaris),- which trans- 
mits the internal maxillary artery. From this canal a branch leads upward and 
forward to open at the foramen alare parvum. The lateral surface is concave, and 
is marked by lines for muscular attachment. The medial surface is convex; it is 
largely concealed by the overlapping palate and pterygoid bones. 

The pterygoid canal (Canalis pterygoideus)^ continues the groove noted on the 
ventral surface of the temporal wing at its junction with the body. It extends for- 
ward and upward between the root of the pterygoid process, the presphenoid, and 
the pterygoid bone, and opens in the posterior part of the pterygo-palatine fossa. 
It transmits the nerve of the pterygoid canal. 

Development. — The sphenoid is ossified in cartilage, and consists in early life 
of two distinct parts, the presphenoid and postsphenoid. The former develops 
from two centers, one in each wing; the latter has three centers, one for the body 
and one for each wing. The pterygoid processes ossify from the centers of the 
temporal wings. 

In the new-born foal the unossified dorsal part of the orbital wing fits into a hiatus of the 
frontal bone; in some cases it comes to the surface through a defect in the frontal bone at the place 
where the horn process is situated in animals which have frontal horns. 

The Ethmoid Bone 

The ethmoid bone (Os ethmoidale) lies in front of the body and orbital wings 
of the sphenoid. It projects forward between the orbital parts of the frontal bones 
and enters into the formation of the cranial, nasal, and paranasal cavities.^ It 
consists of four parts — the cribriform plate, two lateral masses, and the perpen- 
dicular plate. 

The cribriform plate (Lamina cribrosa) is a sieve-like partition between the 

^ Also termed the temporal foramen. 

^ This is also called the subsphenoidal canal or pterygoid foramen. 

^ Also known as the Vidian canal. 

^ On account of its deep situation and the fact that it cannot be separated from its surround- 
ings, the ethmoid must be studied by means of appropriate sagittal and transverse sections of the 
ekuU. 



THE ETHMOID BONE 



55 



cranial and nasal cavities. Its margin joins the orbital wings of the sphenoid 
laterally, the body of the sphenoid ventrally, and the cranial plate of the frontal 
bones dorsally. Its cerebral surface is divided into two parts by a median ridge, 
the crista galli, which may be regarded as the intracranial projection of the perpen- 
dicular plate. Each half forms a deep oval cavity, the ethmoidal fossa, which 
lodges the olfactory bulb. The plate is perforated by numerous small foramina for 
the passage of the olfactory nerve filaments, and on either side is the much larger 
ethmoidal foramen. The nasal surface is convex, and has the lateral masses 
attached to it. 

Each lateral mass or labyrinth (Labyrinthus ethmoidalis) is conical in shape and 
its base is attached to the cril)riform plate. It projects forward into the posterior 




Vomer 

Fig. .32. — Cross-section of Cranium of Horse. The Section Passes Through the Middle of the Orbits and 

IS Viewed from In Front. 
1, Lateral mass of ethmoid bone; 2, perpendicular plate of same; 3, common nasal meatus; 4, sphenopalatine 
sinu=i; .■>, perpendicular part of palatine bone; 6, zygomatic process of temporal bone; 7, zygomatic arch; 8, orbital 
part of frontal bone. 



part of the nasal cavity. The medial surface is separated by a narrow space from the 
perpendicular plate. The lateral surface is convex and faces chiefly into the frontal 
and maxillary sinuses, but is attached behind to the inner wall of the orbital cavity; 
it is covered by a very thin layer of bone, the lamina lateraUs. The mass consists 
of a large number of delicate, scroll-like plates of bone, termed ethmo-turbinates.^ 
These are attached to the lamina lateralis, and are separated by narrow intervals 
termed ethmoidal meatuses, which communicate with the nasal cavity. In the 
fresh state the ethmo-turbinates are covered with mucous membrane. 

The lateral mass is a very complex structure, the arrangement of which may be understood 
by examination of cross-sections. Each mass consists of six turbinates which extend almost to the 

' The term "ethmoid cell," borrowed from human anatomy, should not be retained, since 
it connotes an entirely erroneous conception of these structures in macrosmatic animals, such as 
those under consideration. 



56 



THE SKELETON OF THE HORSE 



perpendicular plate and are termed endoturbinates. These diminish in size from above down- 
ward; the largest is attached to the nasal bone, and is hence usually called the dorsal or nasal 
turbinate; the second is much smaller, and is very commonly termed the great ethmoid cell. 
The cavaty enclosed by this communicates laterally with the maxillary sinus, but not directly 
with the nasal cavity. Between the endoturbinates are twenty-one small ectoturbinates, and 
all are beset ^\-ith secondary and tertiary coiled lamellae. 

The perpendicular plate (Lamina perpendicularis) is median, and forms the 
posterior part of the septum nasi. Its lateral surfaces are nearly plane, but are 
marked below by some grooves and ridges; they are covered by the nasal mucous 
membrane. The anterior border is irregular and is continuous with the septal 
cartilage. The posterior border projects into the cranial cavity as a ridge, the 

Posterior end Siipraorbital 
of frontal sinus process 

{sawn off) 




Frontal bone {temporal pari) 
Orbital icing of sphenoid 



Foramen orbitale 
— Foramen rotundum 
Alar canal 



Body of sphenoid Pterygoid process 



Fig 33. — Cross-section of Cranium of Horse. The Section is Cut Just in Front of the Temporal Condyle 

AND Is Viewed from Behind. 

1, Internal plate of frontal bone; 2, crista galli; 3, cribriform plate; 4, ethmoidal foramen; 5, ethmoidal spine of 

sphenoid bone; 6, optic foramina. 



crista galli. The dorsal border joins the frontal l^ones at their line of junction. 
The ventral border is received into the groove of the vomer. 

Development. — The ethmoid develops in cartilage from five centers, two for 
each lateral mass, and one for the perpendicular plate; from the latter ossification 
extends into the cribriform plate. At birth the perpendicular and cribriform plates 
are cartilaginous. By the time ossification is complete the ethmoid has united 
with surrounding bones to such an extent that it cannot be separated intact for 
study. 

The Interparietal Bone 

This bone (Os interparietale) is centrally placed between the squamous part 
of the occipital and the parietal bones. It is usually described as a single bone, 
although it ossifies from two chief lateral centers, and is often distinctly paired in 
skulls of young foals. 



THE PARIETAL BONES 



57 



The external, parietal surface (Facies parietalis) is quadrilateral and is flat and 
smooth in the very young foal; later it presents the parietal crest. 

The internal, cerebral surface (Facies cerebralis) presents the internal occipital 
protuberance, a three-sided process which projects downward and forward into the 
cranial cavity between the cerebral hemispheres and the cerebellum; it has three 
concave surfaces, and three sharp borders which form part of the tentorium osseum. 
Behind the base of the protuberance there is a transverse groove for the sinus com- 
municans of the dura mater. 

The posterior border is thick; it joins the squamous part of the occipital 
bone. The lateral and anterior borders are 
united with the parietal bones. Squaytwus part of 

Development.— The interparietal ossi- occipital bone 

fies in membrane from two chief lateral cen- 
ters.^ It fuses first with the parietals, some- 
what later with the occipital, but the period 
at which this union takes place is quite 
variable. 

The Parietal Bones 

The two parietal bones (Ossa parie- 
talia) form the greater part of the roof of 
the cranium; they unite in the median line, 
forming the parietal suture. Each is quadri- 
lateral in outline and has two surfaces and 
four borders. 

The external, parietal surface (Facies 
parietalis) is convex, and is marked by a 
more or less prominent curved line, the ex- 
ternal parietal crest; this is median in its 
posterior part, and is continuous with the 
crest of like name on the interparietal and 
occipital; in front it curves outward and is 
continuous with the frontal crest. The sur- 
face lateral to the crest (Planum temporale) 
enters into the formation of the temporal 
fossa, and is roughened for the attachment 
of the temporal muscle. 

The internal, cerebral surface (Facies 
cerebralis) is concave. It presents numerous 
digital impressions (Impressiones digitatae) 

which correspond to the gyri, and ridges (Juga cerebralia) which correspond to the 
sulci, of the cerebrum. There are also furrows (Sulci vasculosi) for the meningeal 
arteries. Along the medial border there is a sagittal groove (Sulcus sagittalis) for 
the superior longitudinal sinus. 

The anterior border joins the frontal bone at the parieto-frontal suture (Sutura 
parieto-f rontalis) . 

The posterior border meets the occipital bone at the parieto-occipital suture. 
Below this junction it curves inward and concurs with the temporal bone in the 
formation of the temporal canal (Meatus temporalis) . A transverse groove (Sulcus 
transversus) connects this canal with the sagittal sulcus. 

The medial border is thick and serrated. It joins its fellow in great part at the 
parietal suture, but (in the young subject) meets the interparietal at its posterior 

^ According to Martin, there are originally four centers, two anterior and two posterior 
(smaller) ones, which fuse in a variable manner. 




Fig. 34. — Interparietal and Squamous Part or 
Occipital Bone of New-born Foal; Ven- 
tral View. 

1, Junction of interparietal with squamous 
part of occipital bone; 2, interparietal suture; 3, 
internal occipital protuberance; 4, transverse groove 
for sinus; 5, depression for vermis cerebelli; 6, de- 
pression for hemisphere of cerebellum; 7, junction 
of squamous part with lateral part of occipital 
bone; 8, junction of occipital with petro-mastoid; 
9, 9, junction of interparietal with parietal. 



58 



THE SKELETON OF THE HORSE 



part. The line of junction of the two parietal bones is marked internally by the 
internal parietal crest (Crista parietalis interna). 

The lateral border is })eveled and is overlapped by the squamous temporal 




Fig. .35.— Right Parietal Bone of New-born Foal; Dorso-lateral View. 

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamoua 

temporal; .5, junction with frontal, 

bone, forming the squamous suture (Sutura squamosa). The angle of junction of 
the lateral and posterior liorders articulates with the posterior angle of the temporal 
wing of the sphenoid. 

Development. — Each parietal bone ossifies in membrane from a single center. 




Fig. 36. — Right Parietal Bone of New-born Foal, Cerebral Surface. 

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamous 

temporal; 5, junction with frontal; 6, edge which concurs with temporal bone in formation of temporal canal. 



In the young foal the central part of the bone is more convex than in the adult and 
forms a prominence similar to the pronounce 1 tuber parietale of the young child; 
the external parietal crest is not present, and the external surface is smooth. The 



THE FRONTAL BONES 



59 



parietal suture is usually closed at four years, the parieto-occipital at five years, and 
the squamous at twelve to fifteen years. 

The Frontal Bones 

The frontal bones (Ossa frontalia) are situated on the limits of the cranium 
and face, between the parietals behind and the nasal bones in front. Each is 
irregularly quadrilateral, and consists of naso-frontal, orbital, and temporal parts. 

The naso-frontal part (Pars naso-frontalis) forms the basis of the forehead. 
Its external or frontal surface (Fades frontalis) is nearly flat, and is smooth and 
subcutaneous ; it is separated from the temporal part by the external frontal crest 
(Crista frontalis externa). At the junction with the orbital part the supraorbital 
or zygomatic process (Proc. zygomaticus) curves outward and downward to join 
the zygomatic arch. The process partially separates the orbit from the temporal 
fossa; its root is perforated by the supraorbital foramen (Foramen supraorbitale), 
or presents instead a notch on its anterior l)order; its upper surface is convex, while 
the orbital surface is concave and smooth, forming a shallow fossa for the lacrimal 




Fir,. 37. — Left Frontal Bone of New-born Fo.\l; Ventro-medi.\l View. 
.4, Cerebral surface; B, B, vorbital part; C, temporal part; D, nasal surface; 1, surface of junction with opposite 
bone; 2, frontal sinus; 3, ridge to which cribriform plate of ethmoid bone is attached; 5, fissure into which orbital wing 
of .sphenoid bone fits; 6, sphenoidal notch; 7, supraorbital process; 8, junction with nasal bone; 9, junction with pari- 
etal bone; 10, junction with squamous temporal bone. 



gland (Fossa glandulae lacrimalis). The internal surface enters into the formation 
of the cranial and nasal cavities. The two plates of the bone separate and diverge 
in front, and thus inclose a large air-space which is part of the frontal sinus. The 
internal plate curves downward and forward and joins the cribriform plate of the 
ethmoid. Beyond this it inclines upward and joins the external plate at the naso- 
frontal suture. The cerebral surface presents digital impressions for the cerebral 
gyri. The nasal surface is longitudinally grooved. The external plate extends 
forward and joins the nasal and lacrimal bones. 

The orbital part (Pars orbitalis) forms the major part of the medial wall of the 
orbital cavity. It is separated from the naso-frontal part by a prominent ridge 
which is part of the orbital margin. Its orbital surface (Facies orbitalis) is concave 
and smooth, and presents superiorly a small depression (Fovea trochlearis), which 
is bridged by a small bar of cartilage, around which the superior oblique muscle of 
the eye is reflected. The lower border concurs with the orbital wing of the sphenoid 
in the formation of the ethmoidal foramen. The nasal surface faces into the 
frontal sinus and is to a small extent united with the lateral mass of the ethmoid. 

The temporal part (Pars temporalis) is separated from the orbital part by the 



60 THE SKELETON OF THE HORSE 

deep sphenoidal notch (Incisura sphenoidalis), which is closed by the orbital wing 
of the sphenoid. Its lateral svurface forms part of the inner wall of the temporal 
fossa. The medial surface is largely covered by the orbital wing of the sphenoid 
in the young subject, but later forms part of the wall of the frontal sinus. 

The principal connections of the frontal bone are as follows: (1) The medial 
border joins its fellow at the frontal suture. (2) The anterior border meets the 
nasal and lacrimal at the naso-frontal and fronto-lacrimal sutures. (3) Laterally 
it forms the spheno-frontal suture with the orljital wing of the sphenoid, and also 
joins the palatine bone and maxilla at the fronto-palatine and fronto-maxillary 
sutures. (4) Posteriorly it meets the parietal at the parieto-frontal suture, and 
articulates below this with the squamous temporal at the squamous suture. 
(5) The extremity of the supraorbital process unites with the zygomatic process 
of the temporal bone. 

Development. — Each ossifies in membrane from one center which appears in 
the root of the supraorbital process. In the new-born foal there is a slit between 
the cranial plate and the orbital and temporal plates which receives the unossified 
dorsal part of the orbital wing of the sphenoid. 

The Temporal Bones 

The temporal bone (Os temporale) forms the greater part of the lateral wall 
of the cranium. It is situated between the occipital behind, the parietal dorsally, 
the frontal in front, and the sphenoid ventrally. It consists in the horse of two 
distinct parts, squamous and petrous. 

1. The squamous temporal bone (Squama temporalis) is a shell-like plate 
which has two surfaces and four borders. 

The cerebral surface (Facies cerebralis) is concave and is largely overlapped 
by the surrounding bones, but its central part is free and presents digital impres- 
sions and vascular grooves. 

The temporal surface (Facies temporalis) is convex, and enters into the forma- 
tion of the temporal fossa. From its ventral part there springs the zygomatic 
process (Processus zygomaticus) , which forms the lateral boundary of the tem- 
poral fossa. The process is at first directed outward, and is wide and flattened 
dorso-ventrally. It then turns forward, becomes narrower, and is twisted so that 
its surfaces are medial and lateral. Its anterior end is pointed and joins the zygo- 
matic process of the malar bone, wdth which it forms the zygomatic arch (Arcus 
zygomaticus) . The narrow anterior part has a convex lateral surface and a concave 
medial one. Its dorsal border has a rough area for articulation with the supra- 
orbital process of the frontal. Its ventral border is wide and rough. The wide 
posterior part presents on its ventral face a surface for articulation with the condyle 
of the mandible. This surface consists of a transversely elongated condyle (Condy- 
lus temporalis) , behind which is the glenoid cavity. The fossa is limited behind by 
the postglenoid process (Processus postglenoidalis), the anterior surface of which 
is articular. Behind this process there is a fossa, in which is the postglenoid fora- 
men (F. postglenoidale), the external opening of the temporal canal. The dorsal 
surface is concave and forms the lateral boundary of the temporal fossa. The 
dorsal border is sinuous and is continuous behind with the temporal crest. 

The posterior process (Processus aboralis) springs from the posterior part of 
the squama. Its lateral surface bears the temporal crest, which forms here the 
lateral limit of the temporal fossa. The medial surface forms the outer boundary 
of the temporal canal, and is elsewhere applied to the petrous portion. It divides 
into two branches, upper and lower; the upper branch unites with the occipital 
bone, while the lower one curves downward behind the external acoustic process 
and overlaps the mastoid process. 

The dorsal border of the squamous temporal articulates with the parietal, 



THE TEMPORAL BONES 



61 



forming the squamous suture. The ventral border joins the temporal wing of the 
sphenoid at the spheno-squamous suture. The anterior border unites with the 
frontal bone at the squamo-frontal suture, and the posterior with the occipital 
and petrous temporal bones. 

2. The petrous temporal bone (Os petrosum) is placed between the occipital 




Fig. 38. — Right Squamous Temporal Bone of New-born Foal; Lateral View. 
1, Zygomatic process; 2, glenoid cavity; 3, condyle; 4, postglenoid process; 5, notch; 6, posterior process; 7, 
temporal crest; 8, junction with parietal; 9, junction with frontal; 10, junction with supraorbital process; 11, junction 
with zygomatic process of malar; 12, junction with sphenoid; 13, junction with petro-mastoid- 14, junction with oc- 
cipital. 



behind and the parietal in front, and is largely overlapped by the squamous tem- 
poral. It has the form of a four-sided pyramid, the base of which is ventral. 

The lateral surface is mainly concealed by the squamous temporal, but two 
features are visible. A short tube of bone, the external acoustic process (Processus 
acusticus externus) , protrudes from the lowest part through the notch of the squa- 
mous temporal. The process is directed outward, upward, and a little forward. 




Fig. 39. — Right Squamous Temporal Bone op New-born Foal; Medial View. 
F.C., Cerebral surface; 1, zygomatic process; 2, junction with parietal; 3, junction with temporal wing of sphenoid; 
4, posterior process (overlaps petro-mastoid). 



It gives attachment to the annular cartilage of the ear. Its lumen, the external 
acoustic meatus (Meatus acusticus externus), conducts to the cavity of the middle 
ear (tympanum) in the dry skull, but is separated from it by the tympanic mem- 
brane in the natural state. The mastoid process (Processus mastoideus) projects 
ventrally in the interval between the posterior process of the squamous temporal 



62 



THE SKELETON OF THE HORSE 



and the root of the paramastoid process of the occipital bone. It is crossed by a 
groove which leads to the mastoid foramen (Foramen mastoideum), from which a 
canal extends forward to the temporal canal. 

The medial surface faces into the cerebellar fossa of the cranium. It is con- 
cave and smooth. l)ut irregular. In its ventral part is the entrance to a short canal, 
the internal acoustic meatus (Meatus acusticus internus), which transmits the 
seventh and eighth cranial nerves. 

The entrance to the meatus is termed tlie porus acusticus internus. The fundus of the 
meatus is divided by a crest into two fossae. In the superior one is the origin of the facial canal, 
which curves through the bone and opens externally at the stylo-mastoid foramen; it transmits 
the facial (seventh cranial) nerve. The inferior fossa presents small foramina for the passage of 
fibers of the acoustic (eighth cranial) nerve. 

Behind the meatus and near the posterior margin of the surface is the slit-like 
external opening of the aquseductus vestibuli (Apertura externa aquseductus ves- 




FlG. 



40. — Left Petrous Temporal 
Lateral View. 



OF Horse: 



1, External acoustic meatus; 2, mastoid process; 3, 
hyoid process; 4, muscular process; 5, petrosal crest; 6, 
groove which concurs in formation of temporal canal; 
7, groove for posterior meningeal artery. 



Fig. 41. — Left Petrots Temporal Bone of Horse; 
postero-medial view. 
1, Mastoid process; 2, notch which concurs with 
occipital bone in formation of mastoid foramen; 3, apex; 
4, opening of aquseductus vestibuli; 5, medial surface; 
6, petrosal crest; 7, internal acoustic meatus; 8, mus- 
cular process; 9, bullaossea; 10, stylo-mastoid foramen; 
A.c, opening of aquseductus cochleae. 



tibuli), covered by a scale of bone. Below this there is a narrow fissure, the 
orifice of the aquseductus cochleae (Apertura externa aquseductus cochlese). 

The anterior surface looks upward and forward. The greater part articulates 
with the parietal bone, but a small medial part faces into the cerebral fossa of the 
cranium. A sharp border, the petrosal crest (Crista petrosa), separates this sur- 
face from the medial one. 

The posterior surface is slightly concave and is attached to the lateral part of 
the occipital bone. 

The base forms the lateral boundary of the foramen lacerum. It is very 
irregular and presents a number of important features. The hyoid process (Pro- 
cessus hyoideus) is a short rod which projects doAvnward and forward below the 
base of the external acoustic process, inclosed in a bony tube; it is connected by a 
bar of cartilage with the hyoid bone. The stylo-mastoid foramen (F. stylo- 
mastoideum) is situated between the hyoid process and the mastoid process; it is 



BONES OF THE FACE— THE MAXILLAE 63 

the external opening of the facial canal, through which the facial nerve emerges. The 
bulla ossea is a considerable eminence situated centrally; it is thin walled and 
incloses a cavity which is part of the tympanum. The muscular process (Processus 
muscularis)^ is a sharp spine which projects downward and forward from the an- 
terior part of the base; it gives origin to the tensor and levator palati muscles. 
Lateral to the root of the preceding is the small petrotympanic fissure (Fissura 
petrotympanica) for the passage of the chorda tympani nerve. The osseous 
auditory or Eustachian tube (Tuba auditiva ossea) is a semicanal at the medial 
side of the root of the muscular process; it leads to the tympanum. At the medial 
side of the preceding is the slit-like orifice of the petrosal canal, which communi- 
cates Avith the facial canal. 

The apex projects upward and backward between the squamous temporal and 
the occipital bone. 

Development. — The squamous temporal develops in membrane. The pe- 
trous temporal may be regarded as consisting of petro-mastoid and tympanic parts. 
The latter includes the external acoustic process, the bulla ossea, and the muscu- 
lar process; it is developed in membrane. The petro-mastoid is developed in the 
cartilaginous ear capsule. Its petrous part consists of very dense bone which con- 
tains the labyrinth or internal ear and forms the medial wall of the tympanum. 

The auditory ossicles and the interior of the petrous temporal bone are described in the 
section on the organ of hearing. 

The temporal canal (Meatus temporalis)- is a continuation of the transverse 
groove which extends laterally from the base of the tentorium osseum. It is 
directed downward, forward, and somewhat outward, and opens externally in front 
of the root of the acoustic process. It is bounded by the squamous temporal 
laterally, the petrous behind, and the parietal in front and medially. Several 
foramina open from it into the temporal fossa. It contains a large vein (Vena 
cerebralis dorsalis), the continuation of the transverse sinus of the dura mater. 

The foramen lacerum (basis cranii) is a large, irregular opening in the cranial 
base, bounded medially by* the basilar part of the occipital bone, laterally by the 
petrous temporal, and in front by the temporal wing of the sphenoid. It consists 
of a large anterior part (Foramen lacerum anterius), and a narrow posterior part 
(Foramen lacerum posterius) . It transmits the internal carotid artery, the middle 
meningeal artery, the mandibular, ninth, tenth, and eleventh cranial nerves, and 
the ventral cerebral vein. 

In the fresh state the foramen is occupied by a dense fibrous membrane which is perforated 
by apertures for the various structures transmitted. Thus there are three openings in front for 
the internal carotid artery, the mandibular nerve, and the middle meningeal artery; these are 
named (from within outward) the foramen caroticum, ovale, spinosum. 



(B) BONES OF THE FACE 
The bones of the face (Ossa faciei) are the maxilla, premaxilla, palatine, 
pterygoid, nasal, lacrimal, malar, dorsal turbinate, ventral turbinate, vomer, mandi- 
ble, and hyoid. The last three are single, the others paired. 

The MAXILL.E 
The maxillae are the principal bones of the upper jaw and carry the upper 
cheek teeth. They are situated on the lateral aspect of the face, and articulate 
Avith almost all of the facial bones and the frontal and temporal also. For descrip- 
tion each may be divided into a body and two processes. 

1 This has been termed the styloid process. It is not the homologue of the styloid proc- 
ess of man. 

* This is also known as the parieto-temporal canal. 



64 



THE SKELETON OF THE HORSE 



The body (Corpus maxillae) presents two surfaces, two borders, and two ex- 
tremities. The lateral surface (Facies lateralis) is somewhat concave in front and 
convex behind.^ On its posterior part there is a horizontal ridge, the facial crest 
(Crista facialis) ; in a skull of medium size its anterior end is about an inch and a 
half (3 to 4 cm.) above the third or fourth cheek tooth, and it is continued behind 
on the malar bone. About two inches (5 cm.) above and a little in front of the 
anterior end of the crest is the infraorbital foramen (Foramen infraorbitale) ; this 
is the external opening of the infraorbital canal. 

The medial or nasal surface (Facies nasalis) is concave dorso-ventrally; it 
forms the greater part of the lateral wall of the nasal cavity. Its upper part is 
crossed obliquely forward and downward by the shallow lacrimal groove (Sulcus 
lacrimalis), which contains the naso-lacrimal duct; in the adult the posterior part 
of the groove is converted into a canal, which is continuous Avith that on the inner 
surface of the lacrimal bone. Below the groove is the ventral turbinate crest 
(Crista turbinata ventralis), to which the ventral turbinate Ijone is attached. 
Lower down and parallel with the turbinate crest is the palatine process, which 




Fig. 42. — Right Maxilia of New-born Foal; Medial View. 
1, Lacrimal groove; 2, ventral turbinate crest; 3, palatine process; 4, maxillary sinus; 5, 5, area of articulation 
with palatine bone; 0, groove which concurs with one on the palatine bone to form the palatine canal; 7, zygomatic 
process; 8, maxillary tuberosity; 9, junction with nasal bone; 10, junction with nasal process of premaxilla. 



projects horizontally like a shelf. Behind this the surface is rough for articulation 
with the palatine bone; this area is crossed b,y a groove which concurs with one on 
the palatine bone in the formation of the palatine canal (Canalis palatinus). The 
posterior part of the bone is excavated to form part of the maxillary sinus. 

The dorsal border is irregular and scaly. Its anterior part is grooved and 
its posterior part beveled for articulation with the nasal process of the premaxilla 
and the nasal and lacrimal bones. 

The ventral or alveolar border (Processus alveolaris) is in its greater part thick, 
and presents six large cavities, the dental alveoli, for the cheek teeth. The alveoli 
are separated by transverse interalveolar septa. There is often a small alveolus 
for the first premolar ("wolf tooth") close to the first large one. At the bottom 
of the alveoli there are small openings (Foramina alveolaria) for the passage of 
vessels and nerves. Further forward the border is narrow and forms part of the 
interalveolar or interdental space (Margo interalveolaris). Behind the last alve- 
olus is a rough area, the alveolar tuberosity (Tuber alveolare). 

The anterior extremity is pointed. It joins the premaxilla, and forms with it 
the alveolus for the canine tooth. 

- In the young horse the anterior part of the surface is convex over the embedded parts of the 
teeth. As the hitter are extruded the surface flattens and becomes concave in old subjects. 
The form of the underlying teeth may be indicated by ridges (Juga alveolaria), and sometimes in 
young horses there may be defects in the bone over the teeth. 



THE PREMAXILL^ 65 

The posterior extremity forms a rounded prominence, the maxillary tuberosity 
(Tuber maxillare). Medial to the tuberosity is a deep recess (Recessus maxillaris), 
in which are three foramina. The upper one, the maxillary foramen (Foramen 
maxillare) , leads into the infraorbital canal. The lower one, the posterior palatine 
foramen (Foramen palatinum aborale), is the entrance to the palatine canal. The 
sphenopalatine foramen (Foramen sphenopalatinum) perforates the medial wall 
of the recess and opens into the nasal cavity. 

The zygomatic process (Processus zygomaticus) projects backward, dorso- 
lateral to the tuberosity; it is overlapped by the corresponding part of the malar 
and also articulates with the zygomatic process of the temporal. A small curved 
plate (Processus temporalis) extends medially from it and joins the frontal and 
palatine bones, forming part of the floor of the orbit. 

The palatine process (Processus palatinus) is a horizontal plate which projects 
from the lower part of the medial surface of the body. It forms the greater 
part of the basis of the hard palate. Its nasal surface is smooth and is con- 
cave transversely; on its anterior part, close to the medial border, there is a 
shallow groove in which the vomero-nasal organ (of Jacobson) is situated. The 
palatine surface is slightly concave from side to side, and presents along its lateral 
part the palatine groove (Sulcus palatinus); this is continuous at the anterior 
palatine foramen (Foramen palatinum orale) with the palatine canal, and con- 
tains the palatine vessels and nerve. The medial border unites with its fellow to 
form the median palatine suture; its nasal aspect bears the nasal crest (Crista 
nasalis), which forms, with that of the opposite process, a groove for the vomer. 
The posterior border unites with the horizontal part of the palatine bone at the 
transverse palatine suture. Variable accessory palatine foramina perforate the 
process. 

The infraorbital canal (Canalis infraorbitalis)i extends almost horizontally 
from the maxillary foramen to the infraorbital foramen. It is placed at the upper 
edge of the inner plate of the maxilla, and traverses the maxillary sinus. Near the 
infraorbital foramen it gives off a small canal (Canalis alveolaris incisivus) which 
lies above the roots of the premolars and extends also into the premaxilla, carrying 
vessels and nerves to the teeth there. 

Development. — The maxilla ossifies in membrane ventral and lateral to the 
cartilaginous nasal capsule. It has one chief center and a supplementary one in 
the region of the deciduous canine tooth (Martin). 

The Premaxilla 

The premaxillae (Ossa incisiva) form the anterior part of the upper jaw and 
carry the incisor teeth. Each consists of a body, a nasal process, and a palatine 
process. 

The body (Corpus) is the thick anterior part which carries the incisor teeth. 
Its labial surface (Facies labialis) is convex and smooth, and is related to the upper 
lip. The palatine surface (Facies palatina) is concave and often presents a foramen 
a little behind its middle.- The medial surface (Facialis medialis) is rough, and 
joins the opposite bone; it is marked by a curved groove, which forms, with that on 
the opposed surface, the foramen incisivum. The alveolar border (Limbus alveo- 
laris) separates the palatine and labial surfaces ; it is curved and thick, and presents 
three deep alveoli for the incisor teeth; behind the third alveolus it is free, forming 
part of the interalveolar space. 

The nasal process (Processus nasalis) projects backward and upward from the 
body, forming here the lateral wall of the nasal cavity. The two surfaces, facial 

^ This is also known as the superior dental canal. 

"^ This foramen is somewhat variable in position, but is commonly opposite the corner in- 
cisor. Smaller inconstant foramina are often present. 
5 



66 



THE SKELETON OF THE HORSE 



and nasal, are smooth and rounded. The dorsal border is free, thick, and smooth; 
it concurs with the free margin of the nasal bone in forming the naso-maxillary 
notch (Incisura nasomaxillaris). The ventral border is dentated and joins the 
maxilla; at its anterior end it forms with the latter the alveolus for the permanent 

canine tooth. ^ The posterior ex- 
tremity fits into the interval be- 
tween the nasal bone and the 
maxilla. 

The palatine process (Pro- 
cessus palatinus) is a thin plate 
which forms the anterior part of 
the basis of the hard palate. Its 
nasal surface (Facies nasalis) has 
a longitudinal ridge which forms 
with that of the other side a groove 
for the septal cartilage; lateral to 
the ridge there is a groove for the 
vomero-nasal organ. The palatine 
surface (Facies palatina) is flat. 
The medial border is serrated and 
meets its fellow at the median pala- 
tine suture. The lateral border is 
separated from the maxilla and the 
nasal process by the palatine fis- 
sure (Fissura palatina). The pos- 
terior extremity fits into the inter- 
val between the vomer and the 
palatine process of the maxilla. 

Development. — The premax- 
illa ossifies from a single center. 
Fusion of the two bones is com- 
plete at the end of the third or 
the beginning of the fourth year. 

The Palatine Bones 

The palatine bones (Ossa pala- 
tina) are situated on either side of 
the choanse or posterior nares, and 
form the posterior margin of the 
hard palate. Each is twisted so as 
to form a horizontal and a perpen- 
dicular part. 

The horizontal part (Pars hori- 
zontalis) is a narrow^ plate which 
forms the posterior part of the 
hard palate. It presents smooth 
nasal and palatine surfaces (Facies 
nasalis, palatina). The medial border meets its fellow at the median palatine 
suture, on the nasal aspect of which is the nasal crest. The anterior border joins 
the palatine process of the maxilla at the transverse palatine suture, and forms with 
it the anterior palatine foramen (Foramen palatinum anterius). The posterior 
border is concave and free ; it gives attachment to the aponeurosis of the soft palate. 




Fia. 43. — Upper .Jaw of Horse About Four and a Half 
Years Old; Ventral View. 
1, 1, Choanse or posterior nares; 2, vomer; 3, horizontal 
part of palatine bone; 4, anterior palatine foramen; 5, palatine 
groove; 6, transverse palatine suture; 7, median palatine suture; 
8, palatine process of maxilla; 9, palatine process of premaxilla; 
10, foramen incisivum; 11, malar bone; 12, maxilla; 13, anterior 
end of facial crest; 14, interalveolar space; /. 1-3, incisor teeth; 
C, canine tooth; P.l, first premolar or "wolf" tooth. The 
opening lateral to 9 is the palatine fissure. 



The alveolus for the temporary canine is commonly formed in the maxilla alone. 



THE PTERYGOID BONES THE NASAL BONES 67 

The perpendicular part (Pars perpendicularis) is more extensive and forms 
most of the lateral wall of the choanse or posterior nares. The nasal surface (Facies 
nasalis) is in the greater part of its extent concave and smooth, but presents a 
narrow rough area to which the pterygoid bone is attached. Below this the bone 
curves outward, forming the pterygoid process. The maxillary surface (Facies 
maxillaris) presents three areas for consideration. The largest articulates with the 
maxilla; it is rough and is crossed by a groove which concurs with one on the max- 
illa in the formation of the palatine canal. Behind this is a smooth part which 
assists in forming the pterygo-palatine fossa (Fossa pterygopalatina). The rough 
area below this is overlapped by the pterygoid process of the sphenoid bone. The 
dorsal border is perforated by the sphenopalatine foramen. Behind the foramen 
the two plates of the bone separate to inclose part of the sphenopalatine sinus. 
The inner plate curves medially to articulate with the vomer. The outer plate 
joins the maxilla and frontal and the orbital wing of the sphenoid; it may join the 
lacrimal bone also. 

Development. — The palatine bone ossifies in membrane from a single center. 

The Pterygoid Bones 

The pterygoid bones (Ossa pterygoidea) are narrow, thin, bent plates, situated 
on either side of the posterior nares. Each has two surfaces and two extremities. 
The medial surface is smooth, and forms part of the wall of the posterior nares. 
The lateral surface articulates with the palatine, vomer, and sphenoid, concurring 
with the last in the formation of the pterygoid canal. The ventral extremity is 
free, turned slightly outward, and forms the hamulus pterygoideus ; this is grooved 
externally and forms a pulley around which the tendon of the tensor palati muscle 
is reflected. 

Development. — The pterygoid ossifies in membrane from a single center. 

The Nasal Bones 

The nasal bones (Ossa nasalia) are situated in front of the frontal bones and 
form the greater part of the roof of the nasal cavity. They have an elongated 
triangular outline, wide behind, pointed in front. Each presents two surfaces, two 
borders, and two extremities. 

The facial surface is smooth and is convex transversely; the profile contour is 
usually slightly wavy, with a depression about its middle and a variably prominent 
area in front. 

The nasal surface is smooth and concave from side to side. About in its 
middle it presents the dorsal turbinate crest (Crista turbinata dorsalis), which is 
parallel with the medial border, and has the dorsal turbinate bone attached to it. 
Most of this surface faces into the nasal cavity, but its posterior part, lateral to 
the turbinate crest, enters into the formation of the frontal sinus; the latter area is 
marked off by an oblique ridge which corresponds to the septum between the an- 
terior and posterior parts of the dorsal turbinate bone. 

The medial border is straight, and meets the opposite bone at the nasal suture. 

The lateral border is irregular. Its anterior third is free and concurs with 
the nasal process of the premaxilla in forming the naso-maxillary notch (Incisura 
naso-maxillaris) . Behind this it joins the end of the nasal process, the maxilla, 
and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures. 

The greater part of the edge is beveled and fits into a groove on the upper border of the 
nasal process, the maxilla, and the lacrimal bone. 

The posterior extremity or base is beveled and overlaps the frontal bone, 
forming the naso-frontal suture. 

The anterior extremity or apex is pointed and thin. 



68 THE SKELETON OF THE HORSE 

Development. — Each nasal bone ossifies in membrane from a single center. 
The nasal suture does not close completely even in old age. In some cases the two 
plates separate to inclose a small air-space (nasal sinus) in the posterior part. 

The Lacrimal Bones 

The lacrimal bones (Ossa lacrimalia) are situated at the anterior part of the 
orbit, and extend forward on the face to the posterior border of the maxilla. Each 
presents three surfaces and a circumference. 

The lateral face is clearly divided into orbital and facial parts by the orbital 
margin. The orbital surface (Facies orbitalis) is triangular in outline, smooth and 
concave ; it forms part of the medial and front wall of the orbit. Near the orbital 
margin it presents a funnel-like fossa (Fossa sacci lacrimalis), which is the entrance 
to the lacrimal canal; the fossa is occupied by the lacrimal sac, which is the dilated 
origin of the naso-lacrimal duct. Behind this is a depression in which the inferior 
oblique muscle of the eye takes origin. The facial surface (Facies facialis) is more 
extensive, and has the form of an irregular pentagon. It is slightly convex and 
smooth in the foal, flattened in the adult. It usually bears the small lacrimal 
tubercle, which is situated nearly an inch (ca. 2 cm.) from the orbital margin. 
The orbital margin (Margo orbitalis) is concave, rough above, smooth below. 

The nasal surface (Facies nasalis) faces into the frontal and maxillary sinuses. 
It is concave and very irregular, and is crossed almost horizontally by the osseous 
lacrimal canal (Canalis lacrimalis osseus). 

The circumference articulates dorsally with the frontal and nasal bones, 
ventrally with the malar and maxilla, in front with the maxilla, and behind with 
the frontal. The various sutures so formed are designated by combinations of the 
names of the bones. 

Development. — Each ossifies in membrane from a single center. 

The Malar Bones 

The malar or zygomatic bones (Ossa zygomatica) are placed between the lac- 
rimal above and the maxilla below and in front. Each is irregularly triangular in 
outline and presents three surfaces, three borders, and a process. 

The facial surface (Facies facialis) is smooth, slightly convex, wide in front, 
and narrow behind. At its lower part it presents the facial crest, which is continu- 
ous in front with the similar ridge on the maxilla and behind with the zygomatic 
process of the temporal; the crest is rough below, where the masseter muscle is 
attached to it. 

The orbital surface is much smaller than the facial surface, from which it is 
separated by the concave orbital margin (Margo orbitalis). It is concave and 
smooth, and forms part of the lower and front wall of the orbit. 

The nasal surface is concave and faces into the maxillary sinus. In the young 
foal a consideraljle part of it articulates with the maxilla. 

The dorsal border articulates with the lacrimal chiefly, but to a small extent 
behind with the maxilla also. 

The ventral and anterior borders articulate with the maxilla. 

The posterior extremity is formed by the zygomatic process, which is beveled 
above and is overlapped by the zygomatic process of the temporal bone. 

Development. — Each ossifies in membrane from one or two centers. 

The Turbinate Bones 
These (Ossa turbinata) are delicate, scroll-like bones, four in number, which 
are attached to the lateral walls of the nasal cavity. They project into the cavity 
and greatly diminish its extent. Each is composed of a very thin lamina, cribri- 



THE TURBINATE BONES 



69 



form in many places, and covered on both sides witli mucous membrane in the fresh 
state. They are arranged in two pairs, dorsal and ventral. 

The dorsal turbinate bone (Os turbinatum dorsale)^ is somewhat cylindrical in 
form, but is flattened from side to side and tapers at each end. It is attached to 
the turbinate crest of the nasal bone and the nasal plate of the frontal bone. The 
anterior part is rolled like a scroll one and a half times, thus inclosing a cavity which 
communicates with the middle meatus nasi. The arrangement is best seen on a 
cross-section (Fig. 55). The posterior part is not rolled, but its ventral border is 
attached to the lateral nasal wall, thus helping to inclose a large space which is part 
of the frontal sinus. This cavity is separated from that of the scroll-like part by a 
transverse septum. The medial surface is flattened, and is separated from the sep- 
tum nasi by a narrow interval, the common meatus (Meatus nasi communis). 
Another narrow passage, the dorsal meatus (Meatus nasi dorsalis), separates the 
dorsal surface from the roof of the nasal cavity. The space between the ventral 
surface and the ventral turbinate is the middle meatus (Meatus nasi medius). The 



A^asal Frontal 

sinus sinus 



Nasal 
bone 



at nasal 




13 Sphenoidal 
sinus 

Hamulus of 
pterygoid bone 

Fig. 44. — Part of Sagittal Section of Skull op Horse. 
1, Perpendicular plate of ethmoid bone; 2, great ethmo-turbinate; 3, dorsal turbinate; 4, ventral turbinate; 5, 
vomer; 6, middle nasal meatus; 7, ventral nasal meatus; 8, perpendicular part of palatine bone; 9, palatine process of 
maxilla; 10, body of premaxilla; 11, nasal process of premaxilla; 12, palatine process of premaxilla; 13, pterygoid proc- 
ess of palatine bone. Dotted lines indicate septa. 



anterior extremity is prolonged toward the nostril by two small bars of cartilage. 
The posterior extremity is small, and joins the cribriform plate and lateral mass of 
the ethmoid. 

The ventral turbinate bone (Os turbinatum ventrale)^ is shorter and smaller 
than the upper one. It is attached to the ventral turbinate crest, and consists', 
like the upper one, of an anterior coiled and a posterior uncoiled portion. 

To express briefly the mode of coiling of the two bones of the same side we may say that 
they are rolled toward the septum and each other. 

The ventral and posterior borders of the posterior part are attached to the 
maxilla, thus helping to inclose a cavity which is part of the maxillary sinus. The 
lower surface is separated from the floor of the nasal cavity by the ventral meatus 
(Meatus nasi ventralis), which is much larger than the other nasal passages. The 
anterior extremity is prolonged toward the nostril by a curved bar of cartilage. 

Development. — Each ossifies in cartilage from a single center. 

1 This bone is also termed the naso-turbinal ; it is really a greatly developed first ethmor 
turbinate. 

^ This is also called the maxillo-turbinal. 



70 THE SKELETON OF THE HORSE 



The Vomer 

The vomer is a median bone, which assists in forming the ventral part of the 
septum nasi. It is composed of a thin lamina which is bent (except in its posterior 
part) so as to form a narrow groove (Sulcus vomeris) , in which the lower part of the 
perpendicular plate of the ethmoid bone and the septal cartilage are received. The 
lateral surfaces, right and left, are highest near the posterior end and diminish 
gradually to the anterior end; they are slightly convex dorso-ventrally, and are 
covered by the nasal mucous membrane during life. The ventral border is thin 
and free in its posterior third, and divides the choanae or posterior nares medi- 
ally; in the remainder of its extent it is wider and is attached to the nasal crest. 
The anterior extremity lies above the ends of the palatine processes of the premax- 
illae. The posterior extremity consists of two wings (Alae vomeris) which extend 
outward below the body of the presphenoid; posteriorly they form a notch (In- 
cisura vomeris), and laterally join the palatine and pterygoid bones. 

Development. — The vomer is primitively double, and ossifies from a center on 
cither side in the membrane covering the cartilaginous septum nasi; the two 
laminse then fuse below and form a groove. 

The Mandible 

The mandible (Mandibula),^ or lower jaw bone, is the largest bone of the 
face. The two halves of which it consists at birth unite during the second or third 
month, and it is usually described as a single bone. It carries the lower teeth, and 
articulates l^y its condyles with the squamous temporal on either side. It consists 
of a body and two rami.^ 

The body (Corpus mandibulse) is the thick anterior part which bears the incisor 
teeth. It presents two surfaces and a border. The lingual surface (Facies lin- 
gualis) is smooth and slightly concave; during life it is covered by mucous mem- 
brane, and the tip of the tongue overlies it. The mental surface (Facies mentalis) 
is convex and is related to the lower lip. It is marked by a median furrow which 
indicates the position of the primitive symphysis mandibulse. The curved alveolar 
border (Limbus alveolaris) presents six alveoli for the incisor teeth, and a little 
further back two alveoli for the canine teeth in the male; in the mare the latter are 
usually absent or small. 

The rami (Rami mandibulse) extend backward from the body and diverge to 
inclose the mandibular (or submaxillary) space (Spatium mandibulare). Each 
ramus is bent so as to consist of a horizontal part (Pars molaris) which bears the 
lower cheek teeth, and a vertical part (Ramus mandibulse [S. N. A.]) which is ex- 
panded and furnishes attachment to powerful muscles; the term angle is applied 
to the most prominent part of the curve. The ramus presents two surfaces, two 
borders, and two extremities. The lateral surface is smooth and slightly convex 
from edge to edge on the horizontal part; at the junction with the body it presents 
the mental foramen (Foramen mentale), which is the external opening of the man- 
dibular canal. On the vertical part it is somewhat concave and presents a number 
of rough lines for the attachment of the masseter muscle. The medial surface of 
the horizontal part is smooth, and presents a shallow longitudinal depression in its 
middle; above this there is often a faint mylo-hyoid line (Linea mylohyoidea) for 
the attachment of the muscle of like name. At the lower part of the junction with 
the body there is a small fossa for the attachment of the genio-hyoid and genio- 

^ This bone is also commonly called the inferior maxilla. 

^ In the Stuttgart Anatomical Nomenclatm-e (S. N. A.) the body (Corpus) is the part which 
bears the teeth, and is divided into a pars incisiva and a pars molaris. The ramus is the rest of 
the bone. This mode of description is copied from the Basel Nomina Anatomica. It does not 
seem to the author to be well adapted to comparative purposes. 



THE MANDIBLE 71 

glossus muscles. On the vertical part the surface is concave, and is marked in its 
lower and posterior part by rough lines for the attachment of the medial pterygoid 
n^.uscle. In front of its middle is the mandibular foramen (Foramen mandibulare)/ 
which is the posterior orifice of the mandibular canal (Canalis mandibulae).- The 
canal curves downward and passes forward below the cheek teeth, opening exter- 
nally at the mental foramen; it is continued into the body of the bone as a small 
canal (CanaUs alveolaris incisivus), which carries the vessels and nerves to the 
incisor teeth. The dorsal or alveolar border (Limbus alveolaris) forms anteriorly 
part of the interalveolar space; here it is thin. Behind this it is thick and is ex- 
cavated by six alveoli for the lower cheek teeth. Behind the last alveolus it curves 
sharply upward and is narrow and rough. In the young foal there is commonly a 
small alveolus for the vestige of the first premolar ("wolf tooth") close to the first 
large one. The ventral border of the horizontal part is nearly straight; it is thick 
and rounded in the young horse, becoming narrower and sharp in old subjects. At 





6 

Fig. 45. — Left Half of Mandible of Hor.se; Medial View. 
1, Body of mandible (median section); 2, 2', horizontal and vertical parts of ramus; 3, interalveolar border; 4, 
depression for attachment of genio-hyoideus muscle; o, mandibular foramen; 6, vascular impression; 7, angle; 8, 
condyle; 9, coronoid process; 10, mandibular notch; 11, incisor teeth; 12, canine tooth; 13, cheek teeth. 

its posterior part there is a smooth impression (Incisura vasorum) where the facial 
vessels and parotid duct turn round the bone. Behind this point the border curves 
sharply upward, forming the angle of the mandible (Angulus mandibulse) ; this part 
is thick and has two roughened lips, separated by a considerable intermediate space; 
near the condyle it becomes narrower. The anterior extremity joins the body. 
The articular extremity comprises the coronoid process in front and the condyle 
behind, the two being separated by the mandibular notch (Incisura mandibulae), 
through which the nerve to the masseter muscle passes. The coronoid process 
(Processus coronoideus) is thin transversely and curved slightly medially and 
backward. It projects upward in the temporal fossa and furnishes insertion to 
the temporal muscle. The condyle of the mandible (Condylus mandibulae) lies at 
a much lower level than the end of the coronoid process. It is elongated trans- 
versely and articulates with the squamous temporal through the medium of an 

^ This is also commonly called the inferior maxillary foramen. 
^ This is also termed the inferior dental canal. 



72 



THE SKELETON OF THE HORSE 



articular disc. The part below the condyle is usually termed the neck of the 
mandible (CoUum mandibulse) ; on its antero-medial part is a depression, the fovea 
pterygoidea, in which the lateral pterygoid muscle is attached. The middle of the 
vertical part of the ramus consists to a large extent of a single plate of compact 
substance which may be so thin in places as to be translucent. 

Development. — The mandible develops from two chief centers in the connec- 
tive tissue which overlies the paired Meckel's cartilages. At birth it consists of 
two symmetrical halves which meet at the median symphysis mandibulae. Fusion 
usually occurs in the second or third month. 

Age Changes. — These are associated largely with the growth, and later with the reduction, 
of the teeth. In the young horse, in which the teeth are long and are in great part embedded 
in the bone, the body is thick and strongly curved, and the horizontal part of the ramus is also 
thick. Later, as the teeth are extruded from the bone, the body becomes flattened and narrower, 
and the horizontal part of the ramus is thinner, especially in its lower part. In the old subject 
the angle, the vascular impression in front of it, and the lines for the attachment of tendinous 
layers of the masseter and pterygoid muscles are more pronounced. 




The Hygid Bone 

The hyoid bone (Os hyoideum) is situated chiefly between the vertical parts 
of the rami of the mandible, but its upper part extends somewhat further back. 
It is attached to the petrous temporal bones by rods of cartilage, and supports the 

root of the tongue, the pharynx, and the 
larynx. It consists of a body, a lingual 
process, and three pairs of cornua. 

The body or basihyoid (Corpus ossis 
hyoidei) is a short transverse bar, com- 
pressed dorso-ventrally. The dorsal sur- 
face is concave and smooth in its middle, 
and presents at each end a convex facet 
or tubercle for articulation with the small 
cornu. The ventral surface is flattened 
and is slightly roughened for muscular 
attachment. The anterior border carries 
medially the lingual process. The pos- 
terior border is concave and smooth in its 
middle, and carries on either side the thy- 
roid cornu. The body, the lingual proc- 
ess, and the thyroid cornua are fused 
and may be compared to a spur or a fork 
with a very short handle. 

The lingual process (Processus lingu- 

alis) projects forward medially from the 

body, and is embetlded in the root of the 

tongue during life. It is compressed laterally and has a blunt-pointed free end. 

The lateral surfaces are slightly concave. The dorsal border is thin and irregular, 

and the ventral border is thick and rough. 

The thyroid cornua or thyrohyoids (Cornua thyreoidea)i extend backward and 
upward from the lateral parts of the body. They are compressed laterally (except 
at their junction with the body), and the posterior end has a short cartilaginous 
prolongation which is connected with the anterior cornu of the thyroid cartilage 
of the larynx. 

The small cornua or keratohyoids (Cornua minora) are short rods which are 
directed upward and forward from either end of the body. Each is somewhat 
constricted in its middle part and has slightly enlarged ends. The ventral end has 
' These correspond to the great cornua of man. 



Fia. 46. — Hyoid Bone or Horse, Viewed from the 
Side and Somewhat from in Front. 
o. Body; 6, lingual process; c, thyroid cornu; c', 
cartilage of c; d, small cornu; e, middle cornu; /.great 
cornu; /', muscular angle of great cornu; g, cartilage 
of great cornu. (EUenberger-Baum, Anat. d. Haus- 
tiere.) 



THE SKULL AS A WHOLE 73 

a small concave facet which articulates with the body. The dorsal end articulates 
with the great cornu, or with the middle cornu when present. 

The great comua or stylohyoids are much the largest parts of the bone. They 
are directed dorsallj" and backward, and are connected above with the base of the 
petrous temporal bones. Each is a thin plate, seven or eight inches (ca. 18 to 20 
cm.) long, which is slightly curved in its length, so that the lateral surface is con- 
cave and the medial surface is convex; both are smooth. The borders are thin. 
The dorsal extremity is large and forms two angles; the articular angle is connected 
by a rod of cartilage with the hyoid process of the petrous temporal bone; the 
muscular angle is somewhat thickened and rough for muscular attachment. The 
ventral extremity is small, and articulates with the small or the middle cornu. 

The middle comua or epihyoids are small, wedge-shaped pieces or nodules 
interposed between the small and great cornua. They are usually transitory, and 
unite with the great cornua in the adult. 

Development. — The hyoid ossifies in the cartilages of the second and third 
visceral arches. Each part has a separate center, except the lingual process, which 
ossifies by extension from the body. In the foal there is a separate nucleus at each 
end of the body which intervenes between the latter and the thyroid cornu; it 
articulates with the small cornu. The anterior part of the lingual process may be 
a separate piece. 



THE SKULL AS A WHOLE 

The skull of the horse has, as a whole, the form of a long, four-sided pyramid, 
the base of which is posterior. It is convenient, however, to exclude the mandible 
and hyoid from present consideration. The division between the cranium (Cra- 
nium cerebrale) and the face (Cranium viscerale) may be indicated approxi- 
mately by a transverse plane through the anterior margins of the orbits. 

The dorsal or frontal surface (Norma frontalis) is formed by the squamous 
part of the occipital, interparietal, parietal, frontal, nasal, and premaxil- 
lary bones. It may be divided into parietal, frontal, nasal, and premaxillary 
regions. The parietal region extends from the nuchal crest to the parieto-frontal 
suture. It is marked medially by the external parietal crest, which bifurcates in 
front, the branches becoming continuous with the frontal crests. The latter curve 
outward on either side to the root of the supraorbital process. The frontal region 
is the widest part of the surface, and is smooth and almost flat. It is bounded in 
front by the naso-frontal suture. On either side of it is the root of the supraorbital 
process, pierced by the supraorbital foramen. The nasal region is convex from 
side to side, wide behind, narrow in front. Its profile is in some cases nearly 
straight; in others it is undulating, with a variably marked depression about its 
middle and at the anterior end. The premaxillary region presents the osseous 
nasal aperture (Apertura nasalis ossea) and the foramen incisivum. 

The lateral surface (Norma lateralis) (Fig. 28) may be divided into cranial, 
orbital, and preorl)ital or maxillary regions. 

The cranial region presents the temporal fossa, the zygomatic arch, and the 
outer part of the petrous temporal bone. The temporal fossa is bound medially 
by the parietal and frontal crests, laterally by the temporal crest and the zygomatic 
arch, and behind by the nuchal crest. Its upper and middle parts are rough for 
the attachment of the temporal muscle. In its lower posterior part are several 
foramina which communicate with the temporal canal. The fossa is continuous 
in front with the orbital cavity. The zygomatic arch is formed by the zygomatic 
processes of the temporal, malar, and maxilla. Its ventral face presents the con- 
dyle and glenoid cavity for articulation with the lower jaw, through the medium 
of the articular disc. Behind the glenoid cavity is the postglenoid process. The 



74 



THE SKELETON OF THE HORSE 



external acoustic process projects outward through a deep notch in the ventral 
margin of the squamous temporal below the temporal crest. A little further back 
is the mastoid process, crossed in its upper part by a groove for the posterior 
meningeal artery. 

The orbital region comprises the orbit and the pterygo-palatine fossa. The 



Nuchal crest 



Occipital 
Interparietal - 

Parietal ^// / 



Squamous temporal 



Frontal 




Parietal crest 

Temporal fossa 
Temporal crest 



Coronoid process 
Zygomatic arch 

Supraorbital process 
S upraorbital foramen 

Orbit 
Facial crest 



I >ifra orbital foramen 



Nasal process of premaxilla 



Body of premaxilla 



Foramen, incisivum 



Fig. 47. — Skull of Horse; Dorsal View. 
1, Parieto-ocoipital suture; 2, squamous suture; 3, parietal suture; 4, parieto-frontal suture; 5, frontal suture; 
•6, naso-frontal suture; 7, naso-lacrimal suture; 8, lacrimo-malar suture; 9, lacrimo-maxillary suture; 10, maxillo- 
■malar suture; 11, naso-maxillary suture; 12, nasal suture. 



orbit is a cavity which incloses the eyeball, with the muscles, vessels, and nerves 
associated with it. It is not separated in the skeleton from the temporal fossa. 
The axis of the orbit (Axis orbitse), taken from the optic foramen to the middle of 
the inlet, is directed forward, outward, and slightly upward. The medial wall 
(Paries medialis) is complete and extensive. It is concave and smooth, and is 
formed by the frontal and lacrimal and the orbital wing of the sphenoid. In its 



THE SKULL AS A WHOLE 



75 



extreme anterior part is the fossa for the lacrimal sac. Behind this there is a small 
depression in which the inferior oblique muscle of the eye arises; here the plate 
which separates the orbit from the maxillary sinus is very thin. The dorsal wall 
(Paries dorsalis) is formed by the frontal and to a small extent by the lacrimal bone. 
It presents the supraorbital foramen, which perforates the root of the supraorbital 
process. The ventral wall (Paries ventralis) is very incomplete, and is formed by 
the malar, the zygomatic process of the temporal, and to a small extent by the max- 
illa. The lateral wall (Paries lateralis) is the supraorbital process. At the extreme 
posterior part is the orbital group of foramina. Four are situated in front of the 
pterygoid crest. Of these, the uppermost is the ethmoidal foramen, which trans- 




FlG. 48. — Cranial and Orbital Regions of Skull of Horse; Lateral View. The Zygomatic Arch and Supra- 
orbital Process Have Been Sawn Off. 
5. 0., Squamous part of occipital; P, parietal; S, squamous temporal; B.o., basilar part of occipital; B.s., body of 
sphenoid; A. «., temporal wing of sphenoid; A. o., orbital wing of sphenoid; P<. p., pterygoid process of sphenoid; P.p., 
perpendicular part of palate bone; F, F', facial and orbital parts of frontal bone; L, L' , orbital and facial parts of lacri- 
mal bone; M, facial part of malar bone; M.x., maxilla; a, parieto-occipital suture; b, squamous suture; c, d, spheno- 
squamous suture; e, fronto-palatine suture; /, fronto-lacrimal suture. 1, Occipital condyle; 2, condyloid fossa; 3, 
paramastoid process; 4, nuchal crest; 5, external occipital protuberance; 6, external acoustic meatus; 7, mastoid 
process; 8, hyoid process; 9, stylomastoid foramen; 10, muscular process; 11, foramen lacerum; 12, postglenoid 
process; 13, glenoid cavity; 14, temporal condyle; 15, pterygoid groove; 16, alar canal of pterygoid process indicated 
by arrow; 17, alar foramen; 18, ethmoidal foramen; 19, optic foramen; 20, foramen orbitale; 21, maxillary fora- 
men; 22, sphenopalatine foramen; 23, posterior palatine foramen; 24, supraorbital foramen (opened) ; 25, fossa for 
lacrimal sac; 26, depression for origin of obliquus oculi inferior; 27, facial crest; 28, maxillary tuberosity; 29, alveolar 
tuberosity ; 30, hamulus of pterygoid bone. 



mits the ethmoidal vessels and nerve. The optic foramen is situated a little lower 
and further back; it transmits the optic nerve. Immediately below the optic is 
the foramen orbitale, which transmits the ophthalmic, third, sixth, and sometimes 
the fourth nerve; commonly there is a very small trochlear foramen in the crest 
for the last-named nerve. The foramen rotundum is below the foramen orbitale, 
from which it is separated by a thin plate; it transmits the maxillary nerve. The 
alar canal opens in common with the foramen rotundum, and the anterior opening 
of the pterygoid canal is also found here. The foramen alare parvum is just be- 
hind the pterygoid crest and on a level with the foramen orbitale. It is the upper 
opening of a canal which leads from the alar canal, and through it the anterior deep 



76 



THE SKELETON OF THE HORSE 



temporal artery emerges. The inlet of the orbital cavity (Aditus orbitae) is cir- 
cumscribed by a complete bony ring, which is nearly circular. Its infraorbital 
margin (Margo infraorbitalis) is smooth and rounded; the supraorbital margin 
(Margo supraorbitalis) is rough and irregularly notched. During life the cavity is 
completed by the periorbita, a conical fibrous membrane, the apex of which is at- 
tached around the optic foramen. Ventral to the orbital cavity is the pterygo- 
palatine fossa. Its wall is formed by the pterygoid process, the perpendicular 
part of the palate bone, and the tuber maxillare. Its deep anterior recess contains 
three foramina. The upper one, the maxillary foramen, is the entrance to the in- 



Nuchal ere at 

Dorsal border of 

for. magnum 

Foramen magnum 

Hypoglossal foramen 

For. lacenim posterms 

Stylomastoid foramen 

Hyoid process 

Muscular process 
For. lacerum anterius 
Basilar tubercles 

Alar canal 

Pterygoid process 
of sphenoid 
Pterygoid hone 

Vomer {alee) 
Pterygoid process of 

palatine bone 
Palatine bone {per- 
pendicular part) 
Alveolar tuberosity 

Posterior nares 
Last molar tooth 




External occipital pro- 
tuberance 

Occipital condyle 

Paramastoid process 

Condyloid fossa 

Mastoid process 

Bulla ossea 



process 



Glenoid cavity 

Temporal condyle 
Zygomatic process 
Infratemporal fossa 
Zygomatic process of 
malar 



Pterygo-palatine fossa 
Maxillary recess 
Maxillary tuberosity 
Facial crest 
Hatnulus of pterygoid 
Vomer 

Palatine bone {hori- 
zontal part) 
Ant. palatine foramen 

Palatine groove 

Palatine process of 
maxilla 

Fig. 49. — Line Drawing of Posterior Half of Base of Skull of Horse, Without Mandible. (Key to Fig. 50.) 
A, Basilar part of occipital; B, body of sphenoid; C, temporal wing of sphenoid; D, squamous temporal bone; 



£, petrous temporal bone; F, orbital part of frontal bone, i, Incisura carotica; ; 
4, external orifice of temporal canal; 5, osseous auditory or Eustachian tube; 6 
acoustic process; S, hyoid process ; S, pterygoid groove ; iO, supraorbital process. 



ovalis; 3, incisuraspinosa; 
petro-tympanic fissure; 7, external 



fraorbital canal, which transmits the infraorbital nerve and vessels. The spheno- 
palatine foramen perforates the medial wall of the recess and transmits vessels and 
nerves of like name to the nasal cavity. The lower foramen, the posterior palatine, 
transmits the palatine artery and nerve to the palatine canal. The upper part of 
the fossa is smooth, and is crossed by the internal maxillary artery and the maxillary 
nerve. The lower part is chiefly roughened for the attachment of the lateral 
pterygoid muscle, but is crossed in front by a smooth groove in which the palatine 
vein lies. In its extreme posterior part is the small opening of the pterygoid 
canal. 

The preorbital or maxillary region is formed chiefly by the maxilla, but also by 



THE SKULL AS A WHOLE 



77 



the premaxilla, and the facial parts of the lacrimal and malar bones. Its contour 
is approximately triangular, the base being posterior. It offers two principal 
features. The facial crest extends forward from the ventral margin of the orbit, 
and ends abruptly at a point about an inch and a quarter (ca. 3 to 3.5 cm.) above the 




Fig. 50. — Ventral Surface op Skull of Hohse, Posterior Half Without Mandible. 
The skull is inclined slightly. (Notation on key Fig. 49.) 



third or fourth cheek tooth ;i its ventral aspect is rough for the attachment of the 
masseter muscle. The infraorbital foramen is situated in a transverse plane about 
an inch (ca. 2 to 3 cm.) in front of the end of the crest and about two inches (5 cm.) 

1 This relation varies with age. In the new-born foal the posterior part of the second tooth, 
in the young horse the posterior part of the third tooth, in the older subject the fourth, lies below 
the end of the crest. 



78 THE SKELETON OF THE HORSE 

above it. The foramen opens forward, and through it the infraorbital artery and 
nerve emerge. The surface over the premolar teeth varies greatly with age, in 
conformity "s^dth the size of the embedded parts of the teeth. In the young horse 
the surface here is strongly convex, the outer plate of bone is thin and even defective 
sometimes in places, and the form of the teeth is indicated by eminences (Juga 
alveolaria). In the old animal the surface is concave on account of the extrusion 
of the teeth from the bone. The downward curve of the premaxilla is pronounced 
in the young subject, very slight in the aged. 

In some skulls there is a distinct depression a short distance in front of the orbit; here the 
levator labii superioris proprius arises. 

The ventral or basal surface (Norma basalis), exclusive of the mandible, 
consists of cranial, choanal, and palatine regions. 

The cranial region (Basis cranii externa) extends forward to the vomer and 
pter3'goid processes (Fig. 50). x\t its posterior end is the foramen magnum, flanked 
by the occipital condyles. Lateral to these is the condyloid fossa, in which is the 
hypoglossal foramen, which transmits the hypoglossal nerve and the condyloid 
vein. Further outward are the paramastoid processes (Processus jugulares) 
of the occipital bone. Extending forward centrally is a prismatic bar, formed 
by the basilar part of the occipital and the body of the sphenoid bone; at the 
junction of these parts are tubercles for the attachment of the ventral straight 
muscles of the head. On either side of the basilar part of the occipital bone is the 
foramen lacerum (basis cranii), bounded laterally by the base of the petrous tem- 
poral bone. In front of these the region becomes very wide on account of the lateral 
extension of the zygomatic processes, which present ventrally the condyle and 
glenoid cavity for articulation with the mandible. Beyond this the process turns 
forward and joins the zygomatic process of the malar, completing the zygomatic 
arch and the surface for the attachment of the masseter muscle. On either side of 
the body of the sphenoid is the infratemporal fossa, formed by the temporal wing 
and the root of the pterygoid process of the sphenoid bone. It is bounded in front 
by the pterygoid crest, which separates it from the orbit and the pterygo-palatine 
fossa. In it is the alar canal, which transmits the internal maxillary artery. A 
little lower is the entrance to the pterygoid canal. 

The choanal region presents the pharyngeal orifice of the nasal cavity. This 
is elliptical and is divided in its depth medially b}^ the vomer into two choanae or 
posterior nares. It is bounded in front and laterally by the palate and pterygoid 
bones, behind by the vomer. It is flanked by the hamular process of the pterygoid 
bone. The plane of the opening is nearly horizontal, and the length is about 
twice the width. 

The palatine region comprises a little more than half of the entire length 
of the base of the skull (Fig. 43). The hard palate (Palatum durum) is concave 
from side to side, and in its length also in the anterior part. It is formed by the 
palatine processes of the premaxillae and maxillse, and the horizontal parts of the 
palatine bones. It is circumscribed in front and laterally by the alveolar parts of 
the maxilla and premaxilla. The interalveolar space (]\Iargo interalveolaris) is that 
part of the arch in which alveoli are not present. Behind the last alveolus is the 
alveolar tuberosity, and medial to this is a groove for the palatine vein. In the 
middle line is the median palatine suture (Sutura palatina mediana). In the line 
of the suture, a little behind the central incisors, is the foramen incisivum, through 
which the palato-labial artery passes. On either side, parallel with the alveolar 
part of the maxilla, is the palatine groove (Sulcus palatinus), which contains the 
palatine vessels and nerve. It is continuous at the anterior palatine foramen with 
the palatine canal, which is situated between the maxilla and the palatine bone. 
The palatine fissure is the narrow interval along the lateral margin of the palatine 



THE SKULL AS A WHOLE 



79 



process of the premaxilla; it is closed in the fresh state by a process of the cartilage 
of the septum nasi. Scattered along each side of the palate are several accessory 
foramina. The transverse palatine suture (Sutura palatina transversa) is about 
half an inch from the posterior border. The latter is opposite to the fifth cheek 
tooth in the adult, and is concave and free. 

The nuchal or occipital surface (Norma occipitalis) is formed by the occipital 



Zygomatic arch 
Glenoid cavity 

Condyle of 
mandible 

Neck of mandible 




Angle of mandible 

Fig. 51. — Skull of Horse; PosTp:nioR View 



The Hyoii) F,( 



is Been Removed. 

1, External occipital protuberance; 2, curved line; 3, foramen magnum; 4, occipital condyle; 5, paramastoid 
process; 6, basilar part of occipital; 7, mastoid foramen; 8, mastoid process; 9, postglenoid process; 10, muscular 
process of petrous temporal; 11, alar canal; 12, pterygoid process of sphenoid; 13, body of sphenoid; 14, vomer; 15, 
15', perpendicular and horizontal parts of palatine bone; 16, 16, posterior nares or choanae; 17, hamulus of pterygoid 
bone; 18, maxillary tuberosity; 19, palatine process of maxilla; 20, palatine process of premaxilla; 21, palatine fissure; 
22, accessory palatine foramina; 23, bodj' of mandible; 24, mandibular foramen. 



bone. It is trapezoidal in outline, wider below than above, concave dorso-ventrally, 
convex transversely. It is separated from the dorsal surface by the nuchal crest. 
Below the crest are two rough areas for that attachment of the complexus muscles. 
A little lower is a central eminence, the external occipital protuberance, on which the 
ligamentum nuchse is attached. At the lowest part centrally is the foramen mag- 
nmn. This is bounded laterally by the occipital condyle, lateral to which is the 
paramastoid process. 



80 



THE SKELETON OF THE HORSE 





i 



.a g 

li 



i g'^ 



" ft « 

o ^" I 



-2 O m 
a. .S « 



THE CRANIAL CAVITY 



81 



The apex of the skull is formed by the bodies of the premaxillae and mandible, 
carrying the incisor teeth. 

THE CRANIAL CAVITY 

This cavity (Cavum cranii) incloses the brain, with its membranes and vessels. 
It is relatively small and is ovoid in shape. 

The dorsal wall or roof (Calvaria) (Fig. 52) is formed by the supraoccipital, 
interparietal, parietal, and frontal bones. In the middle line is the internal parietal 
crest, which joins the crista galli in front, and furnishes attachment to the falx 
cerebri. Posteriorly the crest is continued by the sharp anterior margin of the 



Occipital bone 
{squamous part) 



Parietal bone 



Frontal bone 




Paramasioid Occipital hone Sphenoid bone 
process {basilar part) {body) 



^^gg^^. 



Fig. 54. — Sagittal Section of Cranium or Horse. 
1, Lateral wall of foramen magnum; 2, hypoglossal foramen; 3, foramen lacerum posterius; 4, 5, 6, carotid, oval, 
and spinous notches; 7, floccular fossa; 8, internal acoustic meatus; 9, petrosal crest; 10, hypophyseal or pituitary 
pons (Fossa pontis) depression below 12 is the hjijophyseal fossa; 11, groove for maxillary nerve; 12, groove for cav- 
ernous sinus; 13, optic foramen; 14, 14, sphenoidal sinus; 15, crista galli; 16, perpendicular plate of ethmoid bone; 
17, vomer; 18, septum between frontal sinuses; 19, orbital wing of sphenoid; 20, temporal wing of sphenoid; 21, in- 
ternal occipital protuberance; 22, canalis transversus; 23, depression for vermis cerebelli. 



tentorium osseum, which projects downward and forward into the cavity, and gives 
attachment to the tentorium cerebelli by its sharp lateral edges. Behind this the 
roof is grooved centrally for the middle lobe or vermis of the cerebellum. Trans- 
verse grooves pass from the base of the tentorium osseum to the temporal canals. 
The anterior part of the roof is hollowed by the frontaj sinus. The occipital part 
is very thick and strong. 

The lateral wall (Fig. 54) is formed chiefly by the temporal and frontal bones 
and the orbital wing of the sphenoid. It is crossed obliquely by the petrosal crest, 
which concurs with the margin of the parietal bone and the internal occipital pro- 
tuberance in dividing the cavity into cerebral and cerebellar compartments. Behind 



32 THE SKELETON OF THE HORSE 

the crest is a depression for the hemisphere of the cerebellum. Behind this are the 
internal acoustic meatus and the openings of the aquseductus vestibuli and aquse- 
ductus cochlese. 

The roof and lateral walls are marked by digital impressions and vascular 
grooves. 

The ventral wall or floor (Basis cranii interna) (Fig. 53) may l)e regarded as 
forming three fossae. The anterior fossa (Fossa cranii oralis) supports the frontal 
and olfactory parts of the cerebrum. It is formed chiefly by the presphenoid, and 
lies at a higher level than the middle fossa. In front the fossa is divided medially 
by the crista galli, lateral to which are the deep ethmoidal fossae for the olfactory 
bulbs. The ethmoidal foramen perforates the cranial wall at the outer side of these 
fossae. Further back the central part of the surface is slightly elevated, and is 
flanked by shallow depressions which support the olfactory tracts. Posteriorly 
is a bony shelf which covers the entrance to the optic foramina; the edge of this 
shelf and the posterior borders of the orbital wings of the sphenoid may be taken as 
the line of demarcation between the anterior and middle fossae. The middle fossa 
(Fossa cranii media) is the widest part of the cavity. It extends backward to the 
spheno-occipital and petrosal crests, thus corresponding to the postsphenoid. In its 
middle is the hypophyseal fossa in which the hypophysis cerebri lies. On either side 
are two grooves: the medial one transmits the cavernous sinus and the ophthalmic, 
third, and sixth nerves to the foramen orbitale; the lateral one leads to the foramen 
rotundum, and lodges the maxillary nerve. Lateral to the grooves is a depression 
for the piriform lobe of the cerebrum. The posterior fossa (Fossa cranii posterior) 
corresponds to the basilar part of the occipital bone. It contains the medulla 
oblongata, pons, and cerebellum. In front is a median depression (Fossa pontis) 
for the pons. The surface behind this (Fossa meduUae oblongatae) is concave trans- 
versely and slopes gently downward to the foramen magnum; it supports the 
medulla oblongata. On either side are the foramen lacenmi and the h3rpoglossal 
foramen. 

The anterior or nasal wall (Fig. 33) is formed by the cribriform plate of the 
ethmoid, which separates the cranium from the nasal cavity. It is perforated by 
numerous foramina for the passage of the olfactory nerve-bundles. 



THE NASAL CAVITY 

The nasal cavity (Cavum nasi) is a longitudinal passage which extends through 
the upper part of the face. It is divided into right and left halves by a median 
septum nasi. The lateral walls are formed by the maxilla, premaxilla, the per- 
pendicular part of the palatine, and the turbinate and ethmoid bones in part. This 
wall is crossed obliquely by the lacrimal canal and groove for the naso-lacrimal 
duct, and its posterior part is perforated by the sphenopalatine foramen. The 
dorsal wall or roof is formed by the frontal and nasal bones, which form a median 
prominence at their junction. It is concave from side to side, and nearly straight 
longitudinally, except in the posterior part, where it curves downward. The ven- 
tral wall or floor is formed by the palatine processes of the premaxillae and max- 
illae, and the horizontal parts of the palate bones. It is wider but considerably 
shorter than the roof. It is concave transversely, and nearly horizontal from 
before backward, except in the posterior third, where there is a slight declivity. 
The anterior part presents a median groove for the cartilage of the septum, and a 
furrow for the vomero-nasal organ (of Jacobson) on either side. Posteriorly there 
is a median elevation, the nasal crest, to which the vomer is attached. Lateral to 
the palatine process of the premaxilla is the palatine fissure. 

The septum nasi osseum is formed by the perpendicular plate of the ethmoid 



THE NASAL CAVITY 



83 



behind, and the vomer below. In the fresh state it is completed by che cartilage 
of the septum nasi (Cartilago septi nasi). 




Fig. 55. — Cross-section of Nasal Region op Skull 
OF Horse; the Section Passes Through the 
Anterior End of the Facial Crest, and Be- 
tween the Third and Fourth Cheek Teeth. 
a, Dorsal, 6, ventral, turbinate bone; c, d, cavities 
of a and 6; e, common meatus; /, g, h, dorsal, middle, 
ventral meatus; i, k, passages to cavities of turbinate 
bones; I, naso-lacrimal duct; m, infraorbital canal; n, 
anterior end of maxillary sinus; o, septal cartilage. 
(After EUenberger, in Leisering's Atlas.) 



Fig. 56. — Cross-section of Nasal Region of Skull 
OF Horse; the Section is Cut About Half- 
way between the Orbit and the Anterior 
End op the Facial Crest, and Passes be- 
tween the Fifth and Sixth Cheek Teeth. 
o. Dorsal, b, ventral, turbinate bone; c, d, cavities 
of a and b; e, common meatus; /, dorsal, g, middle, h, 
ventral meatus; i, placed over ridge in maxillary sinus; 
k, communication between outer and inner (turbinate) 
part of maxillary sinus; I, naso-maxillary opening; m, 
naso-lacrimal canal; n, infraorbital canal. (After 
EUenberger, in Leisering's Atlas.) 



The turbinate bones divide each half of the nasal cavity into three meatus 
nasi. 

The dorsal meatus (Meatus nasi dorsalis) is a narrow passage between the 
roof and the dorsal turbinate bone. It ends at the cribriform plate of the ethmoid. 




Fig. 57. — Skull of Young Horse; Lateral View, with Sinuses Opened Up. 
A', A, Anterior and posterior compartments of maxillary sinus; B, B' , frontal and turbinate parts of frontal siiiu.i, 
C, orbit; 1, septum between compartments of maxillary sinus; 2, 2, infraorbital canal; 3, turbinate part of maxillary 
Binus; 4, 5, 6, last three cheek teeth (covered by thin plate of bone) ; 7, anterior limit of maxillary sinus in older subject; 
8, infraorbital foramen; 9, anterior end of facial crest; 10, course of naso-lacrimal duct; 11, fossa for lacrimal sac; 12, 
dorsal turbinate bone; 13, fronto-maxillary opening. 



The middle meatus (Meatus nasi medius) is the space between the two turbinate 
bones. In its posterior part is the very narrow opening into the maxillary sinus. 
The ventral meatus (Meatus nasi ventralis) is the channel along the floor which is 



84 



THE SKELETON OF THE HORSE 



overhung by the ventral turbinate bone; it is much the largest and is the direct 
path between the nostrils and posterior nares. 

The osseous nasal aperture (Apertura nasi 
ossea) is bounded by the nasal bones and the 
premaxillse. 

The posterior extremity or fundus is separ- 
ated from the cranial cavity by the cribriform 
plate of the ethmoid, and is largely occupied by 
the lateral masses of that bone. 



THE PARANASAL SINUSES 

Connected directly or indirectly with the 
nasal cavity, of which they are diverticula, are 
four pairs of air-sinuses (Sinus paranasales), 
viz., maxillary, frontal, sphenopalatine, and 
ethmoidal. 

The maxillary sinus (Sinus maxillaris) is the 
largest. Its lateral wall is formed by the maxilla, 
the lacrimal, and the malar. It is bounded medi- 
ally by the maxilla, the ventral turbinate, and the 
lateral mass of the ethmoid bone. It extends 
backward to a transverse plane in front of the 
root of the supraorbital process, and its anterior 
limit is indicated approximately by a line drawn 
from the anterior end of the facial crest to the 
infraorbital foramen. Its dorsal boundary cor- 
responds to a line drawn backward from the in- 
fraorbital foramen parallel to the facial crest. 
The ventral wall or floor is formed by the alve- 
olar part of the maxilla; it is very irregular and 
is crossed by bony plates running in various 
directions. The last three cheek teeth project 
up into the cavity to an extent which varies 
with age; they are covered by a thin plate of 
bone. The cavity is divided into anterior and 
posterior parts by an oblique septum (Septum 
sinus maxillaris) . The lateral margin of the sep- 
tum is commonly about two inches (ca. 5 cm.) 
from the anterior end of the facial crest; from 
here it is directed inward, backward, and up- 
ward. The upper part of the septum (formed 
by the posterior end of the ventral turbinate 
bone) is very delicate and usually cribriform. 




Fig. 58. — Skull of Young Horse; Dorsal 
View, with Sinuses Opened Up. 
1, 2, Ends of frontal sinus; 3, fronto- 
maxillary opening: 4, dorsal turbinate bone; 
5, lateral mass of ethmoid bone; 6, 6', two 
compartments of maxillary sinus; 7, septum 
between 6 and G'; 8, orbit; 9, anterior end 
of facial crest; A, frontal bone; B, nasal 
bone; C, lacrimal bone; D, maxilla. Note 
difference in position and form of septum in 
maxillary sinus as compared with preceding 
figure. 



The position and shape of the septum are very 
variable. It is often further forward — in some cases 
even as far forward as the anterior end of the facial crest. Exceptionally it is much nearer the 
orbit than is stated above. In the recent state, i. e., when covered by the mucous membrane on 
both surfaces, it is nearly always complete, but in very exceptional cases there is an opening of 
variable size in the upper part. 

The anterior compartment, often called the inferior maxillary sinus, is partially 
divided by the infraorl)ital canal into a lateral maxillary part and a medial smaller 
turbinate part. The latter communicates with the middle meatus by a very narrow 
slit situated at its highest part. The posterior compartment, often called the 



THE PARANASAL SINUSES 



85 



superior maxillary sinus, is also crossed by the infraorbital canal, over which it 
opens freely into the sphenopalatine sinus. It communicates dorsally with the 
frontal sinus through the large oval fronto-maxillary opening, situated at the level 
of the osseous lacrimal canal and the corresponding part of the medial wall of the 
orbit; the orifice is commonly about one and a half to two inches (ca. 4 to 5 cm.) 
long and an inch or more (2 to 3 cm.) wide. Just in front of this, and covered by a 
thin plate, is the narrow naso-maxillary fissure (Aditus naso-maxillaris), by which 
the sinus opens into the posterior part of the middle meatus. 

The foregoing statements refer to the arrangement in the average adult aniinal. In the 
foal the cavity (with the exception of its turbinate part) is largely occupied by the developing 
teeth. In horses five to six years of age the maxillary part of the sinus is filled up to a large degree 
by the embedded parts of the teeth. As the teeth are extruded to compensate the wear, more 
and more of the cavity becomes free, until in old age only the short roots project up in the floor, 
covered by a layer of bone. Other facts in this connection will be given in the description of the 
teeth. In exceptional cases the posterior part of the ventral turbinate is smaller than usual and 
leaves a considerable interval, through which the maxillary sinus communicates with the nasal 
cavity. The fronto-maxillary opening is very variable in size. 



Squamous 
Squamous Parietal temporal 
part of occip- bone bone Frontal 



ital bone 



bone 



Lacrimal Max- 



Nasal bone 



Premaxilla 




Lateral 

part of 

occipital 

bone 



Basilar part of 
occipital bone 



Mandible Incisor teeth 

(first and second) 

Fig. 59. — Skull of Foal About Two Months Old. 
This figure illustrates differential features of skull of young foal as compared with that of adult animal shown in 
Fig. 28. 1, Occipital condyle; 2, paramastoid process; 3, mastoid process; 4, external acoustic meatus; 5, zygomatic 
process of temporal bone; 6, supraorbital process of frontal bone; 7, zygomatic process of malar bone; 8, facial crest; 
9, infraorbital foramen; 10, mental foramen; 11, angle of 'mandible; 12, condyle of mandible; 13, coronoid process 
of mandible. 



The frontal or frbnto-turbinate sinus (Sinus frontalis) consists of frontal and 
turbinate parts. The frontal part is bounded chiefly by the two plates of the 
frontal bone, but its floor is formed in part by the lateral mass of the ethmoid. It 
extends forward to a plane through the anterior margins of the orbits, backward to 
one through the temporal condyles, and outward into the root of the supraorbital 
process. It is separated from the sinus of the opposite side by a complete septum 
(Septum sinuum frontalium). It is partially subdivided by a number of bony 
plates. The turbinate part is situated in the posterior part of the dorsal turbinate 
bone, roofed in by the nasal and lacrimal bones. It extends forward to a transverse 
plane about half-way between the anterior margin of the orbit and the end of the 
facial crest. It is in free communication behind with the frontal part over the 
lateral mass of the ethmoid. It is separated from the nasal cavity by the thin 



80 THE SKELETON OF THE HORSE 

turbinate plate. The frontal and maxillary sinuses communicate through the 
large opening described above. 

The sphenopalatine sinus (Sinus sphenopalatinus) consists of two parts which 
communicate under the lateral mass of the ethmoid. The sphenoidal (posterior) 
part is excavated in the body of the presphenoid. The palatine (anterior) part is 
between the two plates of the perpendicular part of the palatine bone, under the 
lateral mass of the ethmoid; it communicates freely with the maxillary sinus. The 
septum between the right and left sinuses is not usually median in the sphenoidal 
part. 

In about one-third of the cases (according to PauUi) the sphenoidal and palatine parts are 
separated by a transverse septum, and the sphenoidal part then communicates only with the ven- 
tral ethmoidal meatuses. 

The term ethmoidal sinus is often applied to the cavity of the largest ethmo- 
turbinate. It communicates with the maxillary sinus through an opening in the 
lateral lamina. 



The Bones of the Thoracic Limb 
the scapula 

The scapula is a flat bone which is situated on the anterior part of the lateral 
wall of the thorax; its long axis extends obliquely from the fourth thoracic spine 
to the sternal end of the first rib. It is curved slightly and slopes outward in 
adaptation to the form of the thoracic wall. It is triangular in outline, and has 
two surfaces, three borders, and three angles. 

The lateral surface (Facies lateralis) is divided into two fossae by the spine of 
the scapula (Spina scapulae), which extends from the vertebral border to the neck 
of the bone, where it subsides. The free edge of the spine is thick, rough, and in 
great part subcutaneous. A little above its middle there is a variable prominence, 
the tuber spinas, to which the trapezius muscle is attached. The supraspinous 
fossa (Fossa supraspinata) is situated in front of the spine, and the infraspinous 
fossa (Fossa infraspinata) behind it. The former is much the smaller of the two; 
it is smooth and is occupied by the supraspinatus muscle. The infraspinous fossa 
lodges the infraspinatus muscle; it is wide and smooth in its upper part, narrower 
below, where it is marked by several rough lines for muscular attachment; near 
the neck is the nutrient foramen, and a little lower is a vascular groove. 

The costal surface (Facies costalis) is hollowed in its length by the subscapular 
fossa (Fossa subscapularis) ; this occupies nearly the whole of the lower part of the 
surface, but is pointed above and separates two rough triangular areas (Facies 
serrata), to which the serratus ventralis is attached. In the lower third there is a 
vascular groove with several branches. 

The anterior border (Margo cranialis) is convex and rough above, concave and 
smooth below. 

The posterior border (Margo caudalis) is slightly concave. It is thick and 
rough in its upper third, thin in its middle, and thickens again below. 

The vertebral border (Margo vertebralis) carries the scapular cartilage (Car- 
tilago scapulae). In the young subject this edge of the bone is thick, and is pitted 
by impressions into which the cartilage fits. The cartilage is the unossified part 
of the foetal scapula. Its lower edge fits the depressions and elevations of the bone. 
It thins out toward the free edge, which is convex and lies alongside of the vertebral 
spines. In front it continues the line of the bone, but behind it forms a rounded 
projection. The lower part of the cartilage undergoes more or less ossification, so 
that the vertebral border of the bone in old subjects is thin, irregular, and porous. 

The anterior or cervical angle (Angulus cranialis) is at the junction of the 



THE SCAPULA 



87 




/ 




■APULA OF Horse; Lateral Surface, 
1, Spine; 2, tuber spinse; 3, cartilage; 4, anterior 
angh'; 5, posterior angle; 6, supraspinous fossa; 7, in- 
fraspinous fossa; 8, anterior border; 9, posterior bor- 
der; 10, muscular lines; 11, nutrient foramen; 12, 
vascular groove ; 13, neck; 14, tuber scapulse; 15, glen- 
oid cavity. 



Fig. 61. — Right Scapula of Horse; Costal Surface. 
1, Anterior angle; 2, posterior angle; 3, anterior border; 
4, posterior border; 5, neck; 6, vascular groove; 7, glenoid 
cavity; 8, coracoid process; 9, tuber scapulas. 



anterior and vertebral borders and lies opposite to the second thoracic spine. It is 
relatively thin and is about a right angle. 

The posterior or dorsal angle (Angulus caudalis) is thick and rough; it is 
opposite to the vertebral end of the seventh rib, and 
its position can be determined readily in the living 
animal. 

The glenoid or articular angle (Angulus glenoid- 
alis) is joined to the body of the bone by the neck 
of the scapula (Collum scapulae). It is enlarged, 
especially in the sagittal direction. It bears the 
glenoid cavity (Cavitas glenoidalis) for articulation 
with the head of the humerus. The cavity is oval 
in outline, and its margin is cut into in front by the 
glenoid notch (Incisura glenoidalis), and is rounded 
off laterally; just above its postero-lateral part is a 
tubercle to which a tendon of the teres minor is at- 
tached. The tuber scapulae^ is the large rough 
prominence in front, to w^hich the tendon of origin 

» Formerly termed the bicipital tuberosity. 




Glenoid 
cavity 



Fig. 62. — Distal Extremity of Left 
Scapula of Horse; End View. 



88 THE SKELETON OF THE HORSE 

of the biceps brachii is attached; projecting from its medial side is the small coracoid 
process (Processus coracoideus), from which the coraco-brachiahs muscle arises. 

Development. — The scapula has four centers of ossification, viz., one each for 
the body of the bone, the tuber scapulae and coracoid process, the anterior part of 
the glenoid cavity, and the tuber spinae. The last ossifies after birth and fuses with 
the spine about the third year. The tuber scapulae and coracoid process fuse with 
the body of the bone about the end of the first year. 

In old subjects the spongy substance disappears at the middle part of the fossse, so that the 
bone consists here of a thin layer of compact substance. Considerable ossification of the cartilage 
is usual, the borders become much rougher, the muscular lines are more pronounced, and a medul- 
lary cavity may appear in the neck. Aluch variation occurs in dimensions and slope. The aver- 
age ratio between the length and breadth (scapular index) is about 1 : 0..5, but in many cases the 
base is relatively wider. The inclination on a horizontal plane varies from .50 to 6.5 degrees. Ex- 
ceptionally the coracoid process reaches a length of an inch or more (2}^ to 3 cm.), and the chief 
nutrient foramen may be on the posterior border or in the subscapular fossa. 



THE HUMERUS 

The humerus is a long bone which extends from the shoulder above, where it 
articulates with the scapula, to the elbow below and behind, where it articulates 
with the radius and ulna. It is directed obliquely downward and backward, form- 
ing an angle of about 55 degrees with a horizontal plane. It consists of a shaft 
and two extremities. 

The shaft (Corpus humeri) is irregularly cylindrical and has a twisted appear- 
ance. It may be regarded as having four surfaces. The lateral surface (Facies 
lateralis) is smooth and is spirally curved, forming the musculo-spiral groove 
(Sulcus musculi brachialis), which contains the brachialis muscle; the groove is 
continuous with the posterior surface above and winds around toward the front 
below. The medial surface (Facies medialis) is nearly straight in its length, 
rounded from side to side, and blends with the anterior and posterior surfaces. 
Just above its middle is the teres tuberosity (Tuberositas teres), to which the 
tendon of the latissimus dorsi and teres major muscles is attached. The nutrient 
foramen is in the distal third of this surface. The anterior surface (Facies crani- 
alis) is triangular, wide and smooth above, narrow and roughened below. It is 
separated from the lateral surface by a distinct border, the crest of the humerus 
(Crista humeri), which bears above its middle the deltoid tuberosity (Tuberositas 
deltoidea). From the latter a rough line curves upward and backward to the 
lateral surface of the neck, and gives origin to the lateral head of the triceps muscle. 
Below the tuberosity the border inclines forward, becomes less salient, and ends at 
the coronoid fossa. The posterior surface (Facies caudalis) is rounded from side 
to side and smooth. 

The proximal extremity (Extremitas proximalis) consists of the head, neck, 
two tuberosities, and the intertuberal groove. The head (Caput humeri) presents 
an almost circular convex articular surface, which is about twice as extensive as the 
glenoid cavity of the scapula, with which it articulates. In front of the head is a 
fossa, in which are several foramina. The neck (Collum humeri) is well defined 
behind, but is practically absent elsewhere.^ The lateral tuberosity (Tuberositas 
lateralis)- is placed antero-laterally, and consists of two parts: the anterior part 
forms the lateral boundary of the intertuberal or bicipital groove and gives attach- 
ment to the lateral branch of the supraspinatus muscle; the posterior part gives 
attachment to the short insertion of the infraspinatus, while its outer surface is 
coated with cartilage, over which the chief tendon of the same muscle passes to be 

^ The proper "anatomical neck" (Collum anatomicum) is, however, indicated by the shallow 
depression which separates the head from the tuberosities, and gives attachment to the joint capsule. 

"^ The term "tubercle" as used in human anatomy does not apply well to the domestic ani- 
mals. 



THE HUMERUS 



89 



inserted into a triangular rough area below the anterior part. The medial tuber- 
osity (Tuberositas medialis) is less salient, and consists of anterior and posterior 
parts; the anterior part forms the medial boundary of the intertuberal groove, 
and furnishes insertion to the medial branch of the supraspinatus above, and the 
posterior deep pectoral muscle below; the posterior part gives attachment to the 
subscapularis muscle. The intertuberal or bicipital groove (Sulcus intertuberalis)'^ 
is situated in front; it is bounded by the anterior parts of the tuberosities, and is 
subdivided by an intermediate ridge. The groove is covered in the fresh state by 



Intertuberal 
{or bicipital) Lateral 
groove tuberosity 




crest 

Coronoid 

/- 

Medial 
condyle 



Lateral 
condyle 



Head 



Neck 



Lateral 
tuberosity 



Medial 
epicondyle 



Olecra- 
Lateral non fossa 
epicondyle 

Fig. 63. — Left Humerus of Horse; Lateral View. 
1, Rough area to which tendon of infraspinatus is 
attached; 2, crest; 3, depression for attachment of 
lateral Ugament. 



Medial 
tuber- 




Medial 
condyle 



Fig. 64. — Right Humerus of Horse; Front View, 

1, Rough area for attachment of extensor carpi 

radialis and extensor digitalis communis; 2, synovial 



cartilage, and lodges the tendon of origin of the biceps brachii muscle. Just below 
the intermediate ridge is a small fossa in which several foramina open. 

The distal extremity has an oblique surface for articulation with the radius 
and ulna, which consists of two condyles of very unequal size, separated by a ridge. 
The medial condyle (Condylus medialis) is much the larger, and is crossed by a 
sagittal groove, on the anterior part of which there is usually a synovial fossa. Pos- 
teriorly the groove extends upward considerably above the rest of the articular 
surface and reaches the olecranon fossa, and this part articulates with the semilunar 

^The name "intertuberal" is designative of the position of the groove, while the term 
"bicipital" has reference to its occupation by the tendon of the biceps brachii. The term "sulcus 
intertubercular's" is also in common use. 



90 



THE SKELETON OF THE HORSE 



notch of the ulna. The lateral condyle (Condylus lateralis) is much smaller and 
is placed somewhat lower and further back, giving the extremity an oblique ap- 
pearance; it is marked b}^ a wide shallow groove. The coronoid fossa (Fossa coro- 
noidea) is situated in front, above the groove on the medial condjde; it furnishes 
origin to part of the extensor carpi, and lateral to it is a rough depression from 
which the common digital extensor arises. Behind and above the condyles are two 
thick ridges, the epicondyles. The medial epicondyle (Epicondylus medialis) 
is the more salient; it furnishes origin to flexor muscles of the carpus and digit, 
and bears a tul^ercle for the attachment of the medial ligament of the elbow joint. 
The lateral epicondyle (Epicondylus lateralis) bears laterally the condyloid crest 
(Crista condyloidea), which forms here the outer boundary of the musculo-spiral 
groove, and gives origin to the extensor carpi radialis. Below this is a rough excava- 
tion in which the lateral ligament is attached. The distal border of the epicondyle 
gives attachment to the ulnaris lateralis. Between the epicondyles is the deep 
olecranon fossa (Fossa olecrani), into which the processus anconseus projects. 




Fig. Go. — Proximal Extremity of Left Humerus of 
Horse; End View. 
1, Intertuberal (or bicipital) groove; 2, 3, anterior 
parts of lateral and medial tuberosities; 4, fossa; 5, 6, 
posterior parts of lateral and medial tuberosities; 7, 
head. 




Fig. 60. — Dist.vl Extremity of Left Humerus of 
Horse; End View. 
1, Medial condyle; 2, lateral condyle; 3, part of 
medial epicondyle to which medial ligament is attached; 

4, depression in which lateral ligament is attached; 

5, 6, areas of attachment of flexor and extensor muscles 
of carpus and digit; 7, olecranon fossa. 



Development. — The humerus ossifies from six centers, viz., three primary 
centers for the shaft and extremities, and three secondary centers for the lateral 
tuberosity, the deltoid tuberosity, and the medial condyle respectively. The 
proximal end fuses with the shaft at about three and one-half years, the distal at 
about one and a half years of age. 



THE RADIUS 

The radius is much the larger of the two bones of the forearm in the horse. 
It extends in a vertical direction from the elbow, where it articulates with the hum- 
erus, to the carpus. It is gently curved, the convexity being dorsal. It consists 
of a shaft and two extremities. 

The shaft (Corpus radii) is curved in its length, somewhat flattened from before 
backward, and widened at its ends. It presents for description two surfaces and 
two borders. The dorsal surface (Facies dorsalis) is smooth, slightly convex in 
its length, and rounded from side to side. The volar surface (Facies volaris) 



THE RADIUS 



91 



is correspondingly concave in its length and is flattened in the transverse direction. 
At its proximal part there is a smooth shallow groove, which concurs with the ulna 
in the formation of the interosseous space of the forearm (Spatium interosseum 
antibrachii) ; the nutrient foramen is in the lower part of this groove Below this 
there is in the young subject a narrow, rough, triangular area to which the ulna is 



Olecranon 



Processus anconeus 

Semilunar notch 
Humeral articular 
surface v 
Coronoid — i«i:,r— '" 
process 
Radial tu- 
berosity 




Olecranon 



Ridge 
2 



Fig. 07. — Left R.\dius and VhN\ of Hor.se; L.\teral 
View. 
1, Tuberosity for attachment of lateral ligament of 
elbow joint, and common and lateral extensor muscles; 
2, tuberosity for attachment of lateral ligament of 
carpal joint; 3, groove for common extensor tendon; 
4, groove for lateral extensor tendon. 




Processus 

anconceus 
Semilunar notch 

Glenoid cavity 



Radial 
'- 'dM tuberosity 



-Left Radius and Ulna of Horse; Medial 
View. 
1, Tuberosity for attachment of short part of 
medial ligament of elbow; 2, prominence for long part 
of same; 3, groove for end of brachialis muscle; 4, 
tuberosity for attachment of medial ligament of carpal 
joint; 5, oblique groove for tendon of extensor carpi 
obUquus. 



attached by an interosseous ligament; in the adult the two bones are fused here. 
A variable rough elevation distal to the middle and close to the medial border gives 
attachment to the radial check ligament. The medial border (Margo medialis) 
is slightly concave in its length and is largely subcutaneous; at its proximal end 
there is a smooth area on which the tendon of insertion of the brachialis muscle lies, 
and a small rough area just below gives attachment to that muscle and the long 



92 THE SKELETON OF THE HORSE 

medial ligament of the elbow-joint. The lateral border (Margo lateralis) is more 
strongly curved, but presents no special features. 

The proximal extremity or head ((Extremitas proximalis s. capitulum radii) 
is flattened from before backward and wide transversely. It presents the humeral 
articular surface (Facies articularis humeralis) which corresponds to that of the 
distal end of the humerus; it is crossed by a sagittal ridge, which has a synovial 
fossa on its posterior part, and ends in front at a prominent lip, the coronoid proc- 
ess (Processus coronoideus). Just below the posterior border, and separated by 
a depression, there are two concave facets (Facies articularis ulnaris) for articula- 
tion with the ulna, and between these and the interosseous space is a quadrilateral 
rough area at which the two bones are united by an interosseous ligament. At 
the medial side of the dorsal surface is the radial or bicipital tuberosity (Tuberositas 
radii), into which the biceps tendon is inserted. The medial tuberosity (Tuber- 
ositas proximalis meclialis) is continuous with the preceding eminence, and fur- 
nishes attachment to the short part of the medial ligament. The lateral tuberosity 
(Tuberositas proximalis lateralis) is more salient; it gives attachment to the lateral 
ligament and to the common and lateral extensor muscles of the digit. 

The distal extremity is also compressed from before backward. It presents 
the carpal articular surface (Facies articularis carpea), which consists of three parts. 
The medial facet is the largest, is quadrilateral, concavo-convex from before back- 
ward, and articulates with the radial carpal bone; the intermediate one is some- 
what similar in form but smaller, and articulates with the intermediate carpal bone; 
the lateral facet is smaller, is convex, and articulates below with the ulnar carpal 
and behind with the accessory carpal. The dorsal surface presents three grooves, 
separated by ridges. The middle one is vertical and gives passage to the tendon 
of the extensor carpi radialis; the lateral one is similar and contains the tendon of 
the common digital extensor; the medial one is small and oblique and lodges the 
tendon of the extensor carpi obliquus. The volar aspect is crossed by a rough 
ridge, below which are three depressions. On either side is a tuberosity (Tuber- 
culum ligament!) to which the collateral ligament is attached. The lateral one is 
marked by a small vertical groove for the passage of the lateral extensor tendon. 

Development.^ — The radius ossifies from four centers, viz., one each for the 
shaft, the two extremities, and the lateral part of the distal end; the last is morpho- 
logically the distal end of the ulna which has fused with the radius, and the line of 
fusion is often indicated by a distinct groove on the carpal articular surface. The 
proximal extremity unites with the shaft at about one and a half years, the distal 
end at about three and a half years usually. 



THE ULNA 

The ulna of the horse is a reduced long bone situated behind the radius, with 
which it is partially fused in the adult. 

The shaft (Corpus ulnae) is three-sided and tapers to a point distally. The 
dorsal surface (Facies dorsalis) is applied to the volar surface of the radius, and be- 
low the interosseous space the two bones are fused in the adult. The surface which 
enters into the formation of the space is smooth and usually presents a small nu- 
trient foramen, directed upward. Above the space it is rough and is attached to 
the radius by an interosseous ligament which is usually permanent. The medial 
surface (Facies medialis) is smooth and slightly concave. The lateral surface 
(Facies lateralis) is flattened. The medial and lateral borders (Margo medialis, 
lateralis) are thin and sharp, except at the interosseous space. The volar border 
(Margo volaris) is slightly concave in its length and is rounded. The distal end is 
pointed and is usually a little below the middle of the radius. It is commonly 



THE CARPUS 



93 



continued by a fibrous cord to the distal tuberosity of the radius, but this band may 
be replaced in part or entirely by bone. 

The proximal extremity (Extremitas proximalis) is the major part of the bone. 
It projects upward and somewhat backward behind the distal end of the humerus, 
and forms a lever arm for the extensor muscles of the elbow. The medial surface 
is concave and smooth. The lateral surface is convex and is roughened al)ove. 
The dorsal border bears on its middle a pointed projection, the processus anconaeus 
or "beak," which overhangs the semilunar notch 

(Incisura semilunaris).^ The latter is triangular ' " 

in outline, concave from above downward, convex 
transversely, and articulates w4th the humerus; in 
its lower part there is an extensive synovial fossa. 

Just below the notch are two convex facets which *' 

articulate with those on the volar aspect of the 
proximal end of the radius. The volar border is 
nearly straight, and is thick and rounded. The 
free end or summit is a rough tuberosity, the ole- 
cranon, which gives attachment to the triceps 
brachii and other muscles. 

The primitive distal extremity has, as pre- 
viously stated, fused with the radius. 

Development. — The ulna ossifies from three 
centers, of which one is for the main part of the . .. — ^ 
bone, one for the olecranon, and one for the distal 
end. The cartilaginous embryonic ulna extends 
the entire length of the forearm. The distal part 
of the shaft is usually reduced to a small fibrous 
band or may disappear entirely; in some cases a ^v 
variable remnant of it ossifies. The distal ex- "»' . 



-;i5,!'' 





Fig. 69. — Distal End of Left Radius and Ulna of Horse; End 
View. 
1, 2, 3, 4, Facets which articulate with radial, intermediate, ulnar, 
and accessory carpal bones respectively; 5, groove for tendon of exten- 
sor carpi radialis; 6, groove for tendon of common digital extensor; 7, 
tuberosity for attachment of medial ligament of carpal joint. 



Fig. 70. — Sagittal Section of Uppbb 

Part of Radius and Ulna of Horse. 

Cm, Medullary cavity of ulna. 



tremity fuses before birth with the radius. The olecranon unites with the rest 
of the bone at about three and a half years. A medullary cavity appears to occur 
constantly in the adult — contrary to the statements of some authors. 



THE CARPUS 
The carpus of the horse consists of seven or eight carpal bones (Ossa carpi) 



arranged in two rows, proximal or antibrachial and distal or metacarpal, 
1 Formerly called the sigmoid cavity. 



The 



94 THE SKELETON OF THE HORSE 

(abbreviated) names and relative positions of the bones of the left carpus are in- 
dicated below: 

Proximal Row: 
Radial Intermediate Ulnar Accessory 



^. 



Distal Row: 
First Second Third Fourth 



The Radial Carpal Bone 

The radial carpal bone (Os carpi radiale)4s the largest bone of the proximal row; 
it is somewhat compressed transversely, and is clearly six-sided. The proximal 
surface is convex in front, concave behind, and articulates with the medial facet 
on the distal end of the radius. The distal surface is also convex in front and con- 
cave behind; it articulates with the second and third carpal bones. The lateral 
surface bears upper and lower facets on its anterior part for articulation with the 
intermediate; between and behind these it is excavated and rough. The dorsal 
surface is rough and slightly convex. The medial surface and the volar surface 
are rough and tuberculate. 

The Intermediate Carpal Bone 

The intermediate carpal bone (Os carpi intermedium)- is somewhat wedge- 
shaped, wider in front than behind. The proximal surface is saddle-shaped, and 
articulates with the middle facet on the distal end of the radius. The distal sur- 
face is smaller, convex in front, concave behind, and articulates with the third and 
fourth carpal bones. The medial surface has upper and lower facets for articula- 
tion ^v^th the radial carpal, and between these it is excavated and rough. 
The lateral surface is similar to the preceding and articulates with the ulnar car- 
pal. The dorsal surface is rough and slightly convex. The volar siuiace bears a 
tuberosity on its lower part. 

The Ulnar Carpal Bone 

The ulnar carpal bone (Os carpi ulnare)^ is the smallest and most irregular 
bone of the proximal row. The proximal surface is concave and fits the lower part 
of the lateral facet on the distal end of the radius. The distal surface is oblique 
and undulating for articulation with the fourth carpal bone. The medial surface 
has upper and lower facets for articulation with the intermediate. The dorsal and 
lateral surfaces are continuous, convex, and rough. The volar surface is oblique, 
and bears a concave facet for articulation with the accessory carpal bone; below 
this is a tubercle. 

The Accessory Carpal Bone 

The accessory carpal bone (Os carpi accessorium)* is situated behind the ulnar 
carpal bone and the lateral part of the distal end of the radius. It is discoid and pre- 
sents for description two surfaces and a circumference. The medial surface is con- 
cave and forms the lateral wall of the carpal groove. The lateral surface is con- 
vex and rough; a smooth groove for a tendon crosses its anterior part obliquely 
downward and slightly forward. The dorsal border bears two facets; the proximal 
one is concave and articulates with the back of the lateral facet on the distal end of 
the radius; the distal one is convex and articulates with the ulnar carpal bone. 
The remainder of the circumference is rounded and rough. 

1 Also known as the scaphoid. ^ ^\^q known as the semilunar or lunar. 

^ Also known as the cuneiform. 

* Also known as the pisiform and erroneously as the trapezium. 



THE FIRST CARPAL BONE THE SECOND CARPAL BONE 



95 



The accessory does not directly bear weight, and may be regarded as a sesamoid bone 
interposed in the course of the tendons of the middle and lateral flexors of the carpus, which it 
enables to act at a mechanical advantage. The posterior border furnishes attachment to the 
transverse carpal ligament, which completes the carpal canal for the flexors of the digit. 

The First Carpal Bone 
The first carpal bone (Os carpale primum)i is a small inconstant bone, com- 
monly about the size and shape of a pea, which is situated in the distal part of the 
medial ligament of the carpus, behind the second carpal bone. 

This bone appears to be absent on both sides in about half of the cases; in a good many 
subjects it is present on one side only. In size it varies from a minute nodule to a discoid or cylin- 
drical mass 12-15 mm. in length. In exceptional cases it articulates with both the second carpal 
and the second metacarpal bone; in other cases with the former only, but in the majority of speci- 
mens no articular facet is present. 




Fig. 7L — Left Corpus of Horse, with Parts of Adjacent Bones; L.^teral View. 
a, Intermediate carpal; Cu, ulnar carpal; Ca, accessory carpal; C3, third carpal; C4, fourth carpal; McIII, 
McIV, metacarpal bones; 1, groove for common extensor tendon; 2, groove for lateral extensor tendon; 3, groove 
for long tendon of ulnaris lateralis; 4, metacarpal tuberosity; o, original distal end of ulna, which is fused with the 
radius and regarded as part of the latter. 



The Second Carpal Bone 

The second carpal bone (Os carpale secundum)- is the smallest constant bone 

of the distal row, and is irregularly hemispherical in shape. The proximal surface 

is a convex facet, which is continued upon the volar surface and articulates with the 

radial carpal. The lateral surface faces obliquely outward and forward, and bears 

1 Also known as the trapezium, and often erroneously called the pisiform. 
^ Also known as the trapezoid. 



96 



THE SKELETON OF THE HORSE 



three facets for articulation with the third carpal bone. The dorsal and 
medial surfaces are continuous and bear a tuberosity to which the collateral liga- 
ment is attached. The distal surface is articular and consists of a large flattened 
facet for the second or inner metacarpal bone, and a small one for the third or large 
metacarpal bone. Some specimens have a small facet on the lower part of the volar 
surface which articulates with the first carpal bone. 



Ca 



^ 



J 



\ 




The Third Carpal Bone 

The third carpal bone (Os carpale tertium)^ is much the largest bone of the 

distal row, forming more than 
two-thirds of the width of the 
latter. It is flattened from 
above downward, and is twice as 
wide in front as behind. The 
proximal surface consists of two 
facets separated by an antero-pos- 
terior ridge; the medial facet is 
concave and articulates with the 
radial carpal; the lateral facet — 
for the intermediate carpal — is 
concave in front and convex be- 
hind, where it encroaches on the 
volar surface. The distal surface 
is slightly undulating, and articu- 
lates almost entirely with the third 
or large metacarpal bone, but it 
usually bears a small oblique facet 
at its medial side for the second 
metacarpal, and there is commonly 
a non-articular depression later- 
ally. The medial surface faces 
backward and inward, and bears 
three facets for articulation with 
the second carpal, between which 
it is excavated and rough. The 
lateral surface has two facets for 
articulation with the fourth car- 
pal, and is depressed and rough 
in its middle. The dorsal sur- 
face is convex and is crossed 
by a rough transverse ridge. The 
volar surface is relatively small, 
and is rounded; its upper part 




MdU 



Pig. 72. — Left Carpus of Horse, with Parts of Adjacent 
Bones; Medial View. 
Cr, Radial carpal; Ca, accessory carpal; Ct, first carpal; 
C2, second carpal; McII, McIII, metacarpal bones; 1, tuber- 
osity of radius for attachment of medial ligament of carpus; 
2, groove for tendon of extensor carpi obliquus; 3, third car- 
pal; 4, metacarpal tuberosity. 



is encroached upon by the proximal articular surface, below which it is rough. 



The Fourth Carpal Bone 

The fourth carpal bone (Os carpale quartum)- is somewhat wedge-shaped, and 
is readily distinguished from the second by its greater size and its volar tubercle. 
The proximal surface articulates with the intermediate and ulnar; it is convex and 
curves outward, backward, and downward, encroaching on the lateral and volar sur- 
faces. The distal surface bears two medial facets for the third or large metacarpal 

1 Also known as the os magnum or capitatufti. 

2 Also known as the unciform or hamatum. 



THE FOURTH CARPAL BONE 



97 



and a lateral one for the fourth or lateral metacarpal bone. The medial surface 
has two or three facets for articulation with the third carpal, between which it is 
excavated and rough. The dorsal surface is convex and rough. The lateral sur- 




McIII 



Fig. 73. — Left Carpus of Horse, with Pauts )f Adjacent Bones; Volar View. 
The accessory and first carpal bones have been moved out of their natural position and their articular connections 
indicated by arrows. Cr, Radial carpal; 3, intermediate carpal; Cu, ulnar carpal; Co, accessory carpal; CI, first 
carpal; C2, second carpal; 4, third carpal; C4, fourth carpal; 1, groove for lateral extensor tendon; 2, tuberosity 
of radius for medial ligament of carpal joint; 5, volar tubercle of fourth carpal; 6, rough area on large metacarpal 
bone for attachment of suspensory ligament. 



Intermediate 




Third 



Radidl 



Fig. 74. — Proximal Row of Left Carpus of Horse; 

Proximal View. 

1-4, Articular facets corresponding with those on Fig. 69; 

5, groove for tendon of ulnaris lateralis. 

7 



Fourth 




Second 



First 

Fig. 7.5.— Distal Row of Left Carpus of Horse: 
Proximal View. 
1, Articulation of first carpal with second; 2, 2, 
facets for radial; 3, 3', facets for intermediate 4, 
facet for ulnar. 



THE SKELETON OF THE HORSE 



face is small, being encroached upon b}- the proximal articular surface. 
surface bears a tubercle on its distal part.^ 



The volar 



The Carpus as a Whole 
The bones of the carpus, exclusive of the accessory, form an irregular quadran- 
gular mass, the width of which is about twice the height or the dorso-volar diameter. 
The dorsal surface is convex from side to side, depressed along the line of junction 
of the two rows, and prominent below. The volar surface is in general slightly 
convex, but very irregular. It forms with the accessory 
carpal the carpal groove (Sulcus carpi) , which in the recent 
state is rendered smooth by the volar ligament; it is con- 
verted into the carpal canal (Canalis carpi) for the flexor 
tendons by the transverse carpal ligament, which stretches 
across from the accessory bone to the medial side. The 
proximal surface is widest medially and is elevated in front, 
concave behind ; it is entirely articular and adapted to the 
car])al articular surface of the radius. The distal surface 
is also articular and is irregularly faceted in adaptation to 
the surfaces of the metacarpal bones; each of the distal 
bones usually articulates with two metacarpal bones, but 
sometimes the third rests on the third metacarpal only. 
The medial and lateral surfaces are both irregular and 
rough, the former being the wider. With the exception of 
the accessory, ulnar, and second, each bone articulates 
with two bones of the other row. 

Development. — Each ossifies from a single center. 





McIV 



McIII 



Fig. 76. — Right Metacarpal 
Bones op Horse; Vol.\r 
View. 

1, Nutrient foramen of 
large (third) metacarpal bone; 
2, 3, 4, proximal extremities; 5, 
surface for attachment of sus- 
pensory ligament; 6, sagittal 
ridge of distal end of large meta- 
carpal bone; 7, 7', distal ends of 
small (second and fourth) meta- 
carpal bones. 



Fig. 



McII 
iRPAL Bones of Horse; End 



-Proximal Extremities of Left Metac. 
View. 
2, 2', Facets for second carpal bone; 3, 3', facets for third carpal bone; 4, 4', facets 
for fourth carpal bone; 5, metacarpal tuberosity. 



THE METACARPUS 

Three metacarpal bones (Ossa metacarpalia) are 
present in the horse. Of these, only one, the third or 
large metacarpal bone, is fully developed and carries a 
digit; the other two, the second and fourth, are much 
reduced, and are commonly called the small metacarpal or "splint" bones. 

The Third or Large Metacarpal Bone 
This (Os metacarpal tertium) is a very strong long bone, which is situated ver- 
tically between the carpus and the first phalanx. It consists of a shaft and two ex- 
tremities. 

^ This bone is probably equivalent to the fourth and fifth carpals of forms in which five 
carpal elements are present in the distal row. 



THE SMALL METACARPAL BONES 99 

The shaft (Corpus) is semicylindrical, and presents two surfaces and two 
borders. The dorsal surface is smooth, convex from side to side, and nearly 
straight in its length. The volar surface is somewhat convex from side to side and, 
with the small bones, forms a wide groove which lodges the suspensory ligament. 
On either side of its proximal two-thirds it is roughened for the attachment of the 
small metacarpal bones. The nutrient foramen occurs at the junction of the 
proximal and middle thirds. The distal part is wider and flattened. The borders 
are rounded. 

The proximal extremity (Extremitas proximalis s. basis) bears an undulating 
articular surface adapted to the distal row of carpal bones. The greater part sup- 
ports the third carpal bone; the oblique lateral part, separated from the preceding 
by a ridge, articulates with the fourth, and a small facet for the second is usually 
found at the medio-volar angle. On either side is a notch separating two small 
facets which articulate with the proximal ends of the small metacarpal bones. 
Toward the medial side of the dorsal surface is the metacarpal tuberosity, into 
which the extensor carpi radialis is inserted. The volar surface is roughened for 
the attachment of the suspensory ligament. 

The distal extremity (Extremitas distalis s. capitulum) presents an articular 
surface for the first phalanx and the proximal sesamoid bones, which is composed of 
two condyles, separated by a sagittal ridge; the medial condyle is slightly the larger. 
On either side is a small fossa, surmounted by a tubercle, for the attachment of the 
collateral ligaments of the fetlock joint. 

The large metacarpal is one of the strongest bones in the skeleton. The compact substance 
is specially thick in front and medially. The medullary cavity extends further toward the ends 
than in most of the long bones of the horse and there is little spongy substance. 

The Small Metacarpal Bones 

These, numerically the second and fourth metacarpal bones (Ossa metacarpalia 
secundum et quartum) , are situated on either side of the volar surface of the large 
metacarpal bone, and form the sides of the metacarpal groove. Each consists of a 
shaft and two extremities. 

The shaft (Corpus) is three-sided and tapers to the distal end. It is variably 
curved, convex toward the middle line of the limb. The attached surface is flat- 
tened and is rough, except in its lower part; it is attached to the large metacarpal 
bone by an interosseous ligament, except near the distal end. The dorsal or ab- 
axial surface is smooth and rounded from side to side above, grooved below. The 
volar or axial surface is smooth and concave from edge to edge, except below, 
where it forms a rounded edge. 

The proximal extremity (Extremitas proximalis s. basis) is relatively large. In 
the case of the medial bone it usually bears two facets above which support the sec- 
ond and third carpal bones, while the lateral bone has here a single facet for articu- 
lation with the fourth carpal bone. Each has also two facets for articulation with 
the large metacarpal, and is elsewhere roughened for the attachment of ligaments 
and muscles. The medial bone may present a small facet behind for the first carpal 
bone. 

The distal extremity (Extremitas distalis s. capitulum) is usually a small nod- 
ule, which projects to a variable extent in different subjects, and is easily felt in the 
living animal. It is situated two-thirds to three-fourths of the way down the region. 

The small metacarpal bones vary much in length, thickness, and curvature. In the ma- 
jority of cases the medial bone is the longer; in other subjects the lateral one is the longer or there 
is no material difference. Sometimes the curvature is very pronounced, so that the distal end 
causes a decided projection. The distal end is very variable in size and may be a mere point; in 
other cases, especially in large draft horses, it may present a prolongation wliich is regarded as the 
vestige of the digital skeleton. 

Development. — The large metacarpal bone ossifies from three centers. The 



100 



THE SKELETON OF THE HORSE 



proximal extremity unites with the shaft before birth, the distal extremity toward 
the middle of the second year. The small metacarpal bones ossify from two cen- 
ters, one of which is for the proximal extremity. Their distal ends are cartilaginous 
at birth. Fusion of the middle part of the shaft with the large metacarpal bone is 
common. ■''■■:' 

THE PHALANGES 
The First Phalanx 
The first phalanx (Phalanx prima) ^ is a long bone, and is situated between the 
large metacarpal bone and the second phalanx. It is directed obliquely downward 
and forward, forming an angle of 50 to 55 degrees with the horizontal plane in well- 
formed limbs. It consists of a shaft and two extremities. 



Distal end of small meta- 
carpal bone 



Proximal sesamoid hone 




Distal end of first phalanx 
Proximal end of second phalanx 



Distal sesamoid bone 



Distal end of large metacarpal bone 
Proximal end of first phalanx 




Dorsal groove — 

Angle _ ., '- ' 

DiMal border of third phalanx 
Fig. 78. — Skeleton of Digit and Distal Part of Metacarpus of Horse; Lateral View. 
1-7, Eminences and depression for attachment of ligaments. Cartilage of third phalanx is removed. 



The shaft (Corpus) is wider and much thicker above than below, and presents 
two surfaces and two borders. The dorsal surface is convex from side to side and 
smooth. The volar surface is flattened, and bears a triangular rough area, bounded 
by ridges which begin at the proximal tuberosities and converge distally; this area 
furnishes attachment to the distal sesamoidean ligaments. The borders, medial 
and lateral, are rounded and have a rough area or a tubercle on their middle parts. 

The proximal extremity (Extremitas proximalis s. basis) is relatively large. 
It bears an articular surface adapted to the distal end of the large metacarpal bone, 
^ This bone is also called the large pastern bone or os suffraginis. 



THE FIRST PHALANX 



101 



consisting of two glenoid cavities separated by a sagittal groove; the medial cavity- 
is a little larger than the lateral one. On each side is a buttress-like tuberosity for 
ligamentous attachment. The dorsal surface has a slight elevation for the attach- 
ment of the extensor tendons. 

The distal extremity (Extremitas distalis) is smaller, especially in its dorso- 
volar diameter. It presents a trochlea for articulation with the second phalanx, 
consisting of a shallow sagittal groove separating two condyles; the medial con- 



I Titer mediate groove 

Proximal articular surface 

Tuberosity 

Eminence for extensor tendons 



Dorsal surface - 

Eminence for collateral ligament - 
Distal articular surface ' 

Proximal articular surface - 

Dorsal surface — 
Eminence for collateral ligatncnt 
Distal articular surface 

Articular surface 

Angle .. 

Depression for collateral 
ligament 

Dorsal groove 
Coronary border '''f"'\^ 
Articular surface -'*■'«.' 

Extensor process ■-' 

Dorsal surface 




First phalanx 



Second phalanx 



Distal sesamoid 



Third phalanx 



Distal border ■ ' '' 

Fig. 79. — Phalanges and Distal Sesamoid of Horse; Dorsal Aspect. 



dyle is a little the larger, and the two are separated posteriorly by a notch. On 
either side, just above the margin of the articular surface, is a depression sur- 
mounted b}^ a tubercle, to both of which the collateral ligament is attached. Be- 
hind the tubercle is a distinct mark to which the superficial flexor tendon is 
attached. 

Development. — The first phalanx ossifies from three centers. The distal end 
unites with the shaft before birth, the proximal end at about one year of age. 

The first phalanx contains a small medullary cavity in the middle of the shaft. It may be 



JQ2 THE SKELETON OF THE HORSE 

remarked that the bone is twisted sUghtly; when placed volar surface down on the table, it touches 
the latter by three points only, the proximal tuberosities and the medial condyle. 

The Second Phalanx 
The second phalanx (Phalanx secunda)i is situated between the first and 
third phalanges, its direction corresponding to that of the first phalanx. It is 
flattened from before l)ackward, and its width is greater than its height. It may 
be described as possessing four surfaces. 

The proximal surface presents two glenoid cavities separated by a low ridge, 

and articulates with the first phalanx. 
The middle of the dorsal border is ele- 
vated and roughened in front for the 
attachment of the common extensor 
tendon. The volar border is thick and 
overhanging; in the fresh state its mid- 
dle part is covered with cartilage, over 
which the deep flexor tendon passes. 
On either side there is an eminence, to 
which the collateral ligament and the 
superficial flexor tendon are attached. 
The distal surface is trochlear, 
and articulates with the third phalanx 
and distal sesamoid bone. It resem- 
bles somewhat the trochlea of the first 
phalanx, but is more extensive and en- 
croaches more on the dorsal and volar 
surfaces. 

The dorsal surface is convex from 
side to side and smooth in its middle; 
on each side of its distal part is a rough 
depression, surmounted by a tuber- 
osity, to both of which ligaments are 
attached. 

The volar surface is smooth and 
fiattened. The borders which separate 
the dorsal and volar surfaces are con- 
cave from above downward, rounded 
from before backward. 

Development. — The second pha- 
laiLx ossifies like the first, but the proxi- 
mal end unites with the shaft two or 
three months earlier. 



Tuberosity 



Ridges for 

attachment 

of middle 

distal sesd- 

moid ligament 

Imprint for 

tendon of 

superfici(d 

flexor 

Condyle 

Transverse 
prominence 





-Digital Bones of Fore Limb of Horse; Volar 
Aspect. 



The Third Phalanx 
The third phalanx (Phalanx ter- 
tia)^ is entirely inclosed by the hoof, 
It presents for examination three sur- 



to which it conforms in a general way. 
faces, three borders, and two angles. 

The articular surface (Facies articularis) faces upward and backward, and is 
chiefly adapted to the distal surface of the second phalanx, but a narrow, flattened 
area along the volar border articulates with the distal sesamoid. The proximal or 
coronary border bears a central eminence, the extensor process (Processus exten- 

1 This bone is also called the small pastern bone or os coronse. 

2 This bone is also called the os pedis or coffin bone. 



THE THIRD PHALANX 



103 



sorius), to which the common extensor tendon is attached. On either side is a de- 
pression for the attachment of the collateral ligament. 

The dorsal or wall surface (Facies dorsalis) slopes downward and forward. 
The angle of inclination on the ground plane is about 45 to 50 degrees in front. 



Cartilage 



h Dorsal Angle 

grooir 



) Arlicular surface 

Extensor process 

Depression for collateral ligament 
Dorsal surface 




l)istal border 



Fig. si. — Third Phalanx of Horse; Lateral View. 
a, b. Anterior and posterior extremities of cartilage. 



Laterally the height diminishes, and the slope becomes steeper, especially on the 
medial side. From side to side the curvature is almost semicircular. The surface 
is rough and porous, resembling pumice stone somewhat. It is perforated by nu- 
merous foramina of various sizes; a series of larger ones is situated on or near the 
distal border. On either side the dorsal groove (Sulcus dorsalis)'^ passes forward 
from the angle and ends at one of the 
larger foramina. In the fresh state this 
surface is covered by the corium of the 
wall of the hoof. The distal border is 
thin, sharp, and irregularly notched; 
there is commonly a wider notch in 
front. 

The volar surface (Facies volaris) 
is arched, and divided into two unequal 
parts by a curved rough line, the semi- 
lunar crest (Crista semilunaris) . The 
larger area in front of the crest is cres- 
cent-shaped, concave, and compara- 
tively smooth; it corresponds to the 
sole of the hoof, and may be termed 
the sole surface. The part behind the 
crest is much smaller, and is semilunar; 
it is related to the deep flexor tendon, 
and is hence called the flexor surface 
(Facies flexoria) . It presents a central 
prominent rough area, on either side of 
which is the volar foramen (Foramen 

volare), to which the volar groove (Sulcus volaris) conducts from the angle.^ 
The foramina lead into the semilimar canal (Canalis semilunaris) within the 
bone, from which small canals lead to some of the foramina of the dorsal sur- 




FiG. 82. — Section of Third Phalanx of Horse. 

Section is cut approximately parallel with volar sur- 
face and opens up the semilunar canal (C.s.). Volar for- 
amina indicated by arrows. 



Formerly termed the pyramidal process. 
Formerly termed the plantar groove and foramen. 



Formerly termed the preplantar groove. 



104 



THE SKELETON OF THE HORSE 



face. The deep flexor tendon is inserted into the semilunar crest and the central 

rough area behind it. 

The volar grooves and foramina transmit the terminations of the digital arteries into the 
semilunar canal, where they meet and form a terminal arch, from which branches pass through 
canals in the bone and emerge through the foramina on the dorsal surface. 

The angles or wings (Anguli) are prismatic masses which project l^ackward on 
either side; the medial one is usually the shorter. Each is divided into upper and 
lower parts by a notch, or is perforated by a foramen which leads to the dorsal 
groove.^ The proximal border carries the cartilage. 

The cartilages of the third phalanx (Cartilagines phalangis tertise)- are rhom- 
boid curved plates which surmount the angles on either side. They are relatively 
large and extend above the margin of the hoof sufficiently to be distinctly palpable. 
The abaxial surface is convex, the axial, concave. The proximal border is sinuous 

and thin ; the distal is thicker and is in 
part attached to the wing. The anterior 
end is attached by ligament to the side 
of the second phalanx. The posterior 
end curves toward its fellow at the heel, 
and is perforated by numerous for- 
amina for the passage of veins. 

It wll be noted that the size and form 
of the angles vary much in difTerent specimens. 
In the new-born foal the angle is a small, 
pointed projection. Later the process of ossi- 
fication invades the lower part of the car- 
tilage to a varying extent. In some cases the 
greater part of the cartilage is ossified — a con- 
dition commonly termed " sidebone. " In the 
young subject the cartilage is hyaline, but later 
it changes to the fibrous type. 

Development. — The ossification of 
the third phalanx is peculiar. While 
the proximal articular part is still car- 
tilaginous, a perichondrial cap of bone 
is formed in relation to the hoof. Later 
the process extends into the upper part. 
Structure. — The interior of this 
bone is channeled by numerous canals 
for vessels, most of which radiate from 
the semilunar canal to the dorsal sur- 
face; these are not canals for nutrient 
vessels of the bone, but transmit 
arteries to the corium of the hoof. Thick layers of compact substance are found 
at the articular and flexor surfaces and the extensor process, i. e., at the points of 
greatest pressure and traction. 

The Sesamoid Bones 

The two proximal sesamoids (Ossa sesamoidea phalangis primse) are situated 
behind the distal end of the large metacarpal bone, and are closely attached to the 
first phalanx by strong ligaments. Each has the form of a three-sided pyramid. 
The articular surface (Facies articularis) conforms to the corresponding part of the 

^ The upper and lower divisions of the angle are sometimes termed the basilar and retrossal 
processes respectively. 

^ These are usually called the lateral cartilages, but this designation could not be retained. 
They have the same relation to the third phalanx that the cartilage of the scapula has to the latter 
bone, and are here named in similar fashion. 




Fig. 8.3. I n vi > ,..i - of 
New-born 1'o\l; Dor- 
sal View. 

Cartilages of third phalanx 
removed. 



Fig. 84. — Phalanges and 
Distal Sesamoid of 
New-born Foal; Vo- 
lar View. 

Cartilages of third phalanx 
removed. 



OS COX^ THE ILIUM 105 

distal end of the large metacarpal bone. The flexor surface (Facies flexoria) is 
flattened and oblique; in the fresh state it is covered by a layer of cartilage which 
also fills the interval between the opposed borders of the two bones, and forms a 
smooth groove for the deep flexor tendon. The abaxial surface is concave, and 
gives attachment to part of the suspensory ligament; it is separated from the 
flexor surface by a rough everted border. The base is distal, and furnishes attach- 
ment to the distal sesamoidean ligaments. The apex is proximal and is rounded. 

The distal sesamoid or navicular bone (Os sesamoideum phalangis tertise) is 
shuttle-shaped, and is situated behind the junction of the second and third pha- 
langes. Its long axis is transverse, and it possesses two surfaces, two borders, and 
two extremities. The articular surface (Facies articularis) faces upward and 
forward; it consists of a central eminence, flanked by concave areas, and articulates 
with the distal end of the second phalanx. The flexor or tendon surface (Facies 
flexoria) is directed downward and backward. It resembles the articular surface 
in form, but is more extensive and not so smooth. In the fresh state it is coated 
with cartilage and the deep flexor tendon plays over it. The proximal border 
(Margo proximalis) is wide and grooved in its middle, narrower and rounded on 
either side. The distal border (Margo distalis) bears in front a narrow facet for 
articulation with the third phalanx. Behind this is a groove, which contains a 
number of relatively large foramina, and is bounded behind by a prominent edge. 
The extremities are blunt-pointed. 

Development. — Each ossifies from a single center. 



The Bones of the Pelvic Limb 

The pelvic girdle (Cingulum extremitatis pelvinae) consists of the os coxae, 
which unites ventrally with the opposite bone at the symphysis pelvis, and artic- 
ulates with the sacrum dorsally. 

OS COX^ 

The OS coxae or hip bone^ is the largest of the flat bones. It consists primarily 

of three parts, the ilium, ischium, and pubis, which meet to form the acetabulum, 

a large cotyloid cavity for articulation with the head of the femur. These parts 

are fused at about one year of age, but it is convenient to describe them separately.^ 

The Ilium 

The ilium (Os ilium) is the largest of the three parts. It is irregularly triangu- 
lar and presents two surfaces, three borders, and three angles. 

The wide part of the bone is the wing (Ala ossis ilium). Its gluteal surface 
(Facies glutaa) faces dorso-laterally and backward. It is wide and concave in 
front, narrower and convex behind. The wide part is crossed by the curved 
gluteal line (Linea glutaea), which extends from the middle of the medial border 
toward the tuber coxae. This surface gives attachment to the middle and deep 
gluteal muscles. 

The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex, 
and consists of two distinct parts. The medial triangular part (Pars articularis) 
is roughened for ligamentous attachment, and bears an irregular facet, the auricu- 
lar surface (Facies auricularis) , for articulation with the sacrum. The lateral quad- 
rilateral part (Pars iliaca) is in general smooth. It is crossed by the ilio-pectineal 
line (Linea iliopectinea), which begins below the auricular surface and is continued 

1 Formerly called the os innominatum. 

2 The proper terms, strictly speaking, for these bones are os ilium, os ischii, and os pubis, but 
the names given above are sanctioned by common usage. 



106 



THE SKELETON OF THE HORSE 



on the shaft of the bone to join the anterior border of the pubis. The hne is inter- 
rupted by furrows for the iliaco-femoral vessels, and below these it bears the psoas 
tubercle (Tuberculum psoadicum), which gives attachment to the psoas minor mus- 
cle. The iliacus muscle is attached to the surface lateral to the ilio-pectineal line. 

The anterior border or crest (Crista iliaca) is concave, thick, and rough. 

The medial border (Margo medialis) is deeply concave. Its middle part forms 
the greater sciatic notch (Incisura ischiadica major) and it is continuous behind 
with the ischiatic spine. 

The lateral border (Margo lateralis) is concave and in great part rough. Its 
a,nterior part is crossed l)y grooves for the ilio-lumbar vessels, which are continued 



Sacral spines 



Tuber sacralf Crest of ilium 



Apex of sacrum 




Tuber 
coxce 



Ac( tabular branch of pubis 



Ventral ischiatic 
spine 

Fig. 85. — Right Os Cox-e axd Sacrum op Horse; Right Lateral View. 
1, Gluteal line; 2, impression of ilio-lumbar artery; 3, impression of iliaco-femoral artery; 4, depressions for at- 
tachments of tendons of origin ofj rectus femoris; 5, crest to which lateral tendon of rectus femoris and capsularis are 
attached; G, 6', articular surface of acetabulum (facies lunata) ; 7, acetabular fossa; 8, obturator foramen; 9, line for 
attachment of gemellus muscle; 10, lateral border of sacrum; 11, dorsal sacral foramina. 



Symphyseal branch 
of pubis 



on the pelvic surface. The nutrient foramen is usually situated on or near the 
posterior part of this border. 

The medial angle is termed the tuber sacrale; it curves upward and a little 
backward opposite to the first sacral spine, and forms here the highest point of the 
skeleton. It is somewhat thickened and rough. 

The lateral angle, tuber coxae, forms the basis of the point of the hip. It is a 
large quadrangular mass, narrow in its middle, and enlarged at either end, where 
it bears a pair of tuberosities. It is roughened for muscular attachment. 

The acetabular angle (Angulus acetabularis) meets the other two bones at the 
acetabulum, of which it forms about two-fifths. Its prominent dorsal border forms 



THE ISCHIUM 



107 



part of the ischiatic spine (Spina ischiadica), which is roughened laterally, smooth 
medially. Two depressions above and in front of the acetabulum give attachment 
to the tendons of origin of the rectus femoris muscle. This angle is connected with 
the wing or wide part of the bone by a constricted part, termed the shaft (Corpus 
ossis ilium). The latter is of three-sided, prismatic form. Its lateral surface is 
convex and rough, and gives attachment to the deep gluteus muscle. Its pelvic 
surface is smooth and is grooved for the obturator vessels and nerve. Its ventral 
surface is crossed by vascular grooves, below which there is a rough area, which is 
bounded medially by the psoas tubercle. 



Tuber sacrale 




Ischiatic spine 



Tuber ischii 



Ischial arch 



Fig. 86. — Ossa Cox.\rum of Horse; Dorsal View. 
A, Wing; A', shaft of ilium; B, acetabular, B', symphyseal branch of pubis; C, body, C, acetabular branch (or 
shaft), C", symphyseal branch, of ischium; 1, gluteal line; 2, grooves for obturator nerve and vessels; 3, symphysis 
pelvis; 4, greater sciatic notch; 5, ilio-pectineal eminence; 6, pubic tubercle. Dotted hnes indicate primitive separa- 
tion of three bones. 



The Ischium 

The ischium (Os ischii) forms the posterior part of the ventral wall or floor of 
the bony pelvis. It slopes a little downward and inward, but is practically hori- 
zontal in the longitudinal direction. The body of the ischium (Corpus ossis 
ischii) is irregularly quadrilateral, and may be described as having two surfaces, 
four borders, and four angles. 

The pelvic surface (Facies pelvina) is smooth and slightly concave from side 
to side. 

The ventral surface (Facies ventralis) is nearly flat, and is in great part rough- 
ened for the attachment of the adductor muscles. 

The anterior border forms the posterior margin of the obturator foramen. 



108 



THE SKELETON OF THE HORSE 



The posterior border is thick and rough. It slopes medially and forward 
to meet the border of the other side, forming with it the ischial arch (Arcus 
ischiadicus). 

The medial border meets the opposite bone at the symphysis ischii. 

The lateral border is thick and rounded, but concave in its length; it forms 
the lesser sciatic notch (Incisura ischiadica minor), the lower boundary of the lesser 
sciatic foramen. 

The antero-medial angle or symphyseal branch (Ramus symphyseos) 



C'nsl of ilium 



Grooves for ilio- 
lumbar vessels 
Grooves for 
iliaco-femoral 




Depression for 

medial tendon 

of rectus 

femoris 



Obturator foramen 



Fig. 87. — O.ssa Coxarum of Mare; Ventral View. 
A, Wing, A', shaft of ilium; B, acetabular branch, B', symphyseal branch, of pubis; C, body, C, acetabular 
branch (shaft), C", symphyseal branch, of ischium; 1, auricular surface; 2, ilio-pectineal line; 2', psoas tubercle; 3, 
arcuate hne; 4, articular part, 5, iliac part, of pelvic surface of ihum; 6, ilio-pectineal eminence; 7, pubic tubercle; 8, 
acetabular fossa; 9, articular surface of acetabulum (facies lunata) ; 10, symphysis pelvis; 11, pubic groove. Dotted 
Unes indicate primitive division of os coxae. 



meets the pubis, with which it forms the medial boundary of the obturator 
foramen. 

The antero-lateral angle or acetabular branch (Ramus acetabularis) joins the 
other two bones at the acetabulum, of which it forms more than half. Dorsally 
it bears part of the ischiatic spine (Spina ischiadica), and medially it is grooved for 
the obturator vessels. The term shaft is often applied to the constricted part of 
the acetabular branch. 

The postero-medial angle joins its fellow at the symp?iysis. 

The posterolateral angle is a thick, three-sided mass, the tuber ischii (Tuber 
ischiadicum) ; its lower border is the ventral ischiatic spine, to which the biceps 
femoris and semitendinosus muscles are attached. 



THE PUBIS — THE OBTURATOR FORAMEN 109 



The Pubis 



The pubis (Os pubis) is the smallest of the three parts of the os coxae. It 
forms the anterior part of the pelvic floor, and may be described as having two 
surfaces, three borders, and three angles. 

The pelvic surface (Facies pelvina) is convex in the young subject and the 
stallion, concave and smooth in the mare and usually in the gelding also.^ 

The ventral surface (Facies ventralis) is convex, and in great part rough for 
muscular attachment. Near the anterior border it is crossed by the pubic groove 
(Sulcus pubis), the medial part of which is occupied by a large vein, the lateral part 
by the accessory ligament; the groove leads to the acetabular notch. 

The anterior border is thin in its medial part (except in the young subject and 
the stallion), forming the pecten ossis pubis. Laterally it bears the rough ilio- 
pectineal eminence (Eminentia iliopectinea), beyond which it is continuous with 
the ilio-pectineal line. Near the symphysis is a variable prominence, the tuber- 
culum pubicum. 

The medial border joins the opposite bone at the symphysis pubis. 

The posterior border forms the anterior margin of the obturator foramen, and 
is marked laterally by the obturator groove. 

The medial angle meets its fellow at the anterior end of the symphysis. This 
part is very thick in the young subject and the stalHon, but in the mare, and usually 
in the gelding also, it becomes thin with advancing age. 

The acetabular angle joins the ilium and ischium at the acetabulum. 

The posterior angle joins the ischium, with which it forms the inner boundary 
of the obturator foramen. 

The pubis may conveniently be regarded as consisting of a body (Corpus ossis 
pubis) and two l^ranches; the latter are termed the acetabular branch (Ramus 
acetabularis) and the -symphyseal branch (Ramus symphyseos) . 

The Acetabulum 

The acetabulum is a cotyloid cavity which lodges the head of the femur. It 
faces ventro-laterally, and consists of an articular and a non-articular part. The 
articular part (Facies lunata) is crescentic, and is cut into internally by a rough 
non-articular depression, the acetabular fossa (Fossa acetabuli). The medial 
part of the rim is correspondingly cut into by the acetabular notch (Incisura 
acetabuli), which is converted into a foramen by the transverse ligament in the 
fresh state, and transmits the accessory and round ligaments to the head of the 
femur. 

The Obturator Foramen 

The obturator foramen (Foramen obturatum) is situated between the pubis 
and ischium. It is oval in outline, the longer axis being directed forward and 
outward. Its margin is grooved antero-laterally for the obturator nerve and ves- 
sels. 

Development. — Each division of the os coxse ossifies from one chief center. 
The center for the ilium first appears near the acetabulum, followed quickly by one 
for the ischium, and a little later l\y the pubic center. Secondary centers appear 
for the crest and tuber coxse of the ilium, the tuber and posterior border of the 
ischium, and the acetabular part of the pubis. The symphyseal branches of the 
pubis and ischium are usually united with each other before birth, but the three 

1 The pelvic surface of the pubis is quite variable. In the mare and in geldings which have 
been castrated eariy the two pubic bones form a central depression of variable depth and curvature. 
This depression is bounded posterioriy by two obhque convergent hues or ridges, to which the 
obturator internus muscle is attached. Not rarely small eminences may be present along the 
symphysis. 



110 



THE SKELETON OF THE HORSE 



bones are not fused until the second year. The epiphyseal parts fuse with the 
main mass at four and a half to five years of age. 

The acetabular part of the pubis ossifies from a separate center. It is most distinct in the 
embryo at three months, and is often called the os acetabuli. Martin says that the ilium has a 
center for the acetabular part, one for the shaft and wing, and a third for the crest. He also 
states that there is a special center for the acetabular part of the ischium, and a transitory nucleus 
in the symphyseal part of the pubis. 

THE PELVIS 
The bony pelvis is composed of the ossa coxarum, the sacrum, and the first 
three coccj^geal vertebrae. The dorsal wall or roof is formed by the sacrum and 
first three coccygeal vertebrae, and the ventral wall or floor by the pubic and ischial 



Crest of ilium 



Sacral Tuber 
spines sacrale 



Tuber coxa 




Depressioji in which 
tendon of rectus 
femoris is attached 



I Ho- pectineal eminence 



Acetabidmn 



Tuber ischii 



Ischium 
Pubic tubercle 

Fig. 88. — Pelvic Bones op Mare, Viewed from in Front and Somewhat from Below. 
1, Body of first sacral segment; 2, surface on wing of sacrum for articulation with like surface on transverse process 
of last lumbar vertebra ; 3, wing of sacrum; 4, sacro-iliac articulation ; 5, sacral canal; 6, promontory; 7, apex of sac- 
rum; 8, ilio-pectineal line; 9, ischiaticspine; 10, grooves for ilio-lumbar vessels; 11, grooves for iliaco-femoral vessels. 



bones. The lateral walls are formed by the ilia and the acetabular part of the 
ischia. The defect in the skeleton here is supplied in the fresh state by the sacro- 
sciatic ligaments and semimembranosus muscles. 

The anterior aperture or inlet of the pelvis (Apertura pelvis cranialis) is bounded 
by the terminal line (Linea terminalis) or brim, which is composed of the base of 
the sacrum dorsalh% the ilio-pectineal lines laterally, and the pecten pubis ventrally. 
It is almost circular in the mare, semi-elliptical in the stallion, and faces obliquely 
downward and forward. It has two principal diameters. Of these, the con- 
jugate or sacro-pubic diameter (Conjugata anatomica) is measured from the sacral 
promontory to the anterior end of the symphysis. The transverse diameter 



THE PELVIS 



111 



(Diameter transversa) is measured at the greatest width, i. e., just above the psoas, 
tubercle. 

The posterior aperture or outlet of the pelvis (Apertura pelvis caudalis) i& 
much smaller and is very incomplete in the skeleton. It is bounded dorsally by the 




Fig. 90. — Pelvic Bones op Mare; Front View. 
C, Conjugate, D.t., transverse, diameter of pelvic inlet. 



third coccygeal vertebra and ventrally by the ischial arch; in the fresh state it is 
completed laterally by the sacro-sciatic ligament and the semimembranosus muscle. 

The axis of the pelvis is an imaginary line drawn through the centers of the 
inlet, cavity, and outlet. 

Sexual Differences. — Marked differences exist in the size and form of the pel- 
vis in the two sexes. The average conjugate diameter is about 93^ inches (ca. 23 to 



112 THE SKELETON OF THE HORSE 

24 cm.) in the mare, 73^ inches (ca. 18.75 cm.) in the stallion. The transverse 
diameter of the inlet is about the same as the conjugate in the mare, but is about 
8 inches (ca. 20 cm.) in the stallion. The obliquity of the inlet or inclination of the 
pelvis (Inclinatio pelvis) is greater in the female ; the difference is indicated by the 
fact that a vertical plane from the pecten cuts the fourth sacral segment in the fe- 
male, the second in the male. The outlet is also larger in the mare, the ischial arch 
being about one-third wider than in the stallion. The cavity is much more roomy 
in the female; the transverse diameter between the middles of the superior ischiatic 
spines is about 8 inches (20 cm.) in the mare, 6 inches (15 cm.) in the stallion. The 
pubic part of the floor in the female is concave and lies considerably lower than the 
ischiatic part, which is wide and almost flat. In the stallion the pubis is very thick 
medially, and this part of the floor is convex, while the ischial part is relatively nar- 
row, and is concave from side to side. The obturator foramina are correspondingly 
larger in the female. The ilium is shorter, especially with regard to its shaft, and 
the greater sciatic notch is deeper and narrower in the male. The pelvis of the geld- 
ing, when castration has been performed early, resembles that of the mare; other- 
wise the male characters appear to be retained to a large degree. 

THE FEMUR 

The femur or thigh bone (Os femoris) is the largest and most massive of the 
long bones. It extends obliquely downward and forward, articulating with the 
acetabulum above and the tibia and patella below. It presents for examination a 
shaft and two extremities. 

The shaft (Corpus femoris) is in general cylindrical, but flattened behind, and 
larger above than below. The anterior, medial, and lateral surfaces are continuous 
and strongly convex from side to side; there is often a central vertical rough line 
on the proximal part, but otherwise these surfaces are smooth. They are covered 
by the quadriceps femoris muscle. The posterior surface is wide, flat, and smooth 
in its proximal fourth. Distal to this part there is a rough elevation laterally for 
the attachment of the femoral tendon of the biceps femoris, and a rough line medi- 
ally to which the quadratus femoris is attached. The middle third is narrower, 
and is rough for the attachment of the adductor muscle. Just distal to this area 
an oblique groove crosses the surface, indicating the position of the femoral vessels. 
The medial border l^ears on its proximal part the trochanter minor, a thick rough 
ridge, to which the iho-psoas muscle is attached. From this a rough line curves 
up to the front of the neck and indicates the posterior limit of the attachment of 
the vastus medialis muscle. A narrow rough area about the middle of the border 
gives attachment to the pectineus muscle, and the nutrient foramen is usually 
found just in front of this mark. The medial supracondyloid crest (Crista supra- 
condyloidea medialis) is situated below the groove for the femoral vessels, and gives 
origin to the medial head of the gastrocnemius. The lateral border is prominent 
in its upper part, and bears at the junction of its proximal and middle thirds the 
trochanter tertius ;^ this process is curved forward, and has a thick edge to which 
the tendon of the superficial gluteus muscle is attached. At the distal part is the 
supracondyloid fossa (Fossa supracondyloidea),^ in which the superficial digital 
flexor arises; it is bounded laterally by a thick, rough margin, the lateral supra- 
condyloid crest (Crista supracondyloidea lateralis), to which the lateral head of the 
gastrocnemius muscle is attached. 

The proximal extremity (Extremitas proximalis) is large and consists of the 
head, neck, and trochanter major. The head (Caput femoris) is placed at the 
medial side and is directed inward, upward, and somewhat forward. It is ap- 
proximately hemispherical and articulates with the acetabulum. It is cut intc 

1 Also termed the external trochanter. ^ ^|gQ termed the fossa plantaris. 



THE FEMUR 



113 



medially by a deep notch, the fovea capitis, in which the accessory and round liga- 
ments are attached. The articular surface is surrounded by a distinct margin. 
The neck (Collum femoris) is most distinct in front and medially. The trochanter 
major is situated laterally; it presents three features. The anterior part or con- 
vexity is situated opposite to the head and rises little above the level of the latter; 
it gives attachment to the deep gluteus muscle, and in the fresh state its lateral 
surface is coated with cartilage, over which a tendon of the middle gluteus passes, 
to be inserted into, the crest, which is placed below and behind the convexity. 
The posterior part or summit is separated from the anterior part by a notch; it is 
situated behind the plane of the head and rises to a much greater height. It 




Lateral 

epi- 

cundyle 



Medial 

epi- 

condyle 

Medial 
condyle 



Trochlea 
Fig. 91. — Right Femur of Horse; Froxt View. 




Lateral 
condyle 

I nterco itdyloid fossa 
-Right Femur of Horse; Posterior View. 



furnishes insertion to part of the middle gluteus muscle. Its posterior border is 
continued downward as the trochanteric ridge (Crista trochanterica), which forms 
the lateral wall of the trochanteric fossa (Fossa trochanterica). A number of 
foramina are found in the concave area medial to the convexity. 

The distal extremity (Extremitas distalis) is large in both directions and com- 
prises the trochlea in front and two condyles behind. The trochlea consists of two 
ridges separated by a groove, and forms an extensive surface (Facies patellaris) for 
articulation with the patella. It is very unsymmetrical ; the medial ridge is much 
wider, more prominent, and extends up higher than the lateral one, and the two 
converge below. The condyles, medial and lateral (Condylus medialis, lateralis), 



114 



THE SKELETON OF THE HORSE 



are separated by the deep intercondyloid fossa (Fossa intercondyloidea), and 
articulate with the condyles of the tibia and the menisci of the stifle joint. A ridge 
connects each condyle with the lower part of the corresponding ridge of the trochlea. 
The intercondyloid fossa lodges the spine of the tibia and the cruciate ligaments of 
the stifle joint, which are attached here. 

The condyles are obliquely placed with their long axes directed downward, forward, and 
inward. The articular surface of the lateral condyle is more strongly convex from side to side 
than that of the medial one, and the ridge which connects it with the trochlea is much narrower. 

The medial epicondyle (Epicondylus medialis) is a rounded prominence on 
the medial surface of the distal extremity, to which the collateral ligament and the 
adductor muscle are attached. The corresponding lateral epicondyle (Epicondylus 




Fig. 93. — Proximal Extremity of Right Femur of 

Horse; End View. 

1, Head; 2, fovea capitis; 3, neck; 4, 5, anterior and 

posterior parts of trochanter major. 




Intercondyloid fossa 

Fig. 94. — Distal Extremity of Right Femur of 
Horse; End View. 
1, 1', Medial and lateral ridges of trochlea; 2, 2', 
medial and lateral condyles; 3, 3', medial and lateral 
epicondyles; 4, extensor fossa; 5, depression for origin 
of popliteus. 



lateralis) is less distinct; it presents a mark where the lateral ligament is attached, 
below and behind which there is a depression (Fossa musculi poplitei) in which the 
popliteus muscle arises. Between the lateral condyle and trochlea is the extensor 
fossa (Fossa extensoria), in which the common tendon of origin of the extensor 
digitalis longus and peroneus tertius is attached. 

Development. — The shaft and the distal end each ossify from one center, but 
the proximal end has two centers, one of which is for the head and the other for the 
trochanter major. The edge of the trochanter tertius also has a separate center. 
The proximal end fuses with the shaft at three to three and a half years, the distal 
at about three and a half years. 



THE TIBIA 

The tibia is a long bone which extends obliquely downward and backward 
from the stifle to the hock. It articulates above with the femur, below with the 
tarsus, and laterally with the fibula. It possesses a shaft and two extremities. 

The shaft (Corpus tibiae), large and three-sided above, becomes smaller and 
flattened in the sagittal direction below, but widens at the distal end. It presents 
for notice three surfaces and three borders. The medial surface (Facies medialis) 
is Inroad above, where it presents rough prominences for the attachment of the 



THE TIBIA 



115 



medial ligament and the sartorius and gracilis muscles; below this it is narrower, 
convex from edge to edge and subcutaneous. The lateral surface (Facies lateralis) 
is smooth and somewhat spiral. It is wide and concave in its proximal fourth, 




1— ■ 




95. — Right Tibia axd Fibula of Horse 

ERAL View. 
1, Tuberosity; 2, sulcus muscularis; 3, crest 



4, 
impres- 



spine; 5, lateral condyle; 6, head of fibul 
sion of anterior tibial vessels; 8, shaft of fibula; 9, lat- 
eral border of tibia; 10, lateral malleolus; 11, groove 
for lateral extensor tendon. 



Fig. 96. — Right Tibia and Fibula of Horse; Poste- 
rior View. 
1, Medial condyle; 2, lateral condyle; .3, spine; 4, 
fossa for anterior cruciate ligament; .5, popliteal notch; 
6, tubercle for posterior cruciate ligament; 7, head of 
fibula; 8, vascular impression; 9, interosseous space; 
10, shaft of fibula; 11, muscular lines; 12, tubercle; 13, 
nutrient foramen; 14, medial malleolus; 1.5, groove for 
tendon of flexor digitalis longus; 16, lateral malleolus. 



l)elow which it becomes narrower and convex, and winds gradually to the front of 
the bone; near the distal end it widens a little, becomes fiat, and faces forward. 
The posterior surface (Facies caudalis) is flattened, and is divided into two parts 
by the rough popliteal line (Linea poplitea), which runs obliquely from the proxi- 



116 



THE SKELETON OF THE HORSE 



7 — 



mal part of the lateral border to the middle of the medial border. The triangular 
area above the line is occupied by the popliteus muscle, while the area below is 
marked by rough lines (Linese musculares) to which the deep flexor muscle of the 

digit is attached; the lines fade out distally, 
^ where the surface is smooth and flat. The 

,t nutrient foramen is situated on or near the 

2 -.^ ' popliteal line. The anterior border is very 

prominent in its proximal third, forming the 
crest of the tibia (Crista tibiae) ; distally it is 
reduced to a rough line, which ends at a small 
elevation near the distal end of the bone. The 
medial surface of the crest presents a rough 
prominence for the attachment of the ten- 
don of the semitendinosus. The medial border 
(Margo medialis) is rounded in its proximal 
half, to which the popliteus muscle is attached, 
and a tubercle is found on this part. The dis- 
tal part is a rough line on well-marked bones. 
The lateral border (Crista interossea) is con- 
cave in its proximal part and concurs with the 
fibula in the formation of the interosseous space 
of the leg (Spatium interosseum cruris); a 
smooth impression indicates the course of the 
anterior tibial vessels through the space to the 
front of the leg. About the middle of the bone 
the border divides and incloses a narrow trian- 
gular surface. 

The proximal extremity (Extremitas proxi- 
malis) is large and three-sided. It bears two 
articular eminences, the medial and lateral con- 
dyles (Condylus medialis, lateralis) . Each pre- 
sents a somewhat saddle-shaped surface for ar- 
ticulation with the corresponding condyle of the 
femur and meniscus. The spine or intercondy- 
loid eminence (Eminentia intercondyloidea) is 
the central prominence, upon the sides of which 
the articular surfaces are continued ; it consists 
of a high medial part and a lower lateral part 
(Tuberculum intercondyloideum mediale, lat- 
erale). On, l^efore, and l^ehind the spine are 
the intercondyloid fossae, in which the anterior 
cruciate ligament and the menisci are attached. 
The condyles are separated behind by the deep 
popliteal notch (Incisura poplitea), on the 
medial side of which there is a tubercle for 
the attachment of the posterior cruciate liga- 
ment. The lateral condyle has an overhang- 
ing outer margin (Margo infraglenoidalis), be- 
low which there is a facet (Facies articularis 
fibularis) for articulation -v^dth the fibula. The 
large anterior eminence is the tuberosity of the 
tibia (Tuberositas tibiae). It is marked in front by a groove (Sulcus ligamenti), 
the lower part of which gives attachment to the middle patellar ligament, and 
the groove is flanked b}^ rough areas for the attachment of the medial and lateral 




Fig. 97. — Right Tibia and Fibula of Hor.se; 
Anterior View. 
1, Spine; 2, tuberosity; 3, groove for 
toiddle patellar ligament; 4, medial condyle; 
5, sulcus muscularis; 6, lateral condyle; 7, 
head of fibula; 8, interosseous space; 9, lateral 
surface of tibia; 10, shaft of fibula; 11, imprint 
for attachment of gracilis; 12, crest; 13, promi- 
nence for attachment of semitendinosus; 14, 
medial surface of tibia; 15, medial malleolus; 
16, lateral malleolus. 



THE FIBULA 



117 



patellar ligaments. A semicircular smooth notch, the sulcus muscularis, separates 
the tuberosity from the lateral condyle, and gives passage to the common tendon 
of origin of the extensor digitalis longus and the peroneus tertius. 

The distal extremity (Extremitas distalis) is much smaller than the proximal 
one ; it is quadrangular in form and larger medially than laterally. It presents an 
articular surface (Cochlea tilDise), which is adapted to the trochlea of the tibial 
tarsal bone, and consists of two grooves separated by a ridge. The ridge and 
grooves are directed ol^liquely forward and laterally, and are bounded on either 
side by the malleoli, to which the collateral ligaments of the hock joint are at- 
tached. A shallow synovial fossa is usually present on the middle of the articular 
ridge. The lateral groove is wider and shallower than the medial one; it is fre- 
quently marked by a line or groove which indicates the former demarcation between 
the tibia and fibula. The medial malleolus (Malleolus medialis) is the more prom- 
inent of the two, and forms the anterior Ijoundary of a groove for the tendon of the 
flexor digitalis longus. The lateral malleolus (Malleolus lateralis) is broader, and 
is marked by a vertical groove for the passage of the lateral extensor tendon. 

Development. — The tibia has the usual three chief centers of ossification and 
supplementary ones for the tuberosity and the lateral malleolus. The latter is 
really the distal end of the fibula; it is a separate piece at birth, and the line of 
union is commonly quite evident in the adult in the articular groove. The proxi- 
mal end unites with the shaft at about three and a half years, and the distal end at 
about two years of age. 





Fig. 98. — Proximal Extremity or Right Tibia of 
Horse; End View. 
1, Medial condyle; 2, lateral condyle; 3, groove 
on 2 for popliteus tendon ; 4, popliteal notch ; 5, tuber- 
osity; 6, groove for middle patellar ligament; 7, tuber- 
cles of spine; 8, sulcus mu.scularis; l.c.a., l.c.p., depres- 
sions for attachment of anterior and posterior cruciate 
ligaments; I, m, m, depressions for attachment of 



Fio. 99. — Distal Extremity of Right Tibia (and 
Fibula) of Horse; End View. 
1, 1', Articular grooves; 2, intormeliate ridge and 
synovial fossa; 3, line of fusion of primitive distal end 
of fibula with tibia; 4, medial malleolus; 5, 5', lateral 
malleolus; 6, anterior border. 



THE FIBULA 

The fibula of the horse is a much reduced long bone, situated along the lateral 
border of the tibia. 

The shaft (Corpus fibula?) is a slender rod which forms the lateral boundary of 
the interosseous space of the leg; it usually terminates below in a pointed end about 
one-half to two-thirds of the way down the lateral border of the tibia. 

The proximal extremity or head (Capitulum fibula)) is relatively large, and is 
flattened transversely. Its medial surface presents a narrow area (Facies articu- 
laris capituli) along the upper border for articulation with the lateral condyle of 
tibia. The lateral surface is rough and gives attachment to the lateral ligament 
of the stifle joint. It has rounded anterior and posterior borders. 



118 



THE SKELETON OF THE HORSE 



The distal extremity is fused with the til)ia, constituting the lateral malleolus. 

Development. — Tliis resembles that of the ulna. The embryonic cartilaginous 
fibula extends the entire length of the leg, but does not articulate with the femur. 
The distal part of the shaft is usually reduced to a filjrous band. Three centers of 
ossification appear, one each for the shaft and the extremities. The distal end 
unites early with the tibia, forming the lateral malleolus. 

It is interesting to note that in some cases the entire shaft of the fibula develops, a reversion 
to the condition in the Miocene ancestors of the horse. 



THE PATELLA 

The patella is a large sesamoid bone which articulates with the trochlea of the 
femur. It presents for description two surfaces, two borders, a base, and an apex. 

The anterior, free surface (Facies libera) is quadrilateral, convex, and rough 
for muscular and ligamentous attachment. 

The articular surface (Facies articularis) is also quadrilateral, ]:)ut much less 
extensive. It presents a vertical rounded ridge, which corresponds to the groove 

Base 




Aj)ex 
Fig. 100. — Right Patella of Horse; Anterior View. 
1, Attachment area of middle patellar ligament; 
2, attachment area of lateral patellar ligament and 
biceps femoris. 




Accessory cartilage Apex 

Fig. 101. — Right Patella of Horse; Posterior View. 
1, Medial part, 2, lateral part, of articular surface. 



on the trochlea of the femur, and separates two concave areas. Of the latter, the 
medial one is much the larger, and is not very well adapted to the corresponding 
ridge of the trochlea; in the fresh state, however, it is completed and rendered more 
congruent b}^ the curved accessory fibro-cartilage. 

The borders, medial and lateral, converge to the apex below, and each forms an 
angle at the base. The medial border is concave. The lateral border is rounded 
and its angle is less prominent. The medial angle and the adjacent part of the 
posterior margin of the base give attachment to the fibro-cartilage of the patella 
(Fibrocartilago patellae) . 

The base (Basis patellae) faces upward and backward, and is convex trans- 
versely, concave from before backward. 

The apex (Apex patellae) forms a blunt point directed distally. 

Development. — The patella develops as a sesamoid bone from a single center 
in a cartilaginous deposit in the te'ndon of the quadriceps femoris muscle. 



THE TARSUS 

The tarsus or hock of the horse usually comprises six short bones (Ossa tarsi), 
but exceptionally seven are present. 




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120 



THE SKELETON OF THE HORSE 



The Tibial Tarsal Bone 
The tibial tarsal bone (Os tarsi tibiale) ^ is the medial bone of the proximal row. 
It is extremely irregular in form, but may be considered as offering six surfaces for 
description. 

The proximal and dorsal surfaces are continuous, and form a trochlea (Troch- 
lea tali) for articulation with the distal end of the tibia. The trochlea consists 
_ of two oblique ridges with a deep groove 

between them; these curve spirally for- 
ward, downward, and outward, forming 
an angle of 12 to 15 degrees with a sagittal 
plane. There is usually a shallow synovial 
fossa in the groove. The distal surface is 
convex from before backward, and most 
of it articulates with the central tarsal; 
laterally it has an oblique facet for the 
fourth tarsal, and a non-articular groove 
cuts into the surface to its middle. The 
plantar surface (Facies plantaris) is ob- 
lique and extremely irregular; it presents 
four facets for articulation with the fibular 
tarsal bone; the facets are separated by 

Trochlea 





Fig. 105. — Right Tarsus and Proximal Part of 
Metatarsus of Horse; Lateral View. 
Tt, Tibial tarsal (trochlea); Tf, fibular tarsal 
(body); Tc, central tarsal; T3, third tarsal; T4, 
fourth tarsal; 1, depression for attachment of lateral 
ligament; 2, processus cochlearis; 3, prominence for 
attachment of lateral ligament; 4, groove for great 
metatarsal artery; 5, tuber calcis; Mt. Ill, IV, meta- 
tarsal bones. Arrow points to vascular canal. 



Fig. 106. — Right Tibial Tarsal Bone of Horse; Plan- 
tar A'lEW. 
1-4, Facets for articulation with fibular tarsal; 5, fossa; 
6, distal tuberosity; 7, proximal tuberosity. 



rough excavated areas, and the largest 
fossa (Sulcus tali) forms with a corres- 
ponding one on the fibular tarsal a cavity 
termed the sinus tarsi. The media4 surface bears on its distal part a large tuber- 
osity and on its proximal part a small one for the attachment of the medial liga- 
ment of the hock joint. The lateral surface is smaller than the medial, and is 
marked by a wide rough fossa in which the lateral ligament is attached. 



The Fibular Tarsal Bone 
The fibular tarsal bone (Os tarsi fibulare)^ is the largest bone of the hock. It 
is elongated, flattened from side to side, and forms a lever for the muscles which 



Also termed the astragalus or talus. 



2 Also termed the calcaneum or os calcis. 



THE CENTRAL TARSAL BONE 



121 



extend the hock joint. It consists of a body and a medial process, the sustentacu- 
lum tali. 

The body (Corpus) is enlarged at its proximal end to form the tuber calcis or 
"point of the hock"; the posterior part of this eminence gives attachment to the 
tendon of the gastrocnemius, while in front and on each side it furnishes insertion 
to tendons of the superficial digital flexor, biceps, and semitendinosus muscles. 
The distal extremity bears a concave facet for articulation with the fourth tarsal 
bone. The medial surface of the body has on its lower part a strong process, the 
sustentaculum tali, which projects inward. The process has a large, oval, slightly 
concave facet in front for articulation with the tibial tarsal, and sometimes a small 
articular surface below for the central bone. Its plantar surface forms with the 
smooth medial surface of the body a groove for the deep flexor tendon (Sulcus tarsi) . 
Its medial surface has a prominence on the distal part for the attachment of the 
medial ligament. The lateral surface of the body is flattened, except below, where 
there is a rough prominence for the attachment of the lateral 
ligament. The dorsal border is concave in its length, smooth 
and rounded in its upper part. About its middle is a blunt- 
pointed projection (Processus cochlearis) which bears facets 
on its medial and lower surfaces for articulation with the 
tibial tarsal bone, and is roughened laterally for ligamen- 
tous attachment. Below this are two facets for the tibial 
tarsal, and an extensive rough fossa which concurs in 
the formation of the sinus tarsi. The plantar border is 
straight and broad, and widens a little at each end; it is 
rough, and gives attachment to the long plantar ligament. 



Tuber 
calcis 





Fig. 107. — Right Fibular Fig. 108.— Right Central Tarsal Bone op Horse; Proximal Surface. 

Tarsal Bone of Horse; i_ Articular surface for tibial tarsal; 2, facet for fibular tarsal; 3, non-articular 

Dorsal View. depression. 

1-4, Facets for articulation with 
tibial tarsal bone; 5, fossa. 



The Central Tarsal Bone 
The central tarsal bone (Os tarsi centrale)^ is irregularly quadrilateral, and is 
situated between the tibial tarsal and the third tarsal. It is flattened from above 
downward, and may be described as having two surfaces and four borders. The 
proximal surface is concave from before backward, and almost all of it articulates 
with the tibial tarsal; a non-articular depression cuts into its lateral part, and 
sometimes there is a facet for the fibular tarsal bone on the posterior angle. The 
distal surface is convex, and is crossed by a non-articular groove, which separates 
facets for articulation with the third and the first and second (fused) tarsals. The 
dorsal border and the medial border are continuous, convex, and rough. The 
plantar border bears two prominences, separated by a notch. The lateral border 
is oblique, and bears anterior and posterior facets for articulation with the fourth 
tarsal, between which it is excavated and rough. 

1 Also termed the scaphoid or navicular bone. 



122 



THE SKELETON OF THE HORSE 



First and Second Tarsal Bones 
The first and second tarsal bones (Os tarsale primum et secundum) ^ are usually- 
fused in the horse, forming a ])one of very irregular shape, situated in the medio- 
plantar part of the distal row, below the central and behind the third tarsal. It is 
the smallest of the tarsal bones, and may he described as having four surfaces and 
two extremities. The medial surface faces backward and inward, and is convex. 
Its anterior part is ridged, and gives attachment to the medial ligament, and its 
posterior part l^ears an imprint where the medial tendon of the tibialis anterior is 
inserted. The lateral surface is marked by a deep notch which indicates the divi- 
sion between the first and second tarsal elements; it bears on its anterior part a 
facet for the third tarsal. The proximal surface is concave and has two facets for 
articulation with the central tarsal; it is separated from the medial surface by a 
prominent border. The distal surface is broad in front, where it articulates with 




Fig. 109. — Right First and Sec- 
ond (Fused) Tarsal Bones 
OF Horse; Lateral Surface. 
Tl, T2, First and second tarsal 
bones; 1, 1', articular surface for 
central tarsal; 2, facet for third tar- 
sal; 3, facet for medial small meta- 
tarsal bone. Separation between 
two bones (when present) is indi- 
cated so far as visible by dotted 
line between 1 and 1'. 




Fig. 110.— Right Third Tarsal 
Bone of Horse; Proximal 
Surface. 

1, 2, Facets for central tarsal; 
3, 4, facets for fourth tarsal; 5, non- 
articular depression ; 6, dorsal ridge. 




Fig. 111. — Right Fourth Tarsal 
Bone of Horse; Medial Sur- 
face. 

1, 1', Facets for central tarsal; 
2, 2', facets for third tarsal; 3, facet 
for tibial tarsal; 4, 4', facets for 
fibular tarsal; 5, facet for large 
metatarsal bone; 6, groove which 
concurs with central and third tar- 
sals in formation of vascular canal 
of tarsus. 



the large and medial small metatarsal bones. The dorsal extremity bears a ridge 
or tubercle. The plantar extremity is a blunt point. 

In some cases the first and second tarsal Ijones remain separate — a remarkable reversion to 
the condition in the early ancestors of the horse. In such specimens the first tarsal is a discoid 
bone, articulating above with the central, below with the small metacarpal bone. The second 
tarsal is quadrangular, equivalent to the thick anterior part of the bone as described above, and 
overlapped in part by the first tarsal. 



The Third Tarsal Bone 

The third tarsal bone (Os tarsale tertium)- resembles the central, but is smaller 
and triangular in outline. It is situated between the central above and the large 
metatarsal l)one below. It possesses two surfaces and three borders. 

The proximal surface is concave, and is crossed by a non-articular depression 
which divides it into two unequal facets; it articulates with the central tarsal. 
The distal surface is slightly convex, and rests on the large metatarsal bone; it 
has an extensive central rough excavation. The dorsal border is convex and bears 
a rounded ridge on its medial part. The medial border is deeply notched and has 
a small facet for the second tarsal on its anterior part. The lateral border is also 
divided by a notch into two parts, and bears two diagonally opposite facets for 



Also termed the cuneiform parvum. 



Also termed the cuneiform magnum s. tertium. 



THE METATARSUS 



123 



articulation with the fourth tarsal. In some cases there is a facet for the medial 
small metatarsal bone. 

The Fourth Tarsal Bone 
The fourth tarsal bone (Os tarsale quartum)i jg the lateral bone of the distal 
row, and is eriual in height to the central and third together. It is cuboid m shape 
and presents six sm-f aces. ,. , , n • a 

The proximal surface is convex from side to side, and articulates chietly 
with the fibular tarsal, but to a small extent with the tibial tarsal also. 
The distal surface rests on the large and lateral 
small metatarsal ])ones. The medial surface bears 
four facets for articulation with the central and 
third tarsal bones. It is crossed from before back- 
ward by a smooth groove, which l)y apposition with 
the adjacent bones forms the canal of the tarsus (Can- 
alis tarsi) for the passage of the perforating tarsal 
vessels. The dorsal, lateral, and plantar surfaces are 
continuous and rough. A tuberosity behind gives 
attachment to the plantar ligament. 

Development.— The fibular tarsal bone has two 
centers of ossification, one for the main mass and the 
other for the tuber calcis; the latter fuses with the rest 
of the bone at about three years of age. The first and 
second tarsals have separate centers, but fusion usu- 
ally occurs before birth. Each of the other bones 
ossifies from a single center. 



THE METATARSUS 
The metatarsal bones (Ossa metatarsalia) , three 
in number, have the same general arrangement as 




/ 




Fig. 112. — Right Metatarsal Boxes 
OF Horse; Plantar View. 
1, Rough area for attachment of 
suspensory ligament; 2, nutrient fora- 
men. Compare with Fig. 76. 



Mt.n Ml. HI ML IV 



Fig. 113.— Proximal Extremities of Right Metatarsal Bones of 
Horse; End View. 
1, Facet for first tarsal; 2, 2', facets for second tarsal; 3, 3', facets for 
third tarsal; 4, 4', 4", facets for fourth tarsal; 5, non-articular depr-- 
Compare with Fig. 77. 



the metacarpal bones, but present some important differences. Their direction is 
slightly oblique, downward, and a little forward. , , ,. . ■ , ^„. ^„p 

The third or large metatarsal bone (Os metatarsal tertium) is about one- 
sixth longer than the corresponding metacarpal; in an animal of medium size the 
1 Also termed the cuboid. 



124 



THE SKELETON OF THE HORSE 




difference is about two inches. The shaft is more cyhndrical, and is almost cir- 
cular on cross-section, except in its distal part. At the proximal part of its lateral 
surface there is a groove, which is directed obliquely downward and backward, and 
is continued by the furrow formed by the apposition of the fourth or lateral meta- 
tarsal bone; it indicates the course of the great metatarsal artery. A shallow im- 
pression in a similar place on the medial side marks the position of the corresponding 

vein. The nutrient foramen is rela- 
tively higher than on the metacar- 
pal bone. The proximal extremity 
is much wider from before back- 
ward than that of the metacarpal 
bone. Its articular surface is 
slightly concave, and is marked 
by a large central non-articular de- 
pression, continued outward by a 
deep notch. The greater part of 
the surface articulates with the 
third tarsal, but there is a lateral 
facet for the fourth, and usually a 
small facet postero-medially for the 
second tarsal bone. Posteriorly there are two pairs of facets for articulation with 
the small metatarsal bones. The front is crossed by a rough ridge for insertion, 
which becomes larger and turns downward on the lateral side behind the vascular 
groove. The distal extremity closely resembles that of the corresponding meta- 
carpal bone. 

In some cases the distal part of the shaft is bent backward somewhat. The distal articular 
surface extends a httle higher behind than in the case of the metacarpal bone. The large meta- 
tarsal bone is even more strongly constructed than the metacarpal. The shell of compact sub- 
stance is very thick in the middle of the shaft, especially in front and medially. 




Fig. 114 
Figs. 114, 115. 



Fig. 115. 



OSS-SECTIONS OF LeFT METACARPAL ANI 

Metatarsal Bones. 
Sections are cut a little above middle of bones. 




Fig. 110. — Third Phalanx of Thoracic Limb of Horse. Fig. 117. — Third Phalanx of Pelvic Limb of Horse. 



The small metatarsal bones (Ossa metatarsalia secundum et quartum) are a 
little longer than the corresponding metacarpals. The lateral (fourth) metatarsal 
bone is relatively massive, especially in its upper part. The head is large and out- 
standing, and bears one or two facets above for the fourth tarsal, and two in front 
and medially for articulation with the large metatarsal ; elsewhere it is roughened 
for attachment. The medial (second) metatarsal bone is much more slender than 
the lateral one, especially in its proximal part. The head bears two facets above for 
the first and second tarsals, and sometimes one for the third tarsal. 



SKELETON OF THE OX 



125 



THE PHALANGES AND SESAMOID BONES 

The axis of the phalanges of the hind Hmb forms with the ground plane an 
angle which is about five degrees greater than that of the fore limb, and the chief 
differences in the form and size of the bones are as follows : 

The first phalanx is a little shorter, wider above, and narrower below. 

The second phalanx is narrower and slightly longer. 

The third phalanx is narrower, the angle of inclination of the dorsal surface is a 
little (ca. 5 degrees) greater, the plantar surface is more concave, and the angles 
are less prominent and closer together. The term plantar is to be substituted for 
volar in the designation of corresponding features. 

The proximal sesamoids are a little smaller, except in thickness. The distal 
sesamoid is narrower and shorter. 



SKELETON OF THE OX 

VERTEBRAL COLUMN 

The usual vertebral formula is C7Ti3L6S5Cyi8-2o- 

The cervical vertebrae are much shorter than those of the horse and are smaller 
in their other dimensions. The articular processes are smaller than in the horse, 
and a plate of bone connects each two of the same side. The transverse processes 
of the third, fourth, and fifth are double; the upper part projects backward, and 
is short and stout; the lower part is directed 
downward and forward, and is longer and 
more plate-like. The lower part of the sixth 
transverse process is a large, thick, quadri- 
lateral and almost sagittal plate, directed 
ventrally. The seventh transverse process is 
single, short, and thick, and presents no fora- 
men transversarium; it is in series with the 
upper part of the preceding processes. The 
spinous processes are well developed, and in- 
crease in height from before backward. They 
are directed upward and forward, with the ex- 
ception of the last, which is nearly vertical 
and is about four or five inches (ca. 10 to 12 
cm.) in height. The summit of that of the 
third vertebra is usually bifid. The ventral 
spines are prominent and thick in their pos- 
terior part ; they are absent on the last two. 

The atlas has a large rough tuberosity 
on its dorsal arch. The ventral arch is very 
thick. The wings are less curved than in the 

horse, and the foramen transversarium is absent. The anterior articular cavities for 
the occipital condyles are partially divided into dorsal and ventral parts by a non- 
articular area, and are separated by a narrow interval below. The posterior artic- 
ular surfaces are flattened behind and are continued into the vertebral canal, form- 
ing an extensive area for the dens of the axis. 

The axis is short. The spine projects a little in front, and increases in height 
and thickness behind; its posterior border descends abruptly. The dens is wide, 
and its dorsal surface is deeply concave from side to side. The intervertebral 




Fig. 118. — Third Cervical Vertebra of Ox; 
Lateral View. 
1, Spinous process; 2, 2', anterior and pos- 
terior articular processes; .3, 3', ends of body; 
4, 4', transverse process; 5, foramen transver- 
sarium; 6, ventral spine. 



126 



SKELETON OF THE OX 




VERTEBRAL COLUMN 



127 



foramen is circular and not so close to the anterior border of the arch as in 
the horse. The posterior notches are not so deep. The transverse processes are 
stouter, but the foramen transversarium is small and sometimes absent. 

The thoracic vertebrae, thirteen in number, are larger than those of the horse. 





Fig. 120. — Sixth Cervical Vertebra of Ox; Pos- 
terior View. 
1, Posterior cavity of body; 2, vertebral foramen; 
3, arch; 4, 4', posterior articular processes; 5, 5, an- 
terior articular processes; 6, 6', lateral branches of trans- 
verse processes; 7, 7', ventral branches of transverse 
processes; 8, foramen transversarium; 9, spinous proc- 



/ 9 > # \ 



Fig. 122. — Atlas of Ox; Dorsal View. 
1, Dorsal tubercle; 2, intervertebral foramen; 3, alar 
foramen; 4, wing; 5, 5, posterior articular surfaces ; 6, ven- 
tral arch (surface for dens of asis). 



Fig. 121. — Seventh Cervical Vertebra of Ox; Pos- 
terior View. 
1, Posterior cavity of body; 2, 2', facets for head 
of first rib; 3, vertebral foramen; 4, 4', arch; 5, 5', ar- 
ticular processes; 6, 6', transverse processes; 7, spinous 




Fig. 123.— Axis of Ox; Lateral View. 

1, Body; 2, ventral spine; 3, anterior articular 
process; 4, posterior articular process; 5, dens; 6, 
arch; 7, intervertebral foramen; 8, transverse proc- 
ess; 9, foramen transversarium and canalis trans- 
versarius (dotted line) ; 10, spinous process. 



128 



SKELETON OF THE OX 



The body is longer and is distinctly constricted in the middle. It bears a thin- 
edged ventral crest. The arch — in addition to the usual notches, which are 
shallow — is perforated in the posterior part by a foramen. The transverse proc- 




FiG. 124. — Fourth Lumbar Vertebra of Ox; Posterior View. 
1, Cavity of posterior end of body; 2, notch of arch; 3, 4, articular processes; 5, spinous process; 6, transverse process. 



ess is thick and strong, and bears a rounded mammillary process (except at the 
posterior end of the series) ; the last two, although prominent, do not always articu- 



late with the ribs. The spinous process is long. 



Median crest 



The first is much higher than in 
the horse, the next two are usu- 
ally the most prominent, and be- 
hind this there is a very gradual 
diminution in height. The back- 
ward slope, slight at first, in- 
creases to the tenth; the last is 
vertical and lumbar in charac- 
ter. The summit is usually 
pointed on the first, and the 
thickening on those further back 
is less than in the horse. The 
width diminishes from the fifth 
to the eleventh usually. Both 
borders of the spines are in gen- 
eral thin and sharp, but the last 
three or four sometimes have 
thick posterior margins. 

The lumbar vertebrae, six in 
number, are much longer than in 
the horse. The body is much 
constricted in the middle, ex- 
panded at either end, and bears 
a rudimentary ventral crest. 
The fourth and fifth are usuall}^ 
the longest. The intervertebral 
foramina are often double in 
the anterior part of the series, 
and are very large further back. 
The articular processes are 
large, and their facets are more 
strongly curved than in the 
horse. The transverse proc- 
esses all curve forward. They are separated by considerable intervals, and form 
no articulations with each other or with the sacrum. Their borders are thin and 




Fig. 125. — Sacrum of Ox; Dorsal View. 
1-4, Dorsal sacral foramina; 5, sacral canal; 6, 6, articular processes; 
apex. 



auricular surface; 



VERTEBRAL COLUMN 



129 



irregular, and often bear projections of variable size and form. The first is the 
shortest and the length increases to the fifth, the last being considerably shorter. 
The spinous processes are relatively low and wide, the last being the smallest; 
their summits are moderately thickened. 

The sacrum is longer than that of the horse. It consists originally of five 
segments, but fusion is more complete and involves the spinous processes, which 
are united to form a median sacral crest (Crista sacralis media), with a convex 
thick and rough margin. A lateral sacral crest is formed by the fusion of the ar- 
ticular processes. The pelvic surface is concave in both directions, and is marked 
by a central groove (Sulcus vasculosus), which indicates the course of the middle 
sacral artery. The ventral sacral foramina are large. The wings curve downward 
and forward; they are quad- 
rangular, short, compressed 
from before backward, and 
high dorso-ventrally. They 
have an extensive anterior 
surface, which is concave 
from side to side and non- 
articular. The posterior sur- 
face is rough, and at its lower 
part there is a triangular area 
for articulation with the 
ilium. The body of the first 
segment is very wide, and the 
entrance to the sacral canal 
correspondingly wide and 
low. The anterior articular 
processes are large and 
widely separated; they are 
concave and semicylindrical 
in curvature medially . The 
lateral borders are thin, 
sharp, and irregular. The 
bone does not become nar- 
rower posteriorly, so that the 
apex is usually a little wider 
than the part just behind the 
wings; the posterior end of 
the median crest forms a 
pointed projection over the 
opening of the sacral canal. 

The coccygeal vertebrae 
are longer and better devel- 
oped than in the horse. The first five or six have complete arches and spinous 
processes. The transverse processes are relatively large in the anterior part of 
the series, in which there are also anterior articular processes (which do not articu- 
late), and a pair of ventral spines which form a groove (Sulcus vasculosus) for the 
middle coccygeal artery. 

Vertebral Curves. — The cervical curve is very slight and is concave dorsally. 
The thoracic and lumbar regions form a gentle curve, concave ventrally. The 
promontory is more pronounced than in the horse, especially in subjects in which 
the sacrum is inclined upward behind. Another prominence occurs at the junction 
of the sacrum and first coccygeal vertebrae. 

Length.— The following table gives the lengths (inclusive of the inter- 




FiG. 126. — Sacrum of Ox; Ventral View. 
I-V, Segments; 1-4, ventral sacral foramina; 5, anterior end of body 
of first sacral vertebra; 6, vascular groove; 7, posterior end of body of 
last sacral vertebra. 



130 



SKELETON OF THE OX 



vertebral fibro-cartilages) of the vertebral regions of a shorthorn cow of 
medium size: 

Cervical 50 cm. 

Thoracic SO cm. 

Lumbar 40 cm. 

Sacral 25 cm. 

Coccygeal 75 cm. 

270 cm. 

Variations. — Sometimes fourteen thoracic vertebrae and fourteen pairs of ribs are present; 

reduction to twelve with the normal number 
j^ , rryhcrcle °^ lumbar vertebrae is very rare. According to 

^ Franck there are sometimes seven lumbar verte- 

brae with the normal number in the thoracic 

^^^^ region. The number of coccygeal vertebrae may 

Head ^-J^^BIlt^SI^^ vary from sixteen to twenty-one. 



THE RIBS 




Anterior border- 




Thirteen pairs of ribs are present 
normally, of which eight are sternal and 
five asternal. They are in general longer, 
wider, flatter, less curved, and less regular 
in form than in the horse. The eighth, 
ninth, and tenth are the longest and 
widest. The width of most of the ribs 
increases considerably in the middle, and 



Tubercle 



Head 



Neck 



Anterior border 





Sternal end 
Fig. 127. — Right Eighth Rib of Ox; Medial View. 



/j 



t. 



Sternal end 



Cartilage 



Fig. 12S.— First Rib of Ox; Medial Vi 



the breadth of the intercostal spaces is correspondingly diminished ; this is not the 
case in the posterior part of the series, where the intercostal spaces are very wide. 



THE STERNUM THE THORAX THE SKULL 131 

The neck is long, and forms (except in the posterior part of the series) a smaller 
angle with the shaft than in the horse. The articular surface of the tubercle is 
concave transversely, except on the last two or three, where the facet is small and 
flat or absent. The ventral ends of the second to the tenth or eleventh inclusive 
form diarthrodial joints with the costal cartilages. The first costal cartilages are 
very short; they articulate by their medial surfaces with the sternum, but not with 
each other. 

The presence of a fourteenth rib is not very rare. It is usually floating and may correspond 
to an additional thoracic vertebra or to the first lumbar. Reduction of the thirteenth is more 
common. The eighth cartilage often does not reach the sternum, but articulates with the seventh. 



THE STERNUM 
The sternum consists of seven sternebrse, most of which are developed from 
two lateral centers. It is wider, flatter, and relatively longer than in the horse, 
and the ventral crest or "keel" is absent. The manubrium is somewhat wedge- 
shaped and laterally compressed. Its base forms a diarthrodial joint with the 
body of the bone, and laterally it bears extensive facets for articulation with the 
first pair of costal cartilages. The body widens from before backward, but behind 
the last pair of costal facets it becomes much narrower. The ventral surface is 
prominent on the second and third segments, concave further back. The lateral 
borders are notched for the passage of vessels. The cariniform cartilage is absent. 
The xiphoid cartilage is like that of the horse but is smaller. 



THE THORAX 

The bony thorax is shorter than in the horse. The inlet is higher. The roof 
is short, and the floor is wider and relatively longer. The transverse diameter is 
wider in the posterior part. The summits of the spinous processes are almost in a 
straight line from the second thoracic vertebra to the middle of the lumbar region. 



The Skull 

Bones of the Cranium 
The occipital bone forms the lower part only of the posterior surface of the 
skull, and is separated from the highest part (the frontal eminence) by the parietal 
and interparietal bones. The supraoccipital, interparietals, and parietals fuse 
before birth or soon after, and the mass so formed is separated from the lateral 
parts of the occipital bone by a transverse suture in the skull of the calf. Above 
this suture is a central tuberosity, the external occipital protuberance, to which 
the ligamentum nuchse is attached, and the surface on either side is depressed and 
rough for muscular attachment. There is commonly a median occipital crest 
which extends ventrally from the protuberance. Below the suture the bone is 
much wider than that of the horse. The foramen magnum is wide, so that the 
condyles are further apart, except below. The paramastoid processes are short and 
wide and are bent inward. Usually at least two foramina are found in the condy- 
loid fossa; the ventral one is the hypoglossal, the other (often double) conducts a 
vein from the condyloid canal.^ The latter passes upward from a foramen on the 
medial side of the condyle and opens into the temporal canal. The mastoid for- 

^ The number of foramina here is variable. In exceptional cases the foramen which opens 
into the condyloid canal is very small or absent; much oftener there are two, and sometimes three. 
In some cases there are two hypoglossal foramina. Thus as many as five foramina may be present 
here. 



132 



SKELETON OF THE OX 



amen is situated on each side, at the junction of the occipital and temporal bones; 
it communicates with the temporal and condyloid canals at their junction. The 
cerebral surface of the supraoccipital presents a central depression, and above this 
is a variable but never very pronounced eminence, the internal occipital protuber- 
ance. A groove on either side leads to the temporal canal. The basilar part is short 
and wide ; its cerebral surface is deeply concave, and the internal spheno-occipital crest 
is prominent. Two large tubercles ventrally mark the junction with the sphenoid. 



Processus corniis 



Nasal bone 




Mental foramen 



Mandible 



Angle of mandible 



Fig. 129. — Skull of Ox; Lateral View. 
separated for the sake of clearness. ^, Parietal bone; B, squamous temporal bone; C, occipital bone; 

occipital 



The jaws ; 
D, perpendicular part of palatine bone; E, maxilla; F, malar bone; G, lacrimal bone; H, prema::illa; 
condyle; 2, paramastoid process; 3, meatus acusticus externus; 4, bulla ossea; 5, zygomatic process of temporal bone; 
6, 6', zygomatic and temporal processes of malar bone; 7, supraorbital process; 8, orbital part of lacrimal bone; 9, 
lacrimal bulla; 10, fossa sacci lacrimalis; 11, facial tuberosity; 12, infraorbital foramen; 13, condyle of mandible; 14, 
coronoid process of mandible. 



The foramen lacerum is short and very narrow. In the adult animal the bone is 
excavated to contain an air-cavity which is regarded as a part of the frontal sinus. 

The sphenoid bone is short. The cerebral surface of the body presents a deep 
sella turcica, in front of which it rises abruptly. The high anterior part bears a 
central ridge, the ethmoidal spine, which joins the crista galli of the ethmoid. 
Two foramina occur on either side. Of these, the large anterior one is equivalent 
to the foramen rotundum, orbitale, and trochleare of the horse; it may be termed 



BONES OF THE CRANIUM 



133 




Fig. 130. — Cross-section of Cranium of Ox. 

The section cuts the posterior part of the temporal condyle and is viewed from behind, a, Body of sphenoid; b, 

bulla ossea; c, temporal condyle; 1, dorsum sellae; 2, foramen ovale; .3, hypophy.seal or pituitary fossa; 4, foramen 

orbito-rotundum; .5, optic foramina; 6, crista galli; 7, cribriform plate of ethmoid; 8, orbital wing of sphenoid; 9, 

temporal wing of sphenoid; 10, internal plate of frontal bone; 11, frontal sinus; 12, temporal process of malar bone. 




Fig. 131. — Cross-section of Cranium of Ox. 
The section cuts the posterior part of the temporal condyle and is viewed from in front, a. Basilar part of occipital 
bone; 6, bulla ossea; c, paramastoid process; d, meatus acusticus externus; e, temporal fossa; 1, tympanic cavity; 2, 
internal opening of condyloid canal; 3, internal opening of temporal canal; 4, depression for vermis cerebelli; 5, internal 
occipital protuberance; 6, internal plate of parietal bone; 7, internal plate of frontal bone; 8, frontal sinus; 9, petrous 
temporal bone; 10, postglenoid process; 11, hyoid process. 



134 



SKELETON OF THE OX 



the foramen orbito-rotundum. The posterior one is the foramen ovale, which 

transmits the mandibular nerve. The orbital wing is thick and is overlapped by 
the frontal in such manner as to appear externally to divide into two branches; 
the anterior part joins the ethmoid at the sphenopalatine foramen, and contains a 
small sinus which communicates with an ethmoidal meatus The temporal wing is 
small, but forms a prominent thick pterj'goid crest. The pterygoid process is 
wide, and there is no alar canal. The sphenoidal sinus is absent in the calf and 
small in the adult ; it communicates by one or two small openings with an ethmoidal 
meatus, and so with the nasal cavity. 



zs 




Fig. 132. — Cranial and Orbital Regions op Skull of Ox. 
The horn core, supraorbital process, and greater part of zygomatic arch have been sawn off: A, Frontal bone; 
A', A", temporal and orbital parts of same; B, parietal bone; C, squamous temporal bone; D, D', orbital and facial 
parts of lacrimal bone; E, malar bone; F, maxilla; G, perpendicular part of palatine bone; 1, occipital condyle; 2, 
paramastoid process; 3, temporal crest; 4, temporal condyle; 5, postglenoid process; 6, external opening of temporal 
canal; 7, meatus acusticus externus; S, bulla ossea; 9, sty lo-mastoid foramen; 10, muscular process of temporal bone; 
11, tip of basilar tubercle; 12, foramen ovale; 13, foramen orbito-rotundum; 14, optic foramen; lo, ethmoidal foramen; 
16, orbital opening of supraorbital canal; 17, pterygoid crest; 18, ridge of orbital wing of sphenoid; 19, pterygoid proc- 
ess of sphenoid; 20, hamulus of pterygoid bone; 21, lacrimal bulla; 22, fossa sacci lacrimalis; 23, root of supraorbital 
process; 24, processus cornus (section) ; 25, frontal eminence. 



The ethmoid bone has an extensive perpendicular plate. The lateral mass 
consists of five endoturbinates and eighteen ectoturbinates (Paulli). The largest 
ethmoturbinate is so extensive as to be termed a third or middle turbinate bone ; it 
projects forward between the dorsal and ventral turbinates. The lamina lateralis 
appears to a small extent externally in the pterygo-palatine fossa, forming part 
of the dorsal margin of the sphenopalatine foramen. 

The interparietals are primitively paired, but unite before birth. As already 
mentioned, fusion occurs before or shortly after birth with the parietals and supra- 
occipital. The bone has no intracranial projection. 

The parietal bones do not enter into the formation of the roof of the cranium. 



BONES OF THE CRANIUM 



135 



They constitute the upper part of the posterior wall, bend sharply forward along 
the lateral wall, and enter into the formation of the temporal fossa. The line of 
inflection is marked by the prominent parietal crest, which is continuous with the 
temporal crest below and the frontal crest anteriorly. The parietals are excavated 
to form part of the frontal sinuses in the adult animal. 



Frontal Parietal 
eminence bone 



Ti mporal 
fossa 

Supraorbital foramen 
Supraorbital groove 




Nasal bone 



Palatine fissure 



Facial tuberosity 



Nasal process of premaxilla 



Palatine process of premaxilla 



Daily of premaxilla 



Fig. 133. — Skull of Jersey Cow; Dorsal View. 



The condition in the young subject is as follows: The two parietals are united with each other 
and also with the interparietal and supraoccipital. The resulting mass is somewhat horseshoe- 
shaped. Its occipital part (Planum occipitale) forms the greater part of the posterior wall of 
the cranium and bears about its center the tuberosity for the attachment of the Ugamentum 
nucha}. From either side of this a line curves outward and divides the surface mto an upper 
smooth area and a lower area which is rough for muscular attachment. The upper border joms 
the frontal bone and concurs in the formation of the frontal eminence. The temporal parts 
(Plana temporaha) are much smaller and are concave externally; they join the frontal above and 
the squamous temporal below. A median occipital crest extends ventrally from the external 
occipital protuberance. 

The frontal bones are very extensive, forming about one-half of the entire 



136 



SKELETON OF THE OX 



length of the skull, and all of the roof of the cranium. The posterior borders 
form -with the parietals a large central frontal eminence (Torus frontalis), the 
highest point of the skull. At the junction of the posterior and the lateral border 
is the processus comus or "horn core," for the support of the horn. These proc- 




FiG. 134. — Skull OF Ox, without Mandible; Ventral View. 
1, Foramen magnum; 2, occipital condyle; 3, paramastoid process; 4, condyloid foramen; 5, foramen lacerum; 
6, basilar part of occipital bone; 7, 7', basilar tubercles; 8, bulla ossea; 9, foramen ovale (concealed by muscular proc- 
ess) ; 10, meatus acusticus externus; 11, zygomatic process of temporal bone, 12, condyle of same; 13, external opening 
of temporal canal ; 14, processus cornus; 15, muscular process of temporal bone; 16, pterygoid crest; 17, orbital open- 
ing of supraorbital canal; 18, choanae or posterior nares; 19, hamulus of pterj'goid bone; 20, crest formed by pterygoid 
processes of sphenoid and palatine bones; 21, horizontal part of palatine bone; 22, anterior palatine foramen; 23, 
lacrimal bulla; 24, maxillary tuberosity; 25, palatine process of maxilla; 26, zygomatic process of malar bone; 27. 
facial tuberosity: 28, body of premaxilla; 29, palatine process of same; 30, palatine fissure; 31, incisive fissure; 32, 
premolars; 33, molars. 



esses are of elongated conical form, and vary greatly in size, length, curvature, 
and direction. The external surface is rough and porous, marked by numerous 
grooves and foramina; in the fresh state it is covered by the corium of the horn. 
The base has a constriction, the neck. The interior is excavated to form a number 
of irregular spaces, partially divided by bony septa, and communicating with the 



BONES OF THE FACE 137 

frontal sinus. In the polled breeds these processes are absent, the skull is narrower 
here, and the frontal eminence more pronounced (Fig. 139). The supraorbital proc- 
ess is situated about half-way between the anterior and posterior margins; it is 
short and joins the frontal process of the malar bone. The supraorbital foramen 
(often double) is situated about an inch medially from the root of the process; it 
is the external orifice of the supraorbital canal (Canalis supraorbitalis), which passes 
downward and forward to the orbit. The foramen is in the course of the supra- 
orbital groove (Sulcus supraorbitalis), which marks the course of the frontal vein. 
The anterior ends of the naso-frontal parts form a notch which receives the nasal 
bones, and sutural (or Wormian) bones are often found at this junction (naso- 
frontal suture). The orbital part is extensive; it is perforated behind by the or- 
bital opening of the supraorbital canal, and below by the ethmoidal foramen. It 
does not articulate with the palatine bone, from which it is separated by the or- 
bital wing of the sphenoid. The temporal part is also more extensive than in the 
horse. The frontal sinus is very extensive, being continued into the parietals and 
occipital, and the horn processes when present. 

The squamous and petrous parts of the temporal bone fuse early — in fact 
union is nearly complete at birth. The squamous part is relatively small. Its 
lateral surface is divided into two parts by the prominent temporal crest, which is 
continuous with the parietal crest above and turns forward below, ending at a 
tubercle above the external acoustic meatus. The part behind the crest faces 
backward, and is partly free, partly united with the occipital. The area in front 
of the crest is concave and enters into the formation of the temporal fossa; it is 
perforated by foramina which communicate with the temporal canal. The zygo- 
matic process is much shorter and weaker than in the horse, and articulates with the 
malar only. The condyle is convex in both directions. The postglenoid process 
is less prominent, and behind it is the chief external opening of the temporal canal. 
The cerebral surface is almost completely overlapped by the parietal and sphenoid. 
The petrous part is small, but the tympanic part is extensive. The external 
acoustic meatus is smaller than in the horse and is directed laterally. From it a 
plate projects downward and helps to inclose the deep depression in which the hyoid 
process is placed. Behind this plate is the stylo-mastoid foramen. The muscular 
process is large and often bifid at its free end. The bulla ossea is large and later- 
ally compressed. It is separated from th^ occipital bone by a narrow opening 
which is equivalent to part of the foramen lacerum of the horse. The temporal 
canal is formed entirely in the temporal bone. The facial canal, on the other 
hand, is bounded partly by the occipital bone. 

Bones of the Face 
The maxilla is shorter but broader and relatively higher than in the horse. 
Its lateral surface bears the rough facial tuberosity (Tuber faciale), placed above the 
third and fourth cheek teeth; a rough line which extends backward from it to the 
upper part of the malar bone may be regarded as the facial crest. The infraorbital 
foramen — often double — is situated above the first cheek tooth. The tuber maxil- 
lare is small, laterally compressed, and usually bears a small pointed process (Pro- 
cessus pterygoideus) . The zygomatic process is very small. The interalveolar 
border is concave, and there is no alveolus for a canine tooth. The palatine 
process is wider, but somewhat shorter than in the horse. It incloses a large 
air-space, which is continuous behind with a like cavity in the horizontal part of 
the palate bone, forming the palatine sinus (Sinus palatinus). This communi- 
cates laterally (over the infraorbital canal) with the maxillary sinus; in the 
macerated skull it communicates with the nasal cavity by a large oval opening, 
which is closed by mucous membrane in the fresh state. A median septum sepa- 



138 



SKELETON OF THE OX 



rates the two palatine sinuses. The alveoH for the cheek teeth increase in size 
from before backward. The maxillary sinus proper is small and is undivided. 
The maxillary foramen is a narrow fissure, deeply placed at the medial side of the 
lacrimal bulla. The maxilla takes no part in the formation of the palatine canal. 
Sutural (or Wormian) Iwnes are often present at its junction with the lacrimal and 
malar bones. 

The body of the premaxilla is thin and flattened, and has no alveoli, since 
the canine and upper incisor teeth are absent. A deep notch takes the place of 
the foramen incisivum. The nasal process is short, convex laterally, and does not 
reach to the nasal bone ; the space between the two processes is greater than in the 
horse. The palatine process is narrow and is grooved on its nasal surface for the 
septal cartilage and the vomer. The palatine fissure is very wide. 

The palatine bone is very extensive. The horizontal part forms one-fourth or 



Nasal bone 




Fig. 135. — Sagittal Section of Skull of Ox, without Mandible. 
A, A', Squamous and basilar parts of occipital bone; B, B', postsphenoid, presphenoid; C, lateral mass of ethmoid 
bone; Z), internal plate of frontal bone; jE, parietal bone; F, petrous temporal bone; G, pterygoid bone; //.perpendicu- 
lar part of palatine bone; I, outline of vomer (dotted line) ; J, palatine process of maxilla; K, nasal process of premaxilla; 
L, dorsal turbinate bone; M, ventral turbinate bone; A'^, middle turbinate bone (great ethmo-turbinate) ; 1, occipital 
condyle; 2, paramastoid process; 3, bulla ossea; 4, basilar tubercle; 5, muscular process; 6, hypoglossal foramen; 7, 
openings of condyloid canal; 8, direction of condyloid canal (dotted line); 9, internal opening of temporal canal; 10, 
meatus acusticus internus; 11, foramen lacerum; 12, sella turcica; 13, optic foramen; 14, sphenoidal sinus; 15, orbital 
wing of sphenoid bone; 16, frontal sinus; 16', anterior limit of frontal sinus (dotted line) ; 17, dorsal nasal meatus; 18, 
middle nasal meatus; 18', dorsal branch of middle meatus; 19, ethmoidal meatuses; 20, maxilla; 21, sphenopalatine 
foramen; 22, opening into maxillary sinus; 23, opening into palatine sinus, and arrow indicating communication of 
latter with maxillary sinus; 24, palatine sinus; 25, cross indicates anterior end of palatine sinus; 26, palatine fissure. 



more of the hard palate. The anterior palatine foramen opens near the junction 
with the maxilla, about half an inch from the median palatine suture and crest. 
Accessory palatine foramina (Foramina palatina accessoria) are also present. The 
palatine groove is usually not very distinct. The palatine canal is formed entirely 
in this part, and there is no articulation with the vomer. A rounded ridge occurs 
on the nasal side of the median suture. The interior is hollow, forming part of the 
palatine sinus. The perpendicular part is an extensive, quadrilateral, thin plate, 
which forms the posterior part of the lateral wall of the nasal cavity and in part 
bounds the choanse or posterior nares. Its nasal surface is nearly flat, and is smooth 
and free, except behind, where it is overlapped by the pterygoid bone. The lateral 
surface is attached to a small extent to the pterygoid process behind, and is free else- 
where. The sphenopalatine foramen is a long, elliptical opening, formed by a deep 
notch in the upper edge of the palate bone and completed by the ethmoid and sphe- 



BONES OF THE FACE 139 

noid. The edge behind this foramen articulates with the orbital wing of the sphe- 
noid, not the frontal, as in the horse. 

The pterygoid bone is wider than in the horse, and forms the greater part of the 
lateral boundary of the posterior nares. Its lateral surface is almost entirely united 
to the palatine bone and the pterygoid process, but a small part is free in the pterygo- 
palatine fossa. The hamulus is distinctly hook-like, thin, and sharp. 

The nasal bone is little more than half the length of that of the horse. It is 
straight in its length, but strongly curved from side to side. It does not fuse later- 
ally with the adjacent bones, even in old age. The posterior extremity is pointed 
and fits into the notch between the frontal bones. The anterior end is broader, 
and is divided into two parts by a deep notch. In old animals there is a small 
extension of the frontal sinus into this bone. 

The lacrimal bone is very large. The extensive facial part is concave in its 
length, and bears no lacrimal tubercle. The orbital margin is marked by several 
notches. The orbital part bears ventrally the remarkable lacrimal bulla; this is a 
large and very thin-walled protuberance, which bulges backward into the lower 
part of the orbit, and contains an extension of the maxillary sinus. The fossa for 
the lacrimal sac is small, and is just behind the orbital margin. 

The malar bone is relatively long. The facial surface is extensive; it bears a 
curved crest (Crista facialis) just below the orbital margin which is continued on 
the maxilla, and below this it is concave dorso-ventrally. The zygomatic process 
divides into two branches; of these, the frontal branch (Processus frontalis) turns 
upward and backward and joins the supraorbital process of the frontal bone; 
the temporal branch (Processus temporalis) continues backward, and is over- 
lapped by the zygomatic process of the temporal bone, completing the zygomatic 
arch. 

The dorsal turbinate bone is less cribriform and fragile than in the horse, and 
is widest in its middle, small at either end. It is attached to the turbinate crest 
of the nasal bone, and curves downward, outward, and then upward to be applied 
outwardly to the frontal and lacrimal bones. It thus incloses a cavity which com- 
municates with the middle meatus nasi. (In the macerated skull it opens into the 
frontal sinus, but this communication is closed by mucous membrane in the fresh 
state.) 

The ventral turbinate bone is shorter but much broader than in the horse. It 
is attached to the maxilla by a basal lamella about an inch (ca. 2 to 3 cm.) wide, 
which slopes ventro-medially. At the inner edge of this it splits into two plates 
which are rolled in opposite directions, and inclose two separate cavities, sub- 
divided by several septa. The dorsal one opens into the middle meatus, the 
ventral one into the ventral meatus nasi. 

The vomer forms a wider and deeper groove than in the horse. Its anterior 
end rests in a groove formed by the ends of the palatine processes of the premaxillae. 
The anterior third of its thin ventral edge fits into the nasal crest of the maxilla; 
behind this it is free and is separated by a considerable interval from the nasal floor. 

The two halves of the mandible do not fuse completely even in advanced age, so 
that a symphysis mandibulae is present. The symphyseal surfaces are extremely 
rough and are marked by reciprocal projections and cavities. The body is shorter, 
wider, and flatter than in the horse, and has eight round and relatively shallow 
alveoli for the lower incisors. The interalveolar border is long, curved, thin, and 
sharp. There are no alveoli for the canine teeth, which are absent. The anterior 
part of the ramus is narrow. The mental foramen is further forward than in the 
horse, and is in the posterior end of a fossa. The rami diverge more, so that the 
mandibular space is wilder than in the horse. They are also more strongly curved, 
and the angle is more pronounced. The molar part is not so high, especially in its 
anterior part. Its ventral border is convex in its length. Its alveolar border bears 



140 



SKELETON OF THE OX 



six alveoli for the lower cheek teeth; the first is quite small, and they increase in 
size from before backward. The vertical part is much smaller than in the horse 
and its posterior border is relatively thin below, concave and wider above. The 
mandibular foramen is about in the middle of its medial surface, and a groove for 



Coronoid process 




Condyle 



Angle 



Symphyseal surface 



Fig. 136. — Right Half of Mandible of Ox; Medial View. 
1, Mandibular foramen; 2, groove for lingual nerve. 



the lingual nerve curves downward and forward from it. The condyle projects 
medially further than in the horse, and is concave from side to side. The coronoid 
process is extensive and curves backward. 

The hyoid bone has a short tuberous lingual process. The middle cornua 

are almost as large as the small cornua. 
The great cornua are narrow, except 
at the ends. The upper end divides 
into two branches, which correspond 
to the two angles of that of the horse. 
The thyroid cornua do not fuse with 
the body except in old age. 




SKULL OF THE OX AS A WHOLE 

The skull of the ox is more clearly 
pyramidal than that of the horse, and 
is shorter and relatively wider. The 
cranium is quadrangular and larger 
externally than in the horse ; its large 
size is due mainly to the great extent 
of the frontal sinuses and does not 
affect the cranial cavity, which is 
smaller than in the horse. 

The frontal surface (Fig. 133) is 

formed bj^ the frontals, nasals, and 

premaxillae. The frontal part is 

quadrilateral and very extensive, the greatest width being at the orbits. It 

presents a central depression on its anterior part, and on either side are the 

supraorbital grooves and foramina. Behind is the median frontal eminence, 



Fig. 137. — Hyoid Bone of Ox. 
o, Body; b, lingual process; c, thyroid cornu and cartil 
age, c'; d, small cornu; e, middle cornu; /, great cornu; g 
muscular angle. (Ellenberger-Baum, Anat. d. Haustiere.) 



SKULL OF THE OX AS A WHOLE 141 

and at the lateral angles the "horn cores" project in horned cattle. The 
nasal part is very short. The osseous nasal aperture is wide. The premaxillae 
do not bend downward as in the horse; they are relatively thin and weak, 
and are separated by an interval which has a wide anterior part in place of 
the foramen incisivum. 

The lateral surface (Fig. 129) is more triangular than in the horse. The temporal 
fossa is confined to this surface. It is deep and narrow, and its boundaries are more 
complete. It is limited dorsally by a crest which extends from the postero-lateral 
angle of the frontal bone to the supraorbital process, and is analogous to the pari- 
etal crest of the horse. It is bounded behind by the temporal crest. It is clearly 
marked off from the orbit by a rounded ridge and the pterygoid crest. The zygo- 
matic arch is short, weak, and flattened, and is formed by the temporal and malar 
only. Its condyle is convex and is wide from before backward. The glenoid cavity 
and postglenoid process are small. The orbit is encroached upon below by the 
lacrimal bulla, and presents the orifice of the supraorbital canal behind. The or- 
bital margin is completed behind by the frontal process of the malar; its lower part 
is prominent and rough, not smooth and rounded as in the horse. The pterygo- 
palatine fossa is much larger, deeper, and more clearly defined. It has a long nar- 
row recess between the vertical plate of the palate bone medially and the maxilla 
and lacrimal bulla laterally; thus the sphenopalatine and maxillary foramina are 
deeply placed. The preorbital region is short but relatively high. A tuberosity 
and curved line correspond to the facial crest of the horse. The infraorbital fora- 
men is situated above the first cheek tooth and is often double. 

The basal surface (Fig. 132) is short and wide, especially in its cranial part. The 
occipital condyles are limited in front by transverse ridges. The basilar tubercles at 
the junction of the occipital and sphenoid are large. The condyloid fossse contain two 
foramina, the hypoglossal below and in front, and the condyloid above and behind; 
other inconstant ones occur. The paramastoid processes are short and convergent. 
The foramen lacerum is slit-like. The bulla ossea is a large, laterally compressed 
prominence. The muscular processes are usually long and narrow triangular plates, 
with one or two sharp points. The external acoustic process is directed almost 
straight outward. A curved plate extends ventrally from it and joins the bulla 
ossea medially, completing the deep cavity which receives the articular angle of 
the hyoid bone. The chief external opening of the temporal canal is in front of 
this plate, and an accessory one lies behind it. The infratemporal fossa is small, 
and presents the foramen ovale. The posterior nares are very narrow, and the 
vomer does not reach to the level of their ventral margin. The hard palate is wide, 
and forms about three-fifths of the entire length of the skull. A small central part 
only of its posterior border enters into the formation of the posterior nares; the 
lateral parts are notched and just above them are the posterior palatine foramina. 
The anterior palatine foramina are an inch or more from the posterior margin, 
and about the same distance apart. The palatine grooves are distinct for a short 
distance only. Just beyond the cheek teeth the palate narrows and becomes con- 
cave; beyond this it widens and flattens. 

The nuchal surface is extensive and somewhat pentagonal in outline in the 
adult. About its center is the external occipital protuberance for the attachment 
of the ligamentum nuchae. From this a median occipital crest extends toward the 
foramen magnum, and laterally two lines (Linese nuchse superiores) curve outward, 
marking the upper limit of the area which is roughened for muscular attachment. 
The surface above the lines is relatively smooth, and is covered only by the skin 
and the thin auricular muscles in the living animal. It is separated from the 
frontal surface by a thick border, which forms centrally the frontal eminence, and 
bears at its extremities the processus cornus — except in the polled breeds. The con- 
dyles are further apart, and the articular surfaces are more clearly divided into 



142 



SKELETON OF THE OX 



upper and lower parts than in the horse. The mastoid foramen is at the junction 
of the occipital and temporal bones; it is frequently very small. 




Fig. 138. — Cranium of Jersey Cow, Nuchal View. The Fig. 139. — Cranium op Polled Angus Cow, Nuchal 
Gre.^ter Part of the Processus Cornus has been View. 

Sawn Off. 
1, Foramen magnum; 2, occipital condyle; 3, parama.stoid process; 4, bulla ossea; 5, meatus acusticus externus; 
6, mastoid foramen; 7, external occipital protuberance; 8, median occipital crest; 9, linea nuchse superior; 10, frontal 
eminence. 

Dorsal meatus 

Middle meatus 



Nasal bone 



Dorsal part of ventral turbinate 
Basal lamella 



Ventral part of ventral 
turbinate 




Fig. 140. — Cross-section of Nasal Region of Skull of Ox. Section Passes Through Facial Tuberosity and 

Third Cheek Tooth. 
1, Cartilage of septum nasi; 2, vomer; 3, ventral meatus; 4, anterior extremity of maxillary sinus; 5, palatine 
sinus; 6, infraorbital canal and nerve; 7, palatine process of maxilla. Dotted lines indicate mucous membrane A'hich 
closes gap in bony floor of nasal cavity. 



The cranial cavity is shorter and its long axis is more oblique than in the horse, 
but it is relativel}^ high and wide. The anterior fossa lies at a much higher level 



SKULL OF THE OX AS A WHOLE 



143 



than the rest of the floor. The ethmoidal fossse are smaller, and the hypophyseal 
fossa or sella turcica is much deeper than in the horse. A deep groove leads from 
the petrous temporal forward over the foramen ovale to the foramen rotundum. 
Behind the sella there is often a distinct prominence (Dorsum sellae) . The internal 
parietal crest is prominent anteriorl}^, but subsides further back. A faintly marked 
elevation represents the internal occipital protuberance. The petrous temporal 
bone projects into the cavity laterally. The ridges and digital impressions are very 
pronounced. The temporal canal is formed entirely in the temporal bone, and 
opens internally at the apex of the petrous, where it is joined by the condyloid 
canal. The foramen lacerum is divided into two parts (For. lacerum orale et ab- 
orale) . 

The nasal cavity is incompletely divided l)y the septum, which does not reach 



Dorsal meatus 



Nasal bone 



Dorsal turhinaU 
Middle meatus 



Lacrimal bone 

Aaso-lacrimcd canal 
Maxilla 




Fig. 141.— Cross-section of N.\sal Region of Skull of Ox. Section is Cut between Fourth .a.nd Fifth Cheek 

Tooth. 
1, Cartilage of septum na.si; 2, vomer; 3, ventral meatus; 4, 4', maxillary sinuses; 5, 5', palatine sinuses; 6, infra- 
orbital canal and nerve; 7, horizontal part of palatine bone; 8, communication between maxillarj^ and palatine sinuses. 
Dotted lines indicate mucous membrane which closes gap in bony floor of nasal cavity. 



the floor posteriorly. The floor is relatively long, and is more concave from side to 
side than in the horse. In the dry skull it has a large oval opening (Hiatus maxillaris) 
into the palatine sinus, which is closed during life by mucous membrane. The 
middle meatus is divided behind into upper and lower branches by the great eth- 
moturbinate. The choanal or posterior nares are narrow and obhque. 

The frontal sinus is very large. It involves almost all of the frontal bone and 
a large part of the posterior wall of the cranium. It also extends for a variable dis- 
tance into the horn processes when these are present. A complete median septum 
separates the right and left sinuses. The anterior limit is indicated by a transverse 
plane through the middle of the orbits. It extends laterally to the crest, which 
limits the temporal fossa above, and into the root of the supraorbital process. At 
the highest part of the cranial cavity and at the external occipital protuberance 



144 



SKELETON OF THE OX 



tlie two plates of the bone come together. The cavity is very irregular and is sub- 
divided into numerous spaces by ridges and partial septa. This multilocular 
character is most marked in the anterior part, and here several small spaces appear 
to be cut off from the main cavity. The supraorbital canal passes through the 
sinus. Several small openings lead from the sinus to the ethmoidal meatuses, 
and thus indirectly to the upper division of the middle meatus nasi. The communi- 
cations with the cavity of the dorsal turbinate and with the lacrimal part of the 




Fig. 142. — Skull op Ox; Dorsal View. 
The outer plate of bone has been removed to show the sinuses, a, Frontal sinus; a', cranial plate of frontal bone; 
a", anterior part of frontal sinus, which is separated from remainder by a septum (b) ; c, c', communications between 
frontal sinus and nasal cavity; d, supraorbital foramen; e, supraorbital canal; /, cavity of dorsal turbinate bone, 
and fir, its opening into the nasal cavity; h. lacrimal sinus; i, its communication with the maxillary sinus; k, maxillary 
sinus; Z, orbit; i, frontal bone; /', processus cornus; ^, nasal bone; 3, premaxilla (nasal process) ; 4. maxilla; 5, lacri- 
mal bone; 6, malar bone; 7, dotted line indicating course of nasolacrimal duct. (After Ellenberger, in Leisering's 
Atlas.) 



maxillary sinus which are seen in the macerated skull are closed in the fresh state 
by mucous membrane. 

The maxillary sinus is excavated chiefly in the maxilla, lacrimal, and malar, 
and is not divided by a septum as in the horse. It extends forward as far as the 
facial tuberosity, or a little further in old animals. Its dorsal limit is indicated 
approximately by a line drawn from the infraorbital foramen to the upper margin 
of the orbit. It is continued into the lacrimal bulla to a point nearly opposite to 



BONES OF THE THORACIC LIMB 145 

the bifurcation of the zygomatic process of the malar. It also extends upward and 
backward through a large opening into a cavity formed by the lacrimal, frontal, 
ethmoid, and turbinal bones, at the medial side of the orbit. ^ The floor of the cavity 
is irregular and the roots of the last three or four cheek teeth project up into it, 
covered by a plate of bone. The sinus communicates with the palatine sinus freely 
over the infraorbital canal through an oval opening about two to three inches (ca. 
5 to 7.5 cm.) long. Above this it communicates by a shorter and much narrower 
opening with the middle meatus nasi. 

The palatine sinus is excavated in the hard palate, and is separated from that 
of the opposite side by a median septum. It extends from the posterior border of 
the palate to a plane an inch or more (2.5 to 3 cm.) in front of the first cheek tooth. 
As mentioned above, there is a large communication with the maxillary sinus over 
the infraorbital canal, so that the cavity is sometimes regarded as a part of that sinus. 
The large defect in the bony roof of the sinus is closed by two layers of mucous 



Fig. 143. — Skull op Ox; Lateral View without Mandible. 
The maxillary, lacrimal, and turbinate sinuses have been opened, and part of the orbital margin removed, a. Cavity 
of dorsal turbinate bone; 6, lacrimal sinus; c, maxillary sinus; d, communication between maxillary and palatine 
sinuses; e, opening between maxillary and lacrimal sinuses; /, thin osseous bulla; g, lacrimal bulla; h, orbit; 1-6, cheek 
teeth; 7, nasal bone; 8, premaxilla (nasal process); 9, maxilla; 9', infraorbital foramen; 10, frontal bone; 11, lacri- 
mal bone; 12, malar bone; 13, fissure between nasal bone and maxilla; 74, temporal bone (squamous) ; 75, external 
acoustic meatus; 75, paramastoid process; 77, occipital condyle; 7,?, palate bone (perpendicular part); 7 S, pterygoid 
bone (hamulus); ^0, tympanic part of temporal; ^0', muscular process of petrous temporal. (After EUenberger, in 
Leisering's Atlas.) 

membrane in the fresh state. The palatine canal passes obliquely through the 
posterior part of the sinus. 

The sphenoidal sinus is almost entirely in the sphenoid bone and does not 
communicate with the palatine sinus. It has one or two openings into the ventral 
ethmoidal meatuses. There is no cavity in the perpendicular part of the palate 
bone. 

There are several small air-cavities between the lateral mass of the ethmoid 
and the anterior part of the frontal sinus, which communicate separately with 
ethmoidal meatuses. 

BONES OF THE THORACIC LIMB 

The scapula is more regularly triangular than in the horse, relatively wider at 

the vertebral end and narrower at the distal end. The scapular index is about 

1 : 0.6. The spine is more prominent and is placed further forward, so that the 

supraspinous fossa is narrow and does not extend to the lower part of the bone. 

1 This is termed the lacrimal sinus by some authors. It is similar in location and in the posi- 
tion of its orifice to the turbinate part of the frontal sinus of the horse with the important differ- 
ence that it does not communicate with the frontal sinus in the ox. 
10 



146 



SKELETON OF THE OX 



The spine is sinuous, bent backward in its middle, forward below. Its free border 
is somewhat thickened in its middle, but bears no distinct tuber. Instead of sub- 
siding below as in the horse, the spine becomes a little more prominent, and is pro- 
longed by a pointed projection, the acromion, from which part of the deltoid muscle 
arises. The subscapular fossa is shallow. The areas for the attachment of the 
serratus muscle are not very distinct. The nutrient foramen is usually in the 
lower third of the posterior border. The glenoid cavity is almost circular and 
without any distinct notch. The tuberosity is small and close to the glenoid cavity. 




Fig. 144. — Left Sc.\pul.\ of Ox; L.\teral View. 

1, Anterior angle; 2, posterior angle; 3, supra.spinous fossa; 4, infraspinous fossa; 5, anterior border; 6, posterior 

border; 7, spine; 8, acromion; 9, tuber scapulae; 10, glenoid cavity; 11, nutrient foramen. 



The coracoid process is short and rounded. The cartilage resembles that of 
the horse. The tuberosity unites with the rest of the bone at seven to ten months. 
The humerus has a shallow musculo-spiral groove. The deltoid tuberosity 
is less prominent than in the horse, and the curved line running from it to the neck 
bears a well-marked tubercle on its upper part. The nutrient foramen is usually 
in the distal third of the posterior surface. The lateral tuberosity is very large, 
and rises an inch or more (ca. 3 cm.) above the level of the head. Its anterior part 
curves medially over the intertuberal or bicipital groove, and below it laterally 
there is a prominent circular rough area for the insertion of the tendon of the infra- 
spinatus. The anterior part of the medial tuberosity has a small projection which 



BONES OF THE THORACIC LIMB 



147 



curves over the groove. The groove is undivided. The distal articular surface 
is decidedly oblique, and the grooves and ridge are very well marked. The coro- 
noid and olecranon fossae are deep and wide. The condyloid crest is represented by 
a rough raised area. The proximal end unites with the shaft at three and one-half 
to four years, and the distal at about one and one-half years. 

The radius is short and relatively broad. It is somewhat oblique, the distal 
end being nearer the median plane than the proximal. The curvature is more 
pronounced below than above. The shaft is prismatic in its middle part and has 




Fig. 14.5. — Left Humerus of Ox; 
Lateral View. 
1, Head; 2, neck; 3, 3', lateral 
tuberosity; 4, rough prominence for 
attachment of infraspinatus tendon; 
5, deltoid tuberosity; 6, coronoid 
fossa; 7, lateral condyle; 8, lateral 
epicondyle; 9, medial epicondyle; 
10, olecranon fossa. 




Fig. 146. — Left Humerus of Ox; 
Anterior View. 
1, Lateral tuberosity; 2, medial 
tuberosity; 3, intertuberal groove; 
4, rough prominence for attach- 
ment of infraspinatus tendon; 5, 
deltoid tuberosity; 6, teres tubercle; 
7, musculo-spiral groove; 8, coro- 
noid fossa; 9, medial condyle; 10, 
lateral condyle. 




Fig. 147. — Left Radius and Ulna 
OF Ox; PosTERO-MEDiAL View. 
1, Olecranon; 2, processus an- 
conaeus; 3, semilunar notch; 4, 
proximal extremity of radius; 5, 5', 
proximal and distal interosseous 
spaces; 6, shaft of radius; 7, shaft 
of ulna; 8, vascular groove; 9, sty- 
loid process of ulna. 



dorsal, volar, and lateral faces. There is a marked increase in width and thickness 
distally. The proximal articular surface presents a synovial fossa which extends 
medially from the deep groove between the two glenoid cavities. The radial 
tuberosity is represented by a slightly elevated rough area. The facets for the ulna 
are larger than in the horse. The two bones commonly fuse above the proximal 
interosseous space and always fuse below it, except near the distal end, where there 
is a small distal interosseous space. A groove connects the two spaces laterally. 
The distal extremity is large, and is thickest medially. Its articular surface is 
oblique in two directions, i. e., from within upward and backward. The grooves 



148 



SKELETON OF THE OX 



for the extensor tendons are shallow. The proximal end unites with the shaft at 
one to one and one-half years, and the distal at three and one-half to four years. 

The approximation of the lower ends of the forearms and the carpi gives the "knock-kneed" 
appearance in cattle. The obliquity of the joint surfaces produces lateral deviation of the lower 
part of the hmb in flexion. The facets for the radial and intermediate carpals are narrower than 
in the horse and run obliquely dorso-laterally. The surface for the ulnar carpal is extensive and 
saddle-shaped; its lateral part is furnished by the ulna. 

The ulna is more fully developed than in the horse. The shaft is complete, 
three-sided, and strongly curved. It is fused with the radius in the adult, except 
at the two interosseous spaces mentioned above. Its proximal part contains a 
medullary cavity which extends somewhat into the proximal end. The olecranon is 





i 






—u 


3 


i 
3 




J 




Fig. 148. — Left Carpus and Adjacent Bones op Ox; 
Front View. 
if, Radius; XJ , ulna; C r., radial carpal; C. u., 
ulnar carpal; C. 2+3, fused second and third carpals; 
C. 4, fourth carpal; 1,S, 3, grooves for extensor tendons; 
4, metacarpal tuberosity; 6, vascular groove. Inter- 
mediate carpal bone (between radial and ulnar) not 
marked. 




Mc. 3+4 



Fig. 149. — Left Carpus and Adjacent Bones of 
Ox; Lateral View. 
R, Distal end of radius; U, styloid process of 
ulna; I, distal interosseous space; C. i., intermediate 
carpal; C. u., ulnar carpal; C. a., accessory carpal; 
C. 2 + 3, fused second and third carpals; C. 4, fourth 
carpal; Mc. 3+4. fused third and fourth (large) 
metacarpal; Mc. 5, fifth (small) metacarpal; T, meta- 
carpal tuberosity. 



large and bears a rounded tuberosity. The distal end is fused with the radius; it 
projects below the level of the latter, forming the styloid process of the ulna (Pro- 
cessus styloideus ulna?), which furnishes part of the facet for the ulnar carpal. 
The summit of the olecranon and the distal end unite with the shaft at three and 
one-half to four years. 

The carpus consists of six bones, four in the proximal row and two in the distal. 
The proximal row is oblique in conformity with the carpal articular surface of the 
radius. The radial and intermediate resemble in general those of the horse, but 
are less regular in shape, and their long axes are directed obliquely backward and 
medially. The radial is narrower than in the horse and curves upward behind. The 
intermediate is constricted in its middle, and wider behind than in front. The 
ulnar is large and very irregular. Its proximal surface is extensive and sinuous and 
articulates with both radius and ulna; it has a large oval facet behind for articula- 
tion with the accessory carpal. The accessory is short, thick, and rounded; it 



BONES OF THE THORACIC LIMB 



149 



articulates with the ulnar carpal only. The first carpal is absent. The second and 
third carpals are fused to form a large quadrilateral bone. The fourth carpal is a 
smaller quadrilateral bone. 

The metacarpus consists of a large metacarpal and a lateral small metacarpal 
bone. The large metacarpal bone (Mc. 3+4) results from the fusion of the third 
and fourth bones of the foetus, and bears evidences of its double origin even in the 
adult state. The shaft is shorter than in the horse, and is relatively wider and 
flatter. The dorsal surface is rounded, and is marked by a vertical vascular 
groove connecting two canals which traverse the ends of the shaft from before 
backward. The volar surface is flat and presents a similar but much fainter groove. 
The borders are rough in the proximal third. The proximal end bears two slightly 
concave facets for articulation with the bones of the lower row of the carpus; the 
medial area is the larger, and they are separated by a 
ridge in front and a notch behind. The lateral angle 
has a facet behind for the small metacarpal bone. The 
medial part of the extremity has anterior and posterior 
tuberosities. The distal end is divided into two parts 
by a sagittal notch. Each division bears an articular 
surface similar to that in the horse, but much smaller. 
The medullary cavity is divided into two parts by a ver- 
tical septum which is usually incomplete in the adult. 
The small metacarpal bone (Mc. 5) is a rounded rod 
about an inch and a half (ca. 3.5 to 4 cm.) in length, 
which lies against the proximal part of the lateral bor- 
der of the large bone. Its proximal end articulates with 
the latter, but not with the carpus. The distal end is 
pointed. 

Four cartilaginous metacarpals are present in the early foetal 
state, viz., the second, third, fourth, and fifth. The second com- 
monly either disappears or unites with the third; sometimes it 
develops as a small rod of bone. The third and fourth gradually 
unite, but can be cut apart at birth. Each has three centers of 
ossification; the proximal epiphysis fuses with the shaft before 
birth, the distal at two to two and one-half years. 

Four digits are present in the ox. Of these, two — 
the third and fourth — are fully developed and have 
three phalanges and three sesamoids each. The second 
and fifth are vestiges and are placed behind the fetlock; 
each contains one or two small bones which do not ar- 
ticulate with the rest of the skeleton. 

The first phalanx is shorter and narrower than in 
the horse and is three-sided. The interdigital surface is 
flattened and its volar part bears a prominence for the 

attachment of the interdigital ligaments. The proximal extremity is relatively 
large, and is somewhat compressed from side to side. The articular surface is con- 
cave from before backward and is cUvided by a sagittal groove into two areas, of 
which the abaxial one is the larger and higher. Behind these are two facets for 
articulation with the sesamoid bones. The volar surface bears two tuberosities 
separated by a deep depression. The distal extremity is smaller than the proximal, 
especially in the dorso-volar direction. Its articular surface is divided by a sagittal 
groove into two convex facets, of which the abaxial one is decidedly the larger. 
There are depressions on either side for ligamentous attachment. The bone con- 
sists at birth of two pieces— the distal end and the fused shaft and proximal ex- 
tremity. Union occurs at one and one-half to two years. 

The second phalanx is about two-thirds of the length of the first and is dis- 




FiG. 1.50. — Left Metacarpal 

Bones of Ox; Front View. 

The Small Bone has been 

Moved Laterally. 

1, Metacarpal tuberosity; 2, 
vascular groove; 3, 3', foramina; 
4, 4', condyles; 5, articular facet 
of fifth (small) metacarpal bone. 



150 



SKELETON OF THE OX 



tinctly three-sided. The proximal articular surface is divided by a sagittal ridge 
into two glenoid cavities, of which the abaxial one is much the larger. There is a 
central dorsal prominence and two tubercles are present on the volar face. The 
cUstal extremity is smaller than the proximal. Its articular surface encroaches con- 
siderably on the dorsal and volar surfaces, and is divided into two parts by a 
sagittal groove. There is a deep depression for ligamentous attachment on the inter- 
digital side. The bone contains a small medullary canal. The distal end unites 
^^dth the rest of the bone about the middle of the second year. 

The third phalanges resemble in a general way one-half of the bone of the horse. 
Each has four surfaces. The dorsal surface is marked in its distal part by a shal- 
low groove, along which there are several foramina of considerable size; the 
posterior one of the series is the largest, and conducts to a canal in the interior of 
the bone. Distal to the groove the surface is prominent, rough, and porous. 





Fig. lol. — Boxes of Distal Part of Fore Limb of 
Ox; Lateral View. 
1, Distal end of metacarpal bone; 2, first phalanx; 
3, proximal sesamoid bone; 4, second phalanx; 5, ex- 
tensor process of third phalanx; 6, dorsal surface; 7, 
angle; S, distal sesamoid bone. 



Fio. 152. — Bones of Distal Part of Fore Limb of 
Ox; Volar View. 
1, Metacarpal bone; 2, proximal sesamoid bones; 
3, first phalanx; 4, second phalanx; 5, distal sesamoid 
bone; 6, third phalanx. 



Near and on the extensor process are several relatively large foramina. The slope 
of the surface is very steep posteriorly, but in front it forms an angle of 25 to 30 de- 
grees with the ground plane. The articular surface is narrow from side to side, and 
slopes downward and backward. It is also oblique transversely, the interdigital 
side being the lower. It is adapted to the distal surface of the second phalanx, with 
the exception of a facet behind for the distal sesamoid. The extensor process is 
very rough. The volar surface is narrow and slightly concave, and presents two 
or three foramina of considerable size. It is separated from the dorsal surface 
by a border which is sharp in front, rounded behind. There is no semilunar crest, 
since the deep flexor tendon is attached to the thick posterior border of the volar 
surface. The interdigital surface is smooth and grooved below, rough and porous 
above. At the proximal angle it is perforated by a large foramen, which is equiva- 
lent to the volar foramen of the horse and leads to a cavity in the middle of the bone. 
The surface is separated by a rounded border from the dorsal surface, and by a sharp 



BONES OF THE PELVIC LIMB 151 

edge from the volar surface. The angle is very short and blunt, and there is no 
cartilage. 

Four proximal sesamoids are present, two for each digit. They are much 
smaller than in the horse. The bones of each pair articulate with the correspond- 
ing part of the distal end of the large metacarpal bone by their dorsal surfaces, 
with each other and with the first phalanx by small facets. 

The two distal sesamoids are short and their ends are but little narrower than 
the middle. 

BONES OF THE PELVIC LIMB 

The ilia are almost parallel to each other and are also less oblique with regard 

to the horizontal plane than in the horse. They are relatively small. The gluteal 

line is prominent and is nearly parallel to the lateral border; it joins the ischiatic 

spine. A rounded ridge separates the two parts of the pelvic surface. The surface 



Tuber sacrule 



Greater 
Lesfier sciatic Ischiatic sciatic 

Tuber ischii notch spine notch 



]^^s 



Tuber 
coxce 



" Sliajt of ilium 



Ischium 

^- ' I I Acetabulum 

Ji'tili/i Ohlurator Puliis 
J'oramen 

Fig. 153. — Right Os Cox« of Ox; Lateral View. 
1, Gluteal line; 2, fossa acetabuli. 

for articulation with the sacrum is triangular. The tuber sacralc is truncated, does 
not extend as high as the vertebral spines, and is separated from the opposite angle 
by a wider interval than in the horse. The tuber coxse is relatively large and prom- 
inent; it is not so oblique as in the horse, and is wide in the middle, smaller at either 
end. The shaft is short and compressed from side to side. 

The ischium is large. Its long axis is directed obliquely upward and back- 
ward, forming an angle of about 45 to 50 degrees with the horizontal plane. The 
transverse axis is oblique downward and inward at a similar angle, so that this 
part of the pelvic floor is deeply concave from side to side. The middle of the 
ventral surface bears a rough ridge or imprint for muscular attachment. The 
ischiatic spine is high and thin, and bears a series of almost vertical rough lines 
laterally. The tuber ischii is large and three-sided, bearing dorsal, ventral, and 
lateral tuberosities. The ischial arch is narrow and deep. The symphysis bears a 
ventral ridge, which fades out near the ischial arch. 

The acetabular branch of the pubis is narrow, and is directed laterally and a 



152 



SKELETON OF THE OX 



little forward. The anterior border is marked by a transverse groove which ends 
below the rough ilio-pectineal eminence. The symphyseal branch is wide and 
■/hin. 

The acetabulum is smaller than in the horse. The rim is rounded and is 
usually marked by two notches. One of these is postero-medial and is narrow 
and deep; it leads to the deep acetabular fossa and is often almost converted 
into a foramen by a bar of bone. The other notch is antero-medial, small, and 
sometimes replaced by a foramen or absent. 

The obturator foramen is large and elliptical. Its medial border is thin and 
sharp. 

Fusion of the three bones occurs at seven to ten months. 

The pelvic inlet is elliptical and is more oblique than in the horse. In a cow 




Median 
Wing of crest of Tuber 
sacrum sacrum sacrale 



Ilio-pectineal eminence 

Sym-physis pubis 




Acetabulum 
Tuber ischii 



Obturator foramen 



Ventral ridge 
Fig. 154. — Pelvic Bones of Cow, Viewed from in Front and Somewhat from Below. 



of medium size the conjugate diameter is about nine and a half inches (ca. 23 to 24 
cm.), and the transverse diameter about seven inches (ca. 18 cm.). The anterior 
end of the symphysis lies in a transverse plane through the junction of the third and 
fourth sacral segments. The dorsal wall or roof is concave in both directions. The 
ventral wall or floor is deeply concave, particularly in the transverse direction. 
The cavity is narrower and its axis is inclined strongly upward in the posterior part. 
The distance between the acetabulum and the tuber coxae is only a little (ca. 3 to 
4 cm.) more than the distance between the former and the tuber ischii. 

The femur has a relatively small shaft, which is cylindrical in its middle, pris- 
matic distally. The trochanter minor has the form of a rough tuberosity, and is 
situated higher up than in the horse and encroaches on the posterior surface. The 
trochanteric ridge (Crista intertrochanterica posterior) connects it with the tro- 



BONES OF THE PELVIC LIMB 



153 



chanter major. The third trochanter is absent. The supracondyloid fossa is 
shallow. The proximal extremity is very wide. The head is smaller than in the 
horse, and the articular surface extends considerably on the upper surface of the 
neck. The fovea capitis is a small depression on the middle of the head for the 
attachment of the round ligament. The neck is well defined except above. The 
trochanter major is very massive and is undivided; its lateral surface is very rough. 




Fig. 1.55. — Right Femur of Ox; Poste- 
rior View. 
1, Head; 2, neck; 3, trochanter ma- 
jor; 4, trochanteric fossa; 5, trochanter 
minor; 6, nutrient foramen; 7, vascular 
groove; 8, lateral supracondyloid crest; 
9, supracondyloid fossa; 10, 10', medial 
and lateral condyles; 11, 11', medial and 
lateral epicondyles; 12, intercondyloid 



Fig. 1.50.— liuaii- Ji.MLii of Ox; 
Lateral View. 
Numbers around bone: 1, 
Head; 2, neck; 3, trochanter 
major; 4, lateral border; 5, lateral 
supracondyloid crest; 6, supra- 
condyloid fossa; 7, lateral condyle; 
8, trochlea. Numbers on bone: 1, 
Eminence for attachment of gluteus 
profundus; 2, lateral epicondyle; 
3, depression for origin of popliteus 
muscle; 4, extensor fossa. 



Fig. 157. — Left Tibia and Prox- 
imal Part of Fibula of Ox; 
Posterior View. 
Numbers around bones: 1, 1', 
Medial and lateral condyles of 
tibia; 2, nutrient foramen; 3, 
lateral border; 4, distal extrem- 
ity; 5, medial malleolus; 6, shaft 
of fibula. Numbers on bone: 1, 1', 
Tubercles of spine; 2, intercondy- 
loid fossa; 3, muscular lines. 
Arrow indicates groove for flexor 
digitalis longus. 



The trochanteric fossa is deep, but does not extend so far distally as in the horse. 
The distal end presents no very striking differential features, but the ridges of the 
trochlea are less oblique than in the horse, and converge very slightly below. The 
proximal extremity unites with the shaft at about three and one-half years, the 
distal at three and one-half to four years. 

The tibia resembles that of the horse rather closely, but is somewhat shorter. 



154 



SKELETON OF THE OX 



The shaft is distinctly curved, so that the medial side is convex. The posterior 
surface is not divided into two areas, and the linese musculares are fewer and extend 
up higher than in the horse. The articular grooves and ridge of the distal end are 
almost sagittal in direction, and present an extensive but shallow synovial fossa. 
The lateral groove is separated by a sharp ridge from an outer area which is for 
articulation with the lateral malleolus. The anterior part of the medial malle- 
olus is prolonged do'vvnward and has a pointed end. The groove behind it is broad 
and well defined. Laterally there is a deep narrow groove which separates two 
prominences. The proximal extremity fuses with the shaft at three and one-half 
to four years, the distal at two to two and one-half years. 

Tuber calcis 



M.m. 




M.l. 



Mt. 5+4 




Fig. 15S. — Right Tarsus and Adjacent Boxes of Ox; Fig. 1.59. — Right Tarsus and Adjacent Bones op 
AIedial View. Ox; Dorso-l.\teral View. 

M. m., Medial malleolus; .1/. I., lateral malleolus (distal end of fibula) ; T, tibia; T. t., tibial tarsal bone; T. /., fibulai 
tarsal bone (sustentaculum); T. c+-J, fused central and fourth tarsal bones; T. i, first tarsal bone; T.2+S, fused 
second and third tarsal bones; Mt. 2, small or second metatarsal bone; Mt. S+ 4. large metatarsal or fused third and 
fourth metatarsal bones; 1, groove for tendon of flexor digitalis longus; S, groove for deep flexor tendon. 



The fibula usually consists of the two extremities onlj\ The head is fused with 
the lateral condyle of the tibia and is continued by a small, blunt-pointed prolonga- 
tion below. The distal end remains separate and forms the lateral malleolus (some- 
times called the os malleolare). It is quadrilateral in outline and compressed from 
side to side. The proximal surface articulates with the distal end of the tibia, and 
bears a small spine which fits into the groove on that bone. The distal surface 
rests on the fibular tarsal, and the medial articulates with the lateral ridge of the 
tibial tarsal bone. The lateral surface is rough and irregular. 

The early cartilaginous fibula is complete, but later the shaft is reduced to the 
small prolongation noted in speaking of the head and a fibrous cord which connects 
it with the distal end (lateral malleolus). In some cases, however, the upper part 
undergoes partial ossification, forming a slender rod which is usually united with 
the lateral border of the tibia and is joined to the head by fibrous tissue. 



BONES OF THE PELVIC LIMB 



155 



The patella is long, narrow, and very thick. The free surface is strongly con- 
vex and very rough and irregular. The articular surface is convex from side to 
side and nearly straight in the vertical direction. The large prominence on the 
medial side for the attachment of the fibro-cartilage allows prompt determination 
of the side to which the bone belongs. The apex is more pointed than in the horse. 

The tarsus consists of five pieces; the central and fourth and the second and 
third tarsal bones are fused. 

The tibial tarsal bone is relatively long and narrow, and is somewhat flattened 
from before backward. It bears a trochlea at either end. The groove and ridges 
of the proximal trochlea are not spiral, but almost sagittal; the lateral ridge is the 
wider, and articulates with both tibia and fibula. The distal trochlea consists 
of two condyles divided by a groove, and articulates with the 
combined central and fourth tarsals. The plantar surface bears 
a large oval facet for articulation with the fibular tarsal; this 
occupies most of the surface, and is convex and grooved from 
above downward. The lateral surface presents two facets for 
articulation with the fibular tarsal, and is excavated and rough 
elsewhere. The medial surface bears a tuberosity at its upper 
part, and is flattened below. 

The fibular tarsal ])one is longer and more slender than in 
the horse. The distal part of the body is compressed laterally, 
and bears a projection in front which articulates with the lateral 
malleolus. The tuber calcis is marked posteriorly by a wide 
shallow groove, which is coated with cartilage in the fresh state. 

The central and fourth tarsals are fused to form a large 
bone (Os centrotarsale quartum, scapho-cuboid), which extends 
across the entire width of the tarsus and articulates with all of 
the other bones. The greater part of the proximal surface is 
molded on the distal trochlea of the tibial tarsal, and its medial 
part rises high above the rest posteriorly. Laterally there is a 
narrow, undulating surface for articulation with the distal end 
of the fibular tarsal bone. The plantar surface bears two tuber- 
osities, of which the lateral one is rounded, the medial more 
prominent and narrower. 

The first tarsal bone is quadrilateral and small. It articu- 
lates with the central above, the metatarsus below, and the 
second tarsal in front. 

The second and third tarsals are fused to form a rhomboid 
piece. The proximal surface is concavo-convex, and articulates 
with the central component. The distal surface is undulating 
and rests on the metatarsus. The lateral surface bears a small 
facet in front for the fourth tarsal component, and the plantar 
surface a very small one for the first tarsal bone. 

The large metatarsal bone is about one-seventh (ca. 3 cm.) longer than the 
corresponding metacarpal. Its shaft is compressed transversely and is distinctly 
four-sided. The groove on the dorsal surface is deep and wide. The plantar 
surface is marked by variable grooves. The proximal foramen on this surface does 
not perforate the shaft, but passes obliquely through the extremity, opening on the 
posterior part of its proximal surface. The medio-plantar angle of the proximal 
end bears a facet for articulation with the small metatarsal bone. 

The small metatarsal bone is a quadrilateral disc a little less than an inch in 
width and height. Its anterior face bears a facet for articulation with the large 
metatarsal bone. 




Fig. 160. — L a r g e 
Metatarsal Bone 
OF Ox; Dorsal 
View. 

1, Vascular groove; 
2, foramen; 3, 3', con- 
dyles. 



156 SKELETON OF THE SHEEP 

The large metatarsal bone is usually regarded as consisting of the fused third and fourth 
metatarsal bones, and the small bone as the second metatarsal. The medullary cavity is subdivided 
like that of the large metacarpal bone. Some anatomists, however, consider that the ridges at 
the upper end of each border represent the second and fifth metatarsals (Rosenberg and Retterer). 
On this basis the small bone would be the first metatarsal. 

The phalanges and sesamoids resemble those of the thoracic limb so closely 
as to render separate description unnecessary. 



SKELETON OF THE SHEEP 

VERTEBRAL COLUMN 

The vertebral formula may be given as C7Ti3L6_7S4Cyi6-i8, but it should be 
noted that, except in the cervical region, variation in number is common. 

It is not very rare to find twelve thoracic and seven lumbar, or an ambiguous intermediate 
vertebra. More commonly there are seven lumbar vertebriE without reduction in the thoracic 
region. In some cases there are fourteen thoracic and five or six lumbar vertebrae, and Lesbre 
records a case in which twelve thoracic and seven lumbar were present. In some cases the fourth 
sacral vertebra remains separate, and in others the first coccygeal unites with the sacrum, although 
the fusion here is rarely complete. Nathusius states that the number of coccygeal vertebrae 
varies from tliree to twenty-four or more. 

The cervical vertebrae are relatively longer than those of the ox. The atlas 
differs chiefly in that the prominence on the dorsal arch is much less developed. 
The anterior articular cavities are often separated by a central ridge. The wings 
are produced to form blunt points behind. The spinous process of the axis is not 
enlarged posteriorly; those of the succeeding vertebrae are less developed than in 
the ox; they increase in length from the third to the last. The ventral spines are 
rudimentar5\ The arches are separated dorsally by interarcuate spaces. 

The thoracic vertebrae are usually thirteen in number, but fourteen may be 
present, or, more rarely, only twelve. Their bodies are relatively wider and less 
constricted than those of the ox, and their extremities are not so strongly curved, 
especially toward the end of the series. The intervertebral foramina are larger, in 
correlation with the absence of the foramina which usually occur in the arches of 
these vertebrae in the ox. 

The limibar vertebrae number six or seven, the former being a little more fre- 
quent than the latter. It is not common to find the number reduced to five. In 
some cases there is an ambiguous vertebra at the junction of the thoracic and lum- 
bar regions. The bodies are more flattened dorso-ventrally than those of the ox; 
their anterior ends are somewhat concave transversely, and the posterior ends are 
almost flat. The anterior articular processes are strongly curved and overlap the 
posterior ones. The transverse processes curve forward and have expanded ends. 

The sacrum consists ordinarily of four segments, but the last vertebra may re- 
main separate or undergo orfly partial fusion. There is no vascular groove on the 
pelvic surface. The spines are not fused, ^vith the exception of the flrst and second, 
which may be partially united. The transverse processes of the last segment are 
distinct and outstanding. 

The coccygeal vertebrae vary in number from three (in short-tailed sheep) to 
twenty-four or more. The bodies have no hemal processes on the ventral surface. 
The transverse processes are long and thin and project backward. 



THE RIBS 
The ribs usually number thirteen pairs, but the occurrence of fourteen pairs is 
not at all unconmion. The thirteenth rib is floating and has a cartilage about an 



THE STERNUM — THE SKULL 157 

inch long. The fourteenth rib, when present, is also floating. As compared with 
those of the ox, they are narrower and are more strongly curved in the anterior part 
of the series. The lateral surface is in general smooth and rounded. The second 
to the eleventh form diarthroses with their cartilages. 

The thirteenth rib may be more or less rudimentary on one side or both, and may be fused 
with the corresponding vertebra; the latter may, therefore, be ambiguous in character. 

THE STERNUM 
The sternum resembles in general that of the ox. The number of segments 
may be reduced to six, and the primitive division of the next to the last sternebra 
into two lateral halves may persist for a long time. The first segment is cylindrical, 
with enlarged ends; the second and third are wide and flat; the last is long and nar- 
row. 

THE SKULL 

The more important differences in the skull of the sheep as compared with 
that of the ox are in regard to the cranium. Viewed from above, the cranium is 
irregularly hexagonal in outline; it is widest in the frontal region, between the 
posterior parts of the orbits, and narrows greatly both anteriorly and posteriorly. 
In profile the roof of the cranium is strongly convex; the highest part of the curve 
coincides with the greatest width, and the posterior part slopes at an angle of about 
45 degrees with the basal plane. 

The occipital bone forms all of the nuchal surface of the cranium, except a 
small lateral area occupied by the mastoid part of the temporal bone. A narrow 
part (about 1.5 cm. in width) enters into the formation of the roof of the cranium 
also; it joins the parietal bones at a transverse suture. The parietal and nuchal 
surfaces are separated by a rough transverse ridge, the central part of which is 
united below with the external occipital protuberance, to which the ligamentum 
nuchse is attached. The mastoid foramen is situated between the lateral border 
and the petro-mastoid part of the temporal bone. The paramastoid process is 
grooved laterally, has a concave anterior border, and tapers to a blunt point. The 
basilar part is wide; the tubercles at its junction with the sphenoid are placed 
laterally, and are broad and short. 

The sphenoid bone resembles that of the ox. The posterior wall of the deep 
hypophyseal or pituitary fossa is formed by a plate (Dorsum sellae) which is di- 
rected forward and upward, and bears a projection (Processus clinoideus posterior) 
at each side of its upper part. The sphenoidal sinus is commonly absent or rudi- 
mentary. 

The ethmoid bone resembles that of the ox. 

The parietal bone fuses soon after birth with its fellow and with the inter- 
parietal. From this union there result a central quadrilateral curved plate which 
forms part of the roof of the cranium, and, separated from it by a curved line, a 
narrower lateral part, which extends forward on either side as part of the medial 
wall of the temporal fossa. The frontal sinus does not extend into the parietal bone. 
There is no internal occipital protuberance. 

The frontal bone is relatively less extensive than in the ox. The naso-frontal 
part is strongly curved, but varies considerably in contour in different breeds. In 
horned breeds the processus cornus projects from the lateral part of the external 
surface a little (ca. 1.5 cm.) behind a transverse plane through the posterior margin 
of the orbit. The process varies in size and shape, and does not contain an extension 
of the frontal sinus. In other cases there is a rounded tuberosity or a slight rough- 
ened elevation. The supraorbital foramen is further forward than in the ox, being 
just behind a transverse plane through the middle of the orbit; it is a little nearer 



158 



SKELETON OF THE SHEEP 



to the orbital margin than to the median line. The groove which leads forward 
from it is often rather faint. The orbital part is deeply concave. The infraorbital 
canal opens on the medial wall of the orbit as in the ox. The frontal sinus extends 
backward to a transverse plane through the posterior part of the temporal con- 
dyle, and forward to one through the anterior margin of the orbit. 

The temporal bone consists of distinct squamous, tympanic, and petro-mastoid 
parts. The squamous part in general resembles that of the ox, but has, like that of 
the horse, a notch through which the external acoustic process protrudes. The root 
of the zygomatic process is perforated by a foramen which opens ventrally behind 
the postglenoid process, in front of the chief external opening of the temporal canal. 
The latter extends upward and backward between the petro-mastoid and squamous 
parts and the parietal l:)one, and opens into the cranial cavity in front of the apex 
of the petrous. The tympanic part includes the external acoustic process, the bulla 




Fig. 161. — Skull of Sheep; Lateral View. 
A, Occipital bone; B, parietal bone; C, squamous temporal bone; D, frontal bone; S, nasal bone; F, lacrimal bone; 
G, malar bone; H, maxilla; I, premaxilla; J, mandible; K, perpendicular part of palatine bone; L, hyoid bone; 1, 
occipital condyle; 2, paramastoid process; 3, mastoid process; 4, meatus acusticus externus; 5, bulla ossea; 6, zygo- 
matic process of temporal bone; 7, condyle of mandible; S, coronoid process; 9, supraorbital process; 10, processus 
cornus; 11, 11', openings of supraorbital canal; 12, ethmoidal foramen; 13, optic foramen; 14, fossa sacci lacrimalis; 
15, bulla lacrimalis; 16, external lacrimal fossa; 17, facial tuberosity; 18, infraorbital foramen; 19, mental foramen. 



ossea, and the muscular process; the first resembles that feature in the horse, the 
others those of the ox, but the cavity of the bulla is undivided. The cerebral sur- 
face of the petrous part presents the floccular fossa on its upper part, and a round 
eminence behind the internal acoustic meatus. 

The bones of the face present, aside from the difference in size, few important 
special features. 

In regard to the maxilla it may be noted that the junction with the lacrimal and 
malar is less oblique than in the ox, since the facial parts of these bones are quadri- 
lateral and not produced to a point anteriorly. The facial tuberosity and the infra- 
orbital foramen are a little further back, and lie about over the second and fourth 
cheek tooth respectively. The palatine sinus extends from a point opposite to the 
fir.st cheek tooth backward to the transverse palatine suture. The defect (in the 
dry skull) in its nasal wall is quite small — in marked contrast to that of the ox — 



THE SKULL 



159 



Occipital huno 

\ 



Temporal crest 
( 'oronoid process 

Frontal bone 



Orbit 

Supraorbital 
foramen 



Malar bone 
Lacrimal bone 



since the basal lamella of the ventral turbinate bone curves ventro-medially, joins 
the palatine bone, and is separated only by a narrow hiatus from the nasal plate of 
the palatine process of the maxilla. The anterior palatine foramen is at the trans- 
verse palatine suture. The anterior end of the palatine process tapers to a point. 
The maxillary sinus resembles that of the ox, but is relatively small. 

The premaxilla has a narrow and pointed body. The palatine process is ex- 
tremely narrow in front and is grooved laterally. The palatine fissure is long and 
narrows to a very acute angle behind. 

The palatine bone resembles that of the ox, but there is no air-cavity in its 
horizontal part. The spheno- 
palatine foramen is large and Occipital hum Parietal bom 
oval. 

The pterygoid bone is 
very broad above and narrow 
below, where it ends in a sharp- 
pointed hamulus. 

The nasal bone tapers to 
a point at its anterior end, 
which is not notched. 

The facial part of the 
lacrimal bone has an elongated 
quadrilateral outline; in front 
of the orbit it forms, with the 
adjacent part of the malar, the 
external lacrimal fossa (Fossa 
lacrimalis externa) which 
lodges a cutaneous cul-de-sac 
known as the infraorbital or 
lacrimal pouch. The bone here 
may be more or less cribriform. 
The lacrimal bulla is relatively 
small, is usually cribriform, 
and has a pointed posterior 
end; the maxillary sinus ex- 
tends into it. The orbital 
margin forms a distinct promi- 
nence, and behind the latter is 
the fossa for the lacrimal sac. 

The facial part of the 
malar bone is extensive and 

quadrilateral. Its upper part concurs in the formation of the external lacrimal 
fossa; this area is limited below by a curved crest which continues backward on 
the zygomatic process. The latter divides into two branches, as in the ox. 

The turbinates and the vomer resemble those of the ox. 

The mandible differs from that of the ox chiefly in that the ventral border of 
the ramus, from the body to the angle, is only slightly curved. 

On account chiefly of the limited extent of the frontal sinuses, the cranial 
cavity corresponds to the external form of the cranium more closely than is the case 
in the ox. It is ovoid, and is much longer relatively, but has a much shorter dorso- 
ventral diameter than that of the ox. The parietal bone forms a distinct ridge on 
the lateral wall between the cerebral and cerebellar compartments, but, on the other 
hand, the petrous temporal projects very little into the cavity. 

The nasal cavity resembles that of the ox, but is relatively narrow (especially 
anteriorly), and there is no large hiatus in the nasal plate of the maxilla. 




Facial tuberosity 
Maxilla 

Nasal hone 

Nasal process of pre- 
maxilla 

Palatine process of pre- 
maxilla 
Palatine fissure 

of premaxilla 



Incisor teeth 



Fig. 162. — Skull of Sheep; Dorsal View. 



160 SKELETON OF THE SHEEP 



BONES OF THE THORAaC LIMB 

The scapula differs chiefly from that of the ox in the following points : The ver- 
tebral border is longer and the neck narrower. The spine is less sinuous. The 
glenoid extremity is relatively long, since the tuber scapulae is connected with the 
rim of the glenoid cavity. The subscapular fossa is more extensive. 

The humerus is relatively longer and more slender than that of the ox. The 
anterior part of the lateral tuberosity is blunt and less incurved, while the posterior 
part is small. The deltoid tuljerosity is nearer to the proximal end and is less 
prominent. 

The bones of the forearm are relatively longer than those of the ox. The 
radius is a little more curved than that of the ox, and its dorsal surface is more 
regularly rounded. The shaft of the ulna is more slender, especially in its distal 
half; its fusion with the radius occurs later and is usually much less extensive than 
in the ox. 

The carpal bones resemble those of the ox except in size. The accessory is 
long and less tuberous. 

The large metacarpal bone (Mc. 3 + 4) is long and slender. The lateral small 
metacarpal bone (Mc. 5) is often absent or is represented by a ridge on the large 
metacarpal. 

The phalanges of the chief digits are relatively long and narrow. The third 
phalanx in particular is much flattened on its abaxial side, so as to form a prominent 
dorsal border. Of the proximal sesamoids, the abaxial ones are compressed from 
side to side, and the axial ones from before backward. The flexor surface of the 
distal sesamoids forms a shallow groove, not divided by a ridge. The accessory 
digits usually have no phalanges. 

BONES OF THE PELVIC LIMB 

The OS coxae differs greatly from that of the ox. The long axis of the ilium 
is almost in a line with that of the ischium. The gluteal line appears as a ridge 
which is nearly parallel with the lateral border. The tuber coxa is only slightly 
thickened, and the tuber sacrale is pointed. The crest is concave medially, convex 
laterally. The shaft is relatively long and is flattened laterally. The superior 
ischiatic spine is low and everted. The pubis resembles that of the ox, but its an- 
terior border (pecten) is thin and sharp. The ischium slopes downward and back- 
ward, and forms a much larger angle with its fellow than in the ox. The lesser 
sciatic notch is very shallow. The tuber ischii is flattened and everted; it bears a 
long, blunt-pointed lateral process, and a verj'' short and blunt dorsal prominence. 
There is a very low ventral ridge on the symphysis. The latter is not usually com- 
pletely ossified, even in old animals. The acetabulum is further back than in the 
ox, and is relatively larger and deeper; it has a deep notch posteriorly. The 
pelvic inlet is very oblique, so that a vertical plane from the anterior end of the 
symphysis cuts the first coccygeal vertebra. The brim is elliptical; the conjugate 
cUameter is about five inches (ca. 12 cm.), and the transverse about three and a 
half to four inches (ca. 9.5 cm.). The floor of the pelvic cavity is wide and shallow 
as compared with the ox, and the pelvic axis inclines downward posteriorly. 

The shaft of the femur is slightly curved, the convexity being anterior. A dis- 
tinct line separates the lateral and posterior surfaces. The supracondyloid fossa 
is very shallow. The head has a shallow fovea and the neck is distinct. The tro- 
chanter major is little higher than the head. The ridges of the trochlea are similar 
and parallel, but slightly oblique. 

The tibia is long and slender, but otherwise resembles that of the ox. The 
fibula has no shaft, and its proximal end is represented by a small prominence be- 



SKELETON OF THE PIG VERTEBRAL COLUMN 



161 



low the lateral margin of the lateral condyle of the tibia; the distal end forms the 
lateral malleolus, as in the ox. 

The patella is relatively longer and narrower than that of the ox. 

The tarsal bones resemble those of the ox except in size. 

The metatarsal and digital bones present special characters similar to those of 
the corresponding part of the thoracic limb. 



SKELETON OF THE PIG 

VERTEBRAL COLUMN 

The vertebral formula is C7Ti4_i5L6-7S4Cy2o-23. 

The cervical vertebrae are short and wide. The bodies are elliptical in cross- 
section, the long diameter being transverse. The anterior articular surfaces are 
slightly convex from side to side and concave dorso-ventrally ; the posterior ones 




Fig. 163. — Skeleton of Pig; Lateral View. 
o. Cranium; b, maxilla; c, mandible; 1H.-7H., cervical vertebrae; IR.iv., first thoracic vertebra; 13 Rav., thir- 
teenth thoiacic vertebra (uext to last); IL., first lumbar vertebra; 6L., sixth lumbar vertebra (next to last usually); 
A'., sacrum; S., coccygeal vertebrse; IR., first rib; I4R., last rib; R.hi., costal cartilages; St., sternum; d, supraspin- 
ous fossa; rf', infraspinous fossa; i, spine of scapula; ^, neck of scapula; e, humerus; 3, head of humerus; 4, tuberosities 
of humerus; 5, deltoid tuberosity; 6, lateral epicondyle of humerus; /.radius; g, ulna; 7, olecranon; /j, carpus: 18-26, 
carpal bones; i-i"", metacarpus; Z;-^"", proximal phalanges; Z-Z"", middle phalanges; m-m"", distal phalanges; n, o, 
sesamoids; p, ilium; 5, tuber coxse; S, tuber sacrale; 1 , superior ischiatic spine; g, ischium; ??, tuber ischii; r, pubis; 
12, acetabulum; s, femur; 13, trochanter major; 14, trochanter minor; lo, lateral epicondyle; t. patella; u. tibial- 
is, crest of tibia; i 7, lateral condyle of tibia; w, fibula; m), tarsus; ^^-37, tarsal bones; ^6', tuber calcis. (After Ellen- 
berger, in Leisering's Atlas). 



are slightly concave. A ventral spine is not present. The arches are wide trans- 
versely, but the laminae are narrow, so that a considerable interval (Spatium inter- 
arcuale) separates adjacent arches dorsally. The pedicles are perforated by a 
foramen in addition to the usual intervertebral foramina. The transverse processes 
divide into two branches, both of which increase in size from the third to the sixth. 
The dorsal branch projects outward and backward; it is short and is thickened at 
its free end. The other branch is a quadrilateral plate cUrected ventrally; each 
overlaps the succeeding one to a small extent, and the series forms the lateral 
boundary of a deep and wide ventral groove. The spines increase in height from the 
11 



162 



SKELETON OF THE PIG 



third to the last; the anterior ones are incHned backward, the posterior ones for- 
ward. The last cervical is recognized by the great length of its spine (ca. 10 cm. 
in the adult), the absence of the ventral plate of the transverse process, and the flat- 
ness of the body, which bears a pair of small facets on its posterior margin for the 



r 



. S" 



■?:i 



Fig. 164. — Fouhth Cervical 
Vertebra of Pig; Lat- 
eral View. 

1, 1', Anterior and pos- 
terior ends of body; 2, arch; 
3, foramen of arch; 4, anterior 
articular process; 5, spinous 
process; 6, ventral branch of 
transverse process. 




— Sixth Cervical Vertebra 

OF Pig; Anterior ^'IEW. 

1, Body; 2, transverse process; 

foramen transversarium ; 4, addi- 

nal foramen of arch; 5, articular proc- 

; 6, arch; 7, spinous process. 



^■» 




1^. 5' 


^^ 




3 


^,^ 




1 


4—^ 




^'^ 


1-^^^^ 




) 


Fig. 166.— Seventh 


Cervical 


Vertebra op 


Pig 


Lateral 


View. 







1, 1', Anterior and posterior 
ends of body; 2, facet for head of 
first rib; 3, arch; 4, transverse 
process; 5, 5', articular processes; 
6, spinous process; 1 (number on 
bono), foramina of arch. 




Fig. 1()7. — Atlas of Pig; Dorsal View. 
1, Dorsal tuberosity; 2, alar foramen; 3, wing; 
4, intervertebral foramen; 5, dorsal arch; 6, ventral 
tubercle; 7, surface for dens. 




-Atlas of Pig; Anterior View. 
1, Dorsal tuberosity; 2, wing; 3, alar foramen; 4, ante- 
rior articular cavity; 5, ventral tubercle. 



heads of the first ribs. It has foramina transversaria, and usually two foramina in 
each side of the arch. 

The dorsal tuberosity of the atlas is large. The ventral tubercle is long, com- 
pressed laterally, and projects back under the axis. The wing is flattened and 
bears a posterior tuberosity. The foramen transversarium passes through the 



VERTEBRAL COLUMN 



163 




Fig. 169. — Axis of Pig; Lateral View. 
1, Dens; 2, 2', anterior and posterior articular 
processes; 3, posterior end of body; 4, transverse proc- 
ess; 5, foramen transversarium ; 6, arch; 7, spinous 
process. Arrow indicates intervertebral foramen. 




Fig. 170. — Axis op Pig; Anterior View. 
1, Dens; 2, 2', anterior and posterior articular 
processes; 3, foramen transversarium; 4, arch; o, spi- 
nous process. 



posterior border of the wing to the fossa under the latter, 
it is sometimes very small or absent. The 
sides of the vertebral foramen bear two lat- 
eral projections which partially divide it 
into a ventral narrow part, which receives 
the dens, and a dorsal larger part for the 
spinal cord. In the fresh state the division 
is completed by the transverse ligament, 
which is attached to the projections. 

The axis has a large spinous process, 
which is directed upward and backward. 
The dens is a thick cylindrical rod. The 
transverse process is very small and the 
foramen transversarium is often incom- 
plete. 

The thoracic vertebrae are commonly 
fourteen or fifteen in number. Their 
bodies are relatively long, constricted in 
the middle, and without ventral spines. 
Their extremities are elliptical, depressed 
in the middle, and prominent at the peri- 
phery. The arch is perforated by a fora- 
men on each side and in most of the series 
there is also a foramen in the posterior 
part of the root of the transverse process 
which communicates with the former or 
with the posterior intervertebral foramen. 
Sometimes there is a foramen in the an- 
terior part of the process also. There are 
mammillary processes except on the first 
two ; in the posterior five or six vertebrae 
they project from the anterior articular 
processes. The facet for the tubercle of the 
rib is absent or fused with that for the 
head in the last five or six. The last trans- 



(1 is not visi1)lc dorsally; 




Fig. 171. — Second and Third Thoracic Vertebr.e 
OF Pig; Lateral View. 
Numbers around bones: 1, 1', Anterior and poster- 
ior ends of bodies ; 2, cavities for heads of ribs ; 3, 3', artic- 
ular process; 4, facet for head of rib; 5, spinous process. 
Numbers on bones: 1, 1', Foramina of arches; 2, 2', 
transverse procesaes; 3, 3', facets for tubercles of ribs. 



Jg4 SKELETON OF THE PIG 

verse process is lumbar in character, plate-like, and about an inch (2 cm.) long. 
Small accessory processes occur in the posterior part of the region. The first 
spinous process is broad, very high, and inclined a little forward. The others di- 
minish very gradually in length to the tenth, beyond which they are about equal. 
The seconcl to the ninth are inclined backward, the tenth is vertical (anticlinal), and 
the rest incline forward. The width decreases decidedly from the fourth to the 
tenth, beyond which there is a gradual increase. The summits are slightly enlarged 
and lie almost in a straight line. 

The lumbar vertebrae are six or seven in number. The bodies are longer than 
in the thoracic region and bear a ventral crest. They become wider and flatter 
in the posterior part of the series. The arches are deeply notched, and are separated 
by an increasing space dorsally. The mammillary processes project outward and 
backward. The transverse processes are bent downward and incline a little for- 
ward. Their length increases to the fifth and is much diminished in the last. They 
form no articulation with each other or with the sacrum. The posterior edge of the 
root of the process is marked by a notch in the anterior part of the series, a fora- 




FiG. 172. — Fourth Lttmbar Vertebra of Pig; Anterior View. 
1, Body; 2, transverse process; 3, anterior articular process; 4, mammillary process; 5, posterior articular process; 

6, spinous process. 

men in the posterior part. The spines are broad and incline forward, with the ex- 
ception of the last, which is narrow and vertical. 

Lesbre states that six and seven lumbar vertebra? occur with almost equal frequency. The 
number may be reduced to five, and the number of presacral vertebra; varies from twenty-six to 
twenty-nine. 

The sacrum consists usually of four vertebrae, which fuse later and less com- 
pletely than in the other domesticated animals. It is less curved than in the ox. 
The spines are little developed and commonly in part absent. The middle of the 
dorsal surface is flattened and smooth, and presents openings into the sacral canal 
between adjacent arches (Spatia interarcualia) . On either side are the dorsal 
sacral foramina, and tubercles which indicate the fused articular processes. The 
wings resemble those of the ox. The anterior articular processes are very large. 
The pelvic surface resembles that of the ox, but is not so strongly curved, and the 
transverse lines are very distinct. 

The coccygeal vertebrae are specially characterized by the presence of func- 
tional articular processes on the first four or five, beyond which these processes 
become non-articular and smaller. The arches of the first five or six are complete. 
The transverse processes are broad and plate-like in the anterior part of the series 



THE RIBS 



165 



and diminish very gradually. Not rarely the first coccygeal vertebra unites with 
the sacrum. 

Vertebral Curves. — The cei-vical region is practically straight. The thoracic 
and lumbar regions form a gentle curve, concave ventrally, the highest point of 
which is at the junction of the two regions. The sacral promontory is not so pro- 
nounced as in the ox, and the sacral curve is flatter. 




Fig. 173. — Sacrum and First Coccygeal Vertebra op 
^Pig; Dorsal View. 
/-/]', Arches of sacral vertebrae; 1, 2, 3, dorsal sacral 
foramina; 4, similar foramen between sacrum and first 
coccygeal vertebra; A, body of first sacral vertebra; B, 
articular process; C, wing; D, auricular surface; E, articu- 
lar processes; F, first coccygeal vertebra. 



Fig. 174. — Sacrum and First Coccygeal Vertebra of 
Pig; Ventral View. 
7-7 F, Sacral vertebrae (bodies) ; 1, 2, 3, ventral sacral 
foramina; 4, similar foramen between sacrum and first 
coccygeal vertebra; A, body of first sacral vertebra; B, 
articular process; C, wing; D, auricular surface; E, first 
coccygeal vertebra. 



Length. — The regional lengths of the vertebral column of a large Berkshire sow were as fol- 
lows: Cervical, 24 cm.; thoracic, 53.5 cm.; lumbar, 31 cm.; sacral, 17 cm.; coccygeal, 35 cm. 

Variations. — The occurrence of fifteen thoracic vertebrse is quite common, and the existence 
of sixteen or even seventeen has been recorded. Reduction to thirteen is very rare. Six and 
seven lumbar vertebrse seem to occur with about equal frequency, and reduction to five is on rec- 
ord. The number of coccygeal vertebrae varies from twenty to twenty-six according to the records 
of several observers. Lesbre states that he has found twenty-three most frequently. 



THE RIBS 
The ribs number fourteen or fifteen pairs, of which seven are sternal and seven 
or eight asternal usually. They are in general strongly curved in the improved 
breeds, so that there is a fairly distinct angle, except toward the end of the series. 



166 



SKELETON OF THE PIG 



The backward slope of the posterior ribs is slight. The first rib is prismatic, has a 
large sternal end, and a very short cartilage. The width is greatest in the third 
to the sixth, and the length in the sixth and seventh usually. The tubercle fuses 
A\dth the head on the last five or six. The second 
3 to the fifth form diarthrodial joints mth their car- 

tilages, which are wide and plate-like. 

The fifteenth rib, when present, may be fully developed 
and its cartilage enter into the formation of the costal arch; 
but in most cases it is floating, and in some cases it is only 
about an inch (ca. 2-3 cm.) in length. 




THE STERNUM 
The sternum consists of six segments and re- 
sembles that of the ox in general form. The first 
segment (Manubrium) is long, flattened laterally^ 





Fig. 175. — Eighth Rib of Pig; Lat- 
eral View. 
1, Head; 2, neck; 3, tubercle; 4, ante- 
rior border; 5, sternal extremity. 



Fig. 176. — First Rib or Pig; Lateral View. 
neck; 3, tubercle; 4, anterior border; o, vascular impression; 
6, sternal extremity. 



and bears a blunt-pointed cartilage on its anterior end; its posterior end forms a 
diarthrodial joint with the body. The latter is flattened, wide in its middle, narrow 
at either end. The widest segments are formed of two lateral parts, w^hich are 
not completely fused in the adult. The last segment has a long, narrow part which 
bears the xiphoid cartilage. 

The thorax is long and is more barrel-shaped than in the horse or ox, since the 
ribs are more strongly curved and differ less in relative length. 



BONES OF THE SKULL 
Cranium 

The occipital bone has an extensive squamous part, which forms a very broad 
and prominent nuchal crest. The latter is concave, and is thick and rough above, 
where it forms the highest part of the skull; laterally it becomes thinner, turns 



BONES OF THE SKULL — CRANIUM 



167 



downward, and is continuous with the temporal crest. Two divergent ridges pass 
upward from the foramen magnum, and the surface between them is concave and 
smooth. The greater part of the cerebral surface of the squamous part is united 
with the parietal bones, but a ventral concave area faces into the cranial cavity. 
The foramen magnum is almost triangular, and is narrow above, where it is flanked 
by two small tuberosities. The paramastoid processes are extremely long and pro- 
ject almost straight ventrally. The hypoglossal foramen is at the medial side of 
the root of the process. The basilar part is short and wide; its ventral surface 




Fig. 177. — Skull of Pig; Lateral View. 
A, Occipital bone; B, squamous temporal bone; C, parietal bone; D, frontal bone; E, lacrimal bone; F, malar 
bone; G, maxilla; H, premaxilla; I, nasal bone; J, os rostri; A', mandible; 1, occipital condyle; 2, paramastoid proc- 
ess; 3, condyle of mantlible; 4, meatus acusticus externus; 5, temporal fossa; 6, parietal crest; 7, supraorbital process; 
8, orbital part of frontal bone; 9, fossa for origin of ventral oblique muscle of eyeball; 10, orbital opening of supraorbital 
canal; 11, lacrimal foramina; 12, supraorbital foramen and groove; 13, infraorbital foramen; 14, zygomatic process of 
temporal bone; 15, temporal, and 15', zygomatic, process of malar bone; 16, incisor teeth; 17, canine teeth; 18, 18', 
premolars; 19, 19', molars; 20, mental foramina; 21, mental prominence; 22, angle of mandible. 



bears a thin median ridge and two lateral imprints or tubercles which converge at 
the junction with the sphenoid bone. 

The interparietal bone fuses before birth with the occipital. The internal 
occipital protuberance is absent. 

The parietal bone is overlapped by the occipital bone behind and concurs in the 
formation of the nuchal crest. Its external surface is divided by the parietal crest 
into two parts. The medial part (Planum parietale) faces upward and forward, 
and is flattened and smooth. Its medial border is short and straight and unites 
early with the opposite bone. Its anterior border is concave and joins the frontal 



168 



SKELETON OF THE PIG 



bone. The lateral part (Planum temporale) faces outward and is more extensive; 
it is concave, forms a large part of the temporal fossa, and is overlapped ventrally 
by the squamous temporal. The parietal crest extends in a curve from the nuchal 
crest forward and outward to the supraorbital process. The cerebral surface is con- 
cave and is marked by digital impressions. The ventral border projects into the 
cranial cavity and forms a crest w^hich separates the cerebral and cerebellar compart- 



Squamous -part 
of occipital hone 



Occipital condyle 
Paramastoid process (tip) 




Basilar part of 
occipital bone 

Mastoid process 

Temporal condyle 



Maxillary recess 

Zygomatic proces. 
of malar hone 

Maxilla 



Molar teeth 



Premolar teeth 



Canine tooth 



Prcmaxilla 



Fig. 178. — Skull of Pig, Ventral View, without Mandible and Htoid. 
1, Hypoglossal foramen; 2, foramen lacerum anterius; 3, foramen lacerum posterius; 4, bulla ossea; 5, body of 
sphenoid; 6, pterygoid bone, and 6', hamulus of same; 7, vomer; 8, horizontal, and 8', perpendicular, part of palatine 
bone; 9, pterygoid process of palatine bone; 10, pterygoid process of sphenoid bone; 11, supraorbital process; 12, or- 
bital opening of supraorbital canal; 13, choanae or posterior nares; 14, 11', anterior palatine foramen and groove; 15, 
palatine fissure. 



ments laterally. The interior is excavated and forms part of the frontal sinus in 
the adult. There is no temporal canal. 

The frontal bone is long. The frontal surface slopes downward and forward, 
the inclination varying in different subjects. The anterior part is concave and is 
marked by the supraorbital foramen and the groove leading forward from the 
foramen to the nasal bone. The supraorbital canal opens into the orbit at the 



CRANIUM 169 

upper part of the medial wall of the latter. The supraorbital process is short and 
blunt-pointed, and is not connected with the zygomatic arch. The gap in the or- 
bital margin is closed by the orbital ligament in the fresh state. The orbital part 
is extensive and forms the greater part of the medial wall of the orbit. Its upper 
part is perforated by the orbital orifice of the supraorbital canal, in front of which 
is the distinct fovea trochlearis. The ethmoidal foramen is situated in the ventral 
part near the junction with the orbital wing of the sphenoid. The temporal part 
is very narrow and is separated from the orbital plate by a ridge which joins the 



Parietal bone 
Temporal fossa 

Squamous temporal 
bone 

External acoustic 
meatus 



Zygom.atic process 
of temporal bone 
Supraorbital pro- 
cess 
Frontal bone 

Supraorbital fora- 
men 
Zygomatic process 
of malar bone 
Lacrimal bone 



Infraorbital foramen 

Nasal process of premaxilla 

Nasal bone 

Canine tooth 

Palatine fissure 
Body of premaxilla 




Nuchal crest 
Temporal crest 
Parietal crest 



y,^ — ^ — Lacrimal foramen 
Preorbital fossa 



Fig. 179. — Skull of Pig; Dorsal View. 



pterygoid crest below. The interior of the bone is excavated by the frontal sinus in 
practically its entire extent in the adult. In the young subject the cavity is con- 
fined to the anterior part and the rest of the bone is thick. 

The temporal bone has a general resemblance to that of the ox. The zygo- 
matic process is short and stout and is bent at a right angle. The dorsal border of 
the process is thin; traced from before backward it curves sharply upward and 
forms a high prominence in front of the external acoustic meatus; beyond this 
it drops rather abruptly and is then continued upward to the nuchal crest. The 
anterior part of the ventral border joins the zygomatic process of the malar, which 



170 SKELETON OF THE PIG 

is deeply notched. The condyle is concave in the transverse direction. The post- 
glenoid process is absent, but the articular surface is bounded behind and medially 
by a crest. There is no temporal canal. The external acoustic meatus is very 
long and is directed dorso-laterally. The bulla ossea is large, compressed laterally, 
and bears a pointed muscular process in front. A narrow space intervenes between 
the bulla and the basilar part of the occipital bone, so that the foramen lacerum 
resembles that of the horse. The small hyoid process is situated in a deep de- 
pression in front of the root of the paramastoid process, and the stylo-mastoid 
foramen is lateral to it. The petrous part presents no important differential fea- 
tures. The squamous part (including the root of the zygomatic process) contains 
an air-cavity, which is continuous with the sphenoidal sinus. 

The sphenoid bone is short and resembles that of the ox in general. The body 
is narrow. The hypophyseal or pituitary fossa is very deep, and is limited behind 
by a prominent dorsum sellse; the dorsum bears lateral projections, the posterior 
clinoid processes (Processus clinoidei aborales). The foramen ovale is absent, 
being included in the foramen lacerum anterius. The other foramina are like those 
of the ox. The pterygoid process is broad and twisted. Its base is not perforated 
and its free edge is thin and sharp. It concurs with the pterygoid and palate bones 
in the formation of the pterygoid fossa (Fossa pterygoidea), which opens backward 
and is not present in the horse or ox. The sphenoidal sinus is very large and oc- 
cupies the body, the temporal wings, and a great part of the pterj^goid processes 
in the adult; it is continued into the temporal Ijone as mentioned above. 

The ethmoid bone has a relatively long perpendicular plate, which is marked 
by ridges corresponding to the ethmoidal meatuses. The cribriform plate is ex- 
tensive and very oblique, so that it and the crista galli are almost in line with the 
basi-cranial axis. A linear series of relatively large foramina is found on either 
side of the crista. The lateral mass consists of five endoturbinates and eighteen 
ectoturbinates (Paulli). The lamina lateralis concurs in the formation of the 
pterygo-palatine fossa. The lamina transversalis separates the fundus of the 
nasal cavity from the naso-pharyngeal meatus. 

Face 

The maxilla is extensive. Its facial surface forms a longitudinal groove, 
which is continued upon the premaxilla in front and the facial parts of the lacrimal 
and malar behind. The infraorbital foramen — sometimes double — is large a,nd 
is situated above the third or fourth cheek tooth. The alveolus for the canine 
tooth produces a ridge (Juga canina) at the anterior end which is very pronounced 
in the boar. The facial crest extends forward from the root of the zygomatic proc- 
ess and fades out behind the infraorbital foramen; in some specimens it is prom- 
inent and thin-edged, in others it is rounded and projects little. The zygomatic 
process is short but stout and buttress-like; it is overlapped laterally by the malar. 
The maxillary tuberosity forms in the young subject a long bulla, which occupies 
most of the pterygo-palatine fossa and contains the developing permanent molars; 
after the eruption of the teeth the tuberosity flattens and joins the vertical part of 
the palate bone. The palatine process is very long and is marked in its anterior 
part by transverse grooves (Sulci palatini transversi) corresponding with those of 
the mucous membrane of the palate. The anterior palatine foramen is near the 
junction with the palate bone; from it the palatine groove can be traced distinctly 
along the entire length of the process. The alveolar border presents a large alveolus 
for the canine tooth at its anterior end; behind this are seven alveoli for the cheek 
teeth, which increase in size from first to last. The maxillary foramen and infraor- 
bital canal are very large. The maxillary sinus is small. 

The body of the premaxilla is narrow and prismatic. It presents three alveoli 
for the incisor teeth, which are separated by short intervals and diminish in size 



FACE 171 

from before backward. As in the ox, a narrow space separates the right and left 
bones and takes the place of the foramen incisivum. The palatine process is long 
and narrow. The nasal process is very extensive and is somewhat rhomboid in 
outline. Its dorsal border forms a very long suture with the nasal bone, and the 
ventral articulates to about the same extent with the maxilla. The palatine fissure 
is relatively wide. 

The horizontal part of the palatine bone forms a fourth to a fifth of the length of 
the palate; its palatine surface is triangular, the apex being anterior; its nasal 
surface is deeply grooved and smooth. A pterygoid process (Processus pyramidalis 
of man) projects backward and downward, and its thick rounded end is received 
between the pterygoid process of the sphenoid and the pterygoid bone. The 
perpendicular part is largely overlapped laterally by the maxilla and concurs in 




Fig. 180. — Sagittal Section op Skull op Pig, without Mandible. 
A, A', Basilar and squamous parts of occipital bone; B, body, B', temporal wing, B", orbital wing, of sphenoid 
bone; C, parietal bone; D, D', internal and external plates of frontal bone; E, E', cribriform and perpendicular plates 
of ethmoid bone; F, pterygoid bone; G, G', perpendicular and horizontal parts of palatine bone; H. palatine process of 
maxilla; /, vomer; J, nasal bone; K, body of premaxilla; L, dorsal turbinate bone; M, ventral turbinate bone; 
I, II, III, fossse cranii; 1, hypoglossal foramen; 2, foramen lacerum posterius; 3, meatus acusticus internus; 4, fora- 
men lacerum anterius; 5, hypophyseal or pituitary fossa; 6, foramen orbito-rotundum; 7, lateral crest between cerebral 
and cerebellar parts of cranial cavity; 8, optic foramen; 9, ethmoidal foramen; 10, frontal sinus; 11, meatus naso- 
pharyngeus; 12, 13, 14, dorsal, middle, and ventral nasal meatuses; 15, incisor teeth; 16, canine tooth; 17, premolar 
teeth; 18, molar teeth; 19, paramastoid process; 20, bulla ossea. 



forming part of the palatine canal. The two plates separate dorsally and inclose 
an air-cavity which opens into an ethmoidal meatus. The inner plate curves 
inward and unites with the vomer and ethmoid to form a horizontal plate, the 
lamina transversalis, which divides the posterior part of the nasal cavity into a 
dorsal olfactory part and a ventral respiratory part. 

The pterygoid bone is nearly vertical in direction, and is narrow in its middle, 
wide at each end. The lateral surface is free below and forms the medial wall of 
the pterygoid fossa. The ventral end is notched and forms a distinct hamulus. 

The nasal bone is very long and its width is almost uniform, except at the 
anterior end, which is pointed and reaches almost as far forward as the premaxilla. 
The facial surface is flattened from side to side. In profile it is nearly straight in 
some subjects, variably concave in others. The lateral border is free to a small 
extent in front only; otherwise it is firmly connected with the premaxilla and 



172 



SKELETON OF THE PIG 



maxilla. In the adult the frontal sinus extends into the posterior part of 
the bone. 

The lacrimal bone is very sharply bent. Its facial surface presents a deep 
depression, surmounted by a ridge or tubercle. On or close to the orbital margin 
are two lacrimal foramina which lead to the lacrimal canals. The orbital surface 
presents a fossa in which the inferior oblique muscle of the eyeball arises, and its 
lower part bears a crest, which is crossed obliquely by a vascular furrow. The 
dorsal border articulates with the frontal only. The bone concurs in the formation 
of the maxillary sinus. 

The malar bone is strongly compressed from side to side. Its facial surface 

is small and presents a fossa which is con- 
tinuous with the depressions of the maxilla 
and lacrimal. The orbital surface is still 
smaller and is smooth and deeply grooved. 
The zygomatic process is very extensive, 
especially in the vertical direction. Its 
lateral surface is convex and free, and 
bears a rough eminence in its middle. Its 
medial surface is concave; it is over- 
lapped in front by the maxilla, and in the 
remainder of its extent is free and smooth. 
The dorsal border is thick and rounded in 
front, where it forms the lower part of the 
orbital margin; behind this it forms an 
extensive notch which receives the zygo- 
matic process of the temporal. (It might 
be regarded as dividing into frontal and 
temporal branches.) The ventral border 
is convex and becomes thinner behind. 

The turbinate bones resemble those 
of the ox. The dorsal turbinate is, how- 
ever, relatively longer, less fragile, and 
more firmly attached to the nasal bone. 
There is no middle turbinate. 

The vomer is very long. The anter- 
ior extremity reaches to the body of the 
premaxilla or very close to it. The ven- 
tral border is received into a groove 
formed by the nasal crest of the maxillge 
and palatine bones and in front by the 
palatine processes of the premaxillse. The 
posterior border is concave, thin, and 
sharp. 

The OS rostri (or prenasal bone) is 
situated in the snout between the nostrils. 
It has the form of a short, three-sided prism. The dorsal surface is convex and is 
notched at each end. The lateral surfaces are concave, smooth, and converge 
below, forming a grooved ventral border. The posterior surface is triangular, 
notched centrally, and rough laterally. The anterior surface is deeply pitted and 
is surrounded by an irregular sharp border. 

The mandible is very strong, and differs very much from that of the horse or 
ox. The body narrows decidedly in front; the lingual surface is deeply concave; 
the mental surface is strongly convex, slopes downward and backward, and forms 
a distinct prominence (Tuber mentale) at the point of divergence of the rami. 




Fig. 181. — MandibixE of Pig; Dorsal View. 

A, Body; B, B', horizontal and vertical parts of 
ramus; C, condyle; D, coronoid process; 1, 2, 3, in- 
cisor teeth; 4, canine tooth; 5, 6, 7, premolar teeth 
(first absent) ; 8, 9, 10, molar teeth. 



THE SKULL AS A WHOLE 173 

Above this prominence is a pair of foramina. The alveolar border presents six 
alveoli for the incisor teeth, and a little further back two large cavities for the 
canine teeth. There are two pairs of mental foramina of considerable size and a 
variable number of smaller ones. The rami diverge more than in the horse or ox, 
and the upper part is somewhat incurved. The horizontal part is very thick and 
strong. Its lateral surface is strongly convex from above downward. The medial 
surface is prominent over the roots of the molar teeth and overhangs the concave 
lower part. The alveolar border is thin in front and widens behind; it does not 
follow the axis of the ramus, but runs nearly straight and produces the marked over- 
hang noted above. There are seven alveoli for the lower cheek teeth, which in- 
crease in size from before backward. The first is small, not always present in the 
adult, and is separated by short spaces from the second and the canine alveolus. 
The vertical part is relatively wide above. The condyle is convex in both direc- 
tions, wide in front, narrow and declivitous behind. The very small and thin- 
edged coronoid process is not quite so high as the condyle, from which it is separated 
by a very wide notch. The mandibular foramen is large. The two halves of the 
bone unite soon after birth in the improved breeds. 

The body of the hyoid bone is broad from before backward, short transversely, 
and bears on its ventral aspect a very short pointed lingual process. The thyroid 
cornua are wide and curved, concave and grooved dorsally; their ends are attached 
to the thyroid cartilage of the larynx by rather long bars of cartilage. The small 
cornua are short, wide, and flattened dorso-ventrally ; they are attached to short 
bars which project from the junction of the body and thyroid cornua. The middle 
cornu is a little longer than the small cornu, but is relatively slender; it is largely 
cartilaginous in the young subject and does not ossify at either end. The great 
cornu is a very slender rod, slightly enlarged at either end; the dorsal extremity is 
attached to the hyoid process of the temporal by a rather long and wide bar of 
cartilage. 

THE SKULL AS A WHOLE 

The length and the profile vary greatly in different subjects. Primitively 
the skull is long — especially in its facial part — and the frontal profile is almost 
straight. The condition is very pronounced in wild or serai-feral pigs, and exists 
also — though in less degree — in the improved breeds during extreme youth. Most 
of the latter are decidedly brachycephalic when fully developed; the face is 
"dished" in a pronounced fashion. The frontal region slopes sharply upward, 
and the nasal region is shortened, and in some specimens even distinctly concave 
in profile. The supraorbital foramina are about midway between the orbital mar- 
gin and the frontal suture. The supraorbital grooves extend forward from the 
foramina to the nasal region and turn ventro-laterally toward the infraorbital 
foramina over the ridges which separate the nasal and lateral regions. 

The lateral surface is triangular when the mandible is included. The tem- 
poral fossa is entirely lateral and its long axis is almost vertical. It is bounded 
above by the nuchal crest, behind by the temporal crest, in front by the parietal 
crest, and is marked off from the orbital cavity by the supraorbital process and a 
curved crest which extends from it to the root of the pterygoid process. The 
zygomatic arch is strong, high, and flattened from side to side. Its root is notched 
dorsally and bears a projection ventrally. It curves sharply upward behind and 
forms a pointed recurved projection above and in front of the external acoustic 
meatus. The orbit is small. Its margin is deficient behind in the dry skull, thick 
and rounded in front and below. The cavity is limited below by a ridge on the 
frontal and lacrimal bones, and is separated by a crest from the temporal fossa. 
The medial wall is perforated above by the orbital opening of the supraorbital 
canal, and below by the optic and ethmoidal foramina; on its antero-inferior part 



174 



SKELETON OF THE PIG 



is the fossa in which the inferior oblique muscle of the eye takes origin. Two lac- 
rimal foramina are found on or close to the anterior margin. The pterygo-palatine 
fossa is well defined ; its upper part forms a deep groove which leads from the fora- 
men orbito-rotundum to the very large maxillary foramen. The preorbital region 
is deeply grooved in its length and is clearly marked off by a ridge from the nasal 
and frontal regions. The facial crest is short, usually thin-edged, and lies above the 
fifth and sixth cheek teeth. A little (ca. 2 cm.) in front of it is the infraorbital fora- 



Nuchal crest 




Fig. 182. — Skull of Pig; Posterior View. 
1, 2, 3, Squamous, lateral, and basilar parts of occipital bone; 4, foramen magnum; .5, occipital condyle; 6, para- 
mastoid process; 7, squamous temporal bone; 8, meatus acusticus externus; 9, temporal condyle; 10, zygomatic 
process of malar bone; 11, bulla ossea; 12, 12', perpendicular and horizontal parts of palatine hone; 13, 13', choanae or 
posterior nares; 14, vomer; 15, pterygoid process of sphenoid bone; 16, pterygoid process of palatine bone; 17, con- 
dyle of mandible; 18, mandibular foramen; 19, body of mandible. 



men. There is a ritlged prominence over the canine alveolus. In some skulls the 
anterior part of the upper jaw is inclined upward. 

The most striking features of the basal surface are as follows: The basioc- 
cipital is wide and flattened; it bears a median crest and two lateral tubercles. 
The paramastoid process is extremely long, less flattened than in the horse and ox, 
and nearly vertical. At the medial side of its root is the h3'poglossal foramen, 
and in front of it are the stylo-mastoid foramen and a deep cavity in which the 
hyoid process is concealed. The bulla ossea is long, compressed lateral!}', and bears 
a sharp, short, muscular process. The posterior nares are small and are wider be- 
low than above. On either side of them is the tuberosity of the palate bone, and 



THE SKULL AS A WHOLE 175 

above this is the pterygoid fossa. The palate constitutes about two-thirds of the 
entire length of the skull, and is relatively narrow. It is widest between the canines 
and premolars and narrow at each end. It is marked by a crest medially and by 
the palatine foramen and groove laterally. The anterior part bears transverse 
ridges. It is moderately arched from side to side. In some specimens it is nearly 
straight or slightly concave in its length; in others it curves upward to a variable 
degree in front. The posterior end always slopes upward more or less. 

The nuchal surface is remarkable for its height and the breadth of the nuchal 
crest. The central part above the foramen magnum is smooth and concave from 
side to side, and is bounded laterally by ridges, which converge ventrally and end 
on two tubercles at the upper margin of the foramen magnum. The surface is 
separated from the temporal fossse by the temporal crests, which curve downward 
and outward and blend with the external acoustic meatus. The mastoid process 
has the form of a plate which overlaps the root of the paramastoid process and bears 
a crest on its anterior part. 

The cranial cavity is small, in spite of the great size of the cranium; the 
discrepancy is due to the enormous development of the frontal sinuses in the adult. 
It is relatively longer, but much lower than that of the ox. Its width is greatly 
diminished between the orbits. The olfactory fossse are extensive and very ob- 
lique. The floor resembles that of the ox, but the foramen ovale is absent, the 
dorsum sellse is more developed, and the foramen lacerum is like that of the horse. 
Two oblique lateral crests clearly mark the limit between the cerebral and cerebellar 
compartments. The internal occipital protuberance and the temporal canal are 
absent. 

The nasal cavity is very long. Its posterior part is divided by the lamina 
transversalis into olfactory and respiratory parts. The olfactory' part or fundus is 
dorsal, and contains the ethmoturbinates and ethmoidal meatuses. The ventral 
part is continuous with the ventral meatus and leads to the pharyngeal orifice; 
hence it is called the naso-pharyngeal meatus. The bony roof is almost complete 
in front on account of the great length of the nasal bones. 

The frontal sinus is a vast excavation in the adult animal. It involves all of 
the roof and almost all of the sides of the cranium, and extends forward into the 
roof of the nasal cavity a variable distance — sometimes as far as a transverse plane 
through the infraorbital foramina. The septum between the right and left sinuses 
is usually deflected in an irregular manner in its middle part, but is practically 
median at either end. Each sinus is sul^divided by numerous septa, some of which 
are complete. Thus the sinus is divided into compartments, each of which com- 
municates with an ethmoidal meatus. 

In the young pig the sinus is small and is confined to the anterior part of the frontal bone. 
Later it extends backward, outward, and to a less extent forward. In the old subject it penetrates 
laterally into the supraorbital process and the root of the zygomatic process of the temporal bone, 
and behind almost down to the foramen magnum and the occipital condyles. It then consists 
of six to eight compartments usually. 

The maxillary sinus is relatively small. Its anterior end is a little less than 
an inch (ca. 2 cm.) behind the infraorbital foramen, and it extends upward into 
the lacrimal and backward into the malar bone. The infraorl^ital canal passes 
along its floor, and the roots of the molar teeth do not project up into it. It does 
not communicate with the frontal and sphenoidal sinuses, but with the posterior 
part of the middle meatus nasi by means of a considerable orifice. 

The sphenoidal smus is very large. It involves the body, pterygoid processes, 
and temporal wings of the sphenoid bone, and extends into the squamous temporal. 
It communicates with the ventral ethmoidal meatus. 

There is a small sinus in the perpendicular part of the palatine bone which 
communicates with an ethmoidal meatus. 



176 



SKELETON OF THE PIG 



BONES OF THE THORACIC LIMB 
The scapula is very wide, the index being about 1 : 0.7. The spine is tri- 
angular and is verj^ wide in its middle, which curves backward over the infra- 
spinous fossa and bears a large tuberosity. Its lower part bears a small projection 
(rudimentary acromion). The anterior border is strongly convex in profile, sinuous 
when viewed from the front, and thick and rough in its middle. The posterior 
border is wide, slightly concave, and bears a rough outer lip. The vertebral border 
is convex, and the cartilage is not so extensive as in the horse and ox. The anteri- 
or angle is thin and bent medially a little. The posterior angle is thick and is about 




Fig. 183. — Left Scapula of Pig; Lateral View. 
Anterior angle; 6, posterior angle; c, anterior border; d, posterior border; e, neck; /, glenoid cavity; g, tuber 
scapulae; 1, spine; 2, tuber spinas ; 3, acromion; 4, supraspinous fossa; 5, inf raspinou3 f ossa ; 6, cartilage. 



a right angle. The neck is well defined. The rim of the glenoid cavity is rounded 
and not notched. The tuber scapulae is just above the antero-medial part of 
the glenoid cavity and bears no distinct coracoid process; it unites with the rest of 
the bone at about one year. 

The humerus has an appearance in profile somewhat like an italic / minus the 
cross-bar; this is due to the marked backward and forward inclination of the prox- 
imal and distal ends respectively. The shaft is decidedly compressed from side to 
side. The medial surface is extensive and flattened; it is separated from the 
anterior surface by a distinct border, and bears no teres tubercle. The musculo- 
spiral groove is shallow. The deltoid tuberosity is small, and there is a larger 
rounded eminence midway between it and the lateral tuberosity. The nutrient 



BONES OF THE THORACIC LIMB 177 

foramen is on the posterior surface below its middle. The head is more strongly 
curved and the neck better marked than in the horse or ox. The lateral tuber- 
osity is very large and extends upon the front of the extremity. It is divitled into 
two high prominences by a wide deep groove. There is a third eminence below 
and laterally for the attachment of the supraspinatus muscle. The intertuberal or 
bicipital groove is at the front of the medial side; it is undivided and is almost con- 
verted into a canal. The lateral groove on the distal articular surface is so shallow 
as to give the appearance of two condyles of similar size. The olecranon fossa is 
very deep, and the plate of bone which separates it from the coronoid fossa is thin 
and sometimes perforated. The proximal end unites with the shaft at three and a 
half years, the distal at one year. 




£7 

Fig. 184. — Left Scapula of Pig; Medial View. 

a. Anterior angle; h, posterior angle; c, anterior border; d, posterior border ; e, neck; /, vascular groove; g, glenoid 

cavity; /i, tuber scapulae; 1, subscapular fossa; 2, serratus area; 3, cartilage. 

The radius is short and narrow, but thick. The shaft increases in size distally. 
The greater part of the volar surface is in apposition with the ulna; this part is 
marked by a vascular furrow which runs distally from the proximal interosseous 
space, and has the nutrient foramen at its proximal end. The radial tuberosity is 
represented by a rough area. The distal end is relatively large. Its carpal sur- 
face consists of concavo-convex facets for the radial and intermediate carpal bones. 
There is a wide shallow groove on the middle of the front. The proximal end fuses 
with the shaft at one year, the distal at three and a half years. 

The ulna is massive. It is much longer and considerably heavier than the 

radius. The shaft is curved. The dorsal surface is convex and most of it is rough 

and attached to the radius by the interosseous ligament. There is a smooth area 

on the upper third, which concurs with the radius in forming the proximal inter- 

12 



178 



SKELETON OF THE PIG 



Deltoid 
tuberosity 




Lateral 
tuberosity 



Medial 
condyle 

Lateral 
condyle 



Head 



Lateral 
epicondyle 



Nutrient 
foramen 

Lateral con- 
dyloid crest 

Olecranon 
fossa 

Medial epi- 
condyle 



Intertuberal 

Lateral 

tuberosity 
Head 




Medial 
condyle 



Fia. 185. — Left Humerus of Pig; Lateral View. 



Medial Lateral 
epicondyle condyle 
Fig. 186. — Left Humerus of Pig; Medial Vi 




Olecranon 



-r Olecranon 
I 



Shaft of -I \ '^: 1 ^V/«/^ of ulna 

radiuH 



Carpal surface 
of radius 
-Left Radius and Ulna of Pig; Lateral 
View. 




Distal end 
of radius 
-Left Radius and Ulna of Pig; Medial 
View. 



BONES OF THE THORACIC LIMB 



179 



osseous space, and is marked in its upper part by the nutrient foramen. From this 
space a vascular furrow descends to the distal part of the shaft, where there is often 
a distal interosseous space for the passage of vessels. The medial surface is exten- 
sive, concave, and smooth. The lateral surface is slightly convex, and its proximal 
part is marked by an oblique rough line or ridge. The proximal extremity is 
large and is bent medially somewhat; its length is more than one-third of that of 
the entire bone. The distal extremity is relatively small; it articulates with the 
ulnar and accessory carpal bones, and is notched in front to accommodate the ridge 




Fig. 189. — Skeleton of Distal Part of Left Thor- 
acic Limb of Pig; Dorsal View. 
R, Distal end of radius; U, distal end (styloid proc- 
ess) of ulna; C. r., radial carpal; C. i., intermediate 
carpal; C. u., ulnar carpal; C. 2, C. 3, C. 4, second, 
third, and fourth carpal bones; Mc. 2-5, metacarpal 
bones; Ph.l, Ph. 2, Ph. 3, first, second, and third pha- 
langes. 




Fig. 190. — Skeleton of Distal Part of Left 
Thoracic Limb of Pig; Volar View. 
R, Distal end of radius; U, distal end (styloid proc- 
ess) of ulna; C. r., C. i., C.u., C. a., radial, intermedi- 
ate, ulnar, and accessory carpal bones; C. 1-4, first to 
fourth carpal bones; Mc. 2-5, metacarpal bones; Ph. 1, 
Ph. 2, Ph. 3, first, second, and third phalanges; S, prox- 
imal, and <S', distal sesamoid bones. 



on the radius. The bone contains a considerable medullary canal, and is con- 
solidated at three to three and a half years. 

The carpus comprises eight bones, four in each row. The bones of the prox- 
imal row resemble those of the ox, with the exception of the accessory, which is more 
like that of the horse, but has no lateral groove. The first carpal is small, elon- 
gated from before backward, rounded, and articulates in front with the second carpal. 
The latter is high and narrow, and articulates with the second and third metacarpal 
bones distally. The third carpal articulates with the radial and intermediate 
above, the third metacarpal bone below. The fourth is the largest bone of the row; 
it articulates with the intermediate and ulnar above, the fourth and fifth meta- 
carpals below, and bears a tuberosity on its volar aspect. 



180 



SKELETON OF THE PIG 



Four metacarpal bones are present. The first is absent, the third and fourth 
are large and carry the chief chgits, while the second and fifth are much smaller and 
bear the accessory digits. Their proximal ends articulate with each other and with 
the carpus as indicated above. The distal ends fuse with the shafts at about two 
years of age. 

The third and fourth metacarpals are flattened from before backward, three-sided, and 
placed close together. The distal end of each bears a trochlea for articulation with the first 
phalanx and the sesamoids. The third is the wider of the two, and articulates with all of the distal 
row of the carpus except the first. The fourth articulates with the fourth carpal chiefly, but has a 
small facet for the third. The second and fifth metacarpals are placed further back than the chief 
bones. The fifth is considerably the thicker of the two. The proximal ends are small and articu- 
late with the corresponding carpal and metacarpal bones. The distal end is relatively large; its 
articular surface is condyloid in front, trochlear behind. 

Each chief digit comprises three phalanges and three sesamoids. The bones 
of the chief digits resemble those of the ox in form, but there is no foramen on the 
interdigital side of the extensor process and the proximal sesamoids are narrow and 
ridged behind. The phalanges of the accessory digits (which do not reach the 
ground ordinarily) are similar in form but much smaller. Fusion of the proximal 
ends with the shafts takes place at about two years for the fir.st phalanges, at about 
one year for the second phalanges. 



Crest of ilium Gluteal line 

V / ... ^ 

\ ^ 5*p^- Tuber sacrale 




Ischiatic Lesser sciatic Tuber 

sjiinv notch ischii 



Tuber coxcr 




i? 



Ilium (shaft) 

Acetabulum Ischium 

Fig. 191. — Left Os Cox.e of Pig; Lateral View. 



Tuber sarmh 



( 'n st of ilium 



Lesser 
Tuber sciatic Ischiatic 

ischii notch spine 




Tuber coxce 



\ Ilio-pectineal 
eminence 
Pubis (acstah- 
ular branch) 
Fig. 192. — Left Os Cox.e of Pig; Medial View. 



BONES OF THE PELVIC LIMB 
The OS coxae is long and narrow. The ilium and ischium are almost in line 
with each other and nearly sagittal in direction. The wing of the ilium bends out- 
ward much less than in the horse or ox. The gluteal surface is divided into two fossa? 



BONES OF THE PELVIC LIMB 



181 



by a ridge, which is continuous with the superior ischiatic spine behind. The 
pelvic surface presents an extensive rough area behind, which is in apposition with 
the wing of the sacrum. The smooth iliac area is narrow, and is bounded above 
by a ridge. The crest is convex, and is thick, rough, and prominent in its middle, 
which forms the highest point of the bone. The tuber sacrale is lower than the 
crest, is directed backward, and articulates internally with the sacrum. The tuber 
coxffi is lower still and is very little thickened. The ischia in the female are some- 
what divergent and flattened behind. The tubera are everted and bear three prom- 
inences. There is a crest or tuberosity on the ventral surface. The superior 
ischiatic spine is like that of the cow, but is slightly incurved and the muscular 



Trochant'T 

major //< nd 



Trochan- 
taric Trochanter 

Head fossa / major 





Lateral Trochlea Medial 



condyle condyle 

Fig. 193. — Right Femur of Pig; Anterior View. 



hd r- \ 

Medial condyL- condyloid Lateral condyle 
fossa 

Fig. 194. — Right Femur of Pig; Posterior View. 



ridges on its lateral face are more pronounced. The symphyseal part of the pubis 
is thick and the two bones are almost in a horizontal plane. The ilio-pectineal 
eminence is prominent and the psoas tubercle is well marked. 

The acetabulum is placed a little further back than in the ox. The rim is 
thick and is cut into posteriorly by a narrow fissure, which leads into the deep fossa 
acetabuli. The three pieces of the os coxse are fused by the end of the first year, 
but the crest and the tuber ischii are partially separate till the sixth or seventh year. 
The symphysis does not usually undergo complete ankylosis. Interischial bones 
are present. 

The inlet of the pelvis is elliptical and very oblique. In a sow of full size the 
conjugate diameter measures five to six inches (12.5-15 cm.), and the transverse 



182 



SKELETON OF THE PIG 



about three and a half to four inches (ca. 8.75 to 10 cm.). In the female the tloor 
is relatively wide and flattened, especially at the outlet, where the tubera are 
everted; it also has a decided ventral inclination behind. The pelvic axis is there- 
fore correspondingly oblique. The ischial arch is wide. In the boar the pubis is 
much thicker and the ischia are not everted posteriorly. The inlet is smaller; the 
conjugate diameter is about four and a half to five inches (ca. 11-12.5 cm.), and the 
transverse three to three and a half inches (ca. 7.5-8.75 cm.). The floor is concave 
from side to side and slopes decidedly less than in the sow. The superior ischiatic 
spines are more incurved, and the ischial arch is much narrower and deeper. 

The femur has a relatively wide and massive shaft, on which four surfaces 
might be recognized. The principal nutrient foramen is situated in the proximal 



Spine of tibia Tuberositi/ 

Lateral condyle Js./.-.^ Medial 

'condyle 

Head of 
fibula 



Crest of tibia 




Medial condyle Spine of tibia 

I ateral condyle 



Groove for 
tendons 

Lateral 
malleolus 



Fig. 195. — Right Tibia and Fibula of Pig; Ante- 
rior View. 
Arrow indicates muscular notch of proximal end of 
tibia. 




Distal end of tibia 



Fig. 196. — Right Tibia and Fibula of Pig; Pos- 
terior View. 
o, Groove on medial malleolus for tendon of flexor dig- 
italis longus. 



third of the anterior surface. The posterior surface is wide, and is limited laterally 
by a ridge which extends from the trochanter major to the large lateral supra- 
condyloid crest. There is no supracondyloid fossa. The head is strongly curved, 
and is marked toward the medial side by a rather large fovea for the attachment of 
the round ligament. The neck is distinct. The trochanter major, although massive, 
does not extend above the level of the head. The trochanteric ridge and fossa re- 
semble those of the ox. The third trochanter is absent. The ridges of the trochlea 
are similar and almost sagittal. The extremities unite with the shaft at about 
three and a half years. 

The shaft of the tibia is slightly curved, convex medially. The tuberosity 
is grooved in front, and a narrow sulcus separates it from the lateral condyle. 
The facet for the fibula is on the posterior border of the latter, and is bounded 



BONES OF THE PELVIC LIMB 



183 



medially by an eminence. The proximal part of the crest is very prominent and 
curves outward. The distal end resembles in general that of the ox, but is rela- 
tively narrower transversely and thicker from before backward. The proximal 
end unites with the shaft at about three and a half years, the distal at about two 
years. 

The fibula extends the entire length of the region, and is separated from the 
tibia by a wide interosseous space. The shaft is flattened from side to side; the 
proximal part is wide and deeply grooved laterally; the distal part is narrower 



Tuber calcis 




Tuber calcis 



T. t 



T,c. 



ML 2 



ML 5 




Fig. 197. — Skeleton op Right Pes of Pig; Dorsal 
View. 
T. t., Tibial tarsal; T. /., fibular tarsal; T. c, cen- 
tral tarsal; T. 3, third tarsal; T. 4, fourth tarsal; Mt. 
2-5, metatarsal bones; Ph. 1, Ph. 2, Ph. S, first, second, 
and third phalanges. 



Fig. 198. — Skeleton of Right Pes of Pig; Plantar 
View. 
T.t., Tibial tarsal; T. /., fibular tarsal; T.c, cen- 
tral tarsal; T.l, T.4, first and fourth tarsal bones; 
Mt. 2-5, metatarsal bones; Ph. 1, Ph. 2, Ph. 3, first, sec- 
ond, and third phalanges; .S, proximal sesamoid bones; 
distal sesamoids shown but not marked; a, tarsal 
sesamoid bone. 



and thicker. The proximal end is flattened, grooved laterally, and articulates 
medially with the lateral condyle of the tibia. The distal end forms the lateral 
malleolus. It is grooved laterally, and articulates with the tibia and tibial tarsal 
medially, with the fibular tarsal bone distally. The proximal end unites with the 
shaft at about three and a half years, the distal at about two and a half years. 

The patella is very much compressed transversely and presents three surfaces. 

The tarsus comprises seven bones. The tibial and the fibular tarsals resemble 
in general those of the ox. The axis of the tibial is, however, slightly oblique (ven- 
tro-medial), and its distal end bears a double trochlea for articulation with the cen- 



184 SKELETON OF THE DOG 

tral and fourth tarsals. The tuber calcis is deeply grooved posteriorly. The 
central tarsal is narrow transversely and thick. Its proximal surface is deeply 
concave, and the plantar bears a large tubercle. The first tarsal is high and 
narrow; it articulates with the central and second tarsals and the second metatarsal 
bone. The second tarsal is small and somewhat prismatic; it articulates with 
the central above, the third in front, the first behind, and the second and third 
metatarsals below. The third tarsal is much larger, and is compressed from above 
downward, wide in front, narrow behind. It articulates with the central tarsal 
above, the third metatarsal below, the second tarsal medially, and the fourth tarsal 
laterally. The fourth tarsal is large. Its lateral face is crossed by an oblique 
groove for the tendon of the peroneus longus. The medial surface articulates 
with the central and third tarsals. The proximal surface supports the tibial and 
fibular tarsal bones, and the distal surface rests on the fourth and fifth metatarsals. 
It ossifies from two centers. The summit of the tuber calcis fuses with the rest 
of the bone at two to two and a half years. 

The four metatarsal bones resemble the corresponding bones of the fore limb, 
but are somewhat longer. The proximal ends of the third and fourth each have a 
considerable plantar projection; the process on the third has a facet for articulation 
with a discoid sesamoid bone. The second and fifth are placed more toward the 
plantar aspect of the large bones than is the case in the fore limb. 

The first and second phalanges are a little longer and narrower than those of 
the fore limb. 



SKELETON OF THE DOG 

VERTEBRAL COLUMN 

The vertebral formula is CTTisLrSsCy^o-os- 

The cervical vertebrae are relatively longer than in the ox and the pig. The 
bodies of the typical vertebrae diminish in length from first to last and are com- 
pressed dorso-ventrally. The anterior extremity is moderately convex and the 
posterior slightly concave; both are oblique. The median ridge and lateral grooves 
on the dorsal surface of the body are very well marked. The second, third, and 
fourth have distinct ventral spines. The spinous process of the third has the 
form of a long low crest; in the remainder it is higher, blunt-pointed, and inclined 
forward. The transverse processes of the third, fourth, and fifth project ventrally 
and backward, and divide into two branches; of these, the anterior one is thin, 
and the posterior is thick and tuberculate at its free end. The process of the 
sixth has two parts; one of these is an extensive quadrilateral plate which is di- 
rected ventro-laterally and is ridged on its medial surface; the other part is short and 
blunt, and is directed outward and a little backward and upward. The seventh is 
readily distinguished by its shortness, the length of its spine, and the single trans- 
verse process. The posterior articular processes bear tubercles which are large on 
the third, fourth, and fifth. 

The ventral arch of the atlas is narrow from before backward, and bears a 
small tubercle posteriorly. The dorsal surface of the' dorsal arch is strongly convex 
and rough centrally. The wings are wide, flattened, and almost horizontal. The 
dorsal surface is rough. There is an alar notch (Incisura alaris) on the anterior 
border instead of the alar foramen. The foramen transversarium is present. 

The body of the axis is flattened dorso-ventrally, especially in front. The 
dens is rounded and relatively long, reaching almost to the occipital bone; it is 
inclined upward a little. The articular surfaces which flank it are condyloid in 
form and very oblique. The ventral surface is wide, and is divided by a median 



VERTEBRAL COLUMN 



185 




*■ I 



Fig. 199. — Skeleton or Dog; Lateral View. 
a. Cranium; 6, face; c, mandible; 1H-7H, cervical vertebrse; 13B, last thoracic vertebra; 1L-7L, lumbar verte- 
bra; K, sacrum; S, coccygeal vertebrae; 1R-13R, ribs; R.kn., costal cartilages; St., sternum; d, scapula; d' , supia- 
spinous fossa; d", infraspinous fossa; i, spine of scapula; ^.acromion; 3, tuberosity of scapula; S', articular end of 
scapula; e, humerus; 4, head of humerus; o, lateral tuberosity of humerus; 5', deltoid ridge; 6, 6', epicondyles of 
humerus; 7, lateral condyloid crest ; 7', coronoid fossa; /.radius; ff, ulna; S, olecranon; 5, "beak" of ulna; /», carpus; 
i, metacarpus; k, proximal phalanges; I, middle phalanges; m, distal phalanges; n, sesamoid; p, iUum; 10, wing of 
ilium; ii, shaft of ilium; i^, crest of ilium; i5, tuber coxse; i^i tuber sacrale; i5, superior ischiatic spine; g, pubis; 
r, ischium; iff, tuber ischii; 7 7, acetabulum; s, femur; i 5, head of femur; iS, trochanter major; ^0, trochanter minor; 
^i, trochanter tertius; ^^, ^S, condyles; ^4, ;g5, epicondyles; ^ff, trochlea; /.patella; m, tibia; ^7, tuberosity of tibia; 
;25, ^5, condyles of tibia; SO, medial malleolus; u, fibula; S/, lateral malleolus; S^, head of fibula; w), tarsus; x, meta- 
tarsus; y, phalanges; 33, occipital bone; 34, paramastoid process; 35, parietal bone; 36, frontal bone; 37, lacrimal 
bone; SS, malar bone ; SS, squamous temporal; ^0, maxilla; 4"', infraorbital foramen; 4?. premaxilla; 4^, nasal bone: 
43, external acoustic meatus; 44 ■ canine tooth; 45, masseteric fossa; 4^i angular process of mandible. (After Ellra- 
berger, in Leisering's Atlas.) 





Fig. 200. — Third Cervical Vertebra of Dog; Left 
Lateral View. 
.t, S, Anterior and posterior ends of body; 3, 3, 
articular processes; 4, spinous process; 5, 6, transverse 
process; 7, foramen transversarium. 



Fig. 201. — Fourth Cervical Vertebra of Dog; 
Left Lateral View. 
1, 1', Anterior and posterior ends of body; 2, 2', 
articular processes; 3, transverse process; 4, spinous' 
process. 



186 



SKELETON OF THE DOG 



crest into two fossae. The transverse processes are single, pointed, directed back- 
ward and outward, and perforated by relatively large foramina transversaria. The 

spinous process is thin and of moderate 
height, but very long; it is prolonged for- 
ward so as to overhang the dorsal arch of 
the atlas, and is terminated behind by a 
tuberosity which is connected by two 
crests with the posterior articular proc- 
esses. The anterior notches are large 
and are never converted into foramina. 





Fig. 202. — Seventh Cervical Vertebra of Dog; 
Posterior View. 
1, Body; 2, costal facet; 3, transverse process; 
4, notch; 5, 5', articular processes; 6, spinous process. 



Fig. 203. — Atlas of Dog; Dorsal View. 
1, Dorsal arch; 2, 2, posterior articular cavities; 3, 
ventral tubercle; 4, 4' intervertebral foramina; 5, 5', wings; 
6, 6', alar notches; 7, 7', foramina transversaria. 



The bodies of the thirteen thoracic vertebrae are wide and compressed dorso- 
ventrally, especially at each end of the region. Their con- 
vex anterior surfaces are depressed in the middle. The 
posterior facets for the heads of the ribs are absent on the 
last three or four. The transverse processes resemble those 
of the horse. They bear mammillary processes except at 
the anterior end of the region. The facets for the tubercles 
of the ribs are large and concave in the anterior part of the 
series, and become smaller and slightly convex further back. 




Fig. 204. — Axis or Dog; Left Lateral View. 
1, Dens; 2, anterior articular process; 3, posterior end of body; 4, arch; 5, pos- 
terior notch; 6, transverse process; 7, intervertebral foramen; 8, posterior articular 
process; 9, spinous process. 







Fig. 205. — Fourth Thoracic 
Vertebra of Dog; Left 
View. 

1, Body; 2, 2', costal facets 
of body; 3, posterior notch; 
4, 4', articular processes; 5, 
transverse process; 6, facet for 
tubercle of rib; 7, mammillary 
process; 8, spinous process. 



VERTEBRAL COLUMN 187 

The last three have accessory processes also. The first three or four spinous proc- 
esses are about equal in length. Behind this they become gradually shorter to the 
tenth, and then remain equal. The backward slope is most marked in the ninth 
and tenth. The eleventh is practically vertical (anticlinal vertebra), and the last 
two incline slightly forward. 

The bodies of the seven lumbar vertebrae are decidedly flattened dorso-ventrally, 
and increase in width from first to last. The length increases to the sixth. The 
transverse processes are plate-like and are directed forward and downward. Their 
length increases to the fifth and sixth. They form no joints with each other or 
with the sacrum. Their extremities are enlarged, with the exception of the last. 
The accessory processes project backward over the posterior notches of the first 
five. The anterior articular processes are large, compressed laterally, and bear 
mammillary processes. The spinous processes are broad below, narrower above, 
and with the exception of the last, incline a little forward. Their height diminishes 
behind the fourth. 

The sacrum results from the early fusion of three vertebrae. It is short, 





Fig. 206. — Fifth Lumbar Vertebra op Dog; Dorsal View. Fig. 207. — Sacrum of Dog; Ventral View. 

1, Anterior end of body; 2, spinous process; 3, 3', artic- I, II, III, Bodies of vertebrse; 1, 2, ventral sac- 

ular processes; 4, transverse process; 5, accessory process; ral foramina; 3, 4, lineae transversae; 5, anterior end 
6, groove for spinal nerve. of body of first sacral vertebra; 6, 6', anterior artic- 

ular processes; 7, 7', wings; 8, posterior end of body 
of last sacral vertebra; 9, 9', posterior articular proc- 
esses; 10, sacral canal; 11, spinous ^'process; 12, 
12', transverse processes; 13, auricular surface. 

wide, and quadrangular. The spines are fused to form a median crest, which is 
notched, however, between the summits of the spines. On either side are two 
tubercles, vestiges of the fused articular processes. The pelvic surface is deeply 
concave and presents two pairs of foramina. The wings are prismatic and very 
high. Their lateral surfaces are extensive, face almost directly outward, and bear 
an auricular surface on the lower part. The anterior surface of the body of the 
first vertebra is extensive, depressed in its middle, and bears a prominent lip below. 
The anterior articular processes are large and have extensive, slightly concave 
facets which face dorso-medially. The posterior articular processes are small. 
The transverse processes of the last vertebra project backward and may articulate 
or fuse with those of the first coccygeal. The sacral canal is strongly compressed 
dorso-ventrally. 

The coccygeal vertebrae are fully developed in the anterior part of the region. 
The arch is complete in the first six usually. The first three or four have well de- 
veloped articular processes at each end. Behind this the posterior processes 
quickly disappear, and the anterior ones become non-articular and gradually re- 



188 SKELETON OF THE DOG 

duced in size. The transverse processes of the first five or six are relatively large; 
behind this they quickly disappear. Hemal arches (or chevron bones) in the form 
of a V or Y occur ventrall}^ at the intercentral junctions of the third, fourth, and 
fifth usualh^ They transmit the middle coccygeal artery, which passes between 
pairs of ventral tubercles further back. 

Curves. — A gentle curve, convex ventrally, is formed by the cervical and the 
anterior part of the thoracic region. The posterior thoracic and the lumbar 
vertebrae form a second curve, concave ventrally. The sacral promontory is well 
marked. The sacrum and the anterior part of the coccygeal region constitute 
a third and more pronounced curve, concave ventrally. In long-tailed dogs the 
sacro-coccygeal region is somewhat S-shaped. 

Variations. — Numerical variations are not common except in the coccygeal region. Tlie 
number of thoracic vertebrae may be twelve or fourteen, with or without compensatory change in 
the lumbar region. Girard recorded a case with eight lumbar and the usual number of thoracic 
vertebrae. Six lumbar with foiu-teen thoracic vertebrae have been met with. The first coccygeal 
sometimes unites with the sacrum. 

THE RIBS 

Thirteen pairs of ribs are present, of which nine are sternal and four asternal. 
They are strongly curved, narrow, and thick. Those in the middle of the series 
are the longest. The first eight or nine increase in width in their lower part. I'he 
last rib is usually floating. The costal cartilages are long and curve ventrally and 
forward; the length and curvature of the first pair are striking special features. 



THE STERNUM 

This is long, laterally compressed, and consists of eight sternebrae, which fuse 
only in exceptional cases and in extreme old age. The first segment is the longest-; 
its anterior end is blunt-pointed and bears a short conical cartilage. It widens 
at the point of articulation of the first pair of cartilages. The last segment is 
also long, thinner than its predecessors, wide in front, and narrow behind, where it 
bears a narrow xiphoid cartilage. 

The thorax is distinctly barrel-like and is not decidedly compressed anteriorly 
like that of the horse and ox. The inlet is oval and is relatively wide on account 
of the marked curvature of the first pair of ribs and cartilages. 



BONES OF THE SKULL i 

Cranium 
The occipital bone is similar in position to that of the horse. The nuchal crest 
is prominent, angular, and directed backward. Just below the crest are two rough 
imprints or tubercles for muscular attachment. The surface below these is convex 
from side to side and concave dorso-ventrally. On each side, at the junction 
with the squamous temporal, is the mastoid foramen which opens into the cranial 
cavity. The condyles are somewhat flattened and are widely separated above; 
at the medial side of each is a short condyloid canal, which opens into the temporal 
canal. The paramastoid processes are very short. The basilar part is wide and 
joins the bulla ossea on either side; its ventral surface is flattened and the tubercles 
are at the junction with the bulla. The hypoglossal foramen is small and is close 
to the foramen lacerum posterius ; the latter is bounded in front by the bulla ossea, 
behind and medially by the occipital bone. 

^In the following descriptions of the separate bones an intermediate type — e. g., a fox terrier, 
— is selected, and the most striking differences in the brachycephalic and dolichocephalic breeds 
will be considered in the section on the skull as a whole. 



BONES OF THE SKULL — CRANIUM 



189 



The interparietal bone fuses with the occipital before birth. It bears the high 
posterior part of the parietal crest, and is wedged in between the two parietal bones. 
It forms the central part of the tentorium osseum, which is thin and curved, con- 
cave ventrally. Its base concurs with the occipital and parietal bones in the for- 
mation of a transverse canal which is continuous with the temporal canals. 

The parietal bone is rhomboid in outline and is strongly curved. It is exten- 
sive and forms the greater part of the roof of the cranial cavity. At the junction 
of the right and left bones there is a prominent parietal crest which is continued 
upon the frontal bones. The ventral border articulates with the temporal wing 
of the sphenoid by its anterior part and with the squamous temporal in the remain- 
der of its extent. The external surface enters into the formation of the temporal 

r 








-V*^ 



-14 



Fig. 208. — Sktjll of Dog; Lateral View. 
A, Occipital bone; 5, parietal bone; C, squamous temporal bone; D, frontal bone; E, lacrimal bone; F, malar 
bone; G, perpendicular part of palatine bone; H, maxilla; /, premaxilla; J , nasal bone; K, mandible; 1, parietal 
crest; 2, occipital condyle; 3, paramastoid process; 4, stylo-mastoid foramen; 5, bulla ossea; 6, meatus acusticus 
externus; 7, external opening of temporal canal; 8, postglenoid process; 9, zygomatic process of temporal bone; 10, 
zygomatic process of malar bone; 11, supraorbital process; 12, entrance to lacrimal canal; 13, infraorbital foramen; 
14, mental foramina; 1.5, condyle of mandible; 16, coronoid process; 17, mandibular notch; 18, angular process; 19, 
masseteric fossa; i. i', incisor teeth c, c', canine teeth. 



fossa. The cerebral surface is marked by digital impressions, and by grooves for 
the middle meningeal artery and its branches. 

The external surface of the frontal bone is crossed by a frontal crest, which 
extends in a curve from the parietal crest to the supraorbital process, and separates 
the frontal and temporal parts. The frontal parts of the two bones form a central 
depression and slope downward and forward. The supraorbital process is very 
short, so that the supraorbital margin is incomplete as in the pig. The supraor- 
bital foramen is absent. In front there is a narrow pointed nasal part which fits 
in between the nasal bone and the maxilla. The orbital and temporal parts are 
relatively extensive. Two ethmoidal foramina are commonly present. The 
frontal sinus is confined to the frontal bone. 

The parts of the temporal bone fuse early. The zygomatic process curves 
widely outward and forward. Its anterior part is beveled ventrally and articulates 



190 



SKELETON OF THE DOG 



extensively with the corresponding process of the malar. The articular surface 
for the condyle of the mandible consists of a transverse groove which is continued 
upon the front of the large postglenoid process. Behind the latter is the lower 
opening of the temporal canal. There is no condyle. The mastoid part is small, 
but bears a distinct mastoid process. The external acoustic meatus is wide and 
verj^ short, so that one can see into the tympanum in the dry skull. The bulla ossea 
is very large and is rounded and smooth; its medial side is united to the basilar 
part of the occipital bone. Above this junction and roofed in by the union of the 
petrous part and the basioccipital is the petro-basilar canal (Canalis petrobasilaris) ; 
this transmits a vein from the floor of the cranium to the foramen lacerum posterius. 
The latter opens into a narrow depression behind the bulla ossea. It transmits the 



Interparietal bone 



Parietal crest 



Zygomatic process of 

temporal hone 

Coronoid process 

Frontal crest 
Supraorbital process 



Zygomatic process of 

malar bone 

Lacrimal bone 



Infraorbital foramen 

Nasal process of premaxilla 
Canine tooth 
Incisor teeth 




Parietal bone 
Squamous temporal bone 
Frontal bone 



Body of premaxilla 



Fig. 209. — Skull of Doa; Dorsal View. 



ninth, tenth, and eleventh cranial nerves. The carotid canal branches off from 
the petro-basilar, passes forward lateral to it through the medial part of the bulla 
ossea, and opens in front at the carotid foramen; it transmits the internal carotid 
artery. The Eustachian opening is immediately lateral to the carotid foramen. 
The muscular and hyoid processes are extremely rudimentary. The petrous part 
projects into the cranial cavity and forms a sharp prominent petrosal crest. The 
medial surface presents a deep floccular fossa above the internal acoustic meatus. 
The anterior surface is also free. The anterior angle is perforated by a canal for 
the fifth cranial nerve (Canalis nervi trigemini). 

The body of the sphenoid bone is flattened dorso-ventrally. The hypophyseal 
fossa is shallow, but the dorsum sellse is well developed and bears posterior clinoid 
processes. A pair of anterior clinoid processes (Processus clinoidei orales) pro- 



FACE 191 

ject back from tlie roots of the orbital wings. The latter are relatively small and 
are crossed laterally by a crest, which is continued forward upon the palatine bone. 
The temporal wings are extensive and articulate dorsally with the parietals. Per- 
forating the roots of the wings are the following foramina, named from before back- 
ward : The optic passes through the orbital wing. The foramen orbitale is a little 
lower and is at the junction of the wings. The foramen rotundum opens into the 
alar canal, which passes through the root of the short but wide pterygoid process. 
The foramen ovale is near the posterior border of the temporal wing. There is no 
sphenoidal sinus. 

The ethmoid bone is highly developed. The cribriform plate is extensive, 
and the olfactory fossae are very deep. The crista galli is little developed, and often 
incomplete. The perpendicular plate is long. The lateral masses are greatly 
developed and project into the frontal sinus. There are four large endoturbinates 




Fig. 210. — Cranial and Orbital Regions of Skull of Dog. The Zygomatic Arch Has Bi^en Sawn Off. 
.4, Occipital bone; B, interparietal bone; C, parietal bone; D, squamous temporal bone; E, E', temporal and 
orbital parts of frontal bone; F, F', orbital and temporal wings of sphenoid bone; G, perpendicular part of palatine bone; 
ff, pterygoid bone ; J, lacrimal bone; /.maxilla; 1, parietal crest; 2, nuchal crest; 3, occipital condyle; 4, paramastoid 
process; 5, stylo-mastoid foramen; 6, bulla ossea; 7, meatus acusticus externus; 8, articular surface for condyle of 
mandible; 9, section of root of zygomatic process of temporal bone; 10, alar canal; 11, foramen orbitale; 12, optic 
foramen; 13, ethmoidal foramen; 14, posterior palatine foramen; 15, sphenopalatine foramen; 16, entrance to lacrimal 
canal; 17, supraorbital process; 18, zygomatic process of malar bone (section); 19, maxillary foramen; 20, last molar 
tooth. 

and six ectoturbinates. The lamina lateralis is extensive and forms the medial wall 
of the maxillary sinus. Its ventral border joins the palatine process of the maxilla 
and the horizontal part of the palate bone. A shelf-like plate extends inward from 
its lower part and concurs with the similarly incurved part of the palatine bone in 
forming the lamina transversalis, which divides the olfactory fundus of the nasal 
cavity from the naso-pharyngeal meatus. 



Face 
The maxilla is short, but very high posteriorly. The facial crest is absent. 
The infraorbital foramen is over the alveolus for the third premolar. The frontal 
process fits into a deep notch between the nasal and orbital parts of the frontal 
bone, and the middle part of the posterior border lies along the orbital margin. 
There are more or less pronounced ridges, juga alveolaria, over the canine and 
molar teeth. The zygomatic process is short and thin ; it is completely overlapped 
laterally by the malar, and is perforated by a number of foramina (Foramina 



192 



SKELETON OF THE DOG 



alveolaria). A maxillary tuberosity is not present in the adult, but there is a 
pointed projection, the pterygoid process, behind the last alveolus. The nasal 
surface bears a short turbinate crest on its anterior part, behind which it is deeply 
concave and forms the lateral wall of the maxillary sinus. The palatine process is 
short, wide behind, and moderately arched from side to side. The anterior palatine 



Foramen Foramen Occipital 
hypoglossi magnum condyle 



Foramen lacerum posterius ^^ ^ 
Stylo-mastoid foramen 
Meatus acusticus externus 



Parnmnstoid process 

Bulla ossea 
mporal canal 




Molar teeth 



Premolar teeth 



Canine tooth 



Zygomatic process of malar 
bone 



Palatine process of rnaxilla 



Prcmaxilla 



Incisor teeth 



Fig. 211. — Skull of Dog; Vkntral View, Without Mandible. 
A, Basilar part of occipital bone; B, body of sphenoid bone; C, vomer; D, D', perpendicular and horizontal parts 
of palatine bone; E, pterygoid bone; 1, Eustachian opening; 2, external carotid foramen; 3, foramen ovale; 4, 5, 
posterior and anterior openings of alar canal ; 6, foramen orbitale ; 7, postglenoid process; 8, articular groove of temporal 
bone; 9, supraorbital process; 10, meatus naso-pharyngeus ; 11, anterior palatine foramen; 12, palatine groove; 13, 
palatine fissure; 14, foramen incisivum. 



foramen is situated at or close to the transverse palatine suture and about midway 
between the median suture and the alveolar border. The palatine groove is dis- 
tinct. The large alveolus for the canine tooth is completed by the premaxilla. 
The small alveolus for the first premolar is separated from the preceding one by a 
small interval. The next two consist of anterior and posterior parts for the roots 
of the teeth. The fourth and fifth are much larger and are divided into three 



FACE 193 

parts. The last is small and consists of three divisions. The infraorbital canal is 
short. 

The body of the premaxilla is compressed dorso-ventrally, and contains three 
alveoli for the incisor teeth, which increase in size from first to third; it also com- 
pletes the medial wall of the large alveolus for the canine tooth. The foramen 
incisivum is very small except in large skulls. The interalveolar border is wide 
and very short. The nasal process is wide at its origin and tapers to a sharp point 
behind; the anterior part curves upward, backward, and a little inward, and forms 
the lateral margin of the osseous nasal aperture; the posterior part extends back- 
ward a long distance between the nasal bone and the maxilla. The palatine process 
turns upward and outward, forming with its fellow a wide groove for the septal 
cartilage; the posterior end is pointed and fits into a notch between the palatine 




Fig. 212. — Sagittal Section ok Skull of Dog, Without Mandible. 
A, A', Basilar and squamou.s parts of occipital bone; B, B', presphenoid and postsphenoid; C, C, perpendicular 
and cribriform plates of ethmoid bone; i>, parietal bone; £?, frontal bone; i'', pterygoid bone; G, G", vertical and hori- 
zontal parts of palatine bone; //.vomer; /.premaxilla; J, nasal bone; /C, dorsal turbinate bone; L, ventral turbinate 
bone; /, //, ///, anterior, posterior and middle fossae of cranium; 1, occipital condyle; 2, opening of condyloid canal; 
3, canal for intertransverse sinus of dura mater; 4, internal occipital protuberance; 5, internal opening of temporal 
canal; 6, mastoid foramen; 7, floccular fossa; 8, meatus acusticus internus; 9, canal for trigeminal nerve; 10, internal 
carotid foramen; 11, 12, openings into petro-basilar canal; 13, foramen hypoglossi; 14, petrosal crest; 15, dorsum sellae; 
16, hypophyseal or pituitary fossa; 17, optic foramen; 18, ethmoid foramen; 19, meatus naso-pharyngeus; 20,21,22, 
dorsal, middle, and ventral meatus nasi; 23, incisor teeth; 24, canine tooth; 25, premolar teeth; 26, molar teeth; 27, 
septum between frontal 



processes of the maxillae, and supports the end of the vomer. The palatine fissare 
is short but wide. 

The horizontal part of the palatine bone is extensive, forming about one-third 
of the hard palate. It presents a variable number of accessory palatine foramina. 
There is usually a pointed posterior nasal spine (Spina nasalis aboralis) at the end 
of the median suture. The palatine canal is sometimes formed entirely in this bone. 
The perpendicular part is even more extensive. Its lateral surface is chiefly free 
and forms most of the medial wall of the large pterygo-palatine fossa. The max- 
illary foramen is situated in a deep recess between this bone and the zygomatic 
process of the maxilla. Just above it there is commonly another foramen which 
opens into the nasal cavity. The posterior palatine and sphenopalatine foramina 
are situated further back and a little lower; the former is ventral to the latter. A 
horizontal plate extends from the nasal surface, meets that of the opposite bone, and 
completes the lamina transversalis spoken of in the description of the ethmoid bone. 
There is no palatine sinus. 

The pterygoid bones are very wide and short. They form a considerable part 
13 



194 



SKELETON OF THE DOG 



of the lateral boundaries of the posterior nares. The lower and posterior borders 
are free and at their angle of junction there is a variable hamulus. 

The nasal bones are (in most breeds) long and wider in front than behind. 
The facial surface is variably concave in its length and is inclined toward the 
median suture so as to form a central groove. The medial borders turn downward 
and form an internal nasal crest which becomes very prominent behind. The pos- 
terior parts fit into a notch formed by the frontal bones. The anterior ends form 
an almost semicircular nasal notch. 

The lacrimal bone is very small. The facial part extends very little or not 
at all beyond the orbital margin. The orbital surface is small and triangular, 
and presents the entrance to the lacrimal canal. 

The large zygomatic process constitutes the bulk of the malar bone. It is 
very long and is strongly curved. The dorsal border is convex, free in front, where 
it forms part of the orbital margin, beveled behind for articulation with the similar 
process of the temporal bone. Between these it bears an eminence, the processus 
frontalis, to which the orbital ligament is attached. The body of the bone may be 
considered to consist of a lacrimal process directed dorsally and fitting in between 



Symphyseal 
surface 




Fig. 213. — Right Half of Mandible of Dog; Medial View. 



the lacrimal and maxilla, and a maxillary process directed ventrally. The facial 
surface is convex. 

The dorsal turbinate bone is in its anterior part a simple plate, attached by 
one edge to the nasal bone; it curves ventro-medially, and its free border is thick- 
ened and everted. The posterior part is wider and resembles the ethmoturbinates, 
with which it is connected. 

The ventral turbinate bone is short and very complex. It is attached to the 
nasal surface of the maxilla by a basal lamina, which divides into two secondary 
lamellae. The latter detach numerous tertiary lamellae, which are coiled and have 
thick free edges. 

The vomer is not in contact with the posterior part of the floor of the nasal 
cavity, and does not divide the posterior nares. The posterior end is narrow and 
deeply notched. Near the posterior nares the two plates curve outward and join 
the palatine bones and assist in forming the lamina transversalis. 

The two halves of the mandible do not fuse completely even in old age, so that 
there is a permanent symphysis mandibulae. The body presents six alveoli for the 
incisor teeth and two for the canines. The incisor alveoli increase in size from first 
to third. The canine alveoli extend deeply downward and backward. The rami 
diverge less than in the pig. The ventral border of the horizontal part is convex 
in its length and is thick and rounded. The alveolar border is slightly concave in 



THE SKULL AS A WHOLE 195 

its length and is a little everted, especialty in its middle; it presents seven alveoli 
for the lower cheek teeth, which resemble those of the upper jaw except that the 
fourth and sixth are much smaller and the fifth is like the fourth of the upper series. 
The interalveolar space is very short or even absent. There are two or three men- 
tal foramina on either side. The vertical part is relatively small. Its lateral sur- 
face presents a deep masseteric fossa (Fossa masseterica) which encroaches on the 
coronoid process and is limited by ridges in front and below. The medial surface 
is convex and is marked by the usual mandibular foramen. At about the same 
level as the latter is the rough angular process (Processus angularis), which pro- 
jects backward from the posterior border, and is equivalent to the angle of the 
other animals. The condyle is placed very low — not much higher than the apex 
of the canine tooth when the bone is resting on a flat surface. It is long trans- 
versely and the medial part of the articular surface is much the wider and extends 
over the posterior surface. Its long axis is a little oblique, the medial end being 
inclined somewhat downward and forward. The coronoid process is very exten- 
sive and is bent slightly outward and backward. 

The body of the hyoid bone is a slightly curved transverse rod; it is compressed 
from before backward, and bears no lingual process. The thyroid cornua are per- 
manently attached to the body by cartilage; they diverge widely, curve inward, and 
are compressed laterally. The small cornua are short, prismatic, and strong. The 
middle cornua are commonly a little longer than the great cornua; they are com- 
pressed laterally, and are slightly enlarged at the ends, which are joined by cartilage 
to the adjacent cornua. The great cornua are bent outward and are somewhat 
twisted. 

THE SKULL AS A WHOLE 
The different breeds of dogs display great variations in the form and size of 
the skull. Those which have a long narrow skull (e. g., greyhound, collie) are 
designated dolichocephalic. Other dogs (e. g., bulldog, small spaniels, pugs) have 
very broad, short skulls and are termed brachycephalic. Intermediate forms 
(e. g., fox terrier, dachshund) are mesaticephalic. 

The length is usually measured from the nuchal crest to the anterior end of the premaxil- 
lary suture, and the breadth between the summits of the zygomatic arches. The cephaUc index 
is the relation of the breadth to the length, assuming the latter equal 100; the formula is: 

1 P?h ^ cephalic index. The index of extreme dolichocephalic breeds is about 50, 

as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in the pug and 
some toy terriers. Among the mesaticephalic types are the fox terrier, with an index of about 
70, and the white Pomeranian, with one about 72 to 75. The cranio-facial index is the relation of 
the distance between the nuchal crest and the fronto-nasal sutvu-e to that between the latter and 
the nasal notch. It varies from 10 : 3 in extreme brachycephalic breeds to 10 : 7 in extreme 
dolichocephalic subjects. 

The frontal surface shows the wide outward curve of the zygomatic arches 
and the great extent of the temporal fossae. The latter are separated bj^ the parietal 
crest, which in the larger breeds is very strong and prominent, and is continued by 
the diverging frontal crests to the supraorbital processes. The frontal and nasal 
regions are centrally depressed, and are more or less concave in profile. The nasal 
region is narrow and is terminated in front by a nasal notch. In the extreme 
brachycephalic breeds the differences are very striking. The cranium is strongly 
convex in both directions and is considerably longer than the face. The parietal 
crest is more or less effaced posteriorly and is formed by the interparietal onl3\ The 
parietofrontal crests are separated by an interval behind and diverge to the supra- 
orbital processes, so that the temporal fossae are widely separated. The frontal 
region is wide, strongly convex, and has a shallow central depression. The nasal 
region is very short, relatively wide, and centrally depressed. In profile there is a 



196 



SKELETON OF THE DOG 



marked depression at the fronto-nasal junction, producing what is termed by fan- 
ciers the "stop" of the face. 

On the lateral surface the great extent of the temporal fossa is seen. The 
orbit communicates freely with the fossa, the posterior part of the orbital margin 
being absent in the dry skull. The axis of the orbital cavity forms a much smaller 
angle with the median plane than in the horse and ox. A distinct crest marks the 
limit between the orbital cavity and the extensive pterygo-palatine fossa. The 
preorbital region is somewhat triangular, concave in its length, and convex dorso- 
ventrally ; the infraorbital foramen is on its lower part above the third cheek tooth. 
In extreme brachycephalic breeds the orbit is relatively very large and the preor- 
bital region extremely short but high. In the bulldog the lower jaw protrudes be- 
yond the upper — a condition known as prog- 
nathism. The opposite condition, l^rachygna- 
thism, is seen in the dachshund. 

Striking features on the basal surface of 
the cranium are the width and flatness of the 
basilar part of the occipital bone, the small size 
of the paramastoid processes, the large size and 





Fig. 214. — Skull or Dolichocephalic Dog; 
Dorsal View. 



Fig. 215. — Skull of Brachycephalic Dog; Dorsal View. 



rounded shape of the bulla ossea, and the grooved form of the articular surfaces 
for the mandible. The posterior nares are long and narrow and are not divided 
b}' the vomer. The hard palate is usually about half the length of the skull. It 
is commonly marked b}^ a median crest or rough line, and on each side are the 
anterior and accessory palatine foramina and the palatine grooves. The width 
is greatest between the fourth pair of cheek teeth, and here there is in most skulls 
a pronounced depression on either side. The length, width, and contour vary 
greatly in different breeds. 

The angle of divergence of the rami of the mandible varies from 25 to 30 de- 
grees; it is smallest in the greyhound, largest in extreme brachycephalic types, 
e. g., bulldog, pug. 

The nuchal surface is somewhat triangular, with the base ventral. The sum- 
mit is formed l)y the nuchal crest, which projects very stronglv l)ackward in the 
large breeds. Below it there are two very distinct rough imprints for muscular 
attachment. In some skulls there is a thin median occipital crest, in others a 
rounded elevation. Laterally are the temporal crests and the mastoid processes. 



BONES OF THE THORACIC LIMB 197 

The mastoid foramen is at the junction of the occipital and temporal bones, above 
the root of the paramastoid process; it opens directly into the cranial cavity. 
The foramen magnum varies greatly in form ; most often the transverse diameter is 
the greater, but in some skulls it is equaled or exceeded by the vertical diameter. 

The cranial cavity (Fig. 212) corresponds in form and size with the cranium, 
especially in those breeds in which the various crests are more or less effaced and the 
frontal sinuses are small. The basi-cranial axis is almost parallel with the palate, 
and the floor is flattened. The anterior fossa is narrow and is only slightly higher 
than the middle one. The ethmoidal fossae are very deep and the crista galli is 
little developed. The hj^pophyseal fossa is variable in depth, and the dorsum sellse 
is relatively high and bears clinoid processes laterally. The cerebral and cerebellar 
compartments are well marked off laterally by the petrosal crests and dorsally by 
the tentorium osseum. The base of the latter is traversed by a canal which con- 
nects the two temporal canals. The anterior angle of the petrous temporal is 
perforated by a canal for the fifth cranial nerve. 

The nasal cavity (Fig. 212) conforms to the shape of the face. Its anterior 
aperture is large and nearly circular in most dogs. The complex ventral turbinates 
occupy the anterior part of the cavity to a large extent, except near the aperture. 
Behind the ventral turbinate is the large opening of the maxillary sinus. Behind 
this the cavity is divided by the lamina transversalis into a large upper olfactory 
region or fundus nasi and a lower naso-pharyngeal meatus. The fundus is occupied 
largely by the ethmoturbinates. The posterior nares are undivided and are in 
general long and narrow, but vary with the shape of the skull. 

The frontal sinus is of considerable size in the large breeds, but is confined to 
the frontal bone. It is usually divided into a small anterior and a much larger 
posterior compartment, each of which opens into the dorsal ethmoidal meatus. 
The sinus is very small in extreme brachycephalic types. 

The maxillary sinus is small, and is in such free communication with the nasal 
cavity as to make it rather a recess than a true sinus. It is bounded medially by 
the lamina lateralis of the ethmoid, and its lateral wall is crossed obliquely by the 
naso-lacrimal canal. The roots of the molar teeth do not project up into it. 



BONES OF THE THORACIC LIMB 

The clavicle is a small, thin, irregularly triangular bony or cartilaginous plate. 
It is embedded in the brachiocephalicus muscle in front of the shoulder-joint and 
forms no articulation with the rest of the skeleton. (It is nearly an inch long in 
a large cat and is a slender curved rod.) 

The scapula is relatively long and narrow. The spine increases gradually 
in height from above downward and divides the lateral surface into two nearly 
equal fossae. Its free edge is thick and rough above, and at the lower part is thin 
and bent backward. The acromion is short and blunt and is opposite the rim of 
the glenoid cavity. The subscapular fossa is very shallow and is marked by rough 
lines (Linese musculares). The rough area above it for the attachment of the ser- 
ratus ventralis is large and quadrilateral in front, narrow and marginal behind. 
The anterior border is thin, strongly convex, and sinuous. The posterior border 
is straight and thick. The vertebral border is convex and thick and bears a band 
of cartilage. The anterior angle is rounded. The posterior angle is thick and square. 
The neck is well defined and bears a rough eminence posteriorly, from which the 
long head of the triceps arises. The glenoid cavity is continued forward upon the 
lower face of the tuber scapulae, which is blunt and bears no coracoid process. The 
cervical angle is opposite the first thoracic spine; the dorsal angle lies above the ver- 
tebral end of the fourth rib, and the glenoid angle at a point just in front of the 
sternal end of the first rib in the ordinary standing position. The tuber scapulae 



198 



SKELETON OF THE DOG 



unites with the rest of the bone at six to eight months. The shoulder has a great 
range of movement on the chest wall. 

The humerus is relatively very long, rather slender, and has a slight spiral 
twist. The shaft is somewhat compressed laterally, especially in its proximal two- 
thirds; this part is curved in varying degree, convex in front. The deltoid tuber- 
osity has the form of a low ridge, and it is continued by a crest which runs up- 
ward and backward and bears a tubercle on its proximal part. Another line runs 
from it down the anterior aspect and forms .the medial boundary of the very shallow 
musculo-spiral groove. The nutrient foramen is about in the middle of the posterior 
surface. A slight elevation on the proximal third of the medial surface represents 
the teres tubercle. The head is long and strongly curved from before backward. 
The neck is better marked than in the horse. The undivided lateral tuberosity is 
placed well forward and extends little above the level of the head. The medial tu- 



Cartilage 



Tuber 
scapulce 



Cartilage 



Pos- 
terior 
angle 




I Glenoid catnty 
Acromion 



Fig. 21G. — Left Scapula of Dog; Lateral Viei 



Glenoid cavity 
Fig. 217. — Right Scapula of Dog; Medial View. 



berosity is small. The intertuberal or bicipital groove is undivided and is displaced 
to the medial side by the extension forward of the lateral tuberosity. The distal 
end bears an oblique trochlear articular surface for articulation with the radius and 
ulna, the lateral part of which is the more extensive and is faintl}^ grooved. The epi- 
condyles are prominent. The coronoid and olecranon fossae often communicate 
through a large supratrochlear foramen. The proximal end unites with the shaft 
at about one year, the distal at six to eight months. 

The two bones of the forearm are relatively long and articulate with each other 
at each end in such a manner as to allow of slight movement. A narrow inter- 
osseous space separates their shafts. The radius is flattened from before back- 
ward and increases in size distally. The shaft forms two curves, so that it is con- 
vex dorsally and medially. The dorsal surface is convex in both directions and is 
marked in its distal half by a groove for the oblique extensor of the carpus. The 
volar surface presents the nutrient foramen in its proximal third, and bears a rough 



BONES OF THE THORACIC LIMB 



199 



line (Crista interossea) laterally for the attachment of the interosseous ligament. 
The proximal end (Capitulum radii) is relativel}^ small and is supported by a dis- 
tinct neck (Collum radii). It bears a concave surface (Fovea capituli) for articu- 
lation with the humerus, and a convex marginal area (Circumferentia articularis) 
behind for the ulna. The radial tuberosity is small. There is a large lateral tuber- 
osity and below this a rough eminence. The distal extremity is much wider. 
It has an extensive concave carpal articular surface. Its medial border projects 
downward, forming the styloid process of the radius. Laterally there is a concave 
facet (Incisura ulnaris racUi) for articulation with the ulna. Dorsally are three 
distinct grooves for the extensor tendons. The ulna is well developed, but dimin- 



Lateral 
tuber ositij 



Medial 



I tdert liberal 



tuberosity ^'l'"'' 



Head 



A 




Neck 
Deltoid tuberosity 



Musculo-spiral 
groove 




Coronoid fossa 



Lateral condyloid 
crest 

Olecranon fossa 



Lateral epicondyle ^"^'"^ epicondyle 
FiQ. 218. — Left Humerus of Dog; Lateral View. 



tH- 



Medial condyle 



Fig. 219. — Left Humerus op Dog; Medial View. 

1, Attachment of medial ligament of elbow joint; 2, 

attachment of flexor muscles to medial epicondyle. 



ishes in size distally. It crosses the volar surface of the radius medio-laterally. 
The shaft is large and three-sided in its proximal two-thirds, smaller and more 
rounded below. Its dorsal surface is in general rough. The nutrient foramen is 
near the proximal end. A vascular groove descends from it and indicates the course 
of the interosseous artery. The proximal end is relatively short. It is concave 
and smooth mediall}', convex and rough laterally. The olecranon is grooved and 
bears three prominences, of which the posterior one is large and rounded. The 
semilunar notch is wide below and completes the surface for articulation with the 
trochlea of the humerus. Below it is a concave surface (Incisura radialis), which 
articulates with the back of the head of the radius, and below this is a fossa, which 
receives a tuberosity of the radius. The distal end (Capitulum ulnae) is small and 



200 



SKELETON OF THE DOG 



Olecranon 




Processus anconceus 



Semilunar notch 
y^ Fovea capituli 



Shaft of ulna 



Shaft of 
radius 



is produced to a blunt point (Processus styloideus ulnae). It articulates with the 
ulnar carpal distally, and has a convex facet on its dorso-medial aspect for the radius. 
The proximal end of the radius unites with the shaft at six to eight months, the 
distal at about one and a half years of age. The olecranon and the distal end of the 
ulna fuse with the rest of the bone at about fifteen months. 

The carpus comprises seven bones — -three in the proximal row and four in the 
distal. The numerical reduction in the proximal row is apparently due to the 
fusion of the radial and intermediate, constituting a large bone (radio-intermediate) 

which articulates with almost all of the 
distal surface of the radius and with the 
bones of the distal row. It projects promi- 
nently on the volar surface of the carpus. 
The ulnar carpal is long; it articulates with 
the radius and ulna above and the acces- 
sory behind; below it rests on the fourth 
carpal and is prolonged downward to ar- 
ticulate with the fifth metacarpal also. 
The accessory is cylindrical, constricted 
in its middle and enlarged at each end; the 
anterior extremity articulates with the 
ulna and ulnar carpal bone. The first car- 
pal is the smallest bone of the lower row; 
it articulates ^vith the second carpal later- 
ally and the first metacarpal distall3^ The 
second carpal is wedge-shaped, the base be- 
ing posterior; its proximal surface is con- 
vex, and its distal is concave and rests on 
the second metacarpal. The third carpal 
is somewhat like the second ; its distal sur- 
face is concave and articulates chieflj^ with 
the third metacarpal. The fourth carpal 
is the largest of the row; it articulates with 
the fourth and fifth metacarpals. Two 
small bones or cartilages may be found on 
the volar surface at the junction of the two 
rows, and a third small bone articulates 
with the medial side of the radio-inter- 
mediate.^ 

Five metacarpal bones are present. 
The first is much the shortest; the third 
and fourth are the longest, and are about 
one-fifth longer than the second and fifth. 
The fifth is the widest at the proximal end 
and is slightly shorter than the second. 
They are close together above, but diverge 
somewhat distally; the first is separated 
from the second by a considerable interosseous space. They are so arranged as to 
form a convex dorsal surface and a concave volar surface, which corresponds to 
the hollow of the palm of the hand in man. Each consists of a shaft and two ex- 
tremities. The shaft is compressed from before backward. In the third and fourth 
it is almost four-sided, in the second and fifth three-sided, in the first rounded. 
The proximal ends (Bases) articulate with each other and with the corresponding 

1 The third bone was termed the phacoid in the cat by Strauss-Durckeim, and is regarded 
by some authors as the vestige of an additional digit, the prepollex. 



Styloid process 
of ulna 




Carpal articular 
surfaces 



Fig. 220.- 



-Left Radius and Ulna of Dog; Medial 
View. 
o, Rough area for attachment of biceps brachii 
and brachialis muscles; b, groove for tendon of exten- 
sor carpi obUquus. 



BONES OF THE THORACIC LIMB 



201 



carpal bones. The carpal articular surface formed by them is concave from side 
to side, convex from before backward. The distal ends (Capitula) have articular 
surfaces of the nature of a head, but bear a sagittal ridge on the volar aspect, ex- 
cept the first, which is grooved. Ossification is complete at five or six months of 
age. 

The five digits have three phalanges each, except the first, which has two. 
The third and fourth digits are the 
longest ; the first is very short and does 
not come in contact with the ground 
in walking. The first phalanges of the 
chief digits have four-sided shafts, 
which are slightly curved dorsally. 
The proximal end of each has a con- 
cave surface for articulation with the 
metacarpal bone and is deeply notched 
behind. The distal end has a trochlea 
for articulation with the second pha- 
lanx, and depressions on each side for 
ligamentous attachment. The second 
phalanges are about two-thirds of the 
length of the first phalanges. The 
proximal articular surface consists of 
two cavities separated by a sagittal 
ridge. The distal extremity is wider 
and flatter than that of the first. The 
third phalanges correspond in general 
to the form of the claws. The base has 
an articular surface adapted to the 
second phalanx and is encircled by a 
collar of bone (Crista unguicularis). 
The volar surface bears a wing or tuber- 
osity, and on each side of this is a fora- 
men. The ungual part is a curved rod 
with a blunt-pointed free end. It is 
rough and porous. Its base forms with 
the collar previously mentioned a deep 
groove, into which the proximal border 
of the claw is received. The two pha- 
langes of the first digit resemble in ar- 
rangement the first and third phalanges 
of the other digits. Ossification is 
complete at five or six months. 

Nine volar sesamoids are usually 
present. Two are found at each meta- 
carpo-phalangeal joint of the chief 
digits. They are high and narrow, 
articulate with the distal end of the 

metacarpal bone in front, and have a small facet on the base for the first phalanx. 
On this joint of the first digit there is usually a single flattened sesamoid, but ex- 
ceptionally two are present. The distal volar sesamoids remain cartilaginous. A 
nodular dorsal sesamoid occurs in the capsule of the metacarpo-phalangeal joints, 
and cartilaginous nodules are found in a similar position in connection with the 
joints between the first and second phalanges. 




Fig. 221. — Skeleton of Distal Part op Right Thoracic 
Limb of Dog; Dorsal View. 
The digits are spread. J, Distal end of interosseous 
space; R, distal end of radius; C. r.+ i., radio-intermediate 
carpal; C u., ulnar carpal; C. a., accessory carpal (very 
small part \asible) ; C. 1,C. 2, C. S, C. 4, first to fourth car- 
pal bones; Mc. I, metacarpal bone of first digit; P. 1 + 2, 
fused first and second phalanges of same; P. 3, third phalanx 
of same; Mc. V, fifth metacarpal bone; P. UP. 2, P. 3, 
phalanges of fifth digit; S, dorsal sesamoid; C, C, volar 



202 



SKELETON OF THE DOG 



BONES OF THE PELVIC LIMB 

The ilium is nearly parallel with the median plane and its axis is only slightly 
oblique with regard to the horizontal plane. The gluteal surface is concave. The 
pelvic surface is almost flat. The auricular surface faces almost directly inward, 
and in front of it there is an extensive rough area. The ilio-pectineal line is very 
distinct and is uninterrupted. The crest is strongly convex, thick, and rough. 
The tuber sacrale is represented by a thickened part which bears two eminences, 
homologous with the posterior superior and posterior inferior iliac spines of man. 
The tuber coxse also has two prominences, which are equivalent to the two anterior 
spines present in man. The shaft is almost sagittal and is compressed laterally. 
It is smooth and rounded dorsally, and it bears a ventro-lateral crest (Linea glu- 
tae ventralis), which terminates at a tuberosity in front of the acetabulum. 

The ischium has a twisted appearance, owing to the fact that its acetabular 
part is nearly sagittal while the posterior part is almost horizontal. The two bones 




Fig. 222.— Rk 
1, Gluteal surface of ilium; 2, crest of i 



HT Os Cox« OP Dog; Lateral View. 

3, tuber sacrale; 4, tuber coxa; 5, shaft of ilium; 6, nutrient fora- 

10, ilio-pectineal 



uum; 
Tnen; 7, greater sciatic notch; S, ventral gluteal line; 9, tubercle to which rectus femoris is attached; 
eminence; 11, 11', acetabular and symphyseal branches of pubis; 12, articular surface of acetabulum; 12', fossa acetab- 
uli; 13, obturator foramen; 14, ischiatic spine; 15, lesser sciatic notch; 16, 16', acetabular and symphyseal branches 
of ischium: 17, tuber ischii. 



also diverge behind and the tubera are flattened and everted. The superior ischiatic 
spine is low and thick ; its posterior part is marked by transverse grooves and has a 
prominent outer lip. The greater sciatic notch is elongated and very shallow. There 
is no lesser sciatic notch. The ischial arch is relatively small and is semi-elliptical. 

The symphyseal part of the pubis is thick and fuses late with the opposite bone. 
There is no subpubic groove. 

The acetabulum is about twice as far from the tuber coxae as from the tuber 
ischii. The fossa acetabuli is deep, and is bounded medially by a flat plate of bone; 
its floor is so thin as to be translucent. There is a small notch behind. 

The obturator foramen resembles in outline an equilateral triangle with the 
angles rounded off. 

Union of the three parts of the os coxse has usually taken place at six months, 
but the epiphyses of the ilium and ischium do not fuse with the main part of these 
bones till about the end of the second year. 

The inlet of the pelvis is very oblique. It is almost circular in the female, 
but in the male it is elliptical and the conjugate diameter is the longer. The cavity 
is narrowest between the acetabula, and very wide behind. The floor is concave 
and relatively narrow in front, wide and flat behind. 



BONES OF THE PELVIC LIMB 



203 



The femur is relatively much longer than in the horse or ox. The shaft is regu- 
larly cylindrical, except near the extremities, where it is wider and compressed froiiz 
before backward. It is strongly curved in its distal two-thirds, convex in front. 
The posterior surface is flattened transversely, narrow in the middle, and widens 
toward each end. It is bounded by two rough lines (Labium laterale, mediale) 
which diverge toward the extremities. The third trochanter and the supracondyloid 
fossa are absent. There are two supracondyloid crests, the medial one being small. 
The nutrient foramen is in the proximal third of the posterior surface. The head 
is a little more than a hemisphere and has a shallow fovea behind and lateral to its 
center. The neck is well defined. The trochanter major does not extend as high 



Crest of ilium Tir ■ /• •, • 

V_ n mg of ilium 



Tuber coxce 



Shaft of ilium 



Ilio-pedineal 
eminence 



Acetabular branch of 
pubis 

Symphyseal branch of 
pubis 
Symphyseal branch of _ 
ischium 




Vascular impression 



- Sacro-iliac articulation 

Nutrient foramen 
Ilio-pectineal line 

Tubercle 
Acetabulum 



Obturator foramen 

Acetabular branch of 
ischium 

Tuber ischii 



Ischial arch 
Fig. 223. — Pelvic Bones of Dog; Ventral View. 
1, Body of first sacral vertebra; 2, wing of sacrum; 3, sacral canal; 4, median crest of sacrum; 5, pelvic surface of 



as the head; a thick ridge runs from its anterior surface to the neck. The trochanter 
minor has the form of a blunt tuberosity. The trochanteric fossa is round and 
deep. The ridges of the trochlea are practically sagittal in direction and are al- 
most similar. The intercondyloid fossa is wide. Just above each condyle pos- 
teriorly there is a facet for articulation with the sesamoid bone which is developed 
in the origin of the gastrocnemius muscle. Union of shaft and extremities takes 
place at about one and a half years. 

The tibia is about the same length as the femur. The shaft forms a double 
curve; the proximal part is convex medially, the chstal part laterally. The prox- 
imal third is prismatic, but is compressed laterally and is long from before backward. 
The remainder is almost regularly cylindrical. The crest is short but very prom- 



204 



SKELETON OF THE DOG 



inent. The nutrient foramen is usually in the proximal third of the lateral border. 
The tuberosity is not grooved, but bears a distinct mark where the ligamentum 
patellae is attached. There is a small facet for the fibula on the postero-lateral part 
of the lateral condyle, and a small sesamoid bone in the tendon of origin of the 
popliteus is in contact with the posterior angle of the latter. The distal end is quad- 
rangular and relatively small. The articular grooves and ridge are almost sagittal. 
There is a facet laterally for articulation with the fibula. There is a vertical groove 
medially and a shallower one behind — both for tendons. The proximal end unites 
with the shaft at about eighteen months, the distal at fourteen or fifteen months. 



Head 



Trochanteric 
fossa 




\,. . — ^[ed^al 

Lateral _i £. ( jncondyle 

epicondyle "" \_^, ,^* 

Trochlea 
Fig. 224. — Right Femur of Dog: Anterior View. 




Lateral 
condyle 



I ntercondyloid 

fossa 



Fig. 225. — Right Femur of Dog; Posterior View. 
1, 2, Sesamoid bones. 



The fibula extends the entire length of the region. It is slender, somewhat 
twisted, and enlarged at either end. The proximal part of the shaft is separated 
from the tibia by a considerable interosseous space, but the distal part is flattened 
and closely applied to the tibia. The proximal extremity is flattened and articu- 
lates with the lateral condyle of the tibia. The distal end is somewhat thicker and 
forms the lateral malleolus. It articulates medially with the tibia and the tibial 
tarsal bone. Laterally it l)ears two tubercles. 

The patella is long and narrow. The free surface is convex in both direc- 
tions. The articular surface is convex from side to side and slightly concave from 
above downward. 



BONES OF THE PELVIC LIMB 



205 



The tarsus comprises seven bones. The tibial tarsal consists of a body, neck, 
and head, like the bone in man. The body presents a proximal trochlea for articula- 
tion with the tibia and fibula. The plantar surface has three facets for articulation 
with the fibular tarsal bone. The head is directed a little inward and articulates 
with the central. The fibular tarsal has a long anterior process or "beak," but 
the sustentaculum is short. The tuber calcis presents a sagittal groove. The 
central has a concave proximal surface adapted to the head of the tibial tarsal. 
Its distal surface articulates with the first, second, and third tarsals. It bears two 
plantar tubercles. The first tarsal is flattened and irregularly quadrangular; its 
proximal surface articulates with the central and the distal with the first metatarsal. 



Sulcus muscu-, 
laris 



Head of fibula 



Tuberosity 




Medial 
condyle 



Head of fibula 



Shaft of tibia 



Interosseous space 




Fig. 226. — Right Tibia and FiBUL.'t of Dog; Ante- 
rior View. 



# ^ E- Lateral inalleolus 

-Right Tibia and Fibula of Dog; Poste- 
rior View. 



The second tarsal is the smallest and is wedge-shaped; it articulates distally with 
the second metatarsal bone. The third tarsal is also wedge-shaped, the base being 
in front; it articulates with the third metatarsal distally. The fourth tarsal is 
remarkably high, and resembles a quadrangular prism; its proximal surface 
articulates with the fibular tarsal, its distal with the fourth and fifth metatarsal, 
and the medial with the central and third tarsal bones. A groove for the tendon of 
the peroneus longus crosses its lateral and plantar surface, and above it are one or 
two tubercles. The tuber calcis fuses with the body of the bone at fourteen or 
fifteen months. 

Five metatarsal bones are present. The first is commonly very small and has 
the form of a blunt cone, somewhat compressed laterally. It articulates with the 



206 



THE ARTICULATIONS OR JOINTS 



first tarsal and furnishes insertion to the tibialis anterior muscle. In some cases 
it fuses with the first tarsal; when the first digit is well developed, its metatarsal 
may resemble the others (except in size) or be reduced in its proximal part to a 
fibrous band. The other metatarsals are a little longer than the corresponding: 
metacarpals. Their proximal ends are elongated from before backward and have 
plantar projections, which in the case of the third and fourth usually have facets 




Fig. 228. — Skeleton of Distal Part of Left Pelvic Limb of Dog; Dorsal View. 
L, Lateral malleolus (distal end of fibula); T. t., tibial tarsal bone; T. /., fibular tarsal bone; T. c, central tarsal 
bone; T. 2, T. 3, T. 4, second, third, and fourth tarsal bones; P. l-\- 2, fused first and second phalanges, and P. 3, third 
phalanx, of first digit; Mc. 5, fifth metacarpal bone; P. 1, P. 2, P. 3, phalanges of fifth digit; S, dorsal sesamoid. 



for articulation with two small rounded sesamoid bones. In other respects they 
resemble the metacarpals. 

The first digit is often absent. When present, its development varies and it 
contains one or two phalanges. In other cases — especiall}' in very large dogs — 
a sixth digit is present; it does not articulate with the metatarsus, but is attached 
by fibrous tissue. The phalanges of the other digits resemble those of the tho- 
racic limb. 

Ossification of the metatarsal bones and phalanges is complete at five or six 
months. 



ARTHROLOGY 

THE ARTICULATIONS OR JOINTS 

An articulation or joint is formed by the union of two or more bones or carti- 
lages by other tissue. Bone is the fundamental part of most joints; in some cases 
a bone and a cartilage, or two cartilages, form a joint. The uniting medium is 
chiefly fibrous tissue or cartilage, or a mixture of these. Union of parts of the 
skeleton by muscles (Synsarcosis) , as in the attachment of the thoracic limb in 
the horse, will not be considered in this section. 

Joints may be classified — (a) anatomically, according to their mode of develop- 
ment, the nature of the uniting medium, and the form of the joint surfaces; (6) 
physiologically, with regard to the amount and kind of movement or the absence 
of mobility in them; (c) by a combination of the foregoing considerations. 

The classification of joints is still in a very unsatisfactory state, and unfortunately the same 
term is used in various senses by different authors. The two main subdivisions proposed by Hep- 
burn are: (1) Those in which the uniting medium is coextensive with the opposed joint surfaces, 
and in which a direct union of those surfaces is thereby effected. (2) Those in which the uniting 
medium has undergone interruption in its structural continuity, and in which a ca\'ity of greater 
or less extent is thus formed in the interior of the joint. This distinction is of considerable im- 
portance chnically. 

Three chief subdivisions of joints are usually recognized — viz., sjniarthroses, 
diarthroses, and amphiarthroses. 



SYNARTHROSES 
In this group the segments are united by fibrous tissue or cartilage, or a mix- 
ture of the two in such a manner as practically to preclude movement; hence they 
are often termed fixed or immovable joints. There is no joint cavity. Most of 
these joints are temporary, the uniting medium being invaded by the process of 
ossification, with a resulting ankylosis or synostosis. The chief classes in this 
group of joints are as follows: 

(1) Suture.— This term (Sutura) is applied to those joints in the skull in which 
the adjacent bones are closely united by fibrous tissue — the sutural ligament. In 
many cases the edges of the bones have irregular interlocking margins, forming the 
sutura serrata, e. g., the frontal suture. In others the edges are beveled and 
overlap, forming the sutura squamosa, e. g., the parieto-temporal suture. If the 
edges are plane or shghtly roughened, the term sutura harmonia is applied to the 
joint, e.g., the nasal suture. 

(2) Syndesmosis. — In these the uniting medium is white fibrous or elastic 
tissue or a mixture. As examples are the union of the shafts of the metacarpal bones 
and the attachments to each other of costal cartilages. 

(3) Synchondrosis.— In these the two bones are united by cartilage, e. g., 
the joint between the basilar part of the occipital bone and the sphenoid bone. 
Very few of these joints are permanent. 

(4) Symphysis. — This term is usually limited to a few median joints which 
connect symmetrical parts of the skeleton, e. g., symphysis pelvis, symphysis 
mandibulge. The uniting medium is cartilage and fibrous tissue. In some cases 
a cleft-like rudimentary joint cavity occurs. 

207 



208 



THE ARTICULATIONS 



(5) Gomphosis. — This term is sometimes applied to the implantation of the 
teeth in the alveoli. 

The gomphosis is not, properly considered, a joint at all, since the teeth are not parts of the 
skeleton. 

DIARTHROSES 

These joints are characterized by the presence of a joint cavity and by their 
mobility. They are often called movable or true joints. A simple joint (Articu- 
latio simplex) is one formed by two articular surfaces; a composite joint (Articulatio 
composita), one formed by several articular surfaces. The following structures 
enter into their formation: 

1. The articular surfaces (Facies articulares) are in most cases smooth, and 
vary much in form. The}^ are formed of specially dense bone, which differs his- 
tologically from ordinary compact substance. In certain cases (vide Osteology) 
the surface is interrupted by non-articular cavities known as synovial fossae. 

2. The articular cartilages (Cartilagines articulares), usually hyaline in type, 
form a covering over the articular surfaces of the bones. They vary in thick- 
ness in different joints; they are thickest on those 
which are subject to the most pressure and fric- 
tion. They usually tend to accentuate the curva- 
ture of the bone, ^. e., on a concave surface the 
peripheral part is the thickest, while on a con- 
vex surface the central part is the thickest. The 
articular cartilages are non-vascular, very smooth, 
and have a bluish tinge in the fresh state. They 
diminish the effects of concussion and greatly reduce 
friction. 

3. The articular or joint capsule (Capsula articu- 
laris) is, in its simplest form, a tube, the ends of which 
are attached around the articulating surfaces. It 
consists of two layers — an external one, composed of 
fibrous tissue, and an internal one, the synovial layer 
or membrane. The fibrous layer (Stratum fibrosum) , 
sometimes termed the capsular ligament, is attached 
either close to the margins of the articular surfaces or 
at a variable distance from them. Its thickness varies 
greatly in different situations: in certain places it is extremely thick, and sometimes 
cartilage or bone develops in it; in other places it is practically absent, the cap- 
sule then consisting only of the synovial membrane. Tendons which pass over a 
joint may partially take the place of the fibrous layer; in these cases the deep face 
of the tendon is covered by the synovial layer. Parts of the capsule may undergo 
thickening and so form ligaments, which are not separable, except artificially, from 
the rest of the capsule. The synovial layer (Stratum synoviale) lines the joint 
cavity except where this is bounded by the articular cartilages; it stops normally 
at the margin of the latter. It is a thin membrane, and is richly supplied by close 
networks of vessels and nerves. It frequently forms folds (Plicae synoviales) and 
villi (Villi synoviales), which project into the cavity of the joint. The folds com- 
monly contain pads of fat, and there are in many places masses of fat outside of the 
capsule which fill up interstices and vary in form and position in various phases of 
movement. The synovial membrane secretes a fluid, the synovia, which lubricates 
the joint; it resembles white-of-egg, but has a yellowish tinge.^ In many places the 

^ It is doubtful whether the synovia is a true secretion or a transudate containing products of 
friction. The view given above is that which is more commonly accepted. It contains albumen, 
mucin, and salts, and is alkaline. In it there are commonly cells derived from the synovial mem- 
brane, portions of cells, cells which have undergone fatty degeneration, particles of articular 
cartilage, etc. 




Fig. 229. — Diagram op Section of 

DiARTHROSIS. 

f.l., Fibrous layer, s.L, synovial 
layer of joint capsule. The articular 
cartilages are white, bones dotted, and 
the joint cavity black in the figure. 



DIARTHROSES 209 

membrane forms extra-articular pouches, which facilitate the play of muscles and 
tendons. 

The articular or joint cavity (Cavum articulare) is enclosed by the synovial 
membrane and the articular cartilages. Normally, it is, strictly speaking, only a 
potential cavity, which contains nothing but a small amount of synovia. 

The student must guard against a false conception of the joint cavity which may result from 
dissections and diagrams in which an actual cavity of considerable extent appears to exist. A 
correct idea of the intimate apposition of the parts is best obtained from the study of frozen sec- 
tions. On the other hand, it is instructive to examine joints which have been injected so as to 
distend the capsule fully. It is then seen that the cavity is often of much greater potential extent 
than one might suppose, and that the capsule is often very irregular in form, i. e., forms a variety of 
sacculations. 

The foregoing are constant and necessary features in all diarthroses. Other 
structures which enter into the formation of these joints are ligaments, articular 
discs or menisci, and marginal cartilages. 

4. Ligaments. — These (Ligamenta) are strong bands or membranes, usually 
composed of white fibrous tissue, which bind the bones together. They are pli- 
able, but practically inelastic. In a few cases, however, e. g., the ligamentum 
nuchae, they are composed of elastic tissue. They may be subdivided, according 
to position, into periarticular and intraarticular. Periarticular ligaments are fre- 
quently blended with or form part of the fibrous capsule; in other cases they are 
quite distinct. Those which are situated on the sides of a joint are termed col- 
lateral ligaments (Ligamenta collateralia) . Strictly speaking, intra-articular liga- 
ments, though within the fibrous capsule, are not in the joint cavity; the synovial 
membrane is reflected over them. The term seems justifiable, however, on prac- 
tical grounds. Those which connect directly opposed surfaces of bones are termed 
interosseous ligaments. In many places muscles, tendons, and thickenings of the 
fascia3 function as ligaments and increase the security of the joint. Atmospheric 
pressure and cohesion play a considerable part in keeping the joint surfaces in appo- 
sition. 

5. Articular discs or menisci (Disci s. menisci articulares) are plates of fibro- 
cartilage or dense fibrous tissue placed between the articular cartilages, and divide 
the joint cavity partially or completely into two compartments. They render cer- 
tain surfaces congruent, allow greater range or variety of movement, and diminish 
concussion. 

6. A marginal cartilage (Labrum glenoidale) is a ring of fibro-cartilage which 
encircles the rim of an articular cavity. It enlarges the cavity and tends to pre- 
vent fracture of the margin. 

Vessels and Nerves. — The arteries form anastomoses around the larger joints, 
and give off branches to the extremities of the bones and to the joint capsule. The 
synovial membrane has a close-meshed network of capillaries; the latter form loops 
around the margins of the articular cartilages, but do not usually enter them. 
The veins form plexuses. The synovial membrane is also well supplied with lymph- 
vessels. Nerve-fibers are especially numerous in and around the synovial mem- 
brane and there are special nerve-endings, e. g., Pacinian bodies and the articular 
end-bulbs described by Krause. 

Movements.— The movements of a joint are determined chiefly by the form 
and extent of the joint surfaces and the arrangement of the ligaments. They are 
usually classified as follows: 

1. Gliding.— This refers to the sliding of one practically plane surface on 
another, as in the joints between the articular processes of the cervical vertebrse. 

2. Angular Movements. — In these cases there is movement around one or 
more axes. Motion which diminishes the angle included by the segments forming 
the joint is termed flexion, while that which tends to bring the segments into line 
with each other is called extension. With reference to the joints of the distal parts 

14 



210 THE ARTICULATIONS 

of the limbs, it seems advisable to employ the terms dorsal and volar or plantar 
flexion, since these joints can be "overextended." Similarly the terms dorsal and 
ventral flexion are applied to the corresponding movements of the spinal column. 
The meaning of the term lateral flexion as applied to the vertebral column is evi- 
dent. These movements are all rotations around axes which are approximately 
either transverse or vertical. Depression, elevation, and transverse movement of 
the lower jaw fall in this category. 

3. Circumduction. — This designates movements in which the distal end of 
the limb describes a circle or a segment of one. In man such movement is easily 
performed, but in quadrupeds it is possible to a limited degree only, and is to be 
regarded usually as an indication of disease. 

4. Rotation. — As a matter of convenience, this term is reserved to indicate 
rotation of one segment around the longitudinal axis of the other segment forming 
the joint. It is seen typically in the atlanto-axial joint. 

5. Adduction and abduction designate respectively movement of a limb to- 
ward and away from the medial plane, or of a digit toward and away from the 
axis of the limb. 

Classification. — This is based on the form of the joint surfaces and the move- 
ments which occur. The following chief classes may be recognized : 

1. Arthrodia, or gliding joint. In these the surfaces are practically flat, ad- 
mitting of gliding movement. Examples: carpo-metacarpal joints; joints be- 
tween the articular processes of the cervical and thoracic vertebrse. 

2. Ginglymus, or hinge-joint. In this class the joint surfaces consist usually 
of two condyles, or of a segment of a cylinder or cone, which are received by cor- 
responding cavities. In typical cases the movements are flexion and extension, 
i. e., around a single transverse axis. Examples: atlanto-occipital and elbow 
joints. 

3. Trochoid, or pivot joint. In these the movement is limited to rotation of 
one segment around the longitudinal axis of the other. Example: atlanto-axial 
joint. 

4. Enarthrosis, or ball-and-socket joint. These are formed by a surface of 
approximately spherical curvature, received into a corresponding cavity. They 
are multiaxial, and allow of the greatest variety of movement, e. g., flexion, 
extension, rotation, abduction, adduction, circumduction. Examples: hip and 
shoulder joints."^ 

AMPHIARTHROSES 

These joints, as the name indicates, share some characters with both of the 
preceding groups. In them the segments are directly united by a plate of fibro- 
cartilage, and usually by ligaments also. The amount and kind of movement are 
determined by the shape of the joint surfaces and the amount and pliability of the 
uniting medium.^ These joints are all medial in position, and are best illustrated 
by the joints between the bodies of the vertebrse. There is usually no joint cavity, 
but in certain situations a rudimentary one exists. 

1 This classification makes no claims to scientific accuracy, but is simply a statement of the 
terms in general use. A grouping based on mechanical principles is desirable, but appears to be 
almost impossible on account of the great variety and irregularity of form of the articular surfaces. 

2 The movements in some of these joints are more extensive and varied than in some diar- 
throses. To illustrate this we may compare the movements of the cervical or coccygeal vertebrae 
with those possible in the carpo-metacarpal or the sacro-ihac joints. 



THE ARTICULATIONS OF THE HORSE INTERCENTRAL ARTICULATIONS 211 

THE ARTICULATIONS OF THE HORSE 
Joints and Ligaments of the Vertebrae 

The movable vertebrae form two sets of articulations, viz., those formed by the 
bodies, and those formed by the articular processes of adjacent vertebra; the 
former are termed intercentral, and the latter intemeural. Associated with these 
are ligaments uniting the arches and processes; some of these are special, i. e., con- 
fined to a single joint, while others are common, i. e., extend along the entire ver- 
tebral column or a considerable part of it. The joints between the atlas and axis 
and between the former and the skull require separate consideration. 



Supraspi- 
nous liga- 
ment 




Fig. 230. — Sagittal Section of Last Two Thoracic and First 
Lumbar Vertebr.e, showing Ligaments and Spinal Cord 
(Medulla). (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



INTERCENTRAL ARTICULATIONS 
These are amphiarthroses, formed l)y tlie junction of the extremities of the 
bodies of adjacent vertebrae. The articular surfaces in the cervical region consist 
of a cavity on the posterior 
end of the body of the anter- 
ior vertebra, and a correspond- 
ing convexity or head of the 
succeeding vertebra. In the 
other regions the surfaces are 
much flattened. The uniting 
media are : 

1. The intervertebral 
fibro-cartilages (Fibrocartila- 
gincs intervertebrales). Each 
of these is a disc which fits into 
the space between the bodies 
of two adjacent vertebrae, to 
which it is intimately attached. 
The discs are thinnest in the 
middle of the thoracic region, 
thicker in the cervical and lum- 
bar regions, and thickest in the 

coccygeal region. Each consists of a peripheral fibrous ring (Annulus fibrosus) 
and a soft central pulpy nucleus (Nucleus pulposus) . 

The fibrous ring consists of laminae of fibrous tissue and fibro-cartilage, which pass obliquely 
between the two vertebrae and alternate in direction, forming an X-shaped arrangement. The 
central part of the ring is largely cartilaginous, and gradually assumes the character of the pulpy 
center. The latter is very elastic and is compressed, so that it bulges considerably from the sur- 
face of sections; it consists of white and elastic fibers, connective-tissue cells, and pecuhar clear, 
transparent cells of various sizes. It is a remnant of the notochord. There are joint cavities in 
the cervical intercentral joints, and in those between the last cervical and the first thoracic, and 
between the last lumbar and the sacrum. 

2. The ventral longitudinal ligament (Lig. longitudinale ventrale)^ lies on the 
ventral surface of the bodies of the vertebrae and the intervertebral fibro-car- 
tilages, to which it is firmly attached. It begins to be distinct a little behind the 
middle of the thoracic region, and is at first a narrow, thin band. Further back 
it becomes gradually thicker and wider, and terminates on the pelvic surface of 
the sacrum by spreading out and blending with the periosteum. It is strongest in 
the lumbar region, where the tendons of the crura of the diaphragm fuse with it. 

3. The dorsal longitudinal ligament (Lig. longitudinale dorsale)- lies on the 
floor of the vertebral canal from the axis to the sacrum. It is narrow over the mid- 

^ Also termed the inferior common ligament. 
2 Also termed the superior common ligament. 



212 



THE ARTICULATIONS OF THE HORSE 



dies of the vertebral bodies, and widens over the intervertebral fibro-cartilages, to 
which it is very firmly attached. 

This ligament is in relation with the spinal veins on either side, and in the middle of each 
vertebra a transverse anastomotic vein passes under the hgament. 

INTERNEURAL ARTICULATIONS 

Each typical vertebra presents two pairs of articular processes, which form 
diarthroses with the two adjacent vertebrae. The articular surfaces are extensive, 
almost flat, and oval in the cervical region, small and flat in the thoracic region, 



Atlas 



Funicular part 



on at withers 




Last cervical 
vertebra 



First thoracic 
vertebra 



1, Scapula; /', cartilage of scapul: 



Fig. 231. — Ligamentum Nuch.e of Horse. 

,; 4, lamellar part of ligamentum nuehse; x, 

Baum, Anat. fiir Kiinstler.) 



wing of atlas. (After Ellenberger- 



while in the lumbar region the anterior ones are concave and the posterior convex. 
The joint capsule is strong and ample in the cervical region, in conformity with the 
large size and greater mobility of these joints in the neck. In the thoracic and 
lumbar regions the capsule is small and close. These joints are arthrodia in the 
neck and back, trochoid in the lumbar region. 

Associated with these joints are the ligamenta flava, which connect the arches 
of adjacent vertebrae. They are membranous and consist largely of elastic tissue. 

The supraspinous ligament (Lig. supraspinale) extends medially from the 
occipital bone to the sacrum. Behind the withers it consists of a strong cord of 
white fibrous tissue, attached to the summits of the vertebral spines. In the neck 



SACRAL AND COCCYGEAL ARTICULATIONS 213 

and withers it is remarkably modified to form the Hgamentum nuchse, which re- 
quires more extended notice. 

The ligamentum nuchae is a powerful elastic apparatus, the principal function 
of which is to assist the extensor muscles of the head and neck. It extends from 
the occipital bone to the withers, where it is directly continuous with the lumbo- 
dorsal part of the supraspinous ligament. It consists of two parts — funicular and 
lamellar. The funicular part (Pars occipitalis) arises from the external occipital 
protuberance and is inserted into the summits of the vertebral spines at the withers. 
Two bursas are usually found under it in the adult. The atlantal bursa lies be- 
tween the ligament and the dorsal arch of the atlas. The supraspinous bursa is 
usually over the third and fourth thoracic spines, but may be over the second or 
extend to the fifth. ^ Another bursa may be present at the spine of the axis; this is 
between the funicular part and the large digitation attached to the axis. In the 
neck the funicular part consists for the greater part of two bands closely applied and 
attached to each other. Near and at the withers it broadens greatly, forming an ex- 
pansion about five to six inches (ca. 12 to 15 cm.) in width, the lateral margins of which 
are thin and turn down over the trapezius and rhomboideus muscles. Behind the 
higher spines it becomes narrower and thinner, and is continued by the white fibrous 
lumbo-dorsal part.^ A mass of fat and elastic tissue lies upon the ligament as far 
back as the withers. It varies greatly in amount in different subjects, and is most 
developed in stallions of draft breeds, in which it forms the basis of the so-called 
''crest." The lamellar part (Pars cervicalis) consists of two laminae separated 
medially by a layer of loose connective tissue. Each lamina is formed of digitations 
which arise from the second and third thoracic spines and from the funicular part, 
are directed do^vnward and forward, and end on the spines of the cervical vertebrae, 
except the first and last. The digitation which is attached to the spine of the axis 
is very thick and strong. Behind this they diminish in size and strength; the last 
one, which is attached to the sixth cervical vertebra, is quite thin and feeble, or may 
be absent. 

The interspinous ligaments (Ligg. interspinalia) extend between the spines 
of contiguous vertebrae. In the cervical region they are narrow elastic bands, and 
in the thoracic and lumbar regions they consist of white fibers directed obliquely 
downward and backward. 

The intertransverse ligaments (Ligg. intertransversaria) are membranes 
which connect adjacent transverse processes in the lumbar region. 

INTERTRANSVERSE ARTICULATIONS 
These joints (peculiar to equidae) are diarthroses formed by the transverse 
processes of the fifth and sixth lumbar vertebrae and between the latter and the alae 
of the sacrum. A similar joint between the fourth and fifth lumbar processes is 
frequently present. The articular surfaces have an elongated oval form, the 
anterior one being concave and the posterior one convex. The capsule is tight, 
and is reinforced ventrally. 

SACRAL AND COCCYGEAL ARTICULATIONS 

In the foal the bodies of the five sacral vertebrae form joints which resemble 
somewhat those in the posterior part of the lumbar region. These joints are in- 

1 In dissecting-room subjects these bursse and the adjacent structures are commonly the seat 
of pathological changes. They appear to be the starting-point of "poll evil" and "fistulous 
withers." SulDCutaneous bursa} may be found over the Ugament at the withers. 

- No natural line of demarcation exists between the ligamentum nuchse and the lumbo-dorsal 
part of the supraspinous ligament, since the change from the elastic to the white fibrous structure 
is gradual. 



214 



THE ARTICULATIONS OF THE HORSE 



vaded bj^ the process of ossification early, so that the consolidation of the sacrum 
is usually complete, or nearly so, at three years. 

The coccygeal vertebrae are united by relatively thick intervertebral fibro-cartil- 
ages, which have the form of biconcave discs. Special ligaments are not present, but 
there is a continuous sheath of fibrous tissue. The movement in this region is exten- 
sive and varied. In old horses the first coccygeal vertebra is often fused with the 
sacrum. 

MOVEMENTS OF THE VERTEBRAL COLUMN 

The movements of the spine, exclusive of those at the atlanto-axial joint, are 
dorsal, ventral, and lateral flexion, and rotation. The range of movement at a 
single joint is small, but the sum of the movements is 
considerable. The movements are freest in the cervical 
|i I . yik.>i^ili ^ and coccygeal regions. Rotation is extremely limited 
in the thoracic and lumbar regions. 

ATLANTO-AXML ARTICULATION 

This is a trochoid or pivot joint of a rather peculiar 
character. The articular surfaces are : (1) On the lateral 
masses of the atlas, two somewhat saddle-shaped facets, 
which are separated by a wide notch above and a narrow 
one below; (2) on the axis, reciprocal saddle-shaped sur- 
faces which extend upon the dens and are confluent on 
its ventral aspect. It will be observed that the joint 
surfaces are not at all accurately adapted to each other, 
so that only limited areas are in contact at any time. 

The joint capsule is attached around the margins 
of the articular surfaces. It is loose and ample enough 
laterally to allow extensive movement. 

The dorsal atlanto-axial ligament (Lig. interar- 
cuale) is membranous and reinforces the capsule dor- 
sally. 

The interspinous ligament (Lig. interspinale) con- 
sists of two elastic bands which extend from the dorsal 
arch of the atlas to the spine of the axis. 

The ventral atlanto-axial ligament (Lig. dentis ex- 
ternum) arises from the ventral tubercle of the atlas and 
is attached by two branches on the ventral spine of the 
axis. 

The ligament of the dens or odontoid ligament (Lig. 
dentis internum) is short, very strong, and somewhat fan- 
shaped. It extends from the rough concave dorsal sur- 
face of the dens, widens in front, and is attached to the 
transverse rough area on the inner surface of the ventral 
arch of the atlas. 

Movements. — The atlas and the head rotate upon 
the axis; the axis of rotation passes through the center 
of the bodv of the axis. 




Fig. 232. — Atlanto-occipital and 
Atlanto - AXIAL Joints of 
Horse; Dorsal View after 
Removal of Dorsal Arch of 
Atl.\s. 

a. Joint capsule of left part of 
atlanto-occipital joint; 6, lateral 
ligament of same; c, c', ligament of 
the dens; d, atlanto-axial joint cap- 
sule; e, joint capsule of articulation 
between axis and third cervical 
vertebra; /, interspinous ligament; 
1, occipital bone; 2, atlas; 3, axis; 
4, third cervical vertebra; 5, dorsal 
longitudinal ligament. (Ellenber- 
ger-Baum, Anat. d. Haustiere.) 



THE ATLANTO-OCCIPITAL ARTICULATION 
This joint may be classed as a ginglymus. The articular surfaces of this 
joint are: (1) On the atlas, two deep oval cavities; (2) the corresponding condyles 
of the occipital bone. 



ARTICULATIONS OP THE THORAX — COSTO-VERTEBRAL ARTICULATIONS 



215 



The joint surfaces are oblique, coming very close to the median Hue ventrally, but separated 
by a considerable interval dorsally. A triangular rough area cuts into the medial part of each of 
the atlantal articular surfaces. 

There are two roomy joint capsules, which sometimes communicate ventrally, 
especially in old subjects. 

The dorsal atlanto-occipital membrane (Membrana atlanto-occipitalis dorsalis) 
extends from the dorsal arch of the atlas to the dorsal margin of the foramen mag- 
num. It is blended with the capsules and contains many elastic fibers. 

The ventral atlanto-occipital membrane (Membrana atlanto-occipitalis ven- 
tralis) extends from the ventral arch of the atlas to the ventral margin of the fora- 
men magnum. It is narrower and thinner than the dorsal membrane, and also 
fuses with the joint capsules. 

The lateral atlantal ligaments (Ligg. lateralia atlantis) are two short bands 
which are partially blended with the capsules. Each is attached to the border of 
the wing of the atlas near the intervertebral foramen, and to the lateral surface of 
the paramastoid process of the occipital bone. 

Movements. — These are chiefly flexion and extension. A small amount of 
lateral oblique movement is also possible. 



Articulations of the Thorax 
costo-vertebral articulations 

Each typical rib forms two joints with the vertebral column, one by its head, 
and one by its tubercle. Thej^ are termed respectively costo-central and costo- 
transverse joints. 

I, The costo-central articulation (Articulatio capituli) is a trochoid or rotatory 
joint, formed by the junction of the 
head of the rib with the bodies of 
two adjacent vertebrae and the 
intervertebral fibro-cartilage. The 
two facets on the head of the rib 
are separated by a non-articular 
groove, and correspond to the two 
concave facets (Fovese costales) on 
the vertebral bodies. The joint 
capsule is rather tight, and is cov- 
ered by the accessory ligaments, 
which are as follows: 1. The radiate 
ligament (Lig. capituli costae radi- 
atum) extends ventrally from the 
neck of the rib to spread out on 
the vertebral bodies and the in- 
tervertebral fibro-cartilage. 2. The 
conjugal ligament (Lig. conjugale) 
— absent from the first joint — is 
attached to the groove on the head 
of the rib, passes transversely into 
the vertebral canal, and divides 
under the dorsal longitudinal liga- 
ment into two branches: one of these is attached to the body of the anterior vertebra; 
the other is continued across to the head of the opposite rib, and is also attached to 
the intervertebral fibro-cartilage. The joint cavity is divided into two compart- 
ments by the conjugal ligament. 3. The ligament of the neck of the rib (Lig. colli 




'\^Radiate ligament 
Conjugal ligamen, 



233. — Costovertebral Articulation; Anterior View. 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



216 THE ARTICULATIONS OF THE HORSE 

costse) is a strong band which crosses the joint dorsally. It is attached on the 
vertebra above the costal facet and on the neck of the rib. 

II. The costo-transverse articulation (Articulatio costo-transversaria) . This 
is formed by the facet on the tubercle of the rib and on the transverse proc- 
ess of the vertebra. They are gliding joints. The capsule is reinforced by the 
dorsal costo-transverse ligament (Lig. costo-transversarium dorsale), a distinct 
strong band which arises on the transverse process and ends on the non-articular 
part of the tubercle. It is covered by the levator costae muscle, and begins to be 
quite distinct at the fifth joint. 

The cavity for the head of the first rib is formed by concave facets on the bodies of the last 
cervical and first thoracic vertebrjE. The conjugal ligament is absent, but the hgament of the 
neck is short and strong. The radiate ligament is very strong, and consists of two parts. In the 
case of the last two or three ribs the costo-central and costo-transverse joints are confluent, and the 
various structures are correspondingly modified. 

Movements. — The chief movement is rotation around an axis which connects 
the centers of the head and tubercle of the rib. The movement is very limited in 
the anterior part of the series of joints, but very considerable in the posterior part. 

In the case of the first rib the movement is evidently extremely limited. The facet for the 
tubercle of the rib is deeply concave, and the axis of rotation is almost transverse, so that the 
movement is chiefly sagittal in direction. Further back the facets on the transverse processes 
become flat, and the axis of rotation gradually approaches a longitudinal direction. This, in 
connection with the mobiUty of the ventral ends of the asternal ribs and their elasticity, allows a 
great increase here in the range of movement which is largely transverse, the effect being to enlarge 
(chiefly) the transverse diameter of the thorax. 



COSTO-CHONDRAL ARTICULATIONS 

The costo-chondral junctions are synarthroses. The rib has a concave surface 
which receives the convex end of the cartilage. They are united by the continuity 
of the strong periosteum and perichondrium. 



CHONDRO-STERNAL ARTICULATIONS 

These joints (Articulationes sternocostales) are diarthroses formed by the 
junction of the cartilages of the sternal ribs with the sternum. The articular ends 
of the cartilages (except the first) are somewhat enlarged, and present surfaces of 
cylindrical curvature. The articular surfaces on the sternum for the first pair of 
cartilages are placed close together on the dorsal border of the carinif orm cartilage ; 
the other seven are placed laterally at the junctions of the segments. The capsules 
are strong and tight; the first pair of joints has a common capsule, and the cartil- 
ages articulate with each other medially. The ventral ends of the first pair of ribs 
are firmly attached to each other by dense fibrous tissue, which is prolonged for- 
ward along the upper margin of the carinif orm cartilage and is continuous behind with 
the sternal ligament. Each of the other capsules is reinforced dorsally by the radiate 
costo-stemal ligament (Ligamentum sterno-costale radiatum), composed of radi- 
ating fibers which blend with the sternal ligament. Interarticular bands may be 
present. The movement is rotation around a nearly vertical axis, except in the 
case of the first pair of joints. 



INTERCHONDRAL LIGAMENTS 
The eighth and ninth costal cartilages are firmly united by fibrous tissue. The 
chondro-xiphoid ligament attaches the ninth costal cartilage to the xiphoid carti- 
lage. The remaining cartilages are rather loosely attached to each other by elastic 
tissue. 



THE ARTICULATIONS OF THE SKULL — SYNARTHROSES OF THE SKULL 217 



STERNAL ARTICULATIONS 
In the new-born foal the seven bony segments are united by persisting cartilage 
(Synchondroses intersternales) . The last two segments coalesce within a few weeks 
after birth. In old subjects there is more or less ossification of the intersternebral 
cartilage, which may lead to fusion of adjacent segments, especially posteriorly. 
The internal sternal ligament (Lig. sterni proprium internum) lies on the thoracic 
surface of the sternum. It arises on the first segment, and divides opposite the 
second chondro-sternal joint into three bands. The median band passes back- 
ward and spreads out on the last segment and the xiphoid cartilage. The lateral 
branches — thicker and wider — lie along the lateral borders above the chondro- 
sternal joints, and end at the cartilage of the eighth rib; they are covered by the 
transversus thoracis muscle. 



The Articulations of the Skull 
mandibular articulation 

This joint (Articulatio mandibularis) is a diarthrosis formed between the ramus 
of the mandible and the squamous temporal bone on either side. 

The articular surfaces are dissimilar in form and size. That on the squamous 
temporal bone is concavo-convex, and the long axis is directed outward and some- 
what forward; it consists of a condyle in front and a glenoid cavity, which is con- 
tinued upon the postglenoid process behind. The mandible presents a trans- 
versely elongated condyle. 

The articular disc (Discus articularis) is placed between the joint surfaces, 
which it renders congruent. Its surfaces are molded upon the temporal and man- 
dibular surfaces respectively, and its circumference is attached to the joint capsule; 
thus it divides the joint cavity into upper and lower compartments, the former being 
the more room5^ 

The joint capsule is strong and tight. It is reinforced by two ligaments. The 
lateral ligament (Lig. laterale) extends obliquely across the anterior part of the 
lateral surface of the capsule, from which it is not distinctly separable. The pos- 
terior ligament (Lig. posterius) is an elastic band which is attached above to the 
postglenoid process, and below to a line on the posterior face of the neck of the 
mandible. 

Movements. — The chief movements take place around a transverse axis pass- 
ing through both joints. Associated with this hinge-like action is slight gliding 
movement, as in opening and shutting the mouth. When the mouth is shut, 
the condyle of the mandible lies under the glenoid cavity. When the mandible 
is depressed, the condyle moves forward under the articular eminence of the tem- 
poral bone, carrying the disc with it. In protrusion and retraction of the lower 
jaw the gliding movement just described occurs without the hinge-like rotation 
of the condyle. These movements are similar in both joints. In the transverse 
movements (as usually performed in mastication) the action consists of rotation 
of the condyles around a vertical axis, while the disc glides forward on one side and 
backward on the other. 

SYNARTHROSES OF THE SKULL 
Most of the bones of the skull are united with the adjacent bones by sutures; 
a few are united by cartilage. The difference in the uniting medium depends on 
the fact that most of these bones are developed in membrane, but some are pre- 
formed in cartilage. Most of these joints are temporary, and are obliterated at 



218 THE ARTICULATIONS OF THE HORSE 

various periods during development and groAvth. Their importance lies in the 
fact that so long as they persist, continuous growth is possible. They are usually 
designated according to the bones which enter into their formation, e. g., spheno- 
squamous, naso-frontal, etc. 

Detailed description of the sutures has not sufficient clinical value to justify much addition 
to the statements made in the osteology in this connection. The obhteration or closure of the 
sutures is, however, worthy of brief mention. The cranial sutm-es are. usually all closed at seven 
years, but the apex only of the petrous temporal is fused with the occipital and squamous temporal. 
Most of the facial sutures are {practically closed at ten years, although complete synostosis may in 
some be delayed for years or may not occur at all; the nasal suture, for example, usually persists 
even in advanced age, so far as its anterior part is concerned. 

The principal synchondroses are: (1) That between the basilar part of the 
occipital bone and the bod}' of the sphenoid (Synchondrosis spheno-occipitalis) ; 
(2) that between the presphenoid and postsphenoid (Synchondrosis intersphenoid- 
alis); (3) those between the parts of the occipital bone (Synchondroses intraoc- 
cipitales). The first is ossified at four or five years, the second at three years, and 
the occipital bone is consolidated at two years. 

The symphysis mandibulae ossifies at one to six months. 

THE HYOIDEAN ARTICULATIONS 

The temporo-hyoid articulation is an amphiarthrosis, in which the articular 
angle of the dorsal end of the great cornu of the hyoid bone is attached by a short 
bar of cartilage to the hyoid process of the petrous temporal bone. The cartilage 
(Arthrohyoid) is about half an inch (ca. 1-1.5 cm.) in length. The chief move- 
ment is hinge-like, the axis of motion passing transversely through both joints. 

The intercomual articulation is an amphiarthrosis formed by the junction of 
the ventral extremity of the great cornu with the dorsal end of the small cornu of 
the hyoid bone. They are united by a very short piece of cartilage, in which there 
is usually a small nodule of bone in the young subject. This nodule, the epihyoid 
or middle cornu, is usually fused with the great cornu in the adult. The chief 
movement here is also hinge-like, the angle between the cornua being increased or 
diminished. 

The basi-comual articulation is a diarthrosis formed b^^ the junction of each 
small cornu with the body of the hyoid bone. The small cornu has a concave facet 
which articulates with the convex facet on either end of the dorsal surface of the 
body. The capsule is ample enough to allow considerable movement, which is 
chiefly hinge-like. 

The m.ovements of the hyoid bone are concerned chiefly in the acts of mastica- 
tion and swallowing. In the latter the ventral parts of the hyoid bone are moved 
forward and upward, carrying the root of the tongue and the larynx with them, 
and then return to their former position. 



The Articulations of the Thoracic Limb 

In the absence of the clavicle the thoracic limb forms no articulation with the 
trunk, to which it is attached by muscles. The movement of the shoulder on the 
chest-wall is chiefly rotation around a transverse axis passing through the scapula 
behind the upper part of the spine. 

THE SHOULDER JOINT 

The shoulder or scapulo-humeral joint (Articulatio scapulo-humeralis) is 
formed by the junction of the distal end of the scapula with the proximal end of 
the humerus. The articular siufaces are: (1) On the scapula, the glenoid cavity; 



THE ELBOW JOINT 



219 



(2) on the humerus, the head. Both surfaces are approximately spherical and 
similar in curvature, but the humeral surface is about twice as extensive as that of 
the scapula. 

The joint capsule is ample enough to allow the bones to be drawn apart about 
an inch (ca. 2-3 cm.) ; but this requires a very considerable amount of force unless 
air is admitted into the joint cavity. The fibrous layer is not attached to the mar- 
gin of the joint surfaces, but at a distance of one to two centimeters from it. It is 
strengthened in front by two diverging elastic bands, which arise on the tuber 
scapulae and end on the tuberosities of the humerus. A pad of fat is interposed 
between the capsule and the tendon of the biceps. 

Ligaments are absent from this joint, but the muscles and tendons around it 
afford remarkable security, so that dislocation very seldom occurs. The large ex- 
tent of the head of the humerus is also of importance in this regard. 

The principal muscles which are attached around the joint and act as ligaments are: 
laterally, the supraspinatus, infraspinatus, and teres minor; medially, the subscapularis ; in 
front, the biceps and supraspinatus; behind, the triceps. Fibers of the brachialis are attached to 
the lower edge of the posterior part of the joint capsule, and would evidently tense the latter. In 
some cases the joint cavity communicates with the bicipital or intertuberal bursa. 

Movements. — While it is a typical enarthrosis in structure, and capable of the 
various movements of the ball-and-socket joint, the chief normal movements are 
flexion and extension. In the position of rest the angle formed between the scapula 
and humerus posteriorly is about 110° to 120°; in flexion it is reduced to about 80°, 
and in extension it is increased to about 145°. Adduction and abduction are very 
restricted, the former being limited chiefly by the infraspinatus, the latter by the 
subscapularis and the low insertion of the superficial pectoral muscles. Rotation 
is somewhat freer, but does not exceed 33° when 
all the muscles are removed (Franck). 



THE ELBOW JOINT 

This, the cubital articulation (Articulatio 
cubiti), is a ginglymus formed between the dis- 
tal extremity of the humerus and the proximal 
ends of the radius and ulna. 

The articular surfaces are: (1) A trochlear 
surface formed by the condyles of the humerus 
and the ridge between them ; (2) the correspond- 
ing glenoid cavities and groove on the proximal 
extremity of the radius, together with the semi- 
lunar notch of the ulna. 

The articular surface of the condyles does not ex- 
tend upon the back of the extremity, but the groove which 
receives the semilunar notch of the ulna extends up into 
the olecranon fossa. In the fore part of the gi'oove there 
is a synovial fossa. The surface on the lateral condyle is 
much smaller than that of the medial one, and is sub- 
divided into two unequal parts by a shallow furrow. On 
the lower part of the semilunar notch and the adjacent 
part of the ridge on the radius are synovial fossis. 

The joint capsule is extremely thin behind, 
where it forms a pouch in the olecranon fossa 
under the anconeus muscle and a pad of fat. 




Fig. 231. — Left Elbow Joint of Horse; 
Posterior View. The Capsule is Re- 
moved. (After Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



In front it is strengthened by 
oblique fibers (Ijig. ol)liquum or anterior ligament), and on each side it fuses 
with the collateral ligaments. It also is adherent to the tendons of muscles 
which arise from the distal end of the humerus or end on the proximal end of the 
radius. The synovial membrane sends prolongations to the small radio-ulnar 



220 



THE ARTICULATIONS OF THE HORSE 




THE RADIO-ULNAR ARTICULATION THE CARPAL JOINTS 221 

joints and also pouches downward under the origins of the flexors of the digit and 
the lateral flexor of the carpus. There are two collateral ligaments. 

The medial ligament (Lig. collaterale radiale) is attached above to an 
eminence on the medial epicondyle of the humerus, and divides into two parts: 
the long, superficial part ends on the medial border of the radius, just below the 
level of the interosseous space; the deep, short part is inserted into the medial tu- 
berosity of the radius. 

The lateral ligament (Lig. collaterale ulnare) is short and strong. It is at- 
tached above to a depression on the lateral epicondyle of the humerus, and below 
to the lateral tuberosity of the radius, just below the margin of the articular surface. 

Movements. — This joint is a typical ginglymus, the only movements being 
flexion and extension around an axis which passes through the proximal attachments 
of the collateral ligaments. In the standing position the articular angle (in front) is 
about 140° to 150°. The range of movement is about 55° to 60°. Complete ex- 
tension is prevented chiefly by the tension of the collateral ligaments and the biceps 
muscle. (The axis of movement is slightly oblique, so that in flexion the forearm 
is carried somewhat outward.) 



THE RADIO-ULNAR ARTICULATION 

In the foal the shaft of the ulna is attached to the radius above and below the 
interosseous space by the interosseous ligament of the forearm (Lig. interosseum 
antibrachii). Below the space the two bones become fused before adult age is 
reached. Above the space the ligament usually persists, but may undergo more 
or less ossification in extreme old age. The transverse or arciform ligament (Lig. 
transversum ulnare et radiale ulnae et radii) consists of fibers which pass above the 
interosseous space from each border of the shaft of the ulna to the posterior sur- 
face of the radius. The proximal radio-ulnar articulation (Articulatio radio-ulnaris 
proximalis), formed by two small convex facets on the ulna and the corresponding 
facets on the posterior surface of the proximal extremity of the radius, is inclosed 
in the capsule of the elbow-joint and does not require separate consideration. The 
distal extremity of the ulna fuses early with the radius, and is therefore regarded 
usually as a part of the latter. 

Movement. — This is inapprecia])le, the forearm being fixed in the position of 
pronation. 

THE CARPAL JOINTS 

These joints taken together constitute the composite articulatio carpi, or what 
is popularly termed the "knee-joint" in animals.^ This consists of three chief 
joints, viz., (1) The radio-carpal or antibrachio-carpal joint (Articulatio radiocarpea) 
formed by the distal end of the radius and the proximal row of the carpus; (2) the 
intercarpal joint (Articulatio intercarpea), formed between the two rows of the car- 
pus; (3) the carpo-metacarpal joint (Articulatio carpometacarpea), formed between 
the distal row of the carpus and the proximal ends of the metacarpal bones. The 
proximal and middle joints may be regarded as ginglymi, although they are not 
typical or pure examples of hinge-joints. The distal joint is arthrodial. In addi- 
tion there are arthrodial joints formed between adjacent bones of the same row 
(Articulationes interossese). All these form a composite joint with numerous liga- 
ments. The articular surfaces have been described in the Osteology. 

The joint capsule may be regarded, so far as the fibrous part is concerned, as 
being common to all three joints. It is attached close to the margin of the articu- 

^ The term is a very unfortunate one, since it is a distinct misapplication of the name as it is 
used in regard to man. It is, however, very firmly established, and appears likely to persist in- 
definitely in the absence of a convenient popular equivalent. 



222 



THE ARTICULATIONS OF THE HORSE 



- R 



lar surface of the radius above and the metacarpus below; its deep face is also 
attached to a considerable extent to the carpal bones and to the small ligaments. 
Its anterior part, the dorsal carpal ligament, is loose, except during flexion, and 
assists in forming the fibrous canals for the extensor tendons. Its posterior part, 
the volar carpal ligament (Lig. carpi volare), is very thick and dense, and is closely 
attached to the carpal bones. It levels up the irregularities of the skeleton here, 
and forms the smooth anterior wall of the carpal canal. It is continued downward 
to form the subcarpal or inferior check ligament, which blends with the tendon of 
the deep flexor of the digit about the middle of the metacarpus, and may well be 
regarded as the carpal (tendinous) head of that muscle. 

The synovial membrane forms three sacs corresponding to the three joints. 

The radio-carpal sac is the 
most voluminous; it includes 
the joints formed by the acces- 
sory carpal bone, and also those 
between the proximal carpal 
bones as far as the interosseous 
ligaments. The intercarpal sac 
sends extensions upward and 
downward between the bones 
of the two rows as far as the 
interosseous ligaments; it com- 
municates between the third 
and fourth carpal bones with 
the carpo-metacarpal sac. The 
latter is very limited in extent, 
and is closely applied to the 
bones; it incloses the carpo- 
metacarpal joint, and lubri- 
cates also the lower parts of 
the joints between the distal 
carpal bones and the inter- 
metacarpal joints. 

The lateral ligament (Lig. 
carpi collaterale ulnare) is at- 
tached above to the lateral 
tuberosity of the distal end of 
the radius. Its long superficial 
part is attached below to the 
proximal end of the lateral 
small metacarpal chiefly, but 
some fibers end on the large 
metacarpal bone. A canal for the lateral extensor tendon separates a short deep 
band which ends on the ulnar carpal bone. Other deep fibers connect the latter 
with the fourth carpal bone, and the fourth carpal with the metacarpus. 

The medial ligament (Lig. carpi collaterale radiale) resembles the preceding 
in general, but is stronger and wider distally. It is attached above to the medial 
tuberosity of the distal end of the radius and ends below on the proximal ends of 
the large and medial small metacarpal bones. Deep fasciculi are detached to the 
radial and second carpal bones. The first carpal bone, when present, is usuall^^ 
embedded in the posterior part of the distal end of the ligament. The posterior 
part of the ligament is fused with the transverse ligament of the carpus (Lig. carpi 
transversum), and concurs in the formation of a canal for the tendon of the flexor 
carpi radialis. 




Fig. 238.- 



-Left Carpal Joints of Horse; Dors 
Joint Capsule is Removed. 



.L Vii 



C. u. 



C. 



Mc. IV 



Mc. Ill 



The 



R, Lateral distal tuberosity of radius; M, medial ligament; L, 
lateral ligament; C. r., radial carpal bone; C. u., ulnar carpal bone; 
C. 3, third carpal bone; C. 4, fourth - carpal bone; Mc. Ill, Mc. IV, 
metacarpal bones; 1, intermediate carpal bone; 2-6, dorsal ligaments. 



INTERMETACARPAL JOINTS 



223 



^M 



A number of special short ligaments connect two or more adjacent bones; only the most 
distinct of these will be described here. 

The accessory carpal bone is connected with adjacent bones by three hgaments (Fig. 234). 
The proximal one is a short band which extends from the accessory carpal in front of the groove on 
its lateral face and is inserted into the distal end of the radius behind the groove for the lateral 
extensor tendon. A middle band connects the accessory with tlie ulnar carpal. The distal liga- 
ment consists of two strong bands which pass from the distal margin of the accessory to the fourth 
carpal and the proximal end of the fourth 
metacarpal bone; these bands transmit the 
action of the muscles which are inserted into 
the accessory carpal bone. The other bones 
of the proximal row are connected by two 
dorsal Ugaments, which are transverse m direc- 
tion, and two interosseous Hgaments. An 
oblique ligament passes from an eminence on 
the volar surface of the radial carpal bone to 
a small depression on the radius medial to the 
facet for the accessory carpal bone. 

Two ligaments connect the proximal and 
distal rows posteriorly. The medial one joins 
the radial to the second and third carpal, and 
the lateral one attaches the ulnar to the third 
and fourth carpals. 

The bones of the distal row are con- 
nected by two strong transverse dorsal 
ligaments and two interosseous ligaments. 

There are four carpo-metacarpal liga- 
ments. Two obHque dorsal Hgaments (Ligg. 
carpometacarpea dorsaHa) connect the third 
carpal with the large metacarpal bone. Two 
interosseous Hgaments pass downward from 
the interosseous Hgaments of the distal row 
to end in depressions of the opposed surfaces 
of the proximal ends of the metacarpal bones. 
Volar Hgaments (Ligg. carpometacarpea vo- 
laria) connect the second and third carpal 
bones with the metacarpus. Other short 
special Ugaments have been described, but 
some of them at least are artefacts. 

Movements. — Taking the joint as 
a whole, the chief movements are flex- 
ion and extension. In the standing 
position the joint is extended. When 
the joint is flexed, shght transverse 
movement and rotation can be pro- 
duced by manipulation. The dorsal 
part of the capsule is, of course, tense 
during flexion, the volar part in exten- 
sion. 




The movement practically all occurs at 
the radio-carpal and intercarpal joints, the 
articular surfaces of which are widely separ- 
ated in front during flexion, but remain in 
contact behind. The distal row remains in 
contact with the metacarpus. The inter- 
mediate and ulnar carpals move together as 

one piece, but the radial does not move so far as the intermediate, so that the dorsal and inter- 
osseous Ugaments connecting these bones become tense and obUque in direction. 



Fig. 239. — Left Carpal Joints op Horse; Volar View. 
Accessory Carpal and Capsule have been Re- 
moved. 

R, Dist.al end of radius; M, medial ligament; L, 
lateral ligament; 1, 2, ligaments connecting radial carpal 
bone and radius; 3, ligament connecting intermediate 
carpal with radius; 4, stump of ligament connecting inter- 
mediate and accessory carpal ; 5, ligament connecting radial 
and second carpal; 6, 6', ligaments connecting second 
carpal and metacarpal bones; 7, 7', ligaments connecting 
third carpal and metacarpal bone; 8, ligament connecting 
ulnar and third and fourth carpal bones; 9, deep short part 
of medial collateral ligament; 10, 11, 12, radial, inter- 
mediate, and ulnar carpal bones; 13, 14, 1.5, second, third, 
and fourth carpal bones; 16, 16', 17, metacarpal bones. 
(Of the preceding volar ligaments, 1, 3, and 8 are distinct 
from the capsule.) 



INTERMETACARPAL JOINTS 

The small joints formed between the proximal ends of the metacarpal bones 
(Articulationes intermetacarpeae) are enclosed by the carpal joint capsule, as des- 
cribed above. The opposed surfaces of the shafts of the bones are closely united by 
an interosseous metacarpal ligament (Lig. interosseum metacarpi), which often 
undergoes more or less extensive ossification. 



224 THE ARTICULATIONS OF THE HORSE 



THE FETLOCK JOINT 

This, the metacarpo-phalangeal articulation (Articulatio metacarpo-phalangea), 
is a ginglymus formed by the junction of the distal end of the large (third) meta- 
carpal bone, the proximal end of the first phalanx, and the proximal sesamoid 
bones. 

Articular Surfaces. — The surface on the large metacarpal bone is approxi- 
mately cylindrical in curvature, but is divided into two slightly unequal parts by a 
sagittal ridge. This is received into a socket formed by the first phalanx below and 
the two sesamoids together with the intersesamoid ligament behind. The latter 
is a mass of fibro-cartilage in which the sesamoid bones are largely embedded. It 
extends above the level of the sesamoids, and is grooved to receive the ridge on the 
metacarpal bone; its volar surface forms a smooth groove for the deep flexor ten- 
don. 

The joint capsule is attached around the margin of the articular surfaces. It 
is thick and ample in front; here a bursa is interposed between it and the extensor 
tendons, but the tendons are also attached to the capsule. Posteriorly it forms a 
thin-walled pouch which extends upward between the metacarpal bone and the 
suspensory ligament about as high as the point of bifurcation of the latter.^ The 
capsule is reinforced by two collateral ligaments. 

The collateral ligaments, medial and lateral (Lig. collaterale ulnare, radiale), 
are partially divided into two layers : the superficial layer arises from the eminence 
on the side of the distal end of the large metacarpal bone, and passes straight to 
the rough area below the margin of the articular surface of the first phalanx; the 
deep layer, shorter and much stronger, arises in the depression on the side of the 
distal end of the metacarpal bone, and passes obliquely downward and backward 
to be inserted into the abaxial surface of the sesamoid and the proximal end of the 
first phalanx. 

The capsule is further strengthened by a layer of oblique fibers which pass over the collateral 
ligament on either side and end on the extensor tendon and the proximal extremity of the first 
phalanx. It may properly be regarded as fascia rather than ligament. 

Movements. — These are of the nature of flexion and extension, the axis of 
motion passing through the proximal attachments of the collateral ligaments. In 
the ordinary standing position the joint is in a state of partial dorsal flexion, the 
articular angle (in front) being about 140° to 150°. (In the hind limb it is about 
5° greater.) Diminution of this angle (sometimes termed "overextension") is nor- 
mally very limited on account of the resistance offered by the sesamoidean appa- 
ratus, but it varies considerably in amount in different subjects. Volar flexion is 
limited only by contact of the heels with the metacarpus. During volar flexion 
a small amount of transverse movement is possible. 



THE SESAMOIDEAN LIGAMENTS 

Under this head will be described a number of important ligaments which are 
connected with the sesamoid bones and form a sort of stay apparatus or brace. 

The intersesamoidean ligament (Lig. intersesamoideum) not only fills the 
space between and unites the sesamoid bones, but also extends above them, enter- 
ing into the formation of the articular surface of the fetlock joint. Other facts 
in regard to it have been given above. 

The collateral sesamoidean ligaments, lateral and medial (Ligg. sesamoidea 

^ This pouch is in part bound down by a layer of elastic tissue which arises by two branches 
from the distal part of the volar surface of the shaft of the large metacarpal bone and ends on the 
intersesamoid ligament. It was first described by Skoda who terms it the lig. metacarpo-inter- 
sesamoideum. 



THE SESAMOIDEAN LIGAMENTS 



225 



ulnare et radiale), arise on the abaxial surface of each sesamoid bone, pass forward, 
and divide into two branches, one of which ends in the depression on the distal end 
of the large metacarpal bone, the other on the eminence on the proximal end of the 
first phalanx. They are partly covered by the branches of the suspensory or 
superior sesamoidean ligament. 

The suspensory ligament or interosseous tendon (Tendo interosseus)i lies in 
great part in the metacarpal groove, where it has the form of a wide, thick 
band. It is attached above to the proximal part of the posterior surface of the large 



Extensor tendon 



Proximal end of capsule of fetlock 
joint 

Bursa 

Collateral ligament of fetlock joint 
Fascia 

Branch of suspensory ligament 



Lateral volar ligament of pastern if^ 

joint 



Suspensory ligament of navicidar 
bone 
Band from cartilage to extensor 
tendon 
Collateral ligament of coffin joint 




Superficial flexor tendon 
Deep flexor tendon 
Suspensory ligament 
Lateral interosseous tendon 

Proximal end of digital sheath 
Ring of superficial flexor tendon 
I ntersesamoidean ligament 
Posterior annular ligament (cut) 



Collateral sesamoidean ligament 
Superficial distal sesamoidean 

ligaynent 
Middle distal sesamoidean ligament 

Attachments of proximal digital 
annular ligament 



Pouch of digital sheath 

Distal digital annular ligament 
Cartilage of third phalanx 



Fig. 240. — Ligaments and Tendons of Distal Part of Limb of Horse. 

Mc.in, Large metacarpal bone; Ph. I, first phalanx; Ph.H, second phalanx; Ph.IH, third phalanx; 1, deep flexor 

tendon; 2, band from first phalanx to digital cushion. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



metacarpal bone and to the distal row of carpal bones. At the distal fourth of the 
metacarpus it divides into two diverging branches. Each branch passes to the 
abaxial face of the corresponding sesamoid, on which a considerable part is attached. 
The remainder passes obliquely do^vnward and forward to the dorsal surface of the 
first phalanx, where it joins the extensor tendon; there is a bursa between this ex- 
tensor branch and the proximal end of the first phalanx. This ligament possesses 

^ This is also known as the superior sesamoidean Hgament; it is described here in deference 
to custom and on account of its Ugamentous function. 
15 



226 



THE ARTICULATIONS OF THE HORSE 



considerable elasticity, and is the highly modified interosseous medius muscle. It 
consists mainly of tendinous tissue, but contains a variable amount of striped mus- 
cular tissue, especially in its deep part and in young subjects. Its principal func- 
tion is to support the fetlock, i. e., to prevent excessive dorsal flexion of the joint 
when the weight is put on the limb. The branches which join the common exten- 
sor tendon limit volar flexion of the interphalangeal joints in certain phases of move- 
ment. ^ 

The distal sesamoidean ligaments are three in number. The superficial or 



Large metacarpal bone 

Lateral small metacarpal bone 

Bifurcation of suspensory 
ligament 



Bifurcation of common digital artery 
Medial digital artery 



Oblique or middle distal sesamoid 
ligament 
Straight or superficial distal 
sesamoid ligament 



Distal annular ligament of digit (cut 
and reflected) 




Capsule of fetlock joint (proximal 

pouch) 
Sesarnoid groove 

Volar annular ligament of fetlock 
(cut and reflected) 

Lateral sesamoid ligament 
Stump of proximal digital annular 

ligament 
Extensor branch of suspensory 

ligament 
Volar ligaments of pastern joint 

Insertion of superficial flexor 

tendon 
Fibrous plate 
Deep flexor tendon 

Lateral ligament of pastern joint 
Distal end of digital sheath 
Suspensory ligament of navicular 

bone 
Dorsal branch of digital artery 
Volar branch of digital artery 



Fig. 241. — Deep Dissection of Distal Part of Right Fore Limb of Horse, Showing Joints and Ligaments; 

Posterior View. 
1, Cartilage of third phalanx; 2, flexor surface of navicular bone; 3, diatal navicular ligament; 4, insertion of 
deep flexor tendon. Small arrows point to openings made in capsules of pastern and coffin joints. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



straight sesamoidean ligament (Lig. sesamoideum rectum) is a flat band and is 
somewhat wider above than below. ^ It is attached above to the bases of the sesa- 
moid bones and the intersesamoid ligament, below to the complementary fibro- 
cartilage of the proximal end of the second phalanx. The middle sesamoidean 
ligament is triangular, with thick, rounded margins (Ligg. sesamoidea obliqua) and 
a thin central portion.^ Its base is attached to the sesamoid bones and intersesa- 



* This is often called the Y-shaped ligament — a rather undesirable name, since it is not 
bifurcate. 

^ It is also called the V-shaped ligament. 



THE SESAMOIDEAN LIGAMENTS 



227 



moid ligament, and its deep face to the triangular rough area on the volar surface 
of the first phalanx. The deep or cruciate sesamoidean ligaments (Ligg. sesamoidea 
cruciata) consist of two thin layers of fibers which arise on the base of the sesa- 
moid bones, cross each other, and end on the opposite eminence on the proximal 
end of the first phalanx. 

The two short sesamoidean ligaments (Ligg. sesamoidea brevia) are best seen 



Skin 

Tendon of common extensor 

Bursa 

Capsule of fetlock joint 
Cavity of fetlock joint 




Cavity of pastern joint 



Cavity of coffin joint 



Middle sesamoidean ligament 
Digital synovial sheath 
Cavity of pastern joint 
Superficial sesamoidean ligament 
Deep flexor tendon 
Distal end of digital sheath 



11 

Digital cushion 



Corium of periopl 
Periople 

Coronary corium 

Wall 

Laminae 



Sole Corium of sole 
Fig. 242. — Sagittal Section of Digit and Distal Part of Metacarpus op Horse. 
A, Metacarpal bone; B, first phalanx; C, second phalanx; D, third phalanx; E, distal sesamoid bone; 1, volar 
pouch of capsule of fetlock joint; 2, intersesamoidean ligament; 3, 4, proximal end of digital synovial sheath; 5, ring 
formed by superficial flexor tendon; 6, fibrous tissue underlying ergot; 7, ergot; 8, 9, 9', branches of digital vessels; 10, 
distal ligament of distal sesamoid bone; 11, suspensory ligament of distal sesamoid bone; 12, 12', proximal and distal 
ends of bursa podotrochlearis. By an oversight the superficial flexor tendon (behind 4) is not marked. 



by opening the joint in front and pushing the sesamoid bones backward; they 
are covered by the synovial membrane. Each is a short band which extends from 
the anterior part of the base of the sesamoid bone outward or inward to the posterior 
margin of the articular surface of the first phalanx. 

The distal sesamoidean ligaments may be regarded as digital continuations 
of the suspensory ligament, the sesamoid bones being intercalated in this remark- 
able stay apparatus, by which the fetlock is supported and concussion diminished. 



228 THE ARTICULATIONS OF THE HORSE 



THE PASTERN JOINT 

This, the proximal interphalangeal articulation (Articulatio interphalangea 
proximalis s. phalangis secundffi), is a ginglymus formed by the junction of the 
distal end of the first phalanx and the proximal end of the second phalanx. 

The articular surfaces are: (1) On the first phalanx, two slightly unequal con- 
vex areas ^Adth an intermediate shallow groove; (2) on the second phalanx, a cor- 
responding surface, completed behind by a plate of fibro-cartilage. 

The joint capsule is close-fitting in front and on the sides, where it blends with 
the extensor tendon and the collateral ligaments respectively. Behind it pouches 
upward a little and is reinforced by the straight sesamoidean ligament and the 
branches of the superficial fiexor tendon. 

There are two collateral and four volar ligaments. 

The collateral ligaments, medial and lateral (Lig. collaterale rachale, ulnare), 
are very short and strong bands which are attached above on the eminence and de- 
pression on each side of the distal end of the first phalanx, and below on the em- 
inence on each side of the proximal end of the second phalanx. The direction of 
the ligaments is about vertical and, therefore, does not correspond to the digital 
axis. 

The volar ligaments (Ligg. volaria) consist of a central pair and lateral and 
medial bands which are attached below to the posterior margin of the proximal end 
of the second phalanx and its complementary fibro-cartilage. The lateral and 
medial ligaments are attached above to the middle of the borders of the first phalanx, 
the central pair lower down and on the margin of the triangular rough area. 

These ligaments are very commonly thickened as a result of clironic inflammation, and then 
are not well defined. The central ones blend below with the branches of the superficial flexor 
tendon and with the straight sesamoidean Ugament. 

Movements. — These are very limited, and consist of flexion and extension. 
The axis of motion passes transversely through the distal end of the first phalanx. 
In the standing position the joint is extended. A small amount of volar flexion is 
possible, and in this position slight lateral and medial flexion and rotation can be 
produced by manipulation. Dorsal flexion is prevented by the lateral, volar, and 
straight sesamoidean ligaments. 

THE COFFIN JOINT 

This joint, technically termed the distal interphalangeal articulation (Articu- 
latio interphalangea distalis s. phalangis tertise), is a ginglymus formed by the junc- 
tion of the second and third phalanges and the distal sesamoid bone. 

Articular Surfaces. — The surface on the distal end of the second phalanx is 
convex in the sagittal direction, concave transversely. The articular surface of the 
third phalanx slopes sharply upward and forward; its central part is prominent, 
and is flanked by two glenoid cavities. It is completed behind by the articular 
surface of the distal sesamoid or navicular bone. 

Joint Capsule. — This is attached around the margins of the articular surfaces. 
In front and on the sides it is tight, and is blended with the extensor tendon and the 
collateral ligaments respectively. It forms a considerable pouch behind, which 
extends upward to about the middle of the second phalanx, where it is separated by 
a fibrous membrane from the digital synovial sheath. On each side small pouches 
project (especially during volar flexion) against the cartilages of the third phalanx 
just behind the collateral ligaments.^ 

Ligaments. — The collateral ligaments, medial and lateral (Lig. collaterale 

' Tliis should be noted in regard to resection of the cartilage or other operations in this 
vicinity. 



THE ARTICULATIONS OF THE PELVIC LIMB 



229 



ulnare, radiale), are short, strong bands v/hich are attached above in the depressions 
on either side of the lower part of the second phalanx, under cover of the cartilage 
of the third phalanx. They widen below and end in the depressions on either 
side of the extensor process and on the anterior end of the cartilages. 

The collateral sesamoidean or suspensory navicular ligaments, medial and 
lateral (Lig. sesamoideum coUaterale ulnare, radiale),i are strong, somewhat elastic 
bands, which form a sort of suspensory apparatus for the third sesamoid. They are 
attached superiorly in and above the depressions on each side of the distal end of 
the first phalanx and are here partly blended with the collateral ligaments of the 
pastern joint. They are directed obliquely downward and backward, and end 
chiefly on the ends and proximal border of the distal sesamoid, but detach a 
branch to the axial surface of each cartilage and angle of the third phalanx. 

The phalango-sesamoidean or distal navicular ligament (Lig. phalangeo-sesa- 
moideum) reinforces the capsule distally. It is a strong layer of fibers which 
extend from the distal border of the distal sesamoid to the flexor surface of the third 
phalanx. 

Movemenis.— 'The chief movements are flexion ana extension. In the stand- 
ing position the joint is extended. During volar flexion a very small amount of 
lateral movement and rotation can be produced by manipulation. Dorsal flexion 
is very limited. 

Dorsal flexion appears to be checked mainly by the deep flexor tendon, since in cases of rup- 
ture of the latter the toe turns up. The mobility of the posterior part of the socket for the second 
phalanx (formed by the distal sesamoid) diminishes concussion when the weight comes on the foot 



LIGAMENTS OF THE CARTILAGES OF THE THIRD PHALANX 

In addition to the bands mentioned above, which attach the cartilages to the 
extremities of the navicular bone, there are three ligaments on either side which 
attach the cartilages to the phalanges. 

An ill-defined elastic band passes from the middle part of the border of the first 
phalanx to the upper part of the cartilage, detaching a branch to the digital cushion. 

A short, strong band connects the anterior extremity of the cartilage with the 
rough eminence on the second pha- 
lanx in front of the attachment of the 
collateral ligament of the coffin joint. 

The lower border of the cartil- 
age is covered in part by fibers which 
attach it to the angle of the third 
phalanx. 




The Articulations of the 
Pelvic Limb 

the sacro-iliac articulation 

This joint (Articulatio sacro- 
iliaca) is a diarthrosis formed be- 
tween the auricular surfaces of the 
sacrum and ilium. These surfaces 
are not smooth in the adult, but are 

marked by reciprocal eminences and depressions, and are covered by a thin laj^er of 
cartilage. The joint cavity is a mere cleft, and is often crossed by fibrous bands. 



Sacro-iliac 
articulation 



243. — Left Sacro-iliac Articulation of Horse; An- 
terior View. (Adapted from Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



^ These are termed the postero-lateral ligaments by M'Fadyean. 
suspensory ligaments of the navicular bone. 



Functionally they are 



230 THE ARTICULATIONS OF THE HORSE 

The joint capsule is very close fitting, and is attached around the margins of 
the articular surfaces. It is reinforced by the ventral sacro-iliac ligament (Lig. 
sacro-iliacum ventrale), which surrounds the joint; this is exceedingly strong above, 
where it occupies the angle between the ilium and the wdng of the sacrum; it con- 
sists chiefly of nearly vertical fibers. 

The movements are inappreciable in the adult — stability, not mobility, being 
the chief desideratum. 



LIGAMENTS OF THE PELVIC GIRDLE 

The following ligaments (Ligg. cinguli extremitatis pelvinse) may be regarded 
as accessory to the sacro-iliac joint, although not directly connected with it: 




Fig. 244. — Pelvic Ligaments and Hip Joint. 
1, Dorsal sacro-iliac ligament; S, lateral sacro-iliac ligament; 3, saero-sciatic ligament; 4. greater sciatic foramen; 
S, lesser sciatic foramen; 6, line of attachment of intermuscular septum between biceps femoris and semitendinosus; 
7, capsule of hip joint; 8, capsularis muscle; 9, lateral tendon of origin of rectus femoris; 10, tuber sacrale; 11, tuber 
cox«; /;?, shaft of ilium; ^i?, superior ischiatic spine; /4. pubis; 7.J, tuber ischii; iff, trochanter major; / 7, semimem- 
branosus; IS, fifth lumbar spine; 19, 20, first and second coccygeal vertebrae. 

The dorsal sacro-iliac ligament (Lig. sacro-iliacum dorsale breve) is a strong 
band which is attached to the tuber sacrale and the summits of the sacral spines. 

The lateral sacro-iliac ligament (Lig. sacro-iliacum dorsale longum) is a tri- 
angular, thick sheet which is attachetl in front to the tuber sacrale and adjacent 
part of the medial border of the ilium above the great sciatic notch, and below to 
the lateral border of the sacrum. It blends above with the dorsal sacro-iliac liga- 
ment, below with the sacro-sciatic ligament, and behind with the coccygeal fascia. 

The sacro-sciatic ligament (Lig. sacroischiadicum s. sacrospinosum et tuber- 
osum) is an extensive quadrilateral sheet which completes the lateral pelvic wall. 



SYMPHYSIS PELVIS THE HIP JOINT 231 

Its dorsal border is attached to the border of the sacrum and the transverse processes 
of the first and second coccygeal vertebrae. Its ventral border is attached to the 
superior ischiatic spine and tuber ischii. Between these it bridges over the lateral 
border of the ischium and completes the lesser sciatic foramen (Foramen ischiadi- 
cum minus). The anterior border is concave, and completes the greater sciatic 
foramen (Foramen ischiadicum majus). The posterior border is fused with the 
vertebral head of the semimembranosus muscle. 

The lesser sciatic foramen is closed, except where the tendon of the obturator internus and 
a vein pass tlirough it, by a thin fibrous sheet given off from the sacro-sciatic ligament. 

The ilio-lumbar ligament (Lig. ilio-lumbale) is a triangular sheet which at- 
taches the ends of the lumbar transverse processes to the ventral surface of the 
ilium below the attachment of the longissimus muscle (Fig. 273) . 

SYMPHYSIS PELVIS 
The symphysis pelvis is formed Ijv the junction of the two ossa coxarum at 
the ventral median- line. In the young subject the bones are united by a layer of 
cartilage (Lamina fibrocartilaginea) ; in the adult the latter is gradually replaced 
by bone, the process beginning in the pubic portion and extending backward, 
but commonly the ischia are in part not fused. The union is strengthened by 
white fibrous tissue dorsally and ventrally. A transverse band also covers the 
anterior border of the pubis, and other fibers (Lig. arcuatum ischiadicum) extend 
across at the ischial arch. No appreciable movement occurs even before synosto- 
sis takes place. 

OBTURATOR MEMBRANE 

This (Membrana obturatoria) is a thin layer of fibrous tissue which covers the 
obturator foramen, leaving, however, a passage (Canalis obturatorius) for the 
obturator vessels and nerve. 

THE HIP JOINT 

This joint (Articulatio coxae) is an enarthrosis formed by the proximal end of 
the femur and the acetabulum. 

Articular Surfaces. — The head of the femur presents an almost hemispherical 
articular surface, which is continued a short distance on the upper surface of the 
neck. It is more extensive than the socket which receives it. It is cut into medi- 
ally by a deep notch for the attachment of the round and accessory ligaments. 
The acetabulum is a typical cotyloid cavity. Its articular surface is somewhat 
crescentic, being deeply cut into medially by the acetabular notch and fossa. 

The acetabulum is deepened by a ring of fibro-cartilage, the cotyloid ligament 
(Labrum glenoidale), which is attached to the bony margin; that part of the liga- 
ment which crosses the notch is called the transverse acetabular ligament (Lig. 
transversum acetabuli) (Fig. 291). 

The joint capsule is roomy. It is attached around the margin of the acetab- 
ulum and the neck of the femur. It is thickest laterally. 

The attachment on the femur is about 1 cm. from the margin of the articular surface, except 
above, where 2 to 3 cm. of the neck is intracapsular. A thin, oblique band corresponding in direc- 
tion with the capsularis muscle reinforces the antero-lateral part of the capsule; this appears to 
be the feeble homologue of the very strong ilio-femoral ligament of man. The capsule is very 
thin under the iho-psoas, and is adherent to the muscle. Its fibrous part is perforated medially 
by the accessory and round ligaments and the articular 



The round ligament (Lig. teres) is a short, strong band which is attached 
in the subpubic groove close to the acetabular notch, passes outward, and ends 
in the notch on the head of the femur (Fig. 581). 



232 THE ARTICULATIONS OF THE HORSE 

The accessory ligament (Lig. accessorium)i does not occur in the domestic 
animals other than the equidse. It is a strong band detached from the prepubic 
tendon of the abdominal muscles (Fig. 581). It is directed outward, backward, 
and upward, passes through the acetabular notch dorsal to the transverse ligament, 
and ends behind the round ligament in the notch on the head of the femur. The 
origin of the pectineus muscle is perforated by the ligament, which furnishes at- 
tachment to many fibers of the muscle. 

The synovial membrane is reflected over the intracapsular parts of these lig- 
aments and covers the fossa acetabuli. A pouch also extends from the acetabular 
notch for a variable distance along the subpubic groove above the accessory liga- 
ment. 

Movements. — This joint is capable of all the movements of a ball-and-socket 
joint, viz., flexion, extension, abduction, adduction, rotation, and circumduction. 
The greatest range of movement is displayed in flexion and extension. When 
standing at rest, the joint is partially flexed, the articular angle (in front) being 
about 100° to 115°. The other movements occur to a very limited extent in normal 
action. Abduction appears to be checked by tension of the round and accessory 
ligaments. The accessory ligament is tensed most promptly by inward rotation of 
the thigh. 

THE STIFLE JOINT 

This joint (Articulatio genu), which corresponds to the knee-joint of man, 
is the largest and most elaborate of all the articulations. Taken as a whole, it 
may be classed as a ginglymus, although it is not a typical example of the group. 
In reality it consists of two joints — the femoro-patellar and the femoro-tibial. 

The femoro-patellar articulation (Articulatio femoro-patellaris) is formed 
between the trochlea of the femur and the articular surface of the patella. 

Articular Surfaces. — The trochlea consists of two slightly oblique ridges, 
with a wide and deep groove between them. The medial ridge is much the larger 
of the two, especially at its proximal part, which is wide and rounded. The lateral 
ridge is much narrower, and is more regularly curved; its proximal part lies about 
an inch behind a frontal plane tangent to the medial one. The articular surface 
of the patella is much smaller than that of the trochlea. It is completed medially 
by a supplementary plate of fibro-cartilage (Fibrocartilago patellae), which curves 
over the medial ridge of the trochlea. A narrow strip of cartilage is found along 
the lateral border also. The articular cartilage on the trochlea completely covers 
both surfaces of the medial ridge, but extends only a short distance on the lateral 
surface of the outer ridge. 

Joint Capsule. — This is thin and is very capacious. On the patella it is 
attached around the margin of the articular surface, but on the femur the line of 
attachment is at a varying distance from the articular surface. On the medial side 
it is an inch or more from the articular cartilage; on the lateral side and above, 
about half an inch. It pouches upward under the quadriceps femoris for a distance 
of two or three inches, a pad of fat separating the capsule from the muscle. Be- 
low the patella it is separated from the patellar ligaments by a thick pad of fat, 
but inferiorly it is in contact with the femoro-tibial capsules. The joint cavity is 
the most extensive in the body. It usually communicates with the medial sac of 
the femoro-tibial joint cavity by a slit-like opening situated at the lowest part of 
the medial ridge of the trochlea. A similar, usually smaller, communication with 
the lateral sac of the femoro-tibial capsule is often found at the lowest part of the 
lateral ridge. 

The medial communication is rarely absent in adult horses, but is liable to be overlooked 
on account of the fact that it is covered by a valvular fold of the synovial membrane. It is about 

^ This is also commonly called the pubo-femoral ligament. 



THE STIFLE JOINT 



233 



half an inch ^vnde, and bes under the narrow articular area wliich connects the trochlea and medial 
condyle. Ihe lateral communication occui-s in 18 to 25 per cent, of cases, according to Baum; in 
rare cases it is larger than the inner one. It is instructive to distend this capsule and thus obtain 
an idea of its potential capacity and relations (Fig. 246). 

Ligaments. — The femoro-patellar ligaments, lateral and medial (Lig. femoro- 
patellare fibulare, tibiale), are two thin bands which reinforce the capsule on either 



Patella 



Accessory cartilage of — 
patella 



Medial ridge of trochlea 
Medial patellar ligament 

Medial epicondyh 

Medial femoro-tibial 
ligament 

Medial meniscus 
Medial condyle of tibia 



Tuberosity of tibia 




Biceps femoris 

Lateral patellar ligament 



Lateral femoro-tibial 
ligament 

Lateral meniscus 
Lateral condyle of tibia 



Interosseous space 



Fibula 



hderosseous ligament 



Fig. 245. — Left Stifle Joint of Horse; Froxt View. The Capsules are Removed. 
1, Middle patellar ligament; 2, stump of fascia lata; 3, stump of common tendon of extensor longus and peroneus 



side. The lateral ligament is fairly distinct; it arises from the lateral epicondyle of 
the femur just above the lateral femoro-tibial ligament, and ends on the lateral 
border of the patella. The medial ligament is thinner and is not distinct from the 
capsule; it arises above the medial epicondyle, and ends on the patellar fibro-car- 
tilage. 

The patellar ligaments (Ligg. patellae)^ are three very strong bands which at- 

^ They are also termed the straight ligaments of the patella. This term seems objectionable 
since they are all obUque in direction. 



234 



THE ARTICULATIONS OF THE HORSE 



tach the patella to the tuberosity of the tibia. The lateral patellar ligament ex- 
tends from the lateral part of the anterior surface of the patella to the lateral part 
of the tubcrosit}^ of the tibia. It receives a strong tendon from the biceps femoris 
muscle and also part of the fascia lata. The middle patellar ligament extends 
from the front of the apex of the patella to the distal part of the groove on the 
tuberosit}^ of the tibia; a bursa is interposed between the ligament and the upper 
part of the groove, and a smaller one occurs between the upper part of the ligament 
and the apex of the patella. The medial patellar ligament is attached above to the 



Proximal end of 
femoro- patellar 



Lateral head of gastrocnemius 

Lateral fetnoro-patellar ligament 

Attachment of joint capsule 
Lateral condyle of femur 
Lateral fejnoro-tibial ligament- 
Popliteus 



Deep digital flexor 




Base of patella 



-Distal end of capsule 
— -Middle patellar ligament 
ll'^^ Medial patellar ligament 

Lateral patellar ligament 

{stump) 

Tuberosity of tibia 
Tibialis anterior 



Long extensor 

Lateral extensor 

Fig. 246. — Right Stifle Joint of Horse; Latehal View. 

The femoro-patellar capsule was filled with plaster-of-Paris and then removed after the cast was set. The femoro- 

tibial capsule and most of the lateral patellar ligament are removed. M, Lateral meniscus. 



patellar fibro-cartilage, and ends on the tuberosity of the tibia at the medial side of 
the groove. It is joined by the common aponeurosis of the gracilis and sartorius, 
and its proximal part furnishes insertion to fibers of the vastus medialis. These 
so-called ligaments are, in reality, the tendons of insertion of the quadriceps 
femoris and biceps fe-moris muscles, and transmit the action of the latter to the 
tibia; they also function similarly for the other muscles attached to them as noted 
above. 

It will be noticed that the proximal attachments are further apart than the distal ones, so 
that the ligaments converge below. The medial ligament is especially oblique. The middle 
ligament is more deeply placed than the others, and therefore cannot usually be felt so distinctly 
in the living animal. The lateral ligament is very largely the tendon of the anterior part of the 



THE STIFLE JOINT 



235 



biceps femoris, but it also furnishes insertion to the tensor fasciae latse by means of the fascia 
lata, which blends with it. 

The femoro-tibial articulation (Articulatio femoro-tibialis) is formed between 
the condyles of the femur, the proximal end of the tibia, and the interposed articular 
menisci or semilunar cartilages. 

Articular Surfaces. — The condyles of the femur are slightly oblique in direc- 
tion. The articular surface of the lateral one is more strongly curved than that of 
the medial one; the latter is confluent below with the medial ridge of the trochlea. 



Base of patella 



Medial condyle of 
femur 
Medial femoro-tibial 
ligament 
Medial meniscus 

Medial condyle of 
tibia 




Accessory cartilage 



'^Tf Medial ridge of trochlea 

Medial patellar liga- 



Middle patellar liga- 
metd 



Tuberosity of tibia 



Fig. 247. — Left Stifle Joint of Horse; Medial View. The Capsules are Removed, 



while the narrow ridge which connects the lateral condyle with the trochlea is 
usually non-articular. The saddle-shaped surfaces of the condyles of the tibia are 
not adapted to the femoral condyles, and are in contact with only a small part of 
them. 

The menisci, lateral and medial (Meniscus lateralis, medialis),i are two C- 
shaped or crescentic plates of fibro-cartilage which produce congruence in the ar- 
ticular surfaces. Each has a proximal concave surface adapted to the condyle of 
the femur, and a distal surface which fits the corresponding condyle of the tibia. 
1 These are also commonly termed the semilunar cartilages, although they are not so shaped. 



236 



THE ARTICULATIONS OF THE HORSE 



The lateral meniscus does not cover the lateral and posterior part of the tibial con- 
djde, over which the tendon of origin of the popliteus muscle plays. The peripheral 
border is thick and convex, the central one very thin and concave. The fibrous 
ends or ligaments are attached to the tibia in front of and behind the spine. The 
lateral meniscus has a third attachment by means of an oblique band (Ligamentum 
femorale menisci lateralis) which passes from the posterior end to the posterior 
part of the intercondyloid fossa of the femur. 



Base of patella 



Medial ridge of 
trochlea 



Lateral patellar liga- : 

ment 



Middle patellar liga- 
ment 




Stump of biceps 
femoris 



La teralfem oro-pa tellar 
ligament 



Lateral condyle of 
femur 

Lateral femoro-tihial 

ligament 

Lateral meniscus 



Lateral condyle of 
tibia 



Tvherosity of tibia 



Fig. 248. — Left Stifle Joint of Honsio; Lateral Vie-v. The CAPSULEa are Remov 



1, Stump of tendon of origin of extensor longus and peroneus tertius; 2, stump of fascia lata; 3, patellar attachment of 
biceps femoris and lateral patellar ligament. 



The ligaments of the medial meniscus (Ligamenta tibialia anterius et posterius menisci m.edi- 
alis) are attached in front of and beliind the medial eminence of the spine. The anterior ligament 
of the lateral meniscus (Ligamentum tibiale anterius menisci lateraUs) is attached in front of the 
lateral eminence of the spine. The posterior one bifurcates; the lower branch (Ligamentum tibiale 
posterius menisci lateralis) is inserted at the popliteal notch, the upper (Ligamentum femorale 
menisci lateralis) in a small fossa in the extreme posterior part of the intercondyloid fossa. 

The joint capsule is attached to the margin of the tibial articular surface, 
but on the femur the line of attachment is for the greater part about half an inch 
(ca. 1 cm.) from the articular margin. It is also attacterl to the convex borders of 
the menisci and to the cruciate ligaments. It is thin in front, where it consists 



THE STIFLE JOINT 



237 



practically of the synovial layer only. It is much stronger posteriorly: here it 
is reinforced by what might be regarded as a posterior ligament. This is a 
strong, flat band which arises from the femur just lateral to the origin of the medial 
head of the gastrocnemius, and extends down to the posterior border of the medial 
condyle of the tibia; it is wider below than above. There are two synovial sacs, 
corresponding to the double nature of the articular surfaces; they do not usually 
communicate, and each is partially divided into an upper and a lower compartment 
by the meniscus. The medial sac pouches upward about half an inch over the con- 



Lateral condyle of 

Jem ur 



Lateral femoro- 

tibial ligament 

Shimp of pop- 

liteus tendon 

Lateral meniscus 



Lateral condyle of 
tibia 



Head of fibula 



Interosseous space 



Y* — Medial femoro- 
'\\ tibial ligament 



condyle of 
femur 




Medial meniscus 



Medial condyle of 
tibia 



Fig. 249. — Left Stifle Joint of Horse; Posterior View. The Capsule is Removed. 
1, Femoral ligament of lateral meniscus; 2, posterior ligament of lateral meniscus; 3, anterior cruciate ligament; 4, 

posterior cruciate ligament. 



clyle of the femur. The lateral sac invests the tendon of origin of the popliteus 
muscle, and also pouches downward about three inches (ca. 7.5 cm.) beneath the 
peroneus tertius and extensor longus muscles. As stated above, the lateral sac 
sometimes communicates with the femoro-patellar joint cavity, and the medial 
sac usually does so in the adult. 

Ligaments. — There are four of these — two collateral and two cruciate. 

The medial ligament (Lig. collaterale tibiale) is attached above to the prom- 
inent medial epicondyle of the femur, and below to a rough area below the margin 
of the medial condyle of the tibia. 



238 



THE ARTICULATIONS OF THE HORSE 



The lateral ligament (Lig. collaterale fibulare) is somewhat thicker; it arises from 
the upper depression on the lateral epicondj^e, and ends on the head of the fibula. 



Middle patellar 
ligament 



Lateral patellar 
ligament 



Medial patellar 
ligament 



Medial condyle 




Medial meniscus 



Fig. 250. — Proximal End of Right Tibia with Menisci, Etc. 
1, 2, Anterior and posterior cruciate ligaments; 3, posterior ligament of medial meniscus; 4, femoral ligament of 
lateral meniscus; 5, 5', anterior ligaments of menisci; 6, groove for popliteus tendon; 7, spine of tibia; 8, 9, medial 
and lateral femoro-tibial ligaments. 



It covers the tendon of the origin of the popliteus muscle, a bursa being interposed 

between the two; another bursa is present 
between the lower part of the ligament and 
the margin of the lateral condyle of the tibia. 
The cruciate ligaments are two strong 
rounded bands situated mainly in the inter- 
condyloid fossa of the femur, between the two 
synovial sacs. They cross each other some- 
what in the form of an X, and are named ac- 
cording to their tibial attachments. The 
anterior cruciate ligament (Lig. cruciatum an- 
terius) arises in the central fossa on the tibial 
spine, extends upward and backward, and ends 
on the lateral wall of the intercondyloid fossa. 
The posterior cruciate ligament (Lig. crucia- 
tum posterius) is medial to the preceding, and 
is somewhat larger. It is attached to an emi- 
nence at the popliteal notch of the tibia, is 
directed upward and forward, and ends in the 
anterior part of the intercondyloid fossa of 
the femur. 

It may be added that these ligaments do not lie in a sagittal plane, but are somewhat twisted 
across each other; outward rotation of the leg untwists and slackens them. 

Movements. — The principal movements of the stifle joint as a whole are 




Fig. 251. — Proximal End of Right Tibia of 
Horse, with Areas of Ligamentous At- 
tachment. 
1, 2, Medial and lateral patellar ligaments; 

3, 4, anterior ligaments of menisci; 5, 7, anterior 

and posterior cruciate ligaments; 6, posterior 

ligament of medial meniscus. 



TIBIO-FIBULAR ARTICULATION THE HOCK JOINT 239 

flexion and extension. In the ordinary standing position the articular angle 
(behind) is about 140° to 150°. Flexion is limited only by contact of the leg with 
the thigh, if the hock is also flexed. Extension is incomplete, i. e., the femur and 
tibia cannot be brought into the same straight line. Rotation is limited, and is 
freest during semiflexion. The patella glides on the femoral trochlea upward in 
extension, downward in flexion. 

Extension is checked mainly by tension of the cruciate and collateral ligaments. In extreme 
extension, which is accompanied by slight outward rotation of the leg, the patella can be pushed 
upward and inward so that its fibro-cartilage hooks over the upper end of the medial ridge of the 
trochlea, but it will not remain there unless held in position. When pressure is removed, the base 
of the patella tips forward and the cartilage lies upon the most prominent part of the trochlear 
ridge. During flexion, which is accompanied by slight inward rotation of the leg, the condyles 
of the femur and the menisci gUde backward on the tibia; the movement of the lateral condyle 
and meniscus is gi-eater than that of the medial one. In extreme flexion the patellar and posterior 
cruciate ligaments are tense; the other ligaments are relaxed. The movement of the patella is 
gliding with coaptation, i. e., different parts of the opposing articular surfaces come into contact 
successively. Only a narrow transverse strip (ca. 1.5-2 cm. wide) of the patella is in contact 
with the trochlea at a time. 

TIBIO-FIBULAR ARTICULATION 

This joint (Articulatio tibiofibularis) is formed by the head of the fibula ar- 
ticulating with a crescentic facet just below the outer margin of the lateral condyle 
of the tibia. The joint capsule is strong and close. The shaft of the fibula is at- 
tached to the lateral border of the tibia b}^ the interosseous membrane of the leg 
(Membrana interossea cruris); this is perforated about an inch from its proximal 
end by an opening which transmits the anterior tibial vessels to the front of the tibia. 
A fibrous cord usually extends from the distal end of the shaft of the fibula to the 
lateral malleolus. The latter is the distal end of the fibula which has fused with the 
tibia. No appreciable movement occurs in this joint. 



THE HOCK JOINT 

This is a composite joint made up of a number of articulations (Artie ulationes 
tarsi). These are: (1) The tibio-tarsal articulation; (2) the intertarsal articula- 
tions; (3) the tarso-metatarsal articulation. 

The tibio-tarsal articulation (Articulatio talocruralis) is a typical ginglymus 
formed by the trochlea of the tibial tarsal bone and the corresponding surface of the 
distal end of the tibia. The ridges and grooves of these surfaces are directed ob- 
liquel}^ forward and outward at an angle of about 12° to 15° with a sagittal plane. 
The trochlear surface is about twice as extensive as that on the tibia, and its ridges 
have a spiral curvature. The other articulations are arthrodia, which have joint 
surfaces and ligaments of such a nature as to allow only a minimal amount of glid- 
ing motion. 

As in the case of the carpal joints, it is convenient to describe first the common 
capsule and ligaments, which are the more important practically, and then to 
consider very briefly the special ligaments. 

The fibrous part of the joint capsule is attached around the margin of the 
tibial articular surface above and the metatarsal surfaces below; it is also attached 
in part to the surfaces of the bones which it covers, and blends with the collateral 
ligaments. Its dorsal part (anterior ligament) is rather thin; in distention of the 
capsule, as in "bog-spavin," its antero-medial part, which is not bound down by 
the tendons passing over the joint, forms a fluctuating swelling over the medial 
ridge of the trochlea. The plantar part (posterior and tarso-metatarsal ligaments) 
is very thick below, and is intimately attached to the tarsal bones. It is in part 
cartilaginous, and forms a smooth surface for the deep flexor tendon. The proximal 
part pouches upward behind the distal end of the tibia for a distance of about two 



240 



THE ARTICULATIONS OF THE HORSE 



inches (ca. 5 cm.) ; here it is thin. It is continued downward to form the sub- 
tarsal or check ligament, which unites with the deep flexor tendon about the mid- 
dle of the metatarsus. 

There are four synovial sacs: 1. The tibio-tarsal sac lubricates the proximal 
joint, and is much the largest and most important.^ 2. The proximal intertarsal 
sac lines the joints formed by the tibial and fibular tarsal bones above, and the cen- 
tral and fourth tarsals below; it communicates in front with the til)io-tarsal sac. 
3. The distal intertarsal sac lubricates the joints formed between the central tarsal 
and the bones below and on either side. 4. The tarso-metatarsal sac lubricates 

Tuber calcis 




Medial malleolus 

Long medial ligament 
Trochlea of tibial tarsal bone 



Dorsal ligament 



ML III 




ML II 



Fig. 252. — Right Hock Joixt of Horse; Medial View. The Capsule is Removed. 

1, 2, Branches of short part of medial ligament; 3, tarso-metatarsal ligament; 4, proximal tuberosity of tibial tarsal 

bone; 5, sustentaculum; 6, groove for deep flexor tendon; Mt. II, Ml. Ill, metatarsal bones. 



the joints formed between the tarsal and metatarsal bones, those between the 
proximal ends of the metatarsal bones, and those formed by the third tarsal with 
the bones on either side. 

Common Ligaments. — The lateral ligament (Lig. collaterale fibulare) consists 
of two distinct bands which cross each other. The long lateral ligament (Lig. 
collaterale laterale longum) is superficial ; it arises on the posterior part of the lateral 
malleolus, is directed almost straight downward, and is attached to the fibular and 
fourth tarsal bones and the large and lateral small metatarsal bones. It forms a 
canal for the lateral extensor tendon. The short lateral ligament (Lig. collaterale 

^ It is this part of the capsule which is chiefly involved in distention by excess of fluid in the 
joint cavity (as in "bog-spavin"). 



THE HOCK JOINT 



241 



laterale breve) is deeper; it arises on the anterior part of the lateral malleolus, is 
directed chiefly backward, and ends on the rough excavation on the lateral surface 
of the tibial tarsal and the adjacent surface of the fibular tarsal bone. 

The medial ligament (Lig. collateral tibiale) also consists of two parts which 
cross each other. The long medial ligament (Lig. collateral mediale longum) 
is superficial; it arises on the posterior part of the medial malleolus, becomes wider 
below, and is attached on the distal tuberosity of the tibial tarsal, the large and 
medial small metatarsal bones, and the surface of the lower tarsal bones which it 

Tuber calcis 



Plantar ligament 



ML IV 




Short lateral ligament 
Long lateral ligament 



Fig. 253. — Right Hock .Joint or Hor.se; Lateral View. The Capsule is Removed. 
1, Ligament connecting lateral ridge of tibial tarsal with processus cochlearis of fibular tarsal bone; 2, groove for 
lateral extensor tendon; T. t., lateral ridge of trochlea of tibial tarsal bone; T. c, central tarsal bone; T. 3, third tarsal 
bone; Mt. Ill, Ml. IV, metatarsal bones. 



covers. The short medial ligament (Lig. collaterale mediale breve) lies largely 
under cover of the long one. It extends from the anterior part of the medial malleo- 
lus, runs backward and somewhat downward, and divides into two branches; one 
of these ends on the proximal tuberosity on the medial surface of the tibial tarsal 
bone, the other on the sustentaculum tali. 

The plantar ligament (Lig. tarsi plantare)i is a very strong, flat band which 
covers the outer part of the plantar surface of the tarsus. It is attached to the 
plantar surface of the fibular and fourth tarsal bones and the proximal end of the 
lateral metatarsal bone. 

The dorsal ligament (Lig. tarsi dorsale)^ is a triangular sheet which is attached 

^ Also termed the calcaneo-metatarsal ligament. ^ Also known as the oblique ligament. 
16 



242 



THE ARTICULATIONS OF THE HORSE 



above to the distal tuberosity on the medial face of the tibial tarsal bone, and 
spreads out below on the central and third tarsal bones, and the proximal ends of 
the large and outer small metatarsal bones, to all of which it is attached. 

Special Ligaments. — A considerable number of short bands which connect 
adjacent bones of the tarsus and metatarsus are described by various authors; 
some of these are quite distinct; others are difficult to isolate. Most of them are 
not of sufficient importance to justify detailed description. 



Tuber calcis 



Lateral malleolus 



Short lateral ligament 



Trochlea, of tibial tarsal 
bone 




Short tncdial ligaments 



Ml. IV 



Fig. 254. — Right Hock Joint of Horse. Viewed from the Front and Slightly Laterally After Removal of 

Joint Cap.sule and Long Collateral Ligaments. 

T. t., Tibial tarsal bone (distal tuberosity); T. c, central tarsal bone; T. 3, ridge of third tarsal bone; T.f., fibular tarsal 

bone (distal end); T. 4, fourth tarsal bone; Mt. Ill, Mt. IV, metatarsal bones. Arrow points to vascular canal. 



(1) The tibial and fibular tarsal bones are united by four bands (astragalo-calcaneal liga- 
ments). The medial ligament extends from the sustentaculum tali to the adjacent part of the 
tibial tarsal, blending with the short collateral ligament. The lateral ligament extends from the 
cochlear process of the fibular tarsal to the adjacent part of the lateral ridge of the trochlea. 
The proximal ligament extends from the posterior margin of the trochlea to the fibular tarsal. 
The interosseous ligament is deeply placed in the sinus tarsi between the two bones, and is at- 
tached in the rough areas of the opposed surfaces. 

(2) The smaller bones are attached to each other as follows: The central and third tarsal are 
united by an interosseous and an oblique dorsal ligament (scaphoido-cunean ligaments). The 
central and fourth tarsal are united by an interosseous and a lateral transverse ligament (cuboido- 
ecaphoid ligament). The third and fourth tarsals are similarly connected (cuboido-cunean liga- 
ments). The third tarsal is joined by an interosseous (intercunean) ligament to the (fused) first 
and second tarsals; the latter are connected with the fourth tarsal by a plantar transverse liga- 
ment. 

(3) The smaller bones are connected with the proximal row as follows; The central is 



THE HOCK JOINT 



243 



attached to the tibial by plantar and interosseous (astragalo-scaphoid) ligaments, and to the fibular 
tarsal by a short oblique (calcaneo-scaphoid) band. The fourth is attached to the fibular tarsal 
by interosseous and plantar (calcaneo-cuboid) hgaments. The (fused) first and second tarsals 
are connected with the fibular tarsal by a plantar (calcaneo-cunean) ligament. 

(4) The distal tarsal bones are connected with the metatarsus by tarso-metatarsal hgaments, 
which are not distinct from the common Hgaments, except in the case of the interosseous ligament 
between the third tarsal and metatarsal bones. 

Movements. — These are flexion and extension, which take place at the tibio- 
tarsal joint. The movements between the tarsal bones, and between the latter 
and the metatarsus, are so limited as to be negligible so far as the action of the joint 
as a whole is concerned. In the standing position the articular angle (in front) 



Superficial flexor tendon 

Gastrocnemius tendon 

Tarsal tendon of 
biceps femoris 

Calcanean bursa 

Gastrocnemius 
bursa 

Tuber calcis- 



Upper po^ich of 
joint capsule 



Tibial tarsal bone 

Interosseous ligunient 

Plantar ligament 

Fourth tarsal bone 

Interosseous ligament 
Large metatarsal bone 

Suspensory ligament 
Check ligament 



Tibia 




Tibialis anterior 
Peroneus tertius 



Tibio-tarsal joint cavity 
Joint capsule 
Central tarsal bone 
Third tarsal bone 

Distal annular ligament 



Fig. 255. — Sagittal Section of Hock of Horse. 
The section is cut so far laterally that the deep flexor tendon does not show. 



is about 150° to 160°. Complete extension is prevented by tension of the collateral 
ligaments. Flexion is checked only by contact of the metatarsus with the leg, 
provided the stifle joint is also flexed. Owing to the fact that the axis of motion 
is slightly oblique, the lower part of the limb deviates somewhat outward during 
flexion. The long collateral hgaments are tense in extension, the short ones in 
flexion, of the joint. The movements of the hock joint must correspond with those 
of the stifle on account of the tendinous bands in front and behind (peroneus tertius 
and flexor superficialis), which extend from the lower part of the femur to the tarsus 
and metatarsus. 

The remaining joints differ in no material respect from those of the thoracic 
limb. 



244 



COMPARATIVE ARTHROLOGY 



COMPARATIVE ARTHROLOGY ^ 
Joints and Ligaments of the Vertebrje 

Ox. — The ligamentum nuchse is better developed than in the horse. The 
funicular part is clearly divided into two lateral halves, which are round at their 
occipital attachment, but from the axis backward become rapidly Avider and fiat. 
This wide portion is almost sagittal, lies on either side of the vertebral spines, and 
is covered by the trapezius and rhomboideus muscles. From the highest part of 
the withers (third thoracic spine) it gradually diminishes in size and fades out in 
the lumbar region. The lamellar part is thick, and consists of anterior and pos- 
terior parts. T'he anterior part is double; its fibers proceed from the funicular 
part to the second, third, and fourth cervical spines. The posterior part is single; 
its fibers extend from the first thoracic spine to the fifth, sixth, and seventh cervical 
spines. 

The ventral longitudinal ligament is very strong in the lumbar region. 




Fig. 256. — Ligamentttm Nttch/e of Ox. 

o, Funicular part; 6, its wide portion; <?, rf, lamellar part; e, interspinous ligament; ?, spinous process of first thoracic 

vertebra; 2, axis (Ellenberger-Baum, Anat. d. Haustiere.) 



The intervertebral fibro-cartilages are thicker than in the horse. 

The interspinous ligaments of the back and loins consist largely of elastic 
tissue. 

There are no intertransverse joints in the lumbar region. 

Pig. — The ligamentum nuchae is represented by a fibrous raphe and thin 
layers of elastic tissue which extend between the cervical spines. 

The atlanto-occipital and atlanto-axial joints resemble those of the dog. 

The interspinous ligaments of the neck are elastic. 

Dog. — The ligamentum nuchse consists of a small fibrous band which extends 
from the spine of the axis to the anterior thoracic spines; it may be regarded as a 
mere fibrous raphe between the right and left muscles. 

There are interspinous muscles instead of ligaments in the neck. 

There are three ligaments in connection with the dens of the axis. The two 
alar ligaments (Ligg. alaria) arise on either side of the dens, diverge, and end on 

^ This section consists necessarily only of a brief statement of the most important differences 
in the joints of the other animals. 



ARTICULATIONS OF THE THORACIC LIMB 245 

either side of the foramen magnum. The transverse ligament of the atlas (Lig. 
transversum atlantis) stretches across the dorsal surface of the dens and binds it 
down on the ventral arch of the atlas, a bursa being interposed. It is attached on 
either side to the lateral mass of the atlas. 

The two capsules of the atlanto-occipital joint communicate with each other, 
and usually with the capsule of the atlanto-axial joint also. 



Articulations of the Thorax 

Ox. — The second to the eleventh costo-chondral joints inclusive are diarthroses 
with close capsules, reinforced externall}-. (They are synchondroses in the sheep.) 
The upper parts of the cartilages are attached to each other by cUstinct elastic liga- 
ments (Ligg. intercostalia) . 

The first pair of chondro-sternal joints are separate from each other; inter- 
crossing fibers unite the costo-chondral junctions above the joints. 

The first segment of the sternum forms ^\dth the body a diarthrodial interstemal 
joint (Articulatio intersternalis) . The anterior joint surface is concave, the pos- 
terior convex. The joint is surrounded by a close capsule, and the joint surfaces 
are attached to each by a small inter-articular ligament. Limited lateral move- 
ment is possible. (In the sheep the joint is a synchondrosis.) Both surfaces of the 
sternum are covered by a layer of fibrous tissue (Membrana sterni). 

Pig. — The second to the fifth or sixth costo-chondral joints are diarthroses. 
The intersternal articulation and the sternal ligaments resemble those of the ox. 

Dog. — The first chondro-sternal joints do not coalesce. The internal sternal 
ligament divides into three bands. 



TEMPORO-MANDIBULAR ARTICULATION 

Ox. — The articular surfaces are of such a character as to permit more extensive 
transverse movement than in the horse {vide Osteology). The posterior ligament 
is absent. 

Pig. — The considerable longitudinal diameter of the temporal articular sur- 
faces and the very small size of the postglenoid process allow great freedom of 
protraction and retraction of the lower jaw. Transverse movement is limited. 
The posterior ligament is absent. 

Dog. — The articular surfaces allow extremely little transverse or gliding move- 
ment. They are cylindrical in curvature, and the interarticular disc is very thin. 
The posterior ligament is absent. 

The other articulations of the skull are sufficiently described in the Osteology. 



Articulations of the Thoracic Limb 
shoulder joint 

Ox. — The articular angle is about 100°. 

Pig and Dog. — The joint capsule communicates so freely with the bicipital 
bursa that the latter may well be regarded as a pouch of the capsule. There is a 
rudimentary marginal cartilage around the rim of the glenoid cavity. In the pig 
the front of the capsule is reinforced by cruciate bands. In the dog there is usu- 
ally a strong band extending from the acromion to the lateral part of the capsule; 
another band (Ligamentum coraco-acromiale) often stretches between the scapular 
tuberosity and the acromion. 



246 COMPARATIVE ARTHROLOGY 



ELBOW JOINT 

Ox. — No important differences exist. The upper part of the intero.sseous 
raclio-ulnar hgament is commonly ossified in the adult. 

Pig. — There are no important differences. The radius and ulna are so firmly 
united bj^ the interosseous ligament as to prevent any appreciable movement be- 
tween them. 

Dog. — The joint capsule is reuiforced in front by an oblique ligament which 
arises on the front of the lateral condyle of the humerus above the joint surface, 
and joins the terminal part of the biceps and brachialis below. There is a strong 
reinforcement of the postero-medial part of the capsule, which extends obliquely 
from the medial side of the olecranon fossa to the ulna, just above the processus an- 
coneus. The lateral ligament is much stronger than the medial one. It is attached 
above to the lateral epicondyle of the humerus, and below chiefly to the eminence 
distal to the neck of the radius ; but part of it inclines backward and is attached to 
the ulna. The middle part of the ligament is wide and forms a sort of cap over the 
proxmial tuberosity of the radius. From this part a band, the annular ligament 
of the radius (Lig. annulare radii), extends across the front of the proximal end of 
the radius and ends on the ulna; although incorporated in the joint capsule it is 
easily defined. The medial ligament is more slender. It arises from the medial 
epicondyle of the hmnerus and passes deeply into the proximal part of the inter- 
osseous space, ending chiefly on the posterior surface of the radius a little medial to 
the attachment of the lateral ligament; there is also a small attachment to the 
interosseous border of the ulna. This ligament is very oblique. An elastic band 
(Ligamentum olecrani) extends from the lateral surface of the medial epicondyle 
to the anterior border of the ulna. 

There are two radio-ulnar joints. The proximal radio-ulnar joint (Articulatio 
radioulnaris proximalis)is included in the capsule of the elbow, but is provided \\dth 
an annular hgament, as described above. The distal radio-ulnar joint (Articulatio 
radioulnaris distahs) is formed by a concave facet on the radius and a convex one on 
the ulna, and is surrounded by a tight capsule. The interosseous membrane unites 
the shafts of the two bones; its proximal part is specially strong and is attached to 
prominences on both bones. The movements consist of limited rotation of the 
radius (ca, 20°), carrying the paw with it. The ordinary position is termed prona- 
tion; outward rotation is supination.^ 



THE CARPAL JOINTS 

These have the same general arrangement as in the horse. Numerous minor 
differences naturally exist, but must be excluded from this brief account, which 
contains only important special features. 

The lateral and medial movements are freer, especially in the dog, but flexion is 
not so complete : the anatomical explanation of these facts lies in the nature of the 
articular surfaces and certain hgamentous differences. The coUateral ligaments are 
much weaker, the long lateral one being especially small in the ox. Two obhque, 
somewhat elastic bands cross the front of the radio-carpal and intercarpal joints. 
The proximal one is attached to the distal end of the radius and passes do^vnward 
and outward to the ulnar carpal bone ; the other one connects the radial and fourth 
carpal bones in a similar fashion. 

In the ox the short collateral ligaments are well defined; a ligament connects 
the accessory carpal with the distal end of the ulna, and strong volar bands connect 

1 These movements are best seen in man, in whom the back of the hand may be turned for- 
ward (pronation) or backward (supination). In the dog the rotation is much restricted and is 
freest when the elbow is flexed. 



INTERMETACARPAL JOINTS METACARPO-PHALANGEAL JOINTS 



247 



the distal bones with the metacarpus 
ulnar carpal bone with the meta- 
carpus. 

The dorsal, volar, and interos- 
seous carpal ligaments vary with the 
number of carpal bones present in 
the different species. 

In the dog there are six dorsal 
and six volar ligaments. The inter- 
osseous ligaments are not inter- 
ordinal. The accessory carpal bone 
is attached l)y ligaments to the ulna, 
the radio-intermediate, and the 
third, fourth, and fifth metacarpal 
bones. The distal carpal bones are 
attached to the metacarpal bones by 
dorsal and volar ligaments. 



INTERMETACARPAL JOINTS 

In the ox the small (fifth) meta- 
carpal bone articulates with the large 
metacarpal, but not with the carpus. 
The joint cavity is connected with 
that of the carpo-metacarpal sac. 
The proximal end of the small meta- 
carpal bone is attached by a ligament 
to the fourth carpal, and another 
band extends from its distal part 
to the side of the large metacarpal. 
There is also an interosseous liga- 
ment, which is permanent and allows 
a small amount of movement. 

The chief metacarpal bones of 
the pig, and the second to the fifth of 
the dog, articulate with each other 
at their proximal ends, and are con- 
nected by interosseous ligaments, 
which do not, however, unite them 
closely, as in the horse. There are 
feeble dorsal and volar ligaments 
(Ligg. basium) which unite the 
proximal ends of the metacarpal 
bones in the dog. 



A strong oblique ligament connects the 




Fig. 257. — Distal Part of Limb of Ox, Showing Ligaments 
AND Tendons. One Digit .\nd Corresponding Articu- 
lar Part of Metacarpal Bone are Removed. 
a, Suspensory ligament; a', branch of a to superficial flexor 
tendon; a", a"', lateral and central branches of o; b, deep flexor 
tendon; 6', branch of 6 to digit removed; c, c, superficial flexor 
tendon; d, d', intersesamoid hgament (cut); e, interdigital col- 
lateral hgament of fetlock joint; /, tendon of common extensor; 
g, proximal interdigital hgament; h, digital annular hgament; 
i, posterior annular hgament of fetlock; k, collateral hgament 
of pastern joint; I, distal interdigital ligament; m, cruciate inter- 
digital hgament (cut) ; m', m", attachments of m to second pha- 
lanx and distal sesamoid bone; n, suspensory hgament of distal 
sesamoid; o, dorsal elastic ligament; p, lateral volar ligament 
of pastern joint; 1, metacarpus, sawn off at /'; S, first phalanx; 
3, second phalanx; 4, third phalanx. (EUenberger-Baum, Anat. 
d. Haustiere.) 



METACARPO-PHALANGEAL JOINTS 
Ox. — There are two joints, one 
for each digit. The volar parts of 
the two joint capsules communicate. 
The two interdigital collateral liga- 
ments (Ligg. collateralia interdigi- 
talia) result from the bifurcation of a 

band which arises in the furrow between the divisions of the distal end of the large 
metacarpal bone; they spread out and end on the proximal ends of the first pha- 



248 COMPARATIVE ARTHROLOGY 

langes. The other collateral ligaments are arranged like those of the horse. A strong 
interdigital ligament (Lig. interdigitale) , consisting of short intercrossing fibers, 
unites the middles of the interdigital surfaces of the first phalanges of the chief digits. 
It prevents undue divergence of the phalanges. It is not present in the sheep. 

Cruciate ligaments (Ligg. phalango-sesamoidese) connect the proximal sesamoids 
with the proximal end of the opposite first phalanx. 

The intersesamoid ligament connects all four sesamoids, and extends upward 
much less than in the horse. 

The laterate and medial sesamoidean ligaments end chiefly on the first phalanges, 
but also detach a small part to the large metacarpal bone. 

The superficial or straight distal sesamoidean ligament is absent. The middle 
distal sesamoidean ligaments of each digit are two short, strong bands which extend 
from the distal margins of the proximal sesamoids to the proximal ends of the first 
phalanges. The deep distal sesamoidean ligaments are strong and distinctly 
cruciate. 

The suspensory ligament or interosseus tendon contains more muscular 
tissue than in the horse — indeed, in the young animal it consists almost entirely of 
muscular tissue. At the distal third of the metacarpus it divides into three branches. 
These give rise to five subdivisions, either by bifurcation of the lateral and medial 
branches or trifurcation of the middle branch. The two lateral and two medial 
bands end on the proximal sesamoid bones and the distal end of the large meta- 
carpal bone, and cletach slips to the extensor tendons. The middle band passes 
through the groove between the two divisions of the distal end of the metacarpus, 
and divides into two branches which join the tendons of the proper extensors of the 
digits; it sends fibers also to the interdigital collateral ligaments and to the central 
sesamoids. About the middle of the metacarpus the suspensory ligament detaches 
a band which unites lower down with the superficial flexor tendon, thus inclosing 
the tendon of the deep flexor of the digit ; it also blends with the thick fascia of the 
region. The latter gives off a band on either side to the accessory digits, and a ten- 
dinous band descends from each accessory digit to the third phalanx and distal sesa- 
moid bone, blending with the tendon of the corresponding proper extensor. 

Pig. — There are four metacarpo-phalangeal joints, each of which has a capsule, 
collateral, intersesamoidean, and cruciate sesamoidean ligaments. Since distinct 
interosseous muscles are present, there are, of course, no suspensory ligaments. 

Dog. — There are five metacarpo-phalangeal joints, each having its own capsule 
and indistinct collateral ligaments. A small sesamoid bone occurs in the anterior 
part of each capsule, over which the corresponding extensor tendon plays. The 
intersesamoidean ligaments do not extend above the sesamoids. The cruciate 
ligaments are present, as well as a fibrous layer which attaches the distal margins 
of the sesamoids to the posterior surface of the proximal end of the first phalanx. 



INTERPHALANGEAL JOINTS 

Ox. — The two proximal joints have separate capsules, and broad, but rather 
indistinct, collateral ligaments. Each joint has also central and collateral volar 
ligaments. The central ligaments are largely fused to form a strong band which is 
attached by two branches to the distal end of the first phalanx and to the depression 
on the volar surface of the proximal end of the second phalanx. The collateral ones 
extend from the borders of the first phalanx to the proximal end of the second 
phalanx; those on the interdigital side are weak and indistinct. 

The distal interphalangeal joints have, in addition to the capsules and collateral 
ligaments, bands which reinforce them on either side. The interdigital pair arise 
in the depressions on the distal ends of the first phalanges, receive fibers from the 
second phalanges, and end on the interdigital surfaces of the third phalanges at the 



INTERPHALANGEAL JOINTS 



249 



margin of the articular surface. The abaxial pair have a similar course, but are 
thinner, and end on the corresponding third sesamoid. An elastic band crosses the 
front of the second phalanx obliquely, from the distal end of the first phalanx to the 
extensor process of the third phalanx. 

The cruciate or distal interdigital ligaments (Ligg. cruciata interdigitalia) are 
two strong bands which limit the separation of the digits. They are attached above 
to the abaxial emmences on the proximal ends of the second phalanges (blending 
with the collateral ligaments), cross the deep flexor tendon obliquely, and reach the 





Fig. 2,58. — Ligaments axd Tendoxs of Digits of Pig; 
VoLAB View. 
a, Superficial flexor tendon; 6, deep flexor tendon; b', 
branches of 6 to accessorj' digits; c, c', annular ligaments; 
d-d'", ligaments of accessory digits; e, cruciate interdigital 
ligaments; /, /', spiral band around the flexor tendons of 
the accessory digits; g, abductor of accessory digit. (Ellen- 
berger-Baum, Anat. d. Haustiere.) 



Fig. 259. — Ligaments and Tendons of Digits of 
Dog, Hind Limb; Volak View. 
a, a', Superficial flexor tendon; b, tendon to 
large pad; c, lumbricales muscles; d, interossei 
muscles; e, f, annular ligaments at metatarso- 
phalangeal joints; g, suspensory ligament of large 
pad; /(, digital annular ligaments; i, deep flexor 
tendon; k, distal sesamoid; I, suspensory ligament 
of k; m, suspensory ligament of digital pad; n, 
digital pads. (Ellenberger-Baum, Anat. d. Haus- 
tiere.) 



interdigital space, where they intercross and blend. Most of the fibers end on the 
distal sesamoid of the opposite side, but some are attached to the interdigital as- 
pect of the second phalanx and the distal sesamoid of the same side. In the sheep 
there is, instead of the foregoing, a transverse ligament which is attached on either 
side to the interdigital surfaces of the second and third phalanges and the distal sesa- 
moid bone. It is related below to the skin, above to a pad of fat. 

Pig. — The interphalangeal joints of the chief digits resemble in general those 
of the ox. The distal interdigital ligament resembles, however, that of the sheep, 
and is intimately adherent to the skin. There is, besides, a remarkable arrange- 



250 COMPARATIVE ARTHROLOGY 

ment of ligaments which connect the small digits with each other and with the 
chief digits (Fig. 258). 

This apparatus is somewhat complex, but its chief features are as follows : A proximal inter- 
digital ligament is attached on either side to the third phalanges of the small digits, while centrally 
it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal 
joints of the chief digits. Two bands (central longitudinal interdigital Ugaments) arise on the 
bases of the small digits, cross the flexor tendons obhquely downward and centrally, pass through 
the proximal interdigital hgament, and blend below with the distal interdigital hgament. Two 
collateral bands (collateral longitudinal interdigital ligaments) are attached in common with the 
proximal interdigital Ugaments to the third phalanges of the small digits, and blend below with 
the outer part of the distal interdigital hgament. 

Dog. — Each joint has a capsule and two collateral ligaments. The distal 
joints have also two elastic dorsal ligaments (Ligg. dorsaha), which extend from 
the proximal end of the second phalanx to the ridge at the base of the third 
phalanx. They produce dorsal flexion of the joint, and thus raise or retract the 
claws when the flexor muscles relax. The distal sesamoids are represented by 
complementary cartilages attached to the volar margins of the articular surfaces 
of the third phalanges. 

Three interdigital ligaments restrict the spreading apart of the digits (Fig. 259). 
Two of these cross the volar surface of the proximal parts of the chief digits, i. e., 
one for the second and third, the other for the fourth and fifth ; they blend with the 
annular ligaments on either side. The third ligament is attached on either side to 
the foregoing ligaments and the annular ligaments of the third and fourth digits, 
and curves downward centrally, ending in the large pad on the paw. 



Articulations of the Pelvic Limb 
sacro-iliac joint 

This joint and the pelvic ligaments present no very striking differences in the 
other animals except that the sacro-sciatic ligament in the dog is a narrow but 
strong band which extends from the posterior part of the lateral margin of the 
sacrum to the tuber ischii; it is the homologue of the ligamentum sacro-tuberosum 
of man. 

HIP JOINT 

Ox. — The shallowness of the acetabulum is compensated by the greater size 
of the marginal cartilage, which is specially large laterally. The head of the femur 
has a smaller radius of curvature than that of the horse, and the articular surface 
extends a considerable distance outward on the upper surface of the neck. The 
round ligament is entirely intra-articular; it is small, and sometimes absent. The 
accessory ligament is absent. 

There are no important differences in the other animals. 

STIFLE JOINT 

Ox. — There is a considerable communication between the femoro-patellar 
and medial femoro-tibial joint cavities; this is situated as in the horse, but is wider. 
A small communication with the lateral femoro-tibial capsule sometimes occurs. 
The two femoro-tibial capsules usually communicate. The middle patellar liga- 
ment is not sunken, as there is no groove on the tuberosity of the tibia where it is 
attached. The lateral patellar ligament fuses completely with the tendon of in- 
sertion of the biceps femoris, and a large synovial bursa is interposed between them 
and the lateral condyle of the femur. 

Pig. — The femoro-patellar capsule is strongly reinforced on both sides by bands 



TIBIO-FIBULAR JOINTS — HOCK JOINT 251 

which blend with the collateral femoro-tibial ligaments. The cavity is continuous 
below with that of the femoro-tibial joint. A sagittal synovial fold (rudimentum 
septi) extends up a short distance from the anterior cruciate ligament. The supra- 
patellar pouch extends an inch or more (ca. 2-3 cm.) above the trochlea; from this 
a pouch extends up beneath the quadriceps femoris almost an inch and communi- 
cates through a large round opening with the joint cavity. There is a strong 
ligamentum patellae, which has a bursa under its distal part. The tendon of the 
biceps femoris takes the place of the lateral patellar ligament. A small ligamentum 
transversum connects the anterior faces of the menisci. 

Dog. — The joint in general resembles that of the pig. The posterior part of 
the capsule contains two sesamoid bones, which are imbedded in the origin of the 
gastrocnemius. 

TmiO-FIBULAR JOINTS 

Ox. — The proximal end of the fibula fuses with the lateral condyle of the 
tibia. The distal end remains separate, and forms an arthrosis with the distal end 
of the tibia; the movement here is imperceptible, as the two bones are closely 
united by strong peripheral fibers. 

Pig. — The proxunal joint is provided with a capsule which is reinforced in 
front and behind by fibrous tissue. The interosseous ligament attaches the shaft 
of the fibula to the lateral border of the tibia. The distal joint is included in the 
capsule of the hock joint, and is strengthened by dorsal and plantar ligaments 
(Lig. malleoli lateralis dorsalis, plantaris), which extend almost transversely from 
one bone to the other. There is also an interosseous ligament. 

Dog. — The arrangement is essentially the same as in the pig, but there is no 
interosseous ligament in the distal joint. Not uncommonly the distal part of the 
shaft of the fibula and tibia are ankylosed. 



HOCK JOINT 

Ox. — There is very considerable mobility at the proximal intertarsal joint, the 
capsule of which is correspondingly roomy. The short lateral ligament is attached 
distally on the tibial tarsal only. A strong transverse ligament attaches the lateral 
malleolus (distal end of the fibula) to the back of the tibial tarsal bone. The dorsal 
ligament is narrow and thin. 

Pig. — The arrangement in general resembles that of the ox. The medial liga- 
ment consists of a thin superficial part which extends almost vertically from malleo- 
lus to metatarsus, and a very strong deep part, which runs from the malleolus back- 
ward and downward to the sustentaculum and tibial tarsal. The lateral ligament 
also consists of two parts. The small superficial part exi;ends from the malleolus 
down to the lateral face of the body of the fil^ular tarsal bone. The stronger deep 
part arises from the anterior part of the malleolus, passes cheifly backward, ^videns, 
and ends on a ridge on the lateral surface of the fibular tarsal. A strong band ex- 
tends from the lateral face of the medial malleolus to a depression on the medial 
surface of the proximal part of the tibial tarsal bone. An oblique dorsal band con- 
nects the central and fourth tarsal bones. 

Dog. — The long collateral ligaments are very small, and the short ones double. 
The plantar ligament is weak, and ends on the fourth metacarpal bone. No dis- 
tinct dorsal Hgament is present, unless we regard as such a ligament which extends 
from the neck of the tibial tarsal to the fourth tarsal and third metatarsal bones. 

The remaining joints resemble those of the thoracic limb. 



MYOLOGY 

Myology deals with the muscles and their accessory structures. The muscles 
(Musculi) are highly specialized organs, which are characterized by their property 
of contracting in a definite manner when stimulated. They are the active organs 
of motion. The contractile part of the muscle is the muscular tissue. Three kinds 
of muscular tissue are recognized, viz.: (1) Striated or striped; (2) non-striated, 
unstriped or smooth; (3) cardiac, which may be regarded as a specialized variety 
of striated muscle. Only the first of these will be considered in this section. The 
striated muscles are for the most part connected directly or indirectly with the 
skeleton, upon which they act, and are hence often designated as skeletal muscles 
(Musculi skeleti), in distinction from non-striated muscle, which is often spoken 
of as visceral. The striated muscles cover the greater part of the skeleton, and play 
an important part in determining the form of the animal. They are red in color, 
the shade varying in different muscles and under various conditions. Some are in- 
timately associated with and attached to the skin, and are called cutaneous mus- 
cles (Musculi cutanei) . The muscular part of each is composed of bundles of con- 
tractile fibers surrounded by a thin sheath of connective tissue, the perimysium. 

The description of the muscles may be arranged under the following heads: (1) 
Name; (2) shape and position; (3) attachments; (4) action; (5) structure; (6) 
relations; (7) blood and nerve supply. 

(1) The name is determined by various considerations, e. g., the action, at- 
tachments, shape, position, direction, etc. In most cases two or more of these are 
combined to produce the name, e. g., flexor carpi radialis, longus colli, obliquus 
externus abdominis. 

A satisfactory comparative nomenclature is exceedingly difficult to work out, and much 
confusion exists in this respect. This is due in great part to the lack of a uniform basis for the 
formation of names and the difficulty in determining homologies in various species. 

(2) The shape is in many cases sufficiently definite and regular to allow the 
use of such terms as triangular, quadrilateral, fan-shaped, fusiform, etc. Some 
muscles are characterized as long, broad, short, etc. Orbicular or ring-like muscles 
circumscribe openings; since the contraction of such a muscle closes the orifice, it is 
often termed a sphincter. The position and direction are usually stated with refer- 
ence to the region occupied and to adjacent structures which may be presumed to be 
already known. 

(3) The attachments are in most cases to bone, but many muscles are attached 
to cartilage, ligaments, fascia, or the skin. As a matter of convenience, the term 
origin (Origo) is applied to the attachment which always or more commonly re- 
mains stationary when the muscle contracts; the more movable attachment is 
termed the insertion (Insertio). Such a distinction is often quite arbitrary, and 
cannot always be made, as the action may be reversible or both attachments may be 
freely movable. With respect to the muscles of the limbs, the proximal attaclmient 
is regarded as the origin and the distal one as the insertion. In all cases the attach- 
ment is made by fibrous tissue, the muscular tissue not coming into direct relation 
with the point of attachment. But when the intermediate fibrous tissue is not evi- 
dent to the naked eye, it is customary to speak of a ''fleshy attachment." The 
term "tendinous attachment" is applied to those cases in which the intermediate 
fibrous tissue — tendon or aponeurosis — is evident. A tendon (Tendo) is a band of 

252 



MYOLOGY 253 

dense white fibrous tissue by means of which a muscle is attached; an aponeurosis 
is a broad fibrous sheet which fulfils a similar function. 

(4) The action belongs rather to physiological study, but the main points are 
usually given in anatomical descriptions. In some cases the action is simple, in 
others, complex. Muscles which concur in action are termed synergists; those 
which have opposite actions are antagonists. 

(5) The consideration of structure includes the direction of the muscular fibers, 
the arrangement of the tendons, the synovial membranes, and any other accessory 
structures. The terms fleshy and tendinous are sometimes used to indicate the 
relative amounts of muscular and tencUnous tissue. In the case of the long muscles 
of the limbs, the origin is termed the head (Caput), and when the muscle is fusi- 
form, the large fleshy part is often called the belly (Venter) of the muscle. Some 
muscles have two or more heads, and are hence designated as biceps, triceps, etc. A 
digastric muscle is one having two bellies and an intermediate tendon. In most 
muscles the muscle-fibers join the tendon at an acute angle, like the relation of the 
barbs of a feather to its shaft ; hence the term pennate is applied to such an arrange- 
ment. When the fibers are so arranged on one side of the tendon the muscle is 
unipennate (M. unipennatus) ; while one in which this arrangement exists on both 
sides is bipennate (M. bipennatus). The structure may be still more complex, re- 
sulting in a multipennate muscle. The structure of many muscles is much more 
complex than a superficial examination would lead one to suppose. Frequently 



Fibrous sheath 




Ji^esotendpn J^ibrous ^heafk. 

fSyntwial sheath 




A B 

Fig. 260. — Diagrams of Cross-sections of Synovial Bursa (A) and Synovial Sheath (B); T, Tendon. 
In both the synovial sac is represented for the sake of clearness as though somewhat distended. 



they are intersected by tendinous layers or bands, known as tendinous intersec- 
tions. Intersecting bands or tracts which appear on the surface — usually as zig- 
zag lines — are termed tendinous inscriptions (Inscriptiones tendinese). 

(6) The relations constitute a very important part of anatomical topography, 
and a knowledge of them is fundamental to further study in this respect. 

(7) The blood and nerve supply are, of course, important on clinical grounds. 
The nerve supply is often of value in the determination of homologies. As might 
be expected, the muscles have a large blood supply. They are also provided with 
lymph-vessels. The nerves to the muscles are motor, sensory, and vasomotor in 
function. 

The accessory structures associated with the muscles are the synovial mem- 
branes and the fascise. 

The sjrnovial membranes are thin-walled sacs, similar to the synovial mem- 
branes of the joints, and having a similar function. Two forms are recognized. 
A S5niovial bursa (Bursa synoviafis) is a simple sac which is interposed at a point of 
unusual pressure between a tendon or muscle and some underlying structure, com- 
monly a prominence of the skeleton. A synovial sheath (Vagina synovialis ten- 
dinis) differs from a bursa in the fact that the sac is folded around the tendon so that 
two layers can be distinguished: the inner one is adherent to the tendon, while the 
outer one lines the canal in which the tendon lies. The two layers are continuous 
along a fold termed the mesotendon. The arrangement is showai in the annexed 
diagrams. The synovial membranes of joints in some places form extra-articular 



254 FASCIA AND MUSCLES OF THE HORSE 

pouches which act as bursse. The sj-novial sheath is not to be confused with the 
fibrous sheath of a tendon (Vagina fibrosa tendinis) . 

The student will note in dissection that intermediate forms of these sacs occur. A synovial 
sheath may belong to two or more tendons in common; in such cases the synovial membrane is 
reflected from one tendon to the other, forming a secondary mesotendon. In the normal state 
these sacs cannot be recognized on external examination of the subject. It is only when they are 
distended that their presence is evident. 

The fasciae are sheets of connective tissue, composed mainly of bundles of white 
fibers, Avith a greater or less admixture of elastic fibers in some cases. At least two 
layers may usually be distinguished. The superficial fascia (Fascia superficialis) 
is subcutaneous, and is composed of loose connective tissue which usually contains 
more or less fat. The deep fascia is composed of one or more layers of dense fibrous 
tissue. Its deep face may be very slightly adherent to the underlying structures, 
but in many places it is attached to the skeleton, Hgaments, and tendons. In many 
places laminae are given off from the deep face of the fascia, pass between muscles, 
and are attached to bones or ligaments; such layers are termed intermuscular septa 
(Septa intermuscularia) . The groove in which a tendon lies is converted into a 
canal by a band or fascial sheet known as a vaginal or annular ligament (Lig. 
vaginale). Many fasciae furnish origin or insertion to muscles and thus act as 
tendons; such are tendinous in structure, so as to render the distinction between 
fascia and aponeurosis in these cases arbitrary. Bursse occur in certain situations 
between the fascia and underlying structures, and are distinguished as subfascial 
bursae. Those between the fascia and the skin are subcutaneous bursae. 



FASCIA AND MUSCLES OF THE HORSE 

The cutaneous muscle or panniculus camosus (Musculus cutaneus) is a thin 
muscular layer developed in the superficial fascia. It is intimately adherent in 
great part to the skin, but has very little attachment to the skeleton. It does not 
cover the entire body, and may be conveniently divided into facial, cervical, omo- 
brachial, and abdominal parts. 

The facial part, m. cutaneus faciei, consists of a thin and usually incomplete 
muscular layer, which extends over the mandibular space and the masseter muscle. 
A distinct branch of it passes forward to the angle of the mouth and blends with the 
orbicularis oris. This part, the m. cutaneus labiorum, retracts the angle of the 
mouth, and has therefore been termed the retractor anguli oris. 

The cervical part, m. cutaneus colli, is situated on the ventral region of the neck. 
It arises from the cariniform cartilage and a median fibrous raphe. The fibers are 
directed forward and diverge from the raphe to the sides of the neck in pennate 
fashion. It is thick at its sternal origin, but thins out in front and laterally. On 
the side of the neck it is attached to the cervical fascia, which acts as its aponeurosis. 
It is related deeply to the sterno-cephalicus, the brachio-cephalicus (in part) and 
the jugular vein. Some bundles extend upon the parotid gland, and in well- 
developed subjects it is continuous with the facial part. 

The omo-brachial part, m. cutaneus omo-brachialis, covers the lateral surface 
of the shoulder and arm. Its fibers begin over the upper part of the scapula and 
extend to the proximal part of the forearm. Most of its fibers are vertical, but 
posteriorly they become oblique and are continued by the abdominal part. 

The abdominal part, m. cutaneus tnmci, covers a large part of the body be- 
hind the shoulder and arm. Its fibers are largely longitudinal. It is continuous 
in front with the omo-brachial part, and a tendinous layer from it passes forward 



THE FASCIA AND MUSCLES OF THE HEAD 255 

with the posterior deep pectoral muscle to the medial tuberosity of the humerus. 
Posteriorly it forms a fold, which, covered by the skin, forms the fold of the flank, 
and ends on the fascia above the stifle. The dorsal limit of the muscle corresponds 
approximately with a line drawn from the posterior angle of the scapula to the fold 
of the flank. Ventrally the two muscles are about a handbreadth apart in the um- 
bilical region. Further forward they diverge, so as to overlap the posterior deep 
pectoral muscle only to a small extent. Here the cutaneous muscle is closely ad- 
herent to the pectoral and contains the external thoracic vein. Posteriorly they 
diverge to the fold of the flank. 

The muscle is in general closely adherent to the skin and its contraction twitches 
the skin, thus getting rid of insects or other irritants. 



The Fascia and Muscles of the Head 

The muscles of the head (Mm. capitis) may be divided into three groups, viz.: 
(1) Superficial muscles, including the cutaneous muscle and those of the lips, cheeks, 
nostrils, eyelids, and external ear; (2) the orbital muscles; (3) the mandibular 
muscles; (4) the hyoid muscles. 

The superficial fascia forms an almost continuous layer, but is very scanty 
around the natural orifices. It contains a number of the thin superficial muscles, 
so that care must be exercised in removing the skin. Over the frontal and nasal 
bones the fascia blends with the periosteum. 

The deep fascia is of special interest in three regions. The temporal fascia 
(Fascia temporalis) covers the temporalis muscle, and is attached to the parietal 
and frontal crests medially, and to the zygomatic arch laterally. The buccal fascia 
(F. buccalis) covers the buccinator muscle and the free part of the outer surface of 
the ramus of the mancUble. It is attached to the facial crest, and posteriorly it 
forms a band (Raphe pterygomandibulare) which stretches from the hamulus of the 
pterygoid bone to the mandible behind the last molar tooth. It is directly continu- 
ous with the pharyngeal fascia (F. pharyngea), which is attached to the great and 
thyroid cornua of the hyoid bone and the thyroid cartilage of the larynx ; it covers 
the lateral walls of the pharynx, and blends dorsally with the mecUan raphe of the 
constrictor muscles of the latter. 

Cutaneus faciei. — This has been described (p. 254). 



MUSCLES OF THE LIPS AND CHEEKS 

1. Orbicularis oris. — This is the sphincter muscle of the mouth; it is con- 
tinuous with the other muscles which converge to the lips. It lies between the 
skin and the mucous membrane of the lips, and is intimately adherent to the 
former. Most of the fibers run parallel to the free edges of the lips and have no 
direct attachment to the skeleton. 

Action.— It closes the lips. 

Blood-supply — Palato-labial, facial, and mental arteries. 

Nerve-supphj. — Facial nerve. 

2. Levator nasolabialis.^ — This thin muscle lies directly under the skin, and 
chiefly on the lateral surface of the nasal region. 

Origin. — The frontal and nasal bones. 

Insertion. — (1) The upper lip and the lateral wing of the nostril; (2) the com- 
missure of the lips. 

Action. — (1) To elevate the upper lip and the commissure; (2) to cUlate the 
nostril. 

^A.lso termed the levator labii superioris ala'que nasi. 



256 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — The muscle arises b}- a thin aponeurosis. The belly is also thin, 
and divides into two branches, between which the lateral dilator of the nostril passes. 
The dorsal branch reaches the nostril and upper lip, blending vdih. the lateral di- 
lator; the ventral one is much smaller, and blends at the labial commissure ^^^th 
the orbicularis and buccinator. 

Relations. — Superficially, the skin, fascia, and lateral dilator (in part) ; deeply, 




Fig. 261. — Muscles of Head of Horse; Lateral View. The M. ctttaneus is Removed. 
o, Levator labii superioris proprius; 6, levator nasolabialis; c, brachiocephalicus; d, sterno-cephalicus ; d', 
tendon of d; e, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; h, buccinator; i, depressor labii inferioris; 
k, orbicularis oris; I, lateralis nasi, dorsal part; m, masseter; n, parotido-auricularis; o, zygomatico-auricularis; p, 
interscutularis; p', fronto-scutularis, pars temporalis; q, cervico-auricularis profundus major; r, cervico-auricularis 
superficialis; s, obliquus capitis anterior; <, splenius; r, occipito-mandibularis; i/, mastoid tendon of brachiocephalicus; 
.2, posterior, 3, anterior, border of external ear; S, scutiform cartilage; 9, zygomatic arch; 70, orbital fat; 7S, temporo- 
mandibular articulation; 27, facial crest; 30', angle of jaw; 37, external maxillary vein; 38, jugular vein; 39, facial 
vein; .40, parotid duct; 4 A transverse facial vein; 4^, masseteric vein; 45, facial nerve; 44. parotid gland; 40, chin; 
X, wing of atlas. By an oversight the superior buccal branch of the facial nerve is shown crossing over instead of under 
the zygomaticus. (After EUenberger-Baum, Anat. fiir Kiinstler.) 



the levator labii superioris proprius, lateral dilator (in part), buccinator, branches 
of the facial vessels and nerve, and the infraorbital arterj' and nerve. 

Blood-sup pi y. — Facial and palato-labial arteries. 

Nerve-supphj. — Facial nerve. 

3. Levator labii superioris proprius.^This lies on the dorso-lateral aspect of 
the face, partly covered by the preceding muscle. 

Origin. — The lacrimal, malar, and maxillary bones at their junction. 



MUSCLES OF THE LIPS AND CHEEKS 



257 



Insertion. — The upper lip, by a common tendon with its fellow. 

Action.— Kcimg with its fellow, to elevate the upper lip. This action, if 
carried to the fullest extent, results in eversion of the lip. In unilateral action the 
lip is drawn upward and to the side of 
the muscle acting. 

Structure.- — The muscle has a short, 
thin tendon of origin. The belly is at 
first flattened, but becomes narrower 
and thicker, then tapers over the nasal 
diverticulum, to terminate in a tendon. 
The tendons of the two muscles unite 
over the alar cartilages of the nostrils, 
forming an expansion which spreads 
out in the substance of the upper 
lip.i 

Relations. — Superficially, the skin, 
the levator nasolabialis, and the angu- 
lar vessels of the eye ; deeply, the later- 
alis nasi, the transversus nasi, and the 
infraorbital artery and nerve. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

4. Zygomaticus. — This very thin 
muscle lies immediately under the skin 
of the cheek. 

Origin. — The fascia covering the 
masseter muscle below the facial 
crest. 

Insertion. — The commissure of the 
lips, blending with the buccinator. 

Action. — To retract and raise the 
angle of the mouth. 

Structure. — Fleshy, with a thin 
aponeurotic origin. 

Relatio7is. — Superficially, the skin; 
deeply, the buccinator. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

5. Incisivus superior. — This lies 
under the mucous membrane of the 
upper lip. 

Origin. — The alveolar border of 
the premaxilla from the second incisor 
to the first cheek tooth. 

Insertion. — The upper lip. 

Action. — To depress the upper 
lip. 

6. Incisivus inferior. — This is ar- 
ranged in the lower lip like the pre- 
ceding muscle in the upper one. 

Origin. — The alveolar border of the mandible from the second incisor to a 
point near the first cheek tooth. 

^ In rare cases a branch is given off from the ventral border of the muscle. It passes forward 
and ends in the subcutaneous tissue at the posterior end of the diverticulum nasi. 
17 




Fig. 262. — Muscles of Head of Horse; Dorsal View. 
The M. cutaneus is Removed. 
a, Levator labii superioris proprius; a', common 
tendon of a with opposite muscle; 6, levator nasolabialis; 
/, dilatator naris lateralis; g, zygomaticus; I, lateralis 
nasi; ?i, parotido-auricularis; o", scutulo-auricularis super- 
ficialis superior; p, interscutularis ; p', fronto-scutularis, 
pars temporalis; r, cervico-auricularis superficialis; u, 
corrugator supercilii; x, transversus nasi; 2, posterior, 
S, anterior, border of external ear; 8, scutiform cartilage; 
9, zygomatic arch; 10, supraorbital depression; S3, medial 
wing of nostril, containing lamina of alar cartilage; 39, 
facial vein. (After EUenberger-Baum, Anat. fur Kiinstler.) 



258 FASCIA AND MUSCLES OF THE HORSE 

Insertion. — The skin of the lower hp and the prominence of the chin. 
Action. — To raise the lower lip. The two incisivi bring the lips together, 
concurring with the orbicularis oris in prehension of food. 

7. Mentalis.^ — This is situated in the prominence of the chin. Its fibers arise 
from each side of the body of the mandible and are inserted into the skin of the 
chin. It is mingled with fat and strands of connective tissue, in which the roots 
of the tactile hairs are embedded. It raises and corrugates the skin to which it is 
attached. 

8. Depressor labii inferioris. — This muscle lies on the lateral surface of the 
ramus of the mandible, along the ventral border of the buccinator. 

Origin. — The alveolar border of the mandible near the coronoid process and 
the maxillary tuberosity, in common with the buccinator. 

Insertion. — The lower lip. 

Action. — To depress and retract the lower lip. 

Structure. — The tendon of origin and the belly are fused with the buccinator 
as far forward as the first cheek tooth. From this point forward the belly is dis- 
tinct and rounded, terminating in a tendon which spreads out in the lower lip, 
blending with the orbicularis and the muscle of the opposite side. 

Relations. — Superficially, the skin, masseter, facial vessels, and parotid duct; 
deeply, the mandible and inferior labial artery. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

9. Buccinator. — This muscle lies in the lateral wall of the mouth, extending 
from the angle of the mouth to the maxillary tuberosity. 

Origin. — The lateral surface of the maxilla above the interalveolar space and 
the molar teeth ; the alveolar border of the mandible at the interalveolar space and 
also posteriorly where it turns upward to the coronoid process; the pterygo-mandib- 
ular raphe. 

Insertion. — The angle of the mouth, blending with the orbicularis oris. 

Action. — To flatten the cheeks, thus pressing the food between the teeth; 
also to retract the angle of the mouth. 

Structure. — Two layers ma}^ be recognized. The superficial layer (Pars buc- 
calis) extends from the angle of the mouth to the masseter. It is incompletely pen- 
nate, having a longitudinal raphe on which most of the muscle-fibers converge. 
The upper fibers are directed chiefly downward and backward, the lower ones up- 
ward and backward. The deep layer (Pars molaris) consists mainly of longitudinal 
fibers. It blends in part with the superficial layer of the orbicularis; it has a 
small tendinous attachment to the coronoid process behind, and is united ventrally 
with the depressor labii inferioris. 

Relations. — Superficially, the skin and fascia, the zygomaticus, levator naso- 
labialis, lateral dilator of the nostril, the superior buccal glands, the parotid duct, 
the facial vessels, and branches of the facial nerve; deeply, the mucous membrane 
of the mouth and the inferior buccal glands. 

Blood-supply. — Facial and buccinator arteries. 

Nerve-supply. — Facial nerve. 



MUSCLES OF THE NOSTRILS 

1. Levator nasolabialis. — This has been descriljed (p. 255). 

2. Dilatator naris lateralis (M. caninus). — This thin, triangular muscle lies 
on the lateral nasal region, and passes between the two branches of the levator 
nasolabialis. 

1 Also known as the levator menti. 



MUSCLES OF THE NOSTRILS 



259 



Origin. — The maxilla, close to the anterior extremity of the facial crest. 

Insertion. — The lateral wing of the nostril. 

Action. — To dilate the nostril. 

Structure. — The muscle has a flat tendon of origin, passes between the two 
branches of the levator nasolabialis, and spreads out in the lateral wing of the 
nostril. The lower fibers blend with the orbicularis oris. 

Relations. — Superficially, the skin, fascia, and the labial branch of the levator 
nasolabialis; deeply, the maxilla and the nasal branch of the levator nasolabialis. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

3. Transversus nasi.^^ — This is an unpaired, quadrilateral muscle, which lies 
bet^veen the nostrils. It consists of two layers. 




Fig. 263. — Nasal and Superior Labial Muscles of Horse. 
a, a', Transversus nasi; b, levator labii superioris proprius; 6', tendon of b; b", common tendon of two 
levatores labii superioris proprii; c, c', c", d, ventral part of lateralis nasi; e, dorsal part of lateralis nasi; /, or- 
bicularis oris; g, levator nasolabialis, a portion of which is removed; h, dilatator naris lateralis (the terminal part of 
which is removed); i, cornu of alar cartilage; k, nostril; k', upper commissure of nostril; I, nasal diverticulum; m, 
nasal bone. (After EUenberger-Baum, Top. Anat. d. Pferdes.) 



Attachments. — Superficial layer, the superficial faces of the laminae of the alar 
cartilages; deep layer, the convex edges of the cornua of the same. 

Action. — To dilate the nostrils. 

Structure. — It is composed of transverse fleshy fibers, which blend below with 
the orbicularis. 

Relations. — Superficially, the skin, fascia, and tendinous expansion of the 
levator labii superioris proprius; deeply, the alar cartilages, the extremity of the 
septum nasi, and the palato-labial artery. 

Blood-supply. — Palato-labial artery. 

Nerve-supply. — Facial nerve. 

Lateralis nasi. — This is situated along the margins of the naso-maxillary notch, 
and may be regarded as consisting of dorsal and ventral parts. 

The dorsal part (Pars dorsalis m, lateralis nasi)- is a thin layer which lies along 

^ Also called the dilatator naris transversus. ^ Also known as the dilatator naris superior. 



260 FASCIA AND MUSCLES OF THE HORSE 

the dorsal border of the naso-maxillary notch. Its fibers arise from the nasal bone 
and pass outward and downward to the parietal cartilage and the adjacent part of 
the soft lateral wall of the nasal cavity. 

The ventral part (Pars ventralis m. lateralis nasi)^ is much thicker and lies 
along the ventral border of the notch. It arises from the nasal process of the pre- 
maxilla and the adjacent part of the maxilla, and its fibers curve inward to end on 
the cartilaginous prolongations of the turbinate bones (chiefly the ventral one) and 
on the lateral wall of the vestibule of the nasal cavity. A few bundles pass from 
the cornu of the alar cartilage to the lateral wing of the nostril. 

Action. — To dilate the vestibule of the nasal cavity, to rotate the turbinal car- 
tilages outward, and to assist in dilating the nostril. 

Relations. — Superficially, the skin, fascia, nasal diverticulum, the levator labii 
superioris proprius, the levator nasolabialis, and the lateral nasal artery; deeply, 
the nasal bone, the parietal cartilage, the maxilla, the premaxilla, the nasal mucous 
membrane, and the anterior nasal branch of the infraorbital nerve. 

Blood-supply. — Facial and palato-labial arteries. 

Nerve-supply. — Facial nerve. 

The preceding muscle does not dilate the so-called "false nostril" or nasal diverticulum, aa 
is commonly stated. Both act on the lateral wall of the vestibule of the nasal cavity so as to draw 
it outward, thus tending to constrict, rather than dilate, the nasal diverticulum. The thick part 
of the ventral muscle which is attached to the cartilage of the turbinate bone has a similar effect. 
When the nostril is fully dilated, the so-called "false nostril," i. e., the entrance to the nasal diver- 
ticulum, is closed. The newer term seems preferable. 



MUSCLES OF THE EYELIDS 

1. Orbicularis oculi. — This is a flat, elliptical, sphincter muscle, situated in and 
around the eyelids, the portion in the upper lid being much broader than that in 
the lower. The chief attachment is to the skin of the lids, but some bundles are 
attached to the palpebral ligament at the medial canthus and to the lacrimal bone. 
Its action is to close the lids. 

2. Corrugator supercilii.— This is a very thin, small muscle, which arises over 
the root of the supraorbital process and spreads out in the upper eyelid, blending 
with the orbicularis ocuh (Fig. 262). Its action is to assist in raising the upper lid 
or, especially in pathological conditions, to wrinkle the skin. 

3. Malaris. — This is a very thin muscle, which varies much in different sub- 
jects. It extends from the fascia in front* of the orbit to the lower lid. Its action 
is to depress the lower lid. 

The foregoing muscles receive their blood-supply from the facial, transverse 
facial, supraorbital, and infraorbital arteries; the nerve-supply is derived from the 
facial nerve. 

4. Levator palpebrae superioris. — This slender, flat muscle is almost entirely 
within the orbit (Fig. 561). It arises on the pterygoid crest, passes forward above 
the rectus oculi superior and below the lacrimal gland, and terminates in a thin ten- 
don in the upper lid. 

Action. — To elevate the upper lid. 
Blood-supply. — Ophthalmic artery. 
Nerve-supply. — Oculomotor nerve. 



MANDIBULAR MUSCLES 

The muscles of this group (Mm. mandibulae) are six in number in the horse. 
They arise from the upper jaw and the cranium, and are all inserted into the man- 
dible. 

1 Also known as the dilata' or naris inferior. 



MANDIBULAR MUSCLES 261 

1. Masseter. — This muscle extends from the zygomatic arch and facial crest 
over the broad part of the mandibular ramus. It is semi-elliptical in outline. 

Origin. — By a strong tendon from the zygomatic arch and the facial crest. 

Insertion. — The lateral surface of the broad part of the ramus of the mandible. 

Action. — Its action is to bring the jaws together. Acting singly, it also carries 
the lower jaw toward the side of the contracting muscle. 

Structure. — The superficial face of the muscle in its upper part is covered by a 
strong, glistening aponeurosis, and several tendinous intersections partially divide 
the muscle into layers. The fibers of the superficial layer take origin from the 
malar and maxilla only, and diverge somewhat to their insertion close to the thick 
ventral border of the lower jaw. The fibers of the deep layer arise from the entire 
area of origin, and pass straight to the border of the mandible; it will be noted that 
a small part, near the temporo-mandibular joint, is not covered by the superficial 
layer. The two layers are separable only above and behind; elsewhere they are 
fused. 

Relations. — Superficially, the skin and cutaneus, the parotid gland, the 
transverse facial and masseteric vessels, and the facial nerve; deeply, the ramus of 
the mandible, the buccinator and depressor labii inferioris muscles, the superior 
buccal glands, the buccinator vessels and nerve, and the vena reflexa, which joins 
the facial vein at the anterior edge of the muscle. The facial vessels and parotid 
duct run along the anterior edge of the muscle; the duct, however, bends for- 
ward about the middle of the border and leaves the muscle. 

Blood-supply. — Transverse facial and masseteric arteries. 

Nerve-supply. — Mandibular nerve. 

2. Temporalis. — This muscle occupies the temporal fossa. 

Origin. — The rough part of the temporal fossa and the crests which limit it. 

Insertion. — The coronoid process of the mandible, which it envelops. 

Action. — Chiefly to raise the lower jaw, acting with the masseter and medial 
pterygoid muscles. 

Structure. — The surface of the muscle is covered with a glistening aponeurosis, 
and strong tendinous intersections are found in its substance. The medial edge of 
the muscle is quite thin, but as the fibers converge toward the much smaller area 
of insertion, the muscle becomes nearly an inch thick. It fuses partly with the 
masseter. 

Relations. — Superficially, the scutiform cartilage, the anterior muscles of the 
external ear, and the auricular and orbital fat; deeply, the temporal fossa and the 
deep temporal vessels and nerves. 

Blood-supply. — Superficial and deep temporal, and posterior meningeal arteries. 

Nerve-supply. — Mandibular nerve. 

3. Pterygoideus medialis (s. internus).- — This muscle occupies a position on 
the medial surface of the ramus of the mandible similar to that of the masseter 
laterally. 

Origin. — The crest formed by the pterygoid process of the sphenoid and the 
palatine bone. 

Insertion. — The concave medial surface of the broad part of the ramus of the 
mandible and the medial lip of the ventral border. 

Action. — Acting together, to raise the lower jaw; acting singly, to produce also 
lateral movement of the jaw. 

Structure. — The muscle is capable of division into two parts. The principal 
part is superficial (medial), and its fibers are, for the most part, vertical in direc- 
tion. It contains much tendinous tissue (septa). The smaller portion is lateral 
to the foregoing, and its fibers are directed do^vnward and backward. 

Relations. — Laterally, the ramus of the mandible, the lateral pterygoid muscle, 
the inferior alveolar vessels and nerve, and the lingual and mjdo-hyoid nerves; 



262 



FASCIA AND MUSCLES OF THE HORSE 



medially, the great cornu of the hyoid bone, the pharynx, the larynx, the tensor 
palati, mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural pouch, 
the external maxillary vessels, the ninth and twelfth nerves, the mandibular salivary 
gland, the mandibular and parotid ducts, and the mandibular and pharyngeal lymph- 
fflands. 

Blood-supply. — Internal maxillary, masseteric, and inferior alveolar arteries. 

Nerve-supply. — Mandibular nerve. 

4. Pterygoideus lateralis (s. externus). — This muscle is considerably smaller 
than the preceding one, and is situated lateral to its upper part. 

Origin. — The lateral surface of the pterygoid process of the sphenoid bone. 

Insertion. — The medial surface of the neck, the medial part of the anterior 
border of the condyle of the mandible and the articular disc. 

Actio7i. — Acting together, to draw the lower jaw forward; acting singly, to 



Ethmo- 
turhinates 
Dorsal meatus 
Dorsal turbinate 
Middle meatus 
Ventral iurhitiate 
Ventral meatus 



Septum of 
frontal sinuses 




Digastricus, 
posterior 
belly 



Digastricus, 
anterior belly 



Intermediate tendon 



Fig. 264. — Sagittal Section of Head op Horse, Showing Deep Pterygo-mandibular Region and Nasal and 

Cra.nial Cavities. 
1, Cerebral compartment of cranial cavity; £, cerebellar compartment of same; 3, tentorium osseum; 4i ten- 
torium cerebelli; 5, sphenoidal sinus; 6, hamulus of pterygoid bone-tendon of tensor palati cut off short at anterior 
border of hamulus; 7, mylo-glossus. The olfactory mucous membrane is shaded. 



move the jaw also toward the side opposite to the muscle acting. The latter action 
is due to the fact that the origin is nearer to the median plane than the insertion. 

Structure. — The muscle is almost entirely fleshy, and the fibers are almost 
longitudinal in direction. Some of them are inserted into the edge of the articular 
disc. 

Relations. — Laterally, the temporo-mandibular articulation and the temporalis 
muscle; medially, the medial pterygoid and tensor palati muscles. The internal 
maxillary artery crosses the ventral face of the muscle and dips in between it and 
the tensor palati. The mandibular nerve lies on the ventral surface, and the buc- 
cinator nerve perforates the origin of the muscle. 

Blood-supply. — Internal maxillary and inferior alveolar arteries. 

Nerve-supply. — Mandibular nerve. 

5. Occipito-mandibularisi (M. jugulomandibularis).— This is a short, fusiform 

^ This muscle is also known as the stylo-maxillaris, stylo-mandibularis, etc. 



MANDIBULAR MUSCLES 



263 



muscle extending from the paramastoid process of the occipital bone to the posterior 
border of the lower jaw; it is covered by the parotid gland. 




Fig 265 -Mandibular and Laryngeal Regions of Horse, after Removal of Skin and Cutaneub. 
c Brachiocephalicus: d. sterno-cephalicus; e. omo-hyoideus and sterno-hyoideus; h, buccinator; ^, depressor 
labiiWerLris- m, masseter; «. occipito-mandibularis; u, mylo-hyoideus; ... posterior. 3. anterior, border of external 
ear SO' angi; o jaw; 36 mandibular lymph-glands; ^7. external maxillary vein; 3^. facial continuation of ^7; 
ro'parolid duct; L parotid gland; 4o, prominence of chin; x. wing of atlas. (After EUenberger-Baum. Anat. fur 
Kiinstler.) 



Origin.— The paramastoid process of the occipital bone, in common with the 
posterior belly of the digastricus. 

Insertion.— The posterior border of the ramus of the mandible. 
Action.— To depress the lower jaw and open the mouth. 



264 FASCIA AND MUSCLES OF THE HORSE 

Structure. — The muscle contains a good deal of tendinous tissue. It blends 
with the posterior belly of the digastricus. 

/?e/'a^^ons.— Superficially, the parotid gland, the tendon of the sterno-cephalicus, 
and the fibrous expansion which connects it with the tendon of the brachiocephali- 
cus; deeply, the guttural pouch, the external carotid artery, the ninth and twelfth 
nerves, the pharynx, and the mandibular salivary gland. 

Blood-supply. — External carotid artery. 

Nerve-supply. — Facial nerve. 

6. Digastricus. — This muscle is composed of two fusiform, flattened bellies, 
united by a round tendon. 

Origin. — The paramastoid process of the occipital bone, in common with the 
preceding muscle. 

Insertion.- — The medial surface of the ventral border of the molar part of the 
ramus of the mandible. 

Action. — It assists in depressing the lower jaw and opening the mouth. If the 
mandible be fixed and both bellies contract, the hyoid bone and the base of the 
tongue are raised, as in the first phase of deglutition. 

Structure. — The posterior belly has the appearance of a branch detached from 
the medial surface of the occipito-mandibularis. It passes downward and forward, 
and is succeeded by a small rounded tendon. The latter perforates the tendon of 
insertion of the stylo-hyoideus, and is provided with a synovial sheath. The an- 
terior belly is larger and terminates by thin, tendinous bundles. 

Relations.- — The posterior belly has practically the same relations as the oc- 
cipito-mandibularis. The intermediate tendon is in contact laterally with the me- 
dial pterygoid muscle, the mandibular gland and duct, and the external maxillary 
artery. The anterior belly lies in the mandibular space between the ramus of the 
jaw and the mylo-hyoideus muscle; the sublingual vessels run along its dorsal 
border. 

Blood-supply.- — External carotid and sublingual arteries. 

Nerve-supply. — Facial and mandibular nerves. 

THE HYOID MUSCLES 

This group consists of eight muscles (Mm. ossis hyoidei), one of which, the 
hyoideus transversus, is unpaired. 

1. Mylo-hyoideus.^ — This muscle, together with its fellow, forms a sort of 
sling between the rami of the mandible, in which the tongue is supported. 

Origin. — The medial surface of the alveolar border of the mandible. 

Insertion.- — (1) A median fibrous raphe extending from the symphysis to the 
hyoid bone; (2) the lingual process, body, and thyroid cornu of the hj'oid bone. 

Action.- — It raises the floor of the mouth, the tongue, and the hyoid bone. 

Structure. — Each muscle consists of a thin curved sheet, the fibers passing 
ventrally from their origin and then curving toward the median raphe. It is 
chiefly fleshy, and is thickest behind. There is a tendinous intersection between this 
muscle and the omo-hyoideus, to which both muscles are attached. The anterior 
superficial part of the muscle is termed the mylo-glossus. 

Relations. — On the superficial surface of the muscles are the ramus, the metlial 
pterygoid and digastricus muscles, and the mandibular lymph-glands. The deep 
surface is in contact with the mucous membrane of the mouth, the stylo-glossus, 
hyo-glossus, and genio-hyoideus muscles, the sublingual gland and vessels, the 
mandibular duct, and the lingual and hypoglossal nerves. The sublingual vein 
passes through the posterior part. 

Blood-supply. — Sublingual artery. 

^ Also known as the transversus mandibulae. 



THE HYOID MUSCLES 265 

Nerve-supply. — Mylo-hyoid branch of the mandibular nerve. 

2. Stylo-hyoideus. — This is a slender, fusiform muscle, having a direction 
nearly parallel to that of the great cornu of the hyoid bone (Fig. 559) . 

Origin. — The muscular angle of the dorsal extremity of the great cornu of the 
hyoid bone. 

Insertion. — The anterior part of the thyroid cornu of the hyoid bone. 

Action. — It draws the base of the tongue and the larynx upward and backward. 

Structure.— It arises by a thin, short tendon, and has a fusiform belly. The 
tendon of insertion is perforated for the passage of the intermediate tendon of the 
cUgastricus, and at this point there is a small synovial sheath. 

Relations. — Superficially, the medial pterygoid muscle and the parotid gland; 
deeply, the guttural pouch, the pharynx, the external carotid and maxillary arteries, 
and the hypoglossal nerve. 

Blood-supply. — External carotid artery. 

Nerve-supply. — Facial nerve (stylo-hyoid branch). 

In rare cases an anomalous arrangement is present in which the stylo-hyoideus is not at- 
tached to the thyroid cornu but is continuous with the intermediate tendon of the digastricus, 
and no fibrous ring is formed. The posterior belly of the digastricus is inserted chiefly on the 
thyroid cornu, but also sends a dehcate tenchnous shp to the intermediate tendon. 

3. Occipito-hyoideus (M. jugulo-hyoideus). — This is a small triangular muscle, 
which lies in the space between the paramastoid process and the great cornu of the 
hyoid bone. 

Origin. — The paramastoid process of the occipital bone. 

Insertion. — The dorsal extremity and ventral edge of the great cornu of the 
hyoid bone. 

Action. — It carries the ventral extremity of the great cornu backward. 

Structure. — The muscle is somewhat triangular, its fibers being longer as the 
ventral border is approached. It blends with the posterior belly of the digastricus. 

Relations. — Superficially, the parotid gland; deeply, the guttural pouch. 

Blood-supply.- — Occipital artery. 

Nerve-supply. — Facial nerve. 

4. Genio-hyoideus. — This is a long, spindle-shaped muscle, which lies under 
the tongue in contact with its fellow of the opposite side (Fig. 330) . 

Origin. — A small depression on the medial surface of the ramus of the mandible, 
close to the symphysis. 

Insertion. — The extremity of the lingual process of the hyoid bone. 

Action. — It draws the hyoid bone and tongue forward. 

Structure. — The muscle arises by a short tendon, which is succeeded by the 
belly, composed of long bundles of parallel fibers. 

Relations. — Ventrally, the mylo-hyoideus; dorsally, the hyo-glossus, stylo- 
glossus, genio-glossus, the sublingual gland, mandibular duct, and the lingual nerve. 

Blood-supply. — Sublingual artery. 

Nerve-supply. — Hypoglossal nerve. 

5. Kerato-hyoideus. — This small triangular muscle lies in the space between 
the thyroid and small cornu, under cover of the hyo-glossus (Fig. 331). 

Origin. — The posterior edge of the small cornu and the adjacent part of the 
ventral border of the great cornu. 

Insertion. — The dorsal edge of the thyroid cornu. 

Action.- — It raises the thyroid cornu and the larynx. 

Relations. — The muscle is crossed laterally by the lingual artery. 

Blood-supply. — Lingual artery. 

Nerve-supply. — Glosso-pharyngeal nerve. 

6. Hyoideus transversus. — This is a small, unpaired muscle, which extends 
transversely between the two small cornua of the hyoid bone. 



266 FASCIA AND MUSCLES OF THE HORSE 

Attachments. — The small cornua close to the junction with the great cornua. 
Action. — When relaxed, its dorsal surface is concave; when it contracts, it 
elevates the root of the tongue. 

Structure. — Fleshy, composed of parallel transverse bundles. 
Blood-supply. — Lingual artery. 
Nerve-supply. — Glosso-pharyngeal nerve. 

7. Stemo-thyro-hyoideus, and 

8. Omo-hyoideus. — These are described with the muscles on the ventral sur- 
face of the neck (p. 268). 



The Fascia and Muscles of the Neck 

It is convenient to divide the muscles of the neck (Mm. colli) into ventral and 
lateral groups, the two lateral groups being separated from each other by the liga- 
mentum nuchse. 

THE FASCIA OF THE NECK 

The superficial fascia is in part two-layered, and contains the cervical cutaneous 
muscle. The fasciae of the right and left sides are attached along the dorsal line 
of the neck to the ligamentum nuchas, while along the ventral line they meet in a 
fibrous raphe. A deep layer is detached which passes underneath the cutaneous 
muscle, bridges over the jugular furrow, and crosses over the deep face of the brachio- 
cephalicus and omo-hyoideus to join the superficial layer. It again separates to 
pass under the cervical trapezius, and become attached to the ligamentum nuchse. 
Along the ventral line a septum is detached which separates the sterno-cephalici. 
Two other layers in front of the shoulder enclose the prescapular lymph-glands. 

The deep fascia also forms two layers. The superficial layer is attached to 
the wing of the atlas and the ventral edge of the longissimus capitis et atlantis and 
scalenus. Passing downward it encloses the trachea, and, together with the deep 
layer, furnishes sheaths for the vagus and sympathetic nerves and the carotid 
artery. Passing upward it detaches septa between the extensor muscles of the spine. 
Anteriorly it covers the thyroid gland, the guttural pouch, the adjacent vessels and 
nerves, and the larynx, and is attached to the mastoid process of the temporal bone 
and the thyroid cornel of the hyoid bone. Posteriorly it is attached to the first 
rib and the cariniform cartilage of the sternum. The deep layer (prevertebral 
fascia) covers the ventral surface of the longus colli, and encloses the trachea and 
oesophagus. Anteriorly it forms, with the corresponding layer of the opposite 
side, a septum between the guttural pouches; posteriorly it becomes continuous 
with the endothoracic fascia. A fascia propria forms a tubular sheath around the 
trachea, enclosing also the recurrent nerves. 



VENTRAL CERVICAL MUSCLES 

This group consists of twelve pairs of muscles which lie ventral and lateral to 
the vertebrae. 

1. Cutaneus colli. — This has been described (p. 254). 

2. Brachiocephalicus. — This is described on p. 294. 

3. Stemo-cephalicus.i — This is a long, narrow muscle which extends along the 
ventral and lateral aspects of the trachea from the sternum to the angle of the jaw. 
It forms the ventral boundary of the jugular furrow. 

^ This muscle is probably the homologue of the sternal part of the sterno-cleido-mastoid 
of man. On account of the differences in its insertion in the various animals, it seems desirable 
to adopt the name sterno-cephalicus. It is also known as the sterno-mandibularis or sterno- 
maxillaris. 



VENTRAL CERVICAL MUSCLES 



267 



Origin . — The cariniform cartilage of the sternum. 
Insertion. — The posterior border of the ramus of the mandible. 
Action. — Acting together, to flex the head and neck; acting singly, to incUne 
the head and neck to the side of the muscle contracting. 

Structure. — The two muscles are fused at their origin, which is fleshy. Near 




A 



V 



r ' 




Fig. 266. — Antero-lateral View of Muscles and Skeleton of Horse. 
a, Trapezius; c, brachiocephalicus; d, sterno-cephalicus; /, long head of triceps; /', lateral head of triceps; 
g, anterior superficial pectoral muscle; g', posterior superficial pectoral; h' , anterior deep pectoral; i), cutaneus colli; 
z, supraspinatus; 29, omo-hyoideus; 30, steruo-th>TO-hyoideus; 31, jugular vein; 32, cephalic vein; 1, scapula; 
7', cartilage of scapula; ;?, spine of scapula; 4. shaft of humerus; 4' lateral epicondyle; 5, lateral tuberosity of humerus; 
e, deltoid tuberosity; 74, ventral border ("keel") of sternum; i^'. cariniform cartilage; 7. iJ., first rib. (After Ellen- 
berger-Baum, Anat. fiir Kiinstler.) 



the middle of the neck they separate, and, becoming narrower and thinner, each 
muscle passes under the parotid gland and terminates by a flat tendon. The latter 
is connected by a thin aponeurosis with that of the brachiocephalicus. 

Relations. — Superficially, the cutaneous muscle; deeply, the sterno-thyro- 
hyoideus and omo-hyoideus muscles. The dorsal edge of the muscle is related to 
the jugular vein, which lies in the jugular furrow. The carotid artery, the vagus, 



268 FASCIA AND MUSCLES OF THE HORSE 

sjTnpathetic, and recurrent nerves also lie along the upper edge at the root of the 
neck. The tendon passes under the external maxillary vein and the parotid gland, 
having the mandibular gland and occipito-mandibularis muscle on its medial side. 

Blood-supply. — Carotid artery. 

Nerve-supply. — Ventral branch of the spinal accessor}' nerve. 

4. Stemo-thyro-hyoideus (Sterno-thyreoideus et sterno-hyoideus). — This is a 
long, slender, digastric muscle, applied to the ventral surface of the trachea and 
its fellow of the opposite side. 

Origin. — The cariniform cartilage of the sternum. 

Insertion. — (1) A prominence on the posterior border of the lamina of the thy- 
roid cartilage of the larynx at the ventral end of the oblique line; (2) the body 
and lingual process of the hyoid bone. 

Action. — To retract and depress the hyoid bone, the base of the tongue, and 
the larynx, as in deglutition. It may also fix the hyoid bone when the depressors 
of the tongue are acting, as in sucking. 

Structure. — The origin of the muscle is fleshy, and as far as the middle of the 
neck, it blends with its fellow. The common belly is then interrupted by a tendon, 
or sometimes two tendons, from which arise three or four fleshj^ bands. The lat- 
eral small bands (Sterno-thyroidei) diverge to reach their insertion into the thy- 
roid cartilage by a delicate tendon; while the medial and larger bands (Sterno- 
hyoidei), closely applied to each other and blending with the omo-hyoideus, pass 
straight forward to reach the ventral surface of the hyoid bone. 

Relations. — At the root of the neck the common belly is related ventrall}' to 
the sterno-cephalicus, and the carotid arteries and recurrent nerves dorsally. 
Further forward the trachea becomes the dorsal relation, and near the head the 
omo-hyoideus, skin and fascia, the ventral one. 

Blood-supply. — Carotid artery. 

Nerve-supply. — Ventral branches of the first and second cervical nerves. 

5. Omo-hyoideus.^ — This is a thin, ribbon-like muscle, almost entirely fleshy, 
which crosses the trachea very obliquel}^ 

Origin. — The subscapular fascia close to the shoulder joint. 

Insertion. — The body and adjacent part of the lingual process of the hyoid 
bone, in common with the hyoid branch of the preceding muscle. 

Action.- — To retract the hyoid bone and the root of the tongue. 

Structure. — The muscle is composed of parallel fleshy fibers, except at its origin, 
where it has a thin tendon. 

Relations. — The posterior part of the muscle is related laterally to the supra- 
spinatus, anterior deep pectoral, and brachiocephalicus and the prescapular lymph- 
glands; and medially to the scalenus. It is intimately adherent to the brachio- 
cephalicus. In the middle of the neck it is related superficially to the brachio- 
cephalicus, sterno-cephalicus, and the jugular vein; deeply, to the rectus capitis 
ventralis major, the carotid artery, the vagus, sympathetic, and recurrent nerves, 
the trachea, and, on the left side, the oesophagus. In its anterior part the muscle 
blends with the sterno-hyoideus, the two covering the sterno-thyroideus, the thy- 
roid gland in part, and the ventral face of the larynx. 

Blood-supply. — Carotid and inferior cervical arteries. 

Nerve-supply. — Ventral l^ranch of the first cervical nerve. 

6. Scalenus (M. scalenus primse costae).^ — This muscle is deeply situated on 
the side of the posterior half of the neck. It is composed of two parts, between 
which the cervical roots of the brachial plexus of nerves emerge. 

Origin. — The anterior border and lateral surface of the first rib. 
Insertion. — (1) The dorsal (smaller) part (M. scalenus dorsalis) is attached to 
the transverse process cf the seventh cervical vertebra; (2) the ventral part (M. 
1 Also termed the subscapulo-hyoideus. 



VENTRAL CERVICAL MUSCLES 269 

scalenus ventralis) is attached to the transverse processes of the sixth, fifth, and 
fourth cervical vertebrae. 

Action. — The neck is flexed or inclined laterally, according as the muscles act 
together or singly. If the neck be the fixed point, the muscle may have a respira- 
tory action by pulling forward or fixing the first rib. 

Structure. — The dorsal part is composed of several small fleshy bundles. The 
ventral portion, which is much larger, is almost entirely fleshy, and not so divided. 

Relations. — Superficially, the anterior deep pectoral, brachiocephalicus, and 
omo-hyoideus muscles, the phrenic nerve, and branches of the brachial plexus; 
deeply, the vertebrae, the longus colli and intertransversales muscles, the oesoph- 
agus (on the left side), the trachea (on the right side), the vertebral vessels, 
the vagus, sympathetic, and recurrent nerves. The roots of the brachial plexus 
form a flat anastomosis, which lies between the two parts of the muscle. The 
brachial vessels cross the ventral edge close to the first rib. 

Blood-supply. — Carotid, vertebral, and inferior cervical arteries. 

Nerve- supply. — Ventral branches of the cervical nerves. 

7. Cervicalis ascendens.^ — This muscle is the cervical continuation of the 
longissimus costarum, and is sometimes regarded as a part of the scalenus, with 
which it is partially united. It consists of three or four bundles which are attached 
to the transverse processes of the last three or four cervical vertebrae and the first 
rib. 

Action. — To extend the neck or to flex it laterally. 

Relations. — Superficially, the brachiocephalicus and anterior deep pectoral; 
deeply, the scalenus and intertransversales. 
Blood-supply. — Vertebral artery. 
Nerve-supply. — Cervical nerves. 

8. Rectus capitis ventralis major (M. longus capitis). — This is the largest 
of the three special flexors of the head, and lies along the ventro-lateral surface 
of the anterior cervical vertebrae and the base of the cranium. 

Origin. — The transverse processes of the fifth, fourth, and third cervical ver- 
tebrae. 

Insertion. — The tubercles at the junction of the basilar part of the occipital 
bone with the body of the sphenoid. 

Action. — Acting together, to flex the head; acting singly, to incline it to the 
same side also. 

Structure. — ^The origin of the muscle is by fleshy digitations. The belly in- 
creases in size by the union of these digitations, reaching its maximum at the axis. 
It then diminishes, passes toward the median plane, and terminates on a rounded 
tendon. 

Relations. — Superficially, the brachiocephalicus and omo-hyoideus, the mandib- 
ular gland, the carotid artery (which lies along the ventral border), the occipital 
and internal carotid arteries, and the tenth, eleventh, and sympathetic nerves; 
deeply, the vertebrae, the longus colli, intertransversales, and the rectus capitis 
ventralis minor. The terminal part of the muscle lies in contact with its fellow 
above the pharynx and between the guttural pouches. 

Blood-supply. — Carotid, vertebral, and occipital arteries. 

Nerve-supply. — Ventral branches of the cervical nerves. 

9. Rectus capitis ventralis minor (M. rectus capitis ventralis). — This is a small 
muscle which lies dorsal to and under cover of the preceding one. 

Origin.- — The ventral arch of the atlas. 

Insertion. — The basilar part of the occipital bone, close to the preceding muscle. 

Action. — To flex the atlanto-occipital articulation. 

Structure. — Fleshy . 

1 This muscle is also known as the ilio-costalis cervicis. 



270 FASCIA AND MUSCLES OF THE HORSE 

Relations. — Ventrally, to the preceding muscle; dorsall}-, to the atlas, atlanto- 
occipital articulation, and the basilar part of the occipital bone; laterally, to the 
rectus capitis lateralis and the guttural pouch. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Ventral branch of the first cervical nerve. 

10. Rectus capitis lateralis. — This is a still smaller muscle, which lies for the 
most part under the obliquus capitis anterior. 

Origin. — The atlas, lateral to the preceding muscle. 
Insertion. — The paramastoid process of the occipital bone. 
Action. — The same as the preceding muscle. 
Structure. — Fleshy. 

Relations. — Superficially, the obliquus capitis anterior, the occipital vessels, 
and the ventral branch of the first cervical nerve. 
Blood-supply. — Occipital artery. 
Nerve-supply. — Ventral branch of the first cervical nerve, 

11. Longus colli. — This muscle covers the ventral surfaces of the vertebrae, 
from the sixth thoracic to the atlas, and is united with its fellow. It consists of 
two parts, thoracic and cervical. 

Origin. — (1) Thoracic part, the bodies of the first six thoracic vertebrae; (2) 
cervical part, the transverse processes of the cervical vertebrae. 

Insertion. — (1) Thoracic part, the bodies and transverse processes of the last 
two cervical vertebrae; (2) cervical part, the bocUes of the cervical vertebrae and 
the ventral tubercle of the atlas. 

Action. — To flex the neck. 

Structure. — The muscle is composed of a succession of bundles. The largest 
of these constitute the thoracic part of the muscle, which has a strong tendon in- 
serted into the last two cervical vertebrae. A bursa is interposed between the ten- 
don and the spine at the first costo-vertebral articulation. The cervical part con- 
sists of a number of smaller bundles, each of which passes from its origin on the 
transverse process of one vertebra forward and medially to its insertion into a ver- 
tebra further forward. The most anterior bundle is inserted by a strong tendon into 
the ventral tubercle of the atlas. 

Relations. — The principal relations of the two muscles in the thorax are: 
ventrally, the pleura, and, further forward, the trachea and oesophagus; dorsally, 
the vertebrae and the costo-vertebral joints; laterally, the dorsal, deep cervical, 
and vertebral vessels, the sympathetic nerve, and the thoracic roots of the brachial 
plexus. In the neck important relations are: ventrally, the trachea and oesophagus, 
the carotid artery, the vagus, sympathetic, and recurrent nerves; dorsally, the 
vertebrae and, in the middle third of the neck, the intertransversales muscles; lat- 
erally, the scalenus, the rectus capitis ventralis major, and the intertransversales 
(in the anterior third). The terminal part of the muscle is separated from the 
trachea by the oesophagus, which is here median in position. 

Blood-supply. — Subcostal and vertebral arteries. 

Nerve-supply. — Ventral branches of the spinal nerves. 

12. Intertransversales colli (Mm. intertransversarii cervicis). — These are six 
fasciculi which occupy the spaces between the lateral aspects of the vertebrae and 
the transverse and articular processes. There is thus a bundle for each inter- 
vertebral articulation except the first. Each bundle consists of a dorsal and ven- 
tral part. 

Attachments. — The dorsal bundles pass from transverse process to articular 
process; the ventral bundles extend between adjacent transverse processes. 
Action. — To flex the neck laterally. 

Structure. — They contain strong tendinous intersections. 
Relations. — Superficially, the brachiocephalicus, rectus capitis ventralis ma- 



LATERAL CERVICAL MUSCLES 271 

jor, obliquus capitis posterior, complexus, longissimus capitis et atlantis, splenius, 
scalenus, and longissimus dorsi et costarum muscles; deeply, the vertebrae, the 
longus colli muscle, and the vertebral vessels. The muscles are perforated by 
branches of these vessels and by the primary branches of the cervical nerves. 

Blood-supply. — Vertebral artery. 

Nerve-supply. — The cervical nerves. 

LATERAL CERVICAL MUSCLES 
This group consists of twelve pairs of muscles arranged in layers. 

First Layer 

1. Trapezius cervicalis. — Described on p. 293. 

Second Layer 

2. Rhomboideus cervicalis. — Described on p. 293. 

3. Serratus cervicis. — Described on p. 297. 

Third Layer 

4. Splenius. — This is an extensive, fiat, triangular muscle, partly covered by 
the preceding three muscles. 

Origin. — The second, third, and fourth thoracic spines by means of the dorso- 
scapular ligament and the funicular part of the ligamentum nucha?. 

Insertion. — The nuchal crest, the mastoid process, the wing of the atlas, 
and the transverse processes of the third, fourth, and fifth cervical vertebrse. 

Action. — Acting together, to elevate the head and neck; acting singly, to in- 
cline the head and neck to the side of the muscle acting. 

Structure. — The muscle arises in the withers from the anterior part of the 
dorso-scapular ligament, which also affords attachment to the rhomboideus, ser- 
ratus dorsalis, and complexus muscles. The fibers pass upward and forward 
toward the head and the first cervical vertebra. The insertion on the occipital 
bone and the mastoid process is by means of a thin aponeurosis common to the 
brachiocephalicus and longissimus capitis. The atlantal insertion is by a strong, 
flat tendon, in common with the longissimus atlantis and the brachiocephalicus. 
The remaining insertions are fleshy digitations. 

Relations. — Superficially, the skin and fascia, the trapezius, rhomboideus 
cervicalis, serratus ventralis, and posterior auricular muscles' deeply the com- 
plexus and longissimus dorsi muscles. 

Blood-supply. — Deep cervical and dorsal arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

Fourth Layer 

5. Longissimus capitis et atlantis.^ — This muscle consists of two parallel, fusi- 
form portions. It lies between the deep face of the splenius and the ventral part 
of the complexus. 

Origin. — (1) The transverse processes of the first two thoracic vertebrse; (2) 
the articular processes of the cer'Mcal vertebrse. 

Insertion.- — (1) The mastoid process; (2) the wing of the atlas. 

^di'on.— Acting together, to extend the head and neck; acting singly, to flex 
the head and neck laterally or to rotate the atlas. 

Structure. — The origin from the thoracic vertebrse is by aponeurotic slips 
which blend with the complexus. The succeeding fleshy part, in passing along 
lAIso termed the trachelo-mastoideus. 



272 



FASCIA AND MUSCLES OF THE HORSE 



the neck, receives fasciculi from each of the cervical vertebra except the 
first two. The dorsal division of the muscle (M. longissimus capitis) is 
inserted into the mastoid process by a flat tendon which fuses with that of 
the splenius; the ventral division (M. longissimus atlantis) is inserted into the 




LATERAL CERVICAL MUSCLES 273 

wing of the atlas by a ribbon-like tendon in common with the splenius and 
brachiocephalicus. 

Relations. — Superficially, the splenius muscle and dorsal branches of the 
cervical nerves; deeply, the complexus, the spinalis colli, and the oblique muscles 
of the head. The deep cervical vessels cross the deep face of the muscle obliquely 
at the level of the sixth and seventh cervical vertebrae. 

Blood-supply. — Vertebral and deep cervical arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

6. Complexus (M. semispinalis capitis). — This is a large triangular muscle 
which lies chiefly on the ligamentum nuchse, under cover of the splenius. 

Origin. — (1) The second, third, and fourth thoracic spines, in common with 
the splenius and serratus dorsalis; (2) the transverse processes of the first six or 
seven thoracic vertebrae ; (3) the articular processes of the cervical vertebrae. 

Insertion. — A rough area on the occipital bone just ventral to the nuchal crest. 

Action. — It is the chief extensor of the head and neck. Acting singly, the 
muscle inclines the head to the same side. 

Structure. — The origin of the muscle at the withers is aponeurotic. In the 
neck the bundles arising from the articular processes run obliquely upward 
and forward, giving the lower part of the muscle a distinct pennate character. 
The dorsal part of the belly is crossed obliquely by four or five tendinous 
intersections. The insertion is by a strong tendon. 

Relations. — Superficially, the rhomboideus, serratus ventralis, splenius, and 
longissimus capitis et atlantis; deeply, the ligamentum nuchae, the multifidus 
cervicis, longissimus dorsi, and the oblique and dorsal straight muscles of the head, 
the deep cervical vessels, and the dorsal cutaneous branches of the cervical nerves. 

Blood-supply. — Deep cervical, vertebral, and occipital arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

7. Multifidus cervicis. — This muscle lies on the arches of the last five cervical 
vertebrae. It consists of five or six segments. 

Origin. — The articular processes of the last four or five cervical and the first 
thoracic vertebrae. 

Insertion. — The spinous and articular processes of the cervical vertebrae. 

Action. — Acting together, to extend the neck; acting singly, to flex the neck on 
the side of the muscle contracting and to rotate the neck to the opposite side. 

Structure. — The muscle is composed of two sets of bundles. The superficial 
bundles are directed obliquely forward and inward, each passing from an articular 
process to the spine of the preceding vertebra. The deep bundles are shorter and 
run straight from an articular process to that of the preceding vertebra. 

Relations.- — Superficially, the complexus, longissimi, and obliquus capitis poster- 
ior; deeply, the spinalis, the ligamentum nuchae, and the arches of the vertebrae. 

Blood-supply. — Deep cervical and vertebral arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

8. Spinalis. — Described with the longissimus on p. 278. 

9. Obliquus capitis posterior (s. caudalis) .— This is a strong, quadrilateral 
muscle, which covers the dorso-lateral aspect of the atlas and axis. 

Origin. — The side of the spine and the posterior articular process of the axis. 

Insertion. — The dorsal surface of the wing of the atlas. 

Action. — Chiefly to rotate j^fe atlas, and with it the head, to the same side; 
also to assist in extending and fixing the atlanto-axial joint. 

Structure. — The muscle is composed almost entirely of parallel fleshy fibers 
directed obliquely forward and outward. It is covered by a special fascia. 

Relations. — Superficially, the splenius, complexus, longissimus capitis, and 
brachiocephalicus muscles; deeply, the arch and spine of the axis, the wing of 
the atlas, the atlantoaxial joint, the rectus capitis dorsalis minor, the occipital and 
18 



274 



FASCIA AND MUSCLES OF THE HORSE 



vertebral vessels, and the first and second cervical nerves. The terminal part of 
the vertebral arterj^ joins the posterior branch of the occipital artery under cover 
of the muscle. 

Blood-supply. — Occipital and vertebral arteries. 




m no °^ 
3 3 9 
m C ■*! 



iiJI'lli 



I ". s -^- 



O 05 O — 
^ I3J 73 H 



LATERAL CERVICAL MUSCLES 



275 



Nerve-supply. — Dorsal branch of the second cervical nerve. 

10. Obliquus capitis anterior (s. craniahs). — This short, thick, quadrilateral 
muscle lies on the side of the atlantooccipital articulation. 

Origin. — The anterior edge and ventral surface of the vnng of the atlas. 

Insertion. — The paramastoid process and nuchal crest of the occipital bone 
and the mastoid process. 

Action. — Acting together, to extend the head on the atlas; acting singly, to 
flex the head laterally. 

Structure. — The muscle contains a good deal of tendinous tissue. The direction 
of its fibers is forward, upward, and inward. 




Fig. 269. — Deepest Layer of Muscles of Neck of House. 
a, Obliquus capitis anterior; b, obliquus capitis posterior; c, rectus capitis lateralis; d, rectus capitis ventralia 
minor; e, rectus capitis ventralis major; /, longus colli; s, s', scalenus; A, longissimus costarum; j, longissimus dorsi; 
fc, spinalis et semispinalis; ?, multifidus dorsi ; m, multifidus cervicis; n, intertransversales; o, o', rectus capitis dorsalis 
major; p, rectus capitis dorsalis minor; q, tendon of insertion of complexus; 1, lamellar part, 1', funicular part of liga- 
mentum nuchae; 2, nuchal crest; 3, paramastoid process; 4. edge of wing of atlas; o, transverse, and 6, articular, 
processes of cervical vertebrae; 7, nerves of brachial plexus (cut) ; S, first rib. (Ellenberger-Baum, Anat. d. Haustiere.) 



Relations. — Superficially, the complexus, the aponeurosis of the splenius, longus 
capitis, and brachiocephalicus, overlying which are the posterior auricular muscles, 
artery, and nerve, and the parotid gland; deeply, the dorsal straight muscles, 
the occipito-hyoideus, the atlanto-occipital articulation, the posterior meningeal 
artery, and a branch of the occipital nerve. 

Blood-supply.— Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 

11. Rectus capitis dorsalis major. — This muscle extends from the axis to the 
occipital bone, in contact with the ligamentum nuchse. 

Origin. — The edge of the spinous process of the axis. 



276 FASCIA AND MUSCLES OF THE HORSE 

Insertion. — The occipital bone, below the complexus; the tendon of insertion 
of the complexus. 

Action. — To extend the head. 

Structure. — The muscle is fleshy and may be divided into two parallel parts, 
superficial and deep. The former blends somewhat with the terminal part of the 
complexus. The deep part may be termed the rectus capitis dorsalis medius. 
Bundles frequently arise from the fascia over the obliquus capitis posterior. 

Relations. — Superficially, the obliquus capitis anterior, splenius, and com- 
plexus; medially, the ligamentum nuchse; deeply, the atlas, the atlanto-occipital 
articulation, and the rectus capitis dorsalis minor. The dorsal branch of the first 
cervical nerve appears between this muscle and the obliquus capitis anterior. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 

12. Rectus capitis dorsalis minor. — This small muscle lies under cover of the 
preceding. 

Origin. — The dorsal surface of the atlas. 

Insertion. — The occipital bone beneath the preceding muscle and lateral to the 
funicular part of the ligamentum nuchse. 

Action. — To assist the preceding muscle. 

Structure. — It is fleshy and varies a good deal in volume, being sometimes 
small and difficult to recognize.^ On the other hand, it is sometimes double. 

Relations. — Superficially, the preceding muscle and the obliquus capitis an- 
terior; deeply, the atlas and the atlanto-occipital articulation. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 



The Fascije and Muscles of the Back and Loins 

(fascia et musculi dorsi et lumborum) 

The superficial fascia presents no special features. The lumbo-dorsal fascia 
(Fascia lumbo-dorsalis) closely invests the muscles, but is easily stripped off the 
longissimus. It is attached medially to the supraspinous ligament and the spinous 
processes of the vertebrae; it divides laterally into two layers. The superficial 
layer is practically the aponeurosis of the latissimus dorsi. The deep layer gives 
origin to the serratus dorsalis, the lumbar part of the obliquus abdominis externus, 
the transversus abdominis, and the retractor costae. Its lateral edge curves under 
the longissimus and is attached to the ribs and lumbar transverse processes. Pos- 
teriorly it is continuous with the gluteal fascia. At the withers it forms an impor- 
tant structure, the dorso-scapular ligament. This is a strong tendinous sheet, 
attached to the third, fourth, and fifth thoracic spines. Its upper part is very 
thick and gives origin by its superficial surface to the rhomboideus thoracalis, by 
its anterior part to the splenius. The lower part is thin and elastic, and furnishes 
numerous lamellae which intersect the scapular part of the serratus ventralis and 
are attached to the scapula. Three lamellae are detached from the ligament. 
The deepest of these passes between the longissimus and spinalis and is attached to 
the transverse processes of the first seven thoracic vertebrae; it gives attachment 
to the complexus. The middle one dips in between the longissimus dorsi and 
longissimus costarum. The superficial one gives origin to the serratus dorsalis. 
A strong fascial layer, the ilio-lumbar ligament, extends from the last rib to the 
tuber coxae. 

There are nine pairs of muscles in this region, arranged in four layers. 

^ This seems due to pressure produced by pathological changes in the supra-atloid bursa, 
which are frequently extensive in dissecting-room subjects. 



the fascia and muscles of the back and loins 277 

First Layer 

1. Trapezius thora calls. 

2. Latlsslmus dorsl. 

Second Layer 

3. Rhomboldeus thoracalls. 

The foregoing are described with the other muscles which attach the thoracic 
limb to the trunk (p. 293). 

4. Serratus dorsalis anterior (s. cranialis). — This is a thin quadrilateral muscle, 
named from its serrated ventral border. It lies under cover of the rhomboideus, 
serratus ventralis, and latissimus dorsi. 

Origin. — The lumbo-dorsal fascia and dorso-scapular ligament. 

Insertion. — The lateral surfaces of the fifth or sixth to the eleventh or twelfth 
ribs inclusive. 

Action. — To draw the ribs on which it is inserted forward and outward, thus 
assisting in inspiration. 

Structure. — The muscle arises by means of a thin aponeurosis. The muscle- 
fibers pass ventrally and backward to be attached to the ribs by seven or eight 
digitations below the lateral edge of the longissimus costarum. 

Relations. — Superficially, the rhomboideus, serratus ventralis, latissimus dorsi, 
and serratus dorsalis posterior; deeply, the longissimus dorsi, longissimus costarum, 
external intercostal muscles, and the ribs. 

Blood-supply. — Intercostal arteries. 

Nerve-supply. — Thoracic nerves. 

5. Serratus dorsalis posterior (s. caudalis). — This muscle resembles the pre- 
ceding one, which it partly covers. 

Origin. — The lumbo-dorsal fascia. 

Insertion. — The lateral surfaces of the last seven or eight ribs. 

Action. — To draw the ribs backward, thus assisting in expiration. 

Structure. — Similar to the preceding muscle. The fibers are directed ventrally 
and forward and terminate in seven or eight digitations, one or two of which cover 
the posterior teeth of the anterior muscle. The aponeurosis blends with that of 
the latissimus dorsi. 

Relations. — Superficially, the latissimus dorsi and external oblique; deeply, 
the longissimus dorsi, longissimus costarum, external intercostals, serratus dorsalis 
anterior, and the ribs. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Thoracic nerves. 

Third Layer 

6. Longissimus costarum.^ — This long, segmental muscle extends across the 
series of ribs, in contact with the outer edge of the longissimus dorsi. 

Origin. — (1) The deep layer of the lumbo-dorsal fascia as far back as the third 
or fourth lumbar transverse process. (2) The anterior borders and lateral surface 
of the last fifteen ribs.^ 

Insertion. — The posterior borders of the ribs and the transverse processes of 
the last cervical vertebra. 

Action. — Chiefly to depress and retract the ribs and so help in expiration. 

1 This muscle is also known as the long costal, ilio-costaUs, or transversalis costarum. The 
name given above was introduced by the International Commission for the Reform of Myological 
Nomenclature and appears worthy of general adoption. 

2 The lumbar part of this muscle is subject to variation. It may, in quite exceptional case^ 
extend as far as the ilium, and sometimes, on the other hand, it does not arise quite as far back as 
given above. In some subjects the origin can be traced distinctly to the tips of lumbar transverse, 
processes. 



278 



FASCIA AND MUSCLES OF THE HORSE 



Acting together, they may assist in extending the spine, acting singly in inchning 
it laterally. 

Structure. — This muscle presents a distinct segmental arrangement. It is 
composed of a series of bundles, the fibers of which are directed forward and a little 
ventro-laterally. From these are detached two sets of tendons. The superficial 
tendons spring from the lateral edge of the muscle. They are flat and are about 
half an inch in width. Each crosses two or three intercostal spaces, to be inserted 
on the posterior border of a rib. The deep tendons are detached from the dorsal 
part of the deep face of the muscle. Each passes backward across one or two inter- 
costal spaces to its origin on the anterior border or lateral surface of a rib. Small 

bursae may be found between the ribs and 
tendons. 

Relations. — Superficially, the dorsal and 
ventral serrati; deeply, the external inter- 
costals and the ribs. The lumbar origin is 
covered by the longissimus dorsi. The deep 
cervical and dorsal vessels cross the surface of 
the muscle at the first and second intercostal 
spaces respectively, and branches of the in- 
tercostal vessels and nerves emerge between 
it and the longissimus dorsi; here a fascial 
layer dips in between the two. 

Blood-supply. — Intercostal arteries. 
Nerve-supply. — Dorsal branches of the 
thoracic nerves. 

7. Longissimus dorsi.^ — This is the 
largest and longest muscle in the body. It 
extends from the sacrum and ilium to the 
neck, filling up the space between the spinous 
processes medially and the lumbar trans- 
verse processes and the upper ends of the 
ribs ventrally ; consequently it has the form 
of a three-sided prism. 

Origin. — (1) The tubera, crest, and ad- 
jacent part of the ventral surface of the ilium ; 
(2) the first three sacral spines ; (3) the lum- 
bar and thoracic spines and the supraspinous 
ligament. 

Insertion. — (1) The lumbar transverse 
and articular processes; (2) the thoracic 
transverse processes; (3) the spinous and 
transverse processes of the last four cer- 
vical vertebrae; (4) the lateral surfaces of the ribs, except the first. 

Action. — Acting with its fellow, it is the most powerful extensor of the back 
and loins; by its cervical attachment it assists in extending the neck. By its costal 
attachment it may also assist in expiration. Acting singly, it flexes the spine 
laterally. 

Structure. — This is quite complex. The posterior part of the muscle is greatly 
developed and constitutes the common mass of the loins. This is covered by a 
strong aponeurosis which blends with the supraspinous and sacro-iliac ligaments, 
and is attached to the crest and sacral angle of the ilium and the first and second 
sacral spines; it furnishes origin to the lumbar portion of the middle gluteus. In 

' The muscle as here described includes the longissimus dorsi et cervicis and the spinalis and 
semispinalis components, as the separation of these is largely artificial in the horse. 




Fig. 270. — Right Portion op Cross-section op 
Back op Horse. Section is Cut Through 
Seventh Thoracic Vertebra. 
a, Ligamentum nuchae; 6, trapezius mus- 
cle; c, cartilage of scapula; d, latissimus dorsi; e, 
cutaneus; /, rhomboideus thoracalis; g, ser- 
ratus ventralis; h, serratus dorsalis; h', lumbo- 
dorsal fascia, which divides below into three 
layers; i, longissimus costarum; k, levator costae; 
k', internal intercostal muscle; I, longissimus dorsi; 
m, m', seventh thoracic vertebra; n, head of 
eighth thoracic vertebra; o, head of eighth rib; 
p, seventh rib; r, intercostal artery and nerve; s, 
skin. The fascise are indicated by dotted lines. 
(After Ellenberger, in Leisering's Atlas.) 



THE FASCIA AND MUSCLES OF THE TAIL 279 

its course further forward the muscle receives fasciculi from the lumbar and thoracic 
spines, but diminishes somewhat in volume. About the twelfth thoracic vertebra 
it divides into two parts. The dorsal division (m. spinalis et semispinalis), rein- 
forced by bundles from the first four thoracic spines, passes forward under the com- 
plexus to be inserted into the spines of the last four cervical vertebrae. The ventral 
division passes forward and downward underneath the serratus ventralis to be in- 
serted into the ribs and the transverse processes of the last four cervical vertebrae. 
Three sets of fasciculi may be distinguished, viz. : (1) spinal, which are superficial 
and medial; (2) transverse, attached to the transverse and articular processes, 
which are medial and deep; (3) costal, which are lateral. 

Relations. — Superficially, the middle gluteus, the lumbo-dorsal fascia, the 
latissimus dorsi, serrati dorsales, serratus ventralis, and complexus; deeply, the 
multifidus, intertransversales, external intercostals, levatores costarum, the liga- 
mentum nuchse, and its fellow of the opposite side (in the neck). 

Blood-supply. — Dorsal, deep cervical, intercostal, and lumbar arteries. 

Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves. 

8. Multifidus dorsi. — This is a long segmental muscle which lies along the sides 
of the spinous processes of the vertebrae from the sacrum to the neck. 

Origin. — (1) The lateral part of the sacrum; (2) the articular processes of 
the lumbar vertebrae; (3) the transverse processes of the thoracic vertebrae. 

Insertion. — The spinous processes of the first two sacral, the lumbar, thoracic, 
and last cervical vertebrae. 

Action. — Acting with its fellow, it is an extensor of the spine; acting singly, 
it flexes it laterally. 

Structure. — It is composed of a series of bundles which are directed obliquely 
forward and upward. Each fasciculus passes over several vertebrae to its insertion. 
In the posterior part of the series the bundles cross two or three vertebrae and are 
inserted into the summits of the spines. Anteriorly the bundles have a more 
horizontal direction, cross three to five vertebrae, and are inserted into the sides 
of the spines considerably below their summits. A further complication consists 
in the fusion of several bundles into a common insertion. 

Relations. — Superficially, the longissimus dorsi; deeply, the vertebral spines. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves. 

9. Intertransversales lumborum. — These are very thin muscular and tendin- 
ous strata, which occupy the spaces between the transverse processes of the lumbar 
vertebrae except the fifth and sixth. 

Action. — To assist in flexing the loins laterally or in rendering the region rigid. 
Relations. — Superficially, the longissimus dorsi; deeply, the quadratus lum- 
borum. 

Blood-supply. — Lumbar arteries. 
Nerve-supply. — Lumbar nerves. 



The Fascia and Muscles of the Tail 
(fascia et musculi caud^) 

The muscles of the tail are inclosed in the strong coccygeal fascia, which is 
continuous in front with the gluteal fascia and blends with the lateral sacro-iliac 
ligament. At the root of the tail it is loosely attached to the subjacent muscles, 
l^ut further back it is intimately adherent to them. From its deep face are de- 
tached septa which pass between the muscles to become attached to the vertebrae. 

1. Coccygeus.^ — This is a flat, triangular muscle which lies chiefly between the 
sacro-sciatic ligament and the rectum. 

^ Also termed the ischio-coccygeus or compressor coccygis. 



280 



FASCIA AND MUSCLES OF THE HORSE 



Origin. — The pelvic surface of the sacro-sciatic ligament near the ischiatic spine. 

Insertion. — The first four coccygeal vertebrae and the coccygeal fascia. 

Action. — Acting together, to de- 
press (flex) the tail, compressing it 
over the perineum; acting singly, 
to depress and incline it to the 
same side. 

Structure. — The origin of the 
muscle is aponeurotic. Becoming 
fleshy, its fibers pass upward and 
backward and divide into two 
layers. The lateral layer is at- 
tached to the vertebrae, the medial 
to the fascia; included between 
the two lie the intertransversales. 
When the tail is raised, the ventral 
edges of the muscles produce a dis- 
tinct ridge at either side of the anus. 
Relations. — Laterally, the 
sacro-sciatic ligament and the semi- 
membranosus ; medially, the rectum 
and the sacro-coccygeus ventralis 
muscle. The internal pudic artery 
crosses the origin of the muscle, 
sacrococcygeus dorsalis medialis).^ — This 




Fig. 271. — Cross-section of Tail of Horse. 
1, 2, Branches of lateral coccygeal vessels and nerve; 3, mid- 
dle coccygeal artery; 4, sacro-coccygeus dorsalis; 4', sacro-coccy- 
geus lateralis; 5, 5', intertransversales; 6, sacro-coccygeus ven- 
tralis; 7, recto-coccygeus; 8, coccygeal fascia; 9, fibro-cartilage 
between fourth and fifth coccygeal vertebrae. The veins are black. 



2. Sacro-coccygeus dorsalis (M. 
muscle lies along the dorso-median aspect of the tail, in contact with its fellow 

Origin. — The last three sac- 
ral spines and some of the coccy- 
geal spines. 

Insertion . — The dorsal sur- 
face of the coccygeal vertebrae. 

Action. — Acting together, to 
elevate (extend) the tail; acting 
singly, to elevate and incline it 
laterally. 

Structure. — The muscle has 
a strong rounded belly. It is in- 
serted by means of short tendons 
which fuse with those of the next 
muscle. 

Relations. — Superficially, the 
coccygeal fascia; medially, its 
fellow; laterally, the sacro-coccy- 
geus lateralis; deeply, the verte- 
brae. 

3. Sacro-coccygeus lateralis 
(M. sacro-coccygeus dorsalis later- 
alis).^ — This muscle hes immedi- 
ately lateral to the preceding. 

Origin. — The sides of the 

1 Also termed the erector coccy- 
gis. 

■ Also known as the curvator 
coccygis. 




Fig. 272.- 
a, Coccygeus; b 
d, recto-coccygeus; e 
tor penis; g, bulbo 
pudic artery; k, anus; I, penis. 
Anat. d. Pferdes.) 



Muscles of Perineum of Horse. 
retractor ani; c, c', sphincter ani externus; 



■geus ventralis lateralis; /, retrac- 
h, ischio-cavernosus; i, internal 
(After EUenberger-Baum, Top. 



THE MUSCLES OF THE THORAX 281 

sacral spines, with the multifidus, and the transverse processes of the sacral and 
coccygeal vertebrse. 

Insertion. — The lateral surface of the coccygeal vertebrae, except the first four. 

Action. — Acting with its fellow, to assist the preceding muscle in elevating the 
tail; acting singly, to incline it to the same side. 

Structure.— This, muscle appears to be a direct continuation of the multifidus 
dorsi. The belly is fusiform and receives reinforcing fasciculi from the transverse 
processes of the sacrum. This is succeeded by bundles of tendons, as many as four 
lying alongside of each other. 

Relations. — Superficially, the lateral sacro-iliac ligament and the coccygeal 
fascia; dorsally, the sacro-coccygeus dorsalis; ventrally, the intertransversales; 
deeply, the vertebrae and a branch of the lateral coccygeal artery and accompanying 
vein and nerve. 

4. Intertransversales caudae (Mm. intertransversarii caudse). — These con- 
sist of muscular bundles which lie on the lateral aspect of the tail, between the 
preceding muscle and the sacro-coccygeus ventralis. They begin on the lateral 
edge of the sacrum and occupy the spaces between the transverse processes, to which 
they are attached. They are, however, not arranged in a strict segmental manner. 

Action. — Acting together, to fix the coccygeal vertebrae; acting singly, to assist 
in lateral flexion. 

5. Sacro-coccygeus ventralis (Mm. sacro-coccygei ventrales).^ — This muscle 
lies on the ventral aspect of the sacrum and coccyx. It is composed of two parts, 
described by Bourgelat and the German anatomists as separate muscles. 

(a) The lateral part (M. coccygeus ventralis lateralis) is much the larger of 
the two. It arises from the lateral part of the ventral surface of the sacrum, about 
as far forward as the third foramen, and is inserted into the transverse processes 
and ventral surface of the coccygeal vertebrae. 

(6) The medial part (M. sacro-coccygeus ventralis medialis) arises from the 
ventral surface of the sacrum medial to the preceding muscle and the first eight 
coccygeal vertebrse, and is inserted into the ventral surfaces of the coccygeal ver- 
tebrae. 

Action. — Acting together, to depress (flex) the tail; acting singly, to incline 
it laterally also. 

Structure. — The lateral part has a somewhat compressed belly, and receives 
bundles from the transverse processes of the coccygeal vertebrae. The medial part 
is much smaller and shorter, reaching only about to the middle of the tail. 

Relations.- — Ventrally, the pelvic and coccygeal fasciae; dorsally, the sacrum, 
coccygeal vertebrae, and the intertransversales; laterally, the sacro-sciatic liga- 
ment, the coccygeus, and the coccygeal fascia; medially, its fellow, the recto- 
coccygeus, and the middle coccygeal vessels. Branches of the lateral coccygeal 
vessels and nerves lie between the lateral division of the muscle and the intertrans- 
versales. 

Blood-supply. — Middle and lateral coccygeal arteries. 

Nerve-supply. — Coccygeal nerves. 



The Muscles of the Thorax 
(muscuu thoracis) 

These consists of seven muscles or sets of muscles, which are attached to the 
thoracic vertebrae, to the ribs and their cartilages, and to the sternum. They are 
muscles of respiration. 

1. Levatores costarum. — These constitute a series of small muscles which oc- 
cupy and overhe the dorsal ends of the intercostal spaces. 
1 Also known as the depressor coccygis. 



282 



FASCIA AND MUSCLES OF THE HORSE 



Origin. — The transverse processes of the thoracic vertebrse. 

Insertion. — The lateral surfaces of the upper ends of the ribs posterior to the 
A'ertebral origin. 

Action.— To draw the ribs forward in inspiration. 

Structure. — Arising by tendinous fibers, each muscle passes backward and out- 
ward and expands at its insertion. Some fibers pass over one rib and are inserted 



Seventh cervical vertebra-' 
First thoracic vertebra- 



Section of scapula 



Intertransversales 



Intercostal f 

nervet< *i 



Retractor co. 

Intertransverse luja, 

Ilio-lumbar ligament,. 




Levatores costarum 



External 
intercostal 
XT"- J muscles 



Lateral border of lon- 
gissimus dor si 



Tuber coxce 



Fig. 273. — Deep Dissection op Dorsal and Lumbar Regions of Horse; Dorsal View. (After Schmaltz, Atlas 

d. Anat. d. Pferdes.) 



on a succeecUng one. At the beginning and end of the series the muscle cannot be 
distinguished from the external intercostal, of which it is in reality only a specially 
developed part. 

Relations. — Superficially, the longissimus dorsi; deeply, the ribs, internal in- 
tercostal muscles, and the intercostal vessels and nerves. 

Blood-supply. — Intercostal arteries. 



THE MUSCLES OF THE THORAX 283 

Nerve-supply. — Intercostal nerves. 

2. External intercostals (Mm. intercostales externi). — Each of these occupies 
an intercostal space, from the levatores to the sternal extremity of the rib. They 
do not occupy the intercartilaginous spaces. 

Origin. — The posterior borders of the ribs. 

Insertion. — The anterior borders and lateral surfaces of the succeeding ribs. 

Action. — To draw the ribs forward in inspiration. 

Structure. — The fibers are directed downward and backward. There is a 
considerable admixture of tendinous tissue. The thickness of the muscles grad- 
ually diminishes toward the lower ends of the spaces. 

Relations. — Superficially, the serratus ventralis, latissimus dorsi, serratus 
dorsalis, longissimus dorsi, longissimus costarum, rectus thoracis, deep pectoral, 
obliquus abdominis externus, and cutaneous muscles; deeply, the internal inter- 
costals and (in the upper part of the spaces) the intercostal vessels and nerves. 

Blood-supply. — Intercostal and internal thoracic arteries. 

Nerve-supply . — I nter costal nerves . 

3. Internal intercostals (Mm. intercostales interni). — These extend the en- 
tire length of the intercostal spaces, including their interchondral portion. 

Origin. — The anterior borders of the ribs and their cartilages. 

Insertion. — The posterior borders of the preceding ribs and cartilages. 

Action.- — To draw the ribs backward in expiration. It seems probable, how- 
ever, that the intercartilaginous portion is inspiratory.'- 

Structure. — The direction of the fibers is oblique downward and forward. 
There is a smaller amount of tendinous tissue than in the external set, and the 
thickness diminishes dorsally. In the upper part of the spaces fibers sometimes 
cross a rib in a fashion similar to the subcostals of man. A thin fascia separates 
the internal from the external intercostal muscle in each space. 

Relations. — Superficially, the levatores costarum and the external intercostals; 
deeply, the endothoracic fascia and pleura, the transversus thoracis, diaphragm, 
transversus abdominis, and the internal thoracic and musculo-phrenic vessels. 
In the upper part of the intercostal spaces the intercostal vessels and nerves lie 
between the internal and external intercostal muscle, but below they lie chiefly on 
the deep face of the internal muscle. 

Blood-supply. — Intercostal and internal thoracic arteries. 

Nerve-supply. — Intercostal nerves. 

The muscles in connection with the costal cartilages are sometimes distinguished as Mm. 
intercartilaginei ; their direction is similar to that of the internal intercostal, and they cover the 
cartilages of the asternal ribs more or less. At the ventral ends of some of the intercostal spaces 
there is a layer of longitudinal muscle. 

4. Retractor costae. — This is a small triangular muscle which lies behind the 
last rib, chiefly under cover of the serratus dorsalis. 

Origra. — The transverse processes of the first three or four lumbar vertebrae 
by means of the lumbar fascia. 

Insertion. — The posterior border of the last rib. 

Action. — To retract the last rib. 

Structure. — The muscle arises by a thin aponeurosis. Its fibers are parallel 
to those of the adjacent internal oblique. 

Relations. — Superficially, the serratus dorsalis and external oblique; deeply, 
the transversus abdominis. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

5. Rectus thoracis.^ — This is a thin muscle which lies under cover of the deep 

^ The function of the intercostal muscles is still a subject of much discussion. The state- 
ments made above seem to represent the view most commonly held in regard to their action. 
2 Also known as the transversus costarum or lateralis sterni. 



284 



FASCIA AND MUSCLES OF THE HORSE 



pectoral muscles. It is directed obliquely backward and downward, and crosses 
the lower part of the first three intercostal spaces. 

Origin. — The lateral surface of the first rib, below the scalenus. 

Insertion. — The cartilage of the fourth rib. The aponeurosis usually joins the 
rectus abdominis. It may reach the fifth rib or the sternum. 



Cariniform cartilage 



Sternal ligament 



First rib 
Internal thoracic vessels 



Internal intercostal muscle 




Fig. 274. — Dissection of Floor of Thorax op Horse. 
The ribs have been sawn off near their sternal ends and the diaphragm and transversus abdominis cut off close to their 

attachment. 
1, Eighth rib; 2, 3, cartilages of ninth and tenth ribs; 4, xiphoid cartilage; 5, apex of pericardium. 



Action. — It may assist in inspiration or concur with the rectus abdominis. 
Relations. — Superficially, the deep pectoral muscles; deeply, the intercostal 
muscles and the ribs. 

Blood-supphj. — Internal and external thoracic arteries. 
Nerve-supply. — Intercostal nerves. 



THE MUSCLES OF THE THORAX 285 

6. Transversus thoracis.— This is a flat muscle situated on the thoracic sur- 
face of the sternum and the cartilages of the sternal ribs. 

Origin.- — The sternal ligament, meeting the opposite muscle. 

Insertion. — The cartilages of the ribs, from the second to the eighth inclusive, 
and the adjacent part of some of the ribs. 

Action. — It draws the ribs and costal cartilages inward and backward, thus 
assisting in expiration. 

Structure. — Each muscle has the form of a scalene triangle, of which the base 
is the strongly serrated lateral border. The muscle contains a good deal of ten- 
dinous tissue. The anterior bundles are directed forward and outward; the poste- 
rior, backward and outward. 

Relations. — Dorsally, the endothoracic fascia and pleura; ventrally, the 
costal cartilages, the internal intercostal muscles, and the internal thoracic vessels. 

Blood-supply. — Internal thoracic artery. 

Nerve-supply. — The intercostal nerves. 

7. Diaphragm. — This is a broad, unpaired muscle which forms a partition be- 
tween the thoracic and abdominal cavities. ^ In outline it has some resemblance to 
a palm-leaf fan. In form it is dome-shaped, compressed laterally. On a median 
section it is seen to have a general direction downward and forward from the lumbar 
vertebrae to the xiphoid cartilage. The thoracic surface is strongly convex, and 
is covered by the pleura. The abdominal surface is deeply concave, and is covered 
for the most part by the peritoneum. The muscle consists of a fleshy rim which 
may be subdivided into costal and sternal parts; a lumbar part, composed of two 
crura; and a tendinous center. 

Attachments. — (1) Costal part (Pars costalis): The cartilages of the eighth, 
ninth, and tenth ribs, and behind this to the ribs at an increasing distance from their 
sternal ends. 

(2) Sternal part (Pars sternalis) : The upper surface of the xiphoid cartilage. 

(3) Lumbar part (Pars lumbalis): (a) The right crus (Crus dextrum) is at- 
tached to the ventral longitudinal ligament, and by this means to the first four or 
five lumbar vertebrae. (6) The left crus (Crus sinistrum) is attached in a similar 
fashion to the first and second lumbar vertebrae. 

Action. — It is the principal muscle of inspiration and increases the longitu- 
dinal diameter of the chest. The contraction produces a general lessening of the 
curvature of the diaphragm. In the expiratory phase the costal part and crura lie 
almost entirely on the body walls, so that the bases of the lungs are in contact with 
the tendinous center almost exclusively. In orcUnary inspiration the fleshy rim 
recedes from the chest-wall, so that the bases of the lungs move backward to a line 
about parallel with the costal arches, and about four or five inches (ca. 10-12 cm.) 
therefrom. 

It is stated that the inspiratory movement affects the tendinous center much less than the 
fleshy part, and that the foramen venaj cava; scarcely moves at all, since the posterior vena cava 
is firmly attached to it. It should be noted, however, that the direction of the thoracic part of 
the vena cava in the expiratory phase is oblique upward and backward. Thus it would seem that 
there is no anatomical reason why the diaphragm should not move as a whole in ordinary inspira- 
tion at least; examination of formahn-hardened subjects in which the diaphragm appears to be 
fixed in the inspiratory phase indicates that such is the case. 

Structure. — The costal part consists of a series of digitations which meet, or 
are separated by a very narrow interval from, the transversus abdominis; between 
the two are the musculo-phrenic vessels. From the tenth rib backward the at- 
tachments to the ribs are at an increasing distance above the costo-chondral junc- 
tions. Thus at the last rib the upper limit of the attachment is four to five inches 
(10-12 cm.) from the ventral end. Anteriorly the origin extends along the eighth 

1 It should be noted, however, that in the embryo the diaphragm appears as a paired struc- 
ture, extending from the lateral walls of the ccelom to fuse with the septum transversum. 



286 



FASCIA AND MUSCLES OF THE HORSE 



and ninth costal cartilages to the xiphoid cartilage. From these points of origin 
the fibers curve inward and forward to join the tendinous center.^ The right cms 
is about twice as thick as the left one and is also longer. It arises by a strong tendon 



Longissimus dorsi 

Lumbar transverse 
process 




Costal arch 
Musculo-phrenic 
artery 

Transvcrsus 

abdominalis {cut 

edge) 
Xiphoid cartilage 
(depressed) 



Fig. 275. — Diaphr.^gm of Horse; Abdominal Surface. 
i, Ventral longitudinal ligament; .2, ;2', tendons of crura; 3, lumbar sympathetic trunks; 4, external spermatic 
nerve; o, 5, great splanchnic nerves; 6, cisterna chyli (opened); 7, 7, ce.sophageal continuations of vagus nerves; 
8, lymph-gland; 9, coronary ligament of liver (cut); 10, right lateral ligament of Uver (cut); 11, left lateral ligament of 
liver (cut); 12, falciform ligament of liver (cut); A.I., lumbo-costal arch; N.i., intercostal nerve; C.d., right crus; 
C.S., left crus; A, aorta; Ca, coeliac artery; Oe., oesophagus; V.c, posterior vena cava; V.p., phrenic veins. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



which blends with the ventral longitudinal ligament. The tendon is succeeded by 
a rounded belly which leaves the vertebral column at the last thoracic vertebra. 

1 It is interesting to note that when a nineteenth rib is present (even when it is well developed) 
the diaphragm has no connection with it, but ends on the eighteenth rib at a point a Uttle more 
ventral than usual. 



THE ABDOMINAL FASCIiE AND MUSCLES 287 

Passing downward and forward, its fibers spread out and join the tendinous center. 
The left cms arises by a thin tendon from the ventral longitudinal ligament at the 
first and second lumbar vertebrae. This is succeeded by a triangular belly which 
joins the central tendon. Between the crura and the attachment to the last rib 
the edge of the muscle crosses the ventral surface of the psoas muscles without at- 
tachment, forming the so-called lumbo-costal arch (Arcus lumbocostalis) ; here the 
thoracic and abdominal cavities are separated only by the serous membranes and 
some areolar tissue. The tendinous center (Centrum tendineum) resembles the 
periphery in outline, but is more elongated. It is partially divided into right and 
left parts by the descent of the crura into it. It is composed largely of radiating 
fibers, but many interlace in various directions; this is speciallj^ evident around the 
foramen venae cavae, which is encircled by fibers. A strong tendinous layer extends 
across below the hiatus oescphageus. 

Schmaltz and others describe the lumbar part as consisting of four crura, two medial and two 
lateral. On this basis the left crus of the preceding description becomes the crus lalerale sinistrum, 
and the corresponding part of the right side is the crus laterale dextrtim. The central part is divided 
by the hiatus oesophageus and the sht which extends from it dorsally into a crus mediale dextrum 
and a crus mediale sinistrum. Both modes of division are in part artificial. 

The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an 
interval between the two crura and below the last thoracic vertebra. It contains 
the aorta, vena azygos, and cisterna chyH. (2) The hiatus oesophageus^ perforates 
the right crus near its junction with the tendinous center. It is situated a little to 
the left of the median plane and about a hand breadth ventral to the thirteenth 
and fourteenth thoracic vertebrae. It transmits the oesophagus, the vagus nerves, 
and the oesophageal branch of the gastric artery. (3) The foramen venae cavae^ 
pierces the tendinous center about an inch (ca. 2-3 cm.) to the right of the median 
plane, and about six to eight inches (ca. 15-20 cm.) below the eleventh and 
twelfth thoracic vertebrae. The vena cava is firmly attached to the margin of the 
opening.'^ 

Relations. — The thoracic surface is related to the endothoracic fascia, pleurae, 
pericardium, the bases of the lungs, and the ribs in part. The abdominal surface 
is in great part covered by the peritoneum, and is related chiefly to the liver, stom- 
ach, intestine, spleen, pancreas, kidneys, and adrenals. The sympathetic trunk and 
splanchnic nerve pass between the crus and the psoas muscles on each side. The 
musculo-phrenic vessels perforate the edge of the muscle at the ninth costo-chondral 
joint. 

Blood-supply. — Phrenic and musculo-phrenic arteries. 

Nerve-supply. — Phrenic nerves. 



The Abdominal Fasci^e and Muscles 
(fascle et musculi abdominis) 

The superficial fascia of the abdomen is in part fused dorsally with the lumbo- 
dorsal fascia; in front it is continuous with the superficial fascia of the shoulder and 
arm, behind with that of the gluteal region. In the inguinal region it forms part 
of the fascia of the penis or of the mammary glands. At the lower part of the flank 
it forms a fold which is continuous mth the fascia of the thigh near the stifle joint. 

1 Formerly termed the foramen sinistrum. ^ Formerly termed the foramen dextrum. 

^ In order to get a clear idea of the relative positions of these foramina and of the form of 
the diaphragm, the thoracic surface of the latter should be examined in properly preserved sub- 
jects while the abdominal idscera remain in situ. It will be observed that the distances of the 
hiatus oesophageus and foramen vense cavae from the vertebral column vary according to the ful- 
ness of the abdominal viscera and the degree of contraction of the diaphragm. The statements 
given above are averages. 



288 FASCIA AND MUSCLES OF THE HORSE 

In this fold are the prefemoral lymph-glands. Medially it blends with the linea 
alba. It contains the abdominal cutaneous muscle (described on p. 254). 

The deep fascia is represented chiefly by the abdominal tunic (Tunica flava 
abdominis) . This is a sheet of elastic tissue which assists the muscles in supporting 
the great weight of the abdominal viscera. It is practically coextensive with the 
obliquus externus, which it covers. Ventrally it is thick, and is intimately ad- 
herent to the aponeurosis of the muscle. Laterally it becomes thinner and is more 
easily separated, although fibers from it dip in between the muscle-bundles. It is 
continued for some distance upon the inter costals and serratus ventralis. Traced 
forward, it passes as a thin layer beneath the posterior deep pectoral muscle. Pos- 
teriorly it is attached to the tuber coxae. In the inguinal region it forms the deep 
fascia of the prepuce or of the mammary glands. 

The linea alba is a median fibrous raphe which extends from the xiphoid car- 
tilage to the prepubic tendon. It is formed chiefly by the junction of the aponeu- 
roses of the oblique and transverse muscles, but partly by longitudinal fibers. A 
little behind its middle (about in a transverse plane tangent to the last pair of ribs) 
is a cicatrix, the iimbilicus, which indicates the position of the umbilical opening 
of the foetus. 

1. Obliquus abdominis externus, — This is the most extensive of the abdominal 
muscles. It is a broad sheet, irregularly triangular in shape, widest behind. Its 
fibers are directed chiefly downward and backward. 

Origin. — (1) The lateral surfaces of the last fourteen ribs, and the fascia over 
the external intercostal muscles; (2) the lumbo-clorsal fascia. 

Insertion. — (1) The linea alba and the prepubic tendon; (2) the tuber coxae and 
shaft of the ilium; (3) the medial femoral fascia. 

Action. — (1) To compress the abdominal viscera, as in defecation, micturition, 
parturition, and expiration; (2) to flex the trunk (arch the back) ; (3) acting singly, 
to flex the trunk laterally. 

Structure. — The muscle is composed of a muscular part and an aponeurosis. 
The muscular part lies on the lateral wall of the thorax and abdomen. It arises 
by a series of digitations, the anterior four of which alternate with those of the ser- 
ratus ventralis. The origin may be indicated by a slightly curved line (concave 
dorsally) drawn from the lower part of the fifth rib to the tuber coxae. The fibers 
are directed downward and backward and terminate on the aponeurosis, except in 
the upper part of the flank, where they are less oblique in direction and end on the 
tuber coxae. The line of junction is a curve (concave dorsally) extending from the 
upper edge of the posterior deep pectoral muscle toward the point of the hip. The 
aponeurosis is intimately attached to the abdominal tunic, and its fibers are largely 
interwoven ventrally with those of the aponeurosis of the internal oblique. By 
this fusion is formed the outer sheath of the rectus abdominis, which blends at the 
linea alba with that of the opposite side. In the inguinal region the aponeurosis 
divides into two chief layers; one of these curves dorsally and backward and is in- 
serted into the tuber coxae and the prepubic tendon. Between these points the 
aponeurosis is much strengthened and is called the inguinal ligament (Ligamentum 
inguinale).^ This curves upward and somewhat forward, becomes thin, and blends 
with the iliac fascia. It forms the posterior wall of the inguinal canal. About an 
inch (ca. 2 to 3 cm.) in front of the pubis and about two inches (ca. 4 to 5 cm.) 
from the mecUan plane the aponeurosis is pierced by a slit-like opening, the 
subcutaneous or external inguinal ring (Annulus inguinalis subcutaneus).^ This is 

1 Also commonly known as Poupart's ligament — based on a false historical allusion. It is 
in no proper sense a ligament, but is the inguinal part of the aponeurosis of the obliquus externus; 
it might therefore well be termed the lamina inguinalis. 

- It is narrow and slit-like in the natural condition, but may appear oval in the dissecting- 
room, especially if the hind limb is drawn back and abducted. 



THE ABDOMINAL FASCIA AND MUSCLES 



289 



the external orifice of the inguinal canal. Its long axis is directed outward, for- 
ward, and somewhat ventrally, and is four to five inches (ca. 10-12 cm.) in length. 




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o o 



1 § 
Is 

OS 
S ^ si 



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2 3 g 
M J pp 



The medial angle is rounded and is well defined by the junction of the aponeurosis 
with the prepubic tendon, but the lateral angle is not so sharply defined. The bor- 
ders or crura are constituted by arciform fibers of the aponeurosis (Crus mediale, 
19 



290 FASCIA AND MUSCLES OF THE HORSE 

laterale). The femoral lamina of the aponeurosis (Lamina femoralis) passes on 
to the medial surface of the thigh, where it blends with the femoral fascia. A 
thin iliac lamina (Lamina iliaca) passes over the lateral margin of the iliacus and 
is attached to the lateral border of the ilium. 

Relations. — Superficially, the skin, the abdominal cutaneus, the abdominal 
tunic, and the posterior deep pectoral muscle; deeply, the ribs and their cartilages, 
the intercostal muscles, the obliquus abdominis internus, the contents of the inguinal 
canal, and the sartorius and gracilis. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

2. Obliquus abdominis internus. — This muscle is situated under the preceding 
one. Its fibers are directed do^\aiward, forward, and inward. It forms a triangular 
curved sheet with the base behind. 

Origin. — The tuber coxse and the adjacent part of the inguinal ligament. 

Insertion. — (1) The cartilages of the last four or five ribs; (2) the linea alba 
and the prepubic tendon. 

Action. — Similar to that of the preceding muscle. 

Structure. — Like the external oblique, it is composed of a fleshy portion and 
an aponeurosis. The muscular part is fan-shaped, and is situated chiefly in the 
flank. At its iliac origin it is covered by a glistening aponeurosis. Traced medially 
and ventrally along the abdominal surface of the inguinal ligament, the muscular 
origin is found to become much thinner, and also becomes looselj'' attached to the 
ligament. This medial part of the muscle forms the anterior wall of the inguinal 
canal. The abdominal orifice of the canal, the abdominal or internal inguinal 
ring^ (Annulus inguinalis abdominalis), is found here. It is normally a narrow 
slit, bounded in front by the edge of the internal oblique, and behind by the in- 
guinal ligament. Near the last rib the muscle divides into two parts. The small 
dorsal part is inserted by four or five thin tendinous strips to the medial surface of 
the last four or five costal cartilages. The aponeurosis of the large ventral part 
is to a great extent blended with that of the external oblique, being, indeed, consider- 
ably interwoven Avith it ventrally. Where it covers the rectus abdominis it is at- 
tached to the tendinous inscriptions of that muscle. It may be noted that the dor- 
sal margin of the aponeurosis varies in different subjects in the fact that it may 
cover the costal arch or lie ventral to it. 

Relations. — Superficially, the obliquus externus; deeply, the rectus abdominis^ 
transversus abdominis, and the peritoneum. 

Blood-supply. — Circumflex iUac, lumbar, and intercostal arteries. 

Nerve-supply. — Ventral branches of the lumbar nerves. 

3. Rectus abdominis. — This muscle is confined to the ventral part of the ab- 
dominal wall ; it extends from the sternal region to the pubis. 

Origin. — The cartilages of the fourth or fifth to the ninth ribs inclusive, and the 
adjacent surface of the sternum. 

Insertion. — The pubis, by means of the prepubic tendon. 

Action. — Similar to that of the oblique muscles. It is especially adapted to 
flex the lumbo-sacral joints and the lumbar and thoracic parts of the spine. 

Structure. — The fibers of the muscle are directecl longitudinally. Nine to 
eleven transverse bands of fibrous tissue extend in an irregular maimer across the 

1 It must be admitted that the term "ring" is rather misleading as applied to the abdomi- 
nal opening of the canal, since normally it is a mere dilatable slit. The ring-hke constriction 
which exists here in the male is constituted by the peritoneum, which descends into the canal 
to form the tunica vaginalis. This peritoneal ring is termed the vaginal ring (Annulus vagi- 
nalis), and must not be confused with the subperitoneal ring, i. e., the abdominal or internal 
inguinal ring. The internal inguinal ring is six or seven inches (ca. 16 cm.) in length. Its 
direction corresponds approximately to a line from the lateral margin of the prepubic tendon to the 
ventral part of the tuber coxa;. 



THE ABDOMINAL FASCIA AND MUSCLES 291 

muscle. These are termed inscriptiones tendineaB. They strengthen the muscle 
and serve to prevent separation of its fibers. The width of the muscle is greatest 
about its middle. The anterior part blends with the rectus thoracis. 

Relations. — Superficially, the aponeuroses of the oblique muscles (which con- 
stitute the external rectus sheath) and the posterior deep pectoral; deeply, the 
transversus abdominis, intercostals, the cartilages of the ribs, and the sternum. 
The posterior abdominal artery runs along the lateral edge of the muscle posteriorly, 
and the anterior abdominal artery on or in its anterior part. 

Blood-supply. — Anterior and posterior abdominal arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

4. Transversus abdominis. — This muscle, named from the general direction 
of its fibers, is a triangular curved sheet. Its lateral part is muscular, its ventral 
aponeurotic. 

Origin. — (1) The medial surfaces of the distal ends or the cartilages of the 
asternal ribs, meeting the costal attachment of the diaphragm; (2) the transverse 
processes of the lumbar vertebrae, by means of the deep layer of the lumbo-dorsal 
fascia. 

Insertion. — The xiphoid cartilage and the linea alba. 

Action. — Similar to that of the oblique muscles. 

Structure. — The muscular part is a sheet of parallel bundles of fibers, directed 
ventro-medially. It is thickest along the cartilages of the ribs, and from here it 
thins out greatly toward the aponeurosis and the lumbar region. The fibers of the 
aponeurosis directly continue those of the fleshy part. Posteriorly it becomes ex- 
tremely thin and fades out without reaching the pelvis. It covers the deep face 
of the rectus, so forming the internal rectus sheath. 

Relations. — Superficially, the oblique and straight muscles, the retractor costae, 
the cartilages of the asternal ribs, and the internal intercostal muscles; deeply, the 
fascia transversalis and the peritoneum. The fascia transversalis is little de- 
veloped in the horse, and is very thin in emaciated subjects, but in animals in good 
condition it contains a good deal of fat. It blends with the iliac fascia and de- 
scends into the inguinal canal. The musculo-phrenic artery runs along the inter- 
val between the origin of the transversus and the costal part of the diaphragm. 
The intercostal nerves pass down over the lateral surface of the muscle, to which 
they give branches. Branches of the first three lumbar nerves are similarly cUs- 
posed further back. 

Blood-supply. — Intercostal, lumbar, and musculq|phrenic arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

5. Cremaster extemus. — This small muscle may be regarded as a detached 
portion of the obliquus abdominis internus, with which it blends at its origin (Figs. 
370, 575). 

Origin. — The iliac fascia, near the origin of the sartorius. 

Insertion. — The tunica vaginalis communis. 

Action. — To raise the tunica vaginalis, and with it the testicle. 

Structure.- — The muscle arises by a thin aponeurosis which is succeeded by a 
flat muscular belly about two inches (ca. 5 cm.) in width in the stallion.^ It passes 
down the inguinal canal on the postero-lateral surface of the tunica vaginalis, to 
which it is very loosely attached. On reaching the point where the tunic is reflected 
on to the tail of the epididymis, the muscle is inserted into the outer surface of the 
tunic by short tendinous fibers. 

Relations. — The muscle lies between the peritoneum and the fascia trans- 
versalis in front and the iliac fascia and inguinal ligament behind. On reaching 

1 As might be expected, the cremaster usually undergoes more or less atrophy and is paler 
In the castrated subject. In the mare the muscle is very small, and ends in the connective tissue 
in the inguinal canal. 



292 FASCIA AND MUSCLES OF THE HORSE 

the abdominal ring it descends the inguinal canal on the postero-lateral surface of 
the tunica vaginalis communis. 

Blood-supply. — External spermatic artery. 

Nerve-supply. — External spermatic nerve. 

The Inguinal Canal. — This term (Canalis inguinalis) is applied to an oblique 
passage through the posterior part of the abdominal wall.^ It begins at the ab- 
dominal inguinal ring, and extends obliquely ventro-medially, and somewhat for- 
ward, to end at the subcutaneous inguinal ring. Its anterior wall is formed by the 
fleshy posterior part of the internal oblique muscle, and the posterior wall by the 
strong tendinous inguinal ligament. The average length of the canal, measured 
along the spermatic cord, is about four inches (ca. 10 cm.). The abdominal or 
internal inguinal ring (Annulus inguinalis abdominalis) is the internal opening of 
the canal; it is bounded in front by the thin margin of the internal oblique muscle, 
and behind by the inguinal ligament. It is directed from the edge of the prepubic 
tendon approximately toward the tuber coxae. Its length is about six or seven 
inches (ca. 15-17.5 cm.). The edge of the muscle is attached to the surface of the 
ligament here by delicate connective tissue, except where structures intervene be- 
tween the walls of the canal. The lateral limit of the ring is determined by the 
muscle becoming firmly attached to the ligament, i. e., actually arising from the 
latter. The subcutaneous or external inguinal ring (Annulus inguinalis subcutan- 
eus) is a well-defined slit in the aponeurosis of the external oblique muscle, lateral 
to the prepubic tendon. Its long axis is directed from the edge of the prepubic 
tendon outward, forward, and slightly ventrally, and its length is about four or five 
inches (ca. 10-12 cm.). The canal contains in the male the spermatic cord, the 
tunica vaginalis, the external cremaster muscle, the external pudic artery (and in- 
constantly a small sateUite vein), and the inguinal lymph vessels and nerves. In 
the female it contains the mammary vessels and nerves; in the bitch it also lodges 
the round ligament of the uterus, enclosed in a tubular process of peritoneum. 

The two rings do not correspond in direction, but diverge laterally, so that the length of the 
canal varies greatly when measured at different points. The medial angles of the two rings are 
separated only by a distance equal to the thickness of the prepubic tendon (about a centimeter), 
but the lateral angles are about seven inches (ca. 17.5 cm.) apart. The distance measured along 
the spermatic cord is about four inches (ca. 10 cm.). The medial angle of the subcutaneous ring 
is well defined and distinctly palpable at the side of the prepubic tendon; from here the direction 
of the ring is traceable. 

The Prepubic Tendon. — The prepubic tendon (Tendo prsepubicus) is essentially 
the tendon of insertion of the two recti abdominis, but also furnishes attachment to 
the obliqui, the graciles, and the pectinei. It is attached to the anterior borders of 
the pubic bones, including the ilio-pectineal eminences. It has the form of a very 
strong thick band, with concave lateral borders which form the medial boundaries 
of the subcutaneous inguinal rings. Its direction is oblique upward and backward.^ 
Its structure is somewhat complex. Most of the fibers of the posterior part extend 
from one ilio-pectineal eminence to the other. The fibers which belong to the recti 
curve in to the median line. The aponeuroses of the internal oblique muscles are 
inserted into its abdominal surface, and the inguinal ligaments are attached to and 
continue across it in arciform fashion. The anterior part of the tendon of origin 
of the gracilis is fused with it ventrally, and many of the fibers of the pectineus 
arise from it. It gives off on either side a strong round band, the so-called accessory 
ligament, which is inserted into the fovea of the head of the femur with the round 

^ The term canal is somewhat misleading; it is rather a slit-like passage or space between 
the two obUque muscles, since the inguinal ligament is that part of the aponeurosis of the exter- 
nal obhque muscle which stretches between the tuber coxa; and the prepubic tendon. 

- The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical 
importance in regard to manipulation of the fcstus in obstetrical cases. The slope varies in 
different subjects. In some cases the tendon forms about a right angle with the pubic bones. 



THE MUSCLES OF THE THORACIC LIMB 293 

ligament {vide hip joint). A band from the ventral surface extends backward and 
blends with the tendon of origin of the gracilis on each side. 



The Muscles of the Thoracic Limb 

L the muscles of the shoulder girdle (Figs. 266. 267, 268, 276) 
This group (Mm. cinguli extremitatis thoracalis) consists of those muscles 
which connect the thoracic limb with the head, neck, and trunk. It may be re- 
garded as consisting of two divisions — dorsal and ventral.^ 

A. Dorsal Dfvision 

This division consists of two layers which overlie the proper muscles of the 
neck and back. 

First Layer 

L Trapezius. — This is a flat, triangular muscle, the base of which extends 
along the supraspinous ligament. It is divided by an aponeurotic portion into two 
parts : 

(a) Trapezius cervicalis. — Origin. — The funicular part of the ligamentum 
nuchae, from the second cervical to the third thoracic vertebra. 

Insertion. — The spine of the scapula and the fascia of the shoulder and arm. 

(b) Trapezius thoracalis (s. dorsalis). — Origin. — The supraspinous ligament, 
from the third to the tenth thoracic vertebra. 

Insertion. — The tuber spinse of the scapula. 

Action. — Acting as a whole, to elevate the shoulder; the cervical part draws 
the scapula forward and upward and the thoracic part draws it backward and up- 
ward. 

Structure. — The muscle arises by a narrow, thin aponeurosis, from which the 
fibers of the flat fleshy part converge to the spine of the scapula and the aponeurosis 
which separates the two portions. The cervical fascia joins the ventral edge of the 
cervical portion to the brachiocephalicus, or the two muscles may unite or overlap 
here. 

Relations. — Superficially, the skin and fascia; deeply, the rhomboideus, 
latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus ventralis, 
and anterior deep pectoral muscles, and the cartilage of the scapula. 

Blood-supply. — Deep cervical and intercostal arteries. 

Nerve-supply. — Spinal accessory nerve. 

Second Layer 

This consists of two muscles — the rhomboideus and latissimus dorsi. 
2. Rhomboideus. — This consists of two parts: 

(a) Rhomboideus cervicalis. — Origin. — The funicular part of the ligamentum 
nuchse, from the second cervical to the second thoracic vertebra. 

Insertion. — The medial surface of the cartilage of the scapula. 

(b) Rhomboideus thoracalis (s. dorsalis). — Origin. — The spinous processes of 
the second to the seventh thoracic vertebra by means of the dorso-scapular liga- 
ment. 

Insertion. — The medial surface of the cartilage of the scapula. 
Action.- — To draw the scapula upward and forward. When the limb is fixed 
the cervical part will elevate the neck. 

^ The terms dorsal and ventral are here used in the topographic and not in the ixiorpho- 
logical sense; all the muscles of the group are ventral in the latter sense. 



294 FASCIA AND MUSCLES OF THE HORSE 

Structure. — The cervical part is narrow, pointed at its anterior extremity, and 
lies along the funicular part of the ligamentum nuchse, to which it is attached by 
short tendon bundles. The fibers are directed for the most part longitudinally. 
The thoracic part is quadrilateral in shape, and its fibers are nearly vertical. Its 
deep face is intimately attached to the dorso-scapular ligament. 

Relations. — Superficially, the skin and fascia (over a small area in front), the 
trapezius, and the cartilage of the scapula; deeply, the dorso-scapular ligament, 
the splenius, complexus, longissimus dorsi, and serratus dorsalis. 

Blood-supply. — Dorsal and deep cervical arteries. 

Nerve-supply. — Sixth and seventh cervical nerves. 

3. Latissimus dorsi. — This is a ^vide muscle which has the form of a right- 
angled triangle. It lies for the most part under the skin and cutaneous muscle, 
on the lateral wall of the thorax, from the spine to the arm. 

Origin. — The lumbo-dorsal fascia — and by this means from the lumbar and 
thoracic spines as far forward as the highest point of the withers. 

Insertion. — The teres tubercle of the humerus, in common with the teres 
major. 

Action. — To draw the humerus upward and backward and flex the shoulder- 
joint. If the limb is advanced and fixed, it draws the trunk forward. 

Structure. — The muscle arises by a wide aponeurosis, which fuses with that 
of the serratus dorsalis and with the lumbo-dorsal fascia. The muscular part 
is at first rather thin, but by the convergence of its fibers becomes thicker as it 
approaches the arm. The anterior fibers pass almost vertically downward over 
the dorsal angle of the scapula and its cartilage. The posterior fibers are directed 
downward and forward. The thick belly formed by the convergence of these 
passes under the triceps to end on the flat tendon of insertion, which is common 
to this muscle and the teres major. The tendon of insertion furnishes origin to the 
anterior part of the tensor fasciae antibrachii. 

Relations. — Superficially, the superficial fascia, skin, cutaneus, trapezius, 
and triceps; deeply, the cartilage of the scapula, the rhomboideus, the serrati, the 
external intercostals, and the lumbo-dorsal fascia. 

Blood-supply. — Subscapular, intercostal, and lumbar arteries. 

Nerve-supply . — Thoraco-dorsal nerve . 

B. Ventral Division 

1. Brachiocephalicus.^ — This muscle extends along the side of the neck from 
the head to the arm. It is incompletely divisible into two portions. 

Origin. — (1) The mastoid process of the temporal bone and the nuchal crest; 
(2) the wing of the atlas and the transverse processes of the second, third, and 
fourth cervical vertebrae. 

Insertion. — The deltoid tuberosity, the curved rough line which extends from 
this almost to the distal extremity of the humerus, and the fascia of the shoulder 
and arm. 

Action. — When the head and neck are fixed, to draw the limb forward, ex- 
tending the shoulder joint. When the limb is fixed, to extend the head and neck, 
if the muscles act together; acting separately, to incline the head and neck to 
the same side. By means of its attachment to the strong fascia which extends 
from the deltoid tuberosity to the outer face of the elbow the muscle also acts as 
an extensor of the elbow joint (e. g., in standing). 

Structure. — As already mentioned, the muscle is capable of incomplete di- 
vision into two parts, the line of division being indicated by the emergence of sup- 
erficial branches of the ventral divisions of the cervical nerves. The mastoid part 

^ This muscle is also called the mastoido-humeralis, humero-mastoideus, dero-brachialis and 
levator humeri. 



THE MUSCLES OF THE SHOULDER GIRDLE 295 

(M. cleido-mastoideus) partly overlaps the other (M. cleido-transversarius), which 
lies dorsal to it. The former is attached to the mastoid process and the occipital 
bone by a broad tendon which fuses at its terminal part with that of the splenius 
and longissimus capitis et atlantis; it is also attached to the tendon of insertion of 
the sterno-cephalicus by aponeurosis. The dorsal part is attached to the transverse 
processes by four fleshy digitations. The belly of the muscle is adherent superfi- 
cially to the cervical fascia and the cutaneous muscle, and deeply to the omo- 
hyoideus. In front of the shoulder its deep face may present a tendinous inter- 
section of variable development.^ Here the muscle becomes wider, covers the 
shoulder joint, passes between the brachialis and biceps, and is inserted by means 
of a wide tendon which it shares with the superficial pectoral muscle. 

Relations. — Superficially, the skin, cervical fascia, the parotid gland, the cuta- 
neus, the brachialis, and branches of the cervical nerves; deeply, the splenius, 
longissimus capitis et atlantis, rectus capitis ventralis major, omo-hyoideus, ser- 
ratus ventralis, anterior deep pectoral and biceps muscles, the inferior cervical 
artery, the prescapular lymph glands, and branches of the cervical nerves. The ven- 
tral edge of the muscle forms the dorsal boundary of the jugular furrow. The 
dorsal border may be in contact with the cervical trapezius, or be separated from 
it by a variable interval. 

Blood-supply. — Inferior cervical, carotid, and vertebral arteries. 

Nerve-supply.- — Spinal accessory, cervical, and axillary nerves. 

The pectoral fascia is a thin membrane covering the surface of the pectoral 
muscles, to which it is, for the most part, closely attached. It detaches a layer 
which passes between the superficial and deep pectorals. At the posterior edge of 
the triceps another layer is given off, which passes on the lateral surface of this 
muscle to blend with the scapular fascia; the deeper layer becomes continuous with 
the subscapular and cervical fasciae. 

The pectoral muscles form a large fleshy mass which occupies the space be- 
tween the ventral part of the chest-wall and the shoulder and arm. They are 
clearly divisible into a superficial and a deep layer. The superficial layer may be 
subdivided into two parts by careful dissection; the deep layer is clearly made up 
of two muscles. 

2. Superficial pectoral muscle (M. pectoralis superficialis) . 

(a) Anterior superficial pectoral muscle (pars descendens) .^ — This is a short, 
thick, somewhat rounded muscle, which extends from the manubrium sterni to 
the front of the arm. It forms a distinct prominence on the front of the breast, 
which is easily recognized in the living animal. 

Origin. — The cariniform cartilage of the sternum. 

Insertion. — (1) The curved line of the humerus with the brachiocephalicus; (2) 
the fascia of the arm. 

Action. — To adduct and advance the limb. 

Structure. — The belly of the muscle is convex on its superficial face, but deeply 
it is flattened where it overlaps the posterior superficial pectoral. Here the two 
muscles are usually closely attached to each other, and care must be exercised in 
making the separation. The tendon of insertion blends with that of the brachio- 
cephalicus and with the fascia of the arm. At the middle line of the breast a fur- 
row occurs between the two muscles; laterally, another furrow, containing the 
cephalic vein, lies between the muscle and the brachiocephalicus. 

i^eZa^tows.— Superficially, the skin, fascia, and panniculus; deeply, the pos- 

1 This is regarded as a vestige of the clavicle. On this basis the portion of the muscle from 
the vestige to the arm represents the clavicular part of the deltoid and perhaps the clavicular part 
of the pectoraUs major of man. 

^ Also termed the pectoralis anticus or pars clavicularis. 



296 FASCIA AND MUSCLES OF THE HORSE 

terior division, the deep pectoral, and the biceps. The cephahc vein hes in the 
groove between this muscle and the brachiocephalicus. 

(b) Posterior superficial pectoral muscle (pars transversa). ^^ — This is a wide 
muscular sheet which extends from the ventral edge of the sternum to the medial 
surface of the elbow. 

Origin. — (1) The ventral edge of the sternum as far back as the sixth car- 
tilage; (2) a fibrous raphe common to the two muscles. 

Insertion. — (1) The fascia on the proximal third of the forearm; (2) the 
curved line of the humerus with the preceding muscle. 

Action. — To adduct the limb and to tense the fascia of the forearm. 

Structure. — It is thin and pale, and mixed with a good deal of fibrous tissue. 
The right and left muscles fuse at a median fibrous raphe. The tendon of inser- 
tion unites with the fascia on the medial side of the forearm for the most part; 
only a small part in front, about an inch in width, is attached to the humerus. 

Relations. — Superficially, the skin, fascia, and the preceding muscle; deeply, 
the deep pectoral, the biceps, and the brachialis; at the elbow, the median vessels 
and nerve, and the medial and middle flexors of the carpus. 

3. Deep pectoral muscle (M. pectoralis profundus). — This muscle is much 
thicker and more extensive in the horse than the superficial pectoral. It consists 
of two distinct parts. 

(a) Anterior deep pectoral muscle (pars scapularis).- — This is prismatic and 
extends from the anterior part of the lateral surface of the sternum to the cervical 
angle of the scapula. 

Origin. — The anterior half of the lateral surface of the sternum and the car- 
tilages of the first four ribs. 

Insertion.- — The aponeurosis which covers the supraspinatus at its dorsal 
end, and the scapular fascia. 

Action. — To adduct and retract the limb; when the limb is advanced and 
fixed, to draw the trunk forward. 

Structure.- — The muscle is almost entirely fleshy. It describes a curve (con- 
vex anteriorly), passing at first forward, then upward over the front of the shoulder, 
a little to its medial side, and finally inclines somewhat backward along the anterior 
border of the supraspinatus. It is loosely attached to the latter muscle, and 
terminates in a pointed end which becomes more firmly attached near the cer- 
vical angle of the scapula. 

Relations. — Superficially, the skin and fascia, the cutaneus, superficial pec- 
toral, trapezius, and brachiocephalicus muscles, the cephalic vein, and the in- 
ferior cervical artery; deeply, the posterior deep pectoral, biceps, supraspinatus, 
omo-hyoideus, and serratus ventralis muscles, the brachial vessels, and the branches 
of the brachial plexus of nerves. 

(b) Posterior deep pectoral muscle (pars humeralis s. ascendens).^ — This is 
much the largest of the pectoral group in the horse. It is somewhat triangular or 
fan-shaped. 

Origin. — (1) The abdominal tunic; (2) the xiphoid cartilage and ventral 
aspect of the sternum ; (3) the cartilages of the fourth to the ninth ribs. 

Insertion. — (1) The posterior part of the medial tuberosity of the humerus; (2) 
the anterior part of the lateral tuberosity of the humerus; (3) the tendon of origin 
of the coraco-brachialis. 

Action. — To adduct and retract the limb; if the limb is advanced and fixed, 
to draw the trunk forward. 

Structure. — This muscle is almost entirely fleshy. Its posterior part is wide 

^ Also termed the pectoralis transversus or pars sternocostalis. 
^ Also tenned the pectoralis parvus or pars praescapularis. 
' Also known as the pectoralis magnus. 



THE MUSCLES OF THE SHOULDER GIRDLE 297 

and thin, but as the muscle is traced forward, it becomes narrower and much 
thicker. It passes forward and slightly upward in a gentle curve to its insertion. 
The humeral insertion is just below that of the medial division of the supraspinatus. 
Part of the fibers are inserted by means of a tendinous band which binds down the 
tendon of the biceps and is attached to the lateral lip of the intertuberal or bicipital 
groove, and a small part is attached to the tendon of origin of the coraco-brachialis. 

Relations. — Superficially, the skin, cutaneus, and superficial pectoral; deeply, 
the abdominal tunic, the external oblique, the rectus abdominis et thoracis, the 
brachial vessels, and branches of the brachial plexus of nerves. The external 
thoracic vein lies along the lateral border. 

Blood-supply. — Internal and external thoracic, inferior cervical, anterior 
circumflex, and intercostal arteries. 

N erve-siipply . — Pectoral nerves, from the brachial plexus. 

3. Serratus ventralisi (Figs. 267, 268).— This is a large, fan-shaped muscle, 
situated on the lateral surface of the neck and thorax. It derives its name from 
the serrated ventral edge of its thoracic portion. It consists of cervical and tho- 
racic parts. 

(a) Serratus cervicis. 

Origin. — The transverse processes of the last four or five cervical vertebrae. 
Insertion. — The anterior triangular area on the costal surface of the scapula 
(facies serrata) and the adjacent part of the cartilage. 

(b) Serratus thoracis. 

Origin. — The lateral surfaces of the first eight or nine ribs. 

Insertion. — The posterior triangular area on the costal surface of the scapula 
(facies serrata) and the adjacent part of the cartilage. 

Action. — The two muscles form an elastic support, which suspends the trunk be- 
tween the two scapulae." Contracting together, they raise the thorax; contracting 
singly, the weight is shifted to the limb on the side of the muscle acting. The two 
parts can act separately and are antagonistic in their effect on the scapula. The 
cervical part draws the base of the scapula toward the neck, while the thoracic 
part has the opposite action; these effects concur in the backward and forward 
swing of the limb respectively. With the limb fixed, the cervical part extends 
(raises) the neck or inclines it laterally. The thoracic part may act as a muscle of 
forced inspiration. 

Structure. — In the domesticated animals there is no such clear division of 
the muscle as is found in man and the apes. On account of the difference in action, 
however, it seems desirable to distinguish the two portions. The serratus cervicis is 
thick aiKl almost entirely fleshy. The serratus thoracis has on its superficial face a 
thick, tendinous layer which may sustain the weight of the trunk when the muscle 
substance relaxes. The ventral edge presents distinct digitations, the last four of 
which alternate with those of the obliquus externus abdominis, and are covered by 
the abdominal tunic. The fourth and fifth digitations extend nearly to the sternal 
ends of the ribs. The ninth digitation is small and may be absent. Exceptionally 
additional digitations may be attached to the tenth or eleventh rib or to the fascia 
over the intercostal muscles. The fibers converge to the insertion, which is thick 
and is intersected by elastic lamellae derived from the dorso-scapular ligament. 

Relations. — Superficially, the brachiocephalicus, trapezius, deep pectoral, 
subscapularis, teres major, latissimus dorsi, cutaneus, the abdominal tunic, the 
brachial vessels, and the long thoracic nerve; deeply, the splenius, complexus, 

1 Formerly termed the serratus magnus. 

2 It has been commonly stated that these muscles form a sort of sling in which the trunk is 
suspended. This is not quite correct as the two muscles do not meet ventrally. The arrange- 
ment is admirable, since the pull of the thorax on the muscles presses the scapula? against the body 
wall. 



298 FASCIA AND MUSCLES OF THE HORSE 

serratus dorsalis, longissimi, the ribs and external intercostal muscles, and branches 
of the deep cervical and dorsal arteries. 

Blood-supply. — Deep cervical, dorsal, vertebral, and intercostal arteries. 

Nerve-supply. — Fifth to eighth cervical nerves. 



n. THE MUSCLES OF THE SHOULDER 

The muscles of this group (Mm. omi) arise on the scapula and end on the arm; 
the}' may be divided into two groups — one covering the lateral, the other the costal, 
surface of the scapula. 

The superficial fascia of the shoulder and arm contains the cutaneous muscle 
of this region (vide p. 254), and may be considered to be continued on the medial 
side of the limb by the subscapular fascia. 

The deep fascia of the shoulder and arm (Fascia omobrachialis) is strong and 
tendinous, and is intimately adherent to the muscles on the lateral surface of the 
scapula, between which it detaches intermuscular septa, which are attached to the 
spine and borders of the scapula. The brachial portion is, for the most part, only 
loosely attached to the underlying muscles, for which it forms sheaths; it is attached 
to the proximal and deltoid tuberosities of the humerus. A specially strong part 
extends from the deltoid tuberosity to the lateral surface of the elbow; it furnishes 
insertion to part of the brachiocephalicus and gives origin to fibers of the lateral 
head of the triceps and of the extensor carpi radialis. The fascia blends distally 
•with the tendon of insertion of the biceps, and is continued by the antibrachial 
fascia. 

A. Lateral Group (Figs. 267, 268) 

1. Deltoideus. — This lies partly on the triceps in the angle between the scap- 
ula and humerus, partly on the infraspinatus and teres minor. 

Origin. — (1) The upper part of the posterior border of the scapula; (2) the 
spine of the scapula, by means of the strong aponeurosis which covers the infra- 
spinatus. 

Insertion. — The deltoid tuberosity of the humerus. 

Action. — To flex the shoulder joint and abduct the arm. 

Structure. — The origin of the muscle is partly aponeurotic, partly fleshy. 
The aponeurosis fuses with that which covers the infraspinatus; the posterior part 
is attached to the scapula immediately in front of the origin of the long head of the 
triceps. The belly of the muscle lies for the most part in a cavity formed in the 
triceps. It is widest about its middle. 

i?e?a^ions.— Superficially, the skin, fascia, cutaneus, and brachiocephalicus; 
deeply, the infraspinatus, teres minor, triceps, and brachialis muscles, and branches 
of the posterior circumflex artery and axillary nerve. 

Blood-supply. — Subscapular artery (chiefly through the posterior circumflex). 

Nerve-supply. — Axillary nerve. 

2. Supraspinatus. — This muscle occupies the supraspinous fossa, which it 
fills, and beyond which it extends, thus coming in contact ^vith the subscapularis. 

Origin. — The supraspinous fossa, the spine, and the lower part of the car- 
tilage of the scapula. 

Insertion. — The anterior parts of the proximal tuberosities of the humerus. 

Action. — To extend the shoulder joint. It also assists in preventing dislo- 
cation. 

Structure. — The surface of the muscle is covered by a strong aponeurosis, 
from the deep face of which many fibers arise. The muscle is thin at its origin 
from the cartilage, but becomes considerably thicker distally. At the neck of the 
scapula it divides into two branches, between which the tendon of origin of the 



THE MUSCLES OF THE SHOULDER 299 

biceps emerges. These branches, fleshy superficially, tendinous deeply, are united 
by a fibrous membrane already mentioned in connection with the deep pectoral 
muscle; some fibers are attached to this membrane and the capsule of the shoulder 
joint. A bursa is often present under the muscle at the tuber scapulae. 

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and brachio- 
cephalicus; deeply, the scapula and its cartilage, the subscapularis muscle, and the 
suprascapular vessels and nerve; in front, the anterior deep pectoral muscle; be- 
hind, the spine of the scapula and infraspinatus muscle. 

Blood-supply. — Suprascapular and posterior circumflex arteries. 

Nerve-supply. — Suprascapular nerve. 

3. Infraspinatus. — This muscle occupies the greater part of the infraspinous 
fossa and extends beyond it posteriorly. 

Origin. — The infraspinous fossa and the scapular cartilage. 

Insertion. — (1) The lateral tuberosity of the humerus, distal to the lateral 
insertion of the supraspinatus ; (2) the posterior eminence of the lateral tuberosity. 

Action. — To abduct the arm and rotate it outward.^ It also acts as a lateral 
ligament. 

Structure. — This muscle is also covered by a strong aponeurosis, from which 
many fibers arise, and by means of which the deltoid is attached to the spine of 
the scapula. A thick tendinous layer partially divides the muscle into two strata, 
and, coming to the surface at the shoulder joint, constitutes the chief means of in- 
sertion. This tendon, an inch or more (3 cm.) in width, passes over the posterior 
eminence of the lateral tuberosity of the humerus; it is bound do^\^l by a fibrous 
sheet, and a synovial bursa is interposed between the tendon and the bone. The 
portion of the tendon which crosses the lateral tuberosity is in part cartilagi- 
nous. When the long insertion is cut and reflected, the short insertion, partly 
tenchnous, partly fleshy, is exposed. 

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and deltoid; 
deeply, the scapula and its cartilage, the shoulder joint and capsule, the long head 
of the triceps, the teres minor, and branches of the posterior circumflex artery of the 
scapula. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Suprascapular nerve. 

4. Teres minor. — This is a much smaller muscle than the foregoing. It 
lies chieflj^ on the triceps, under cover of the deltoid and infraspinatus. 

Origin. — (1) The rough lines on the distal and posterior part of the infra- 
spinous fossa; (2) a small part of the posterior border of the scapula, about its 
middle; (3) a tubercle near the rim of the glenoid cavity. 

Insertion. — The deltoid tuberosity and a small area just above it. 

Action. — To flex the shoulder joint and to abduct the arm; also to assist in 
outward rotation. 

Structure. — The muscle is not rounded, but flat and triangular in the horse. 
Its origin from the posterior border of the scapula is by means of a fascicular aponeu- 
rosis which also gives origin to fibers of the infraspinatus and triceps. The short, 
deep part of the muscle which lies on the joint capsule behind the lateral tuberosity 
of the humerus is covered at its origin by the distal edge of the tendon of origin of 
the long head of the triceps. A bursa is commonly found between the terminal 
part of the muscle and the capsule of the shoulder joint, and is often continuous 
with that of the infraspinatus. 

Relations. — Superficially, the deltoid and infraspinatus muscles; deeply, the 
scapula, the shoulder joint, and the triceps muscle. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Axillary nerve. 

1 Giinther states that this muscle assists in extension or flexion according to the position 
of the head of the humerus relative to the glenoid cavity. 



300 FASCIiE AND MUSCLES OF THE HORSE 



B. Medial Group 

1. Subscapularis. — This muscle occupies the subscapular fossa, beyond which, 
however, it extends both before and behind. 

Origin. — The subscapular fossa. 

Insertion. — The posterior eminence of the medial tuberosity of the humerus. 

Action. — To adduct the humerus. 

Structure. — The muscle is flat and triangular. The base is thin and inter- 
digitates with the scapular attachments of the serratus ventralis. Distally the 
belly thickens and becomes narrower. It is covered by an aponeurosis, and con- 
tains a considerable amount of tendinous tissue. The tendon of insertion is crossed 
by the tendon of origin of the coraco-brachialis; it is intimately adherent to the cap- 
sule of the shoulder joint, and may be regarded as replacing the medial ligament of 
the latter. A small bursa usually is present between the tendon and the tuberosity 
of the humerus. 

Relations. — Superficially, the scapula and shoulder joint, the supraspinatus, 
triceps, and teres major muscles; deeply, the serratus ventralis muscle, the bra- 
chial vessels, and the chief branches of the brachial plexus. The subscapular 
vessels run along or near the posterior edge of the muscle. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Subscapular nerves. 

2. Teres major. — This muscle is flat, widest about its middle, and lies chiefly 
on the medial face of the triceps. 

Origin. — The dorsal angle and the adjacent part of the posterior border of 
the scapula. 

Insertion. — The teres tubercle of the humerus, in common with the latissimus 
dorsi. 

Action. — To flex the shoulder joint and adduct the arm. 

Structure. — It is for the most part fleshy, but the origin consists of an apo- 
neurosis which blends with that of the tensor fasciae antibrachii. The insertion 
is by a flat tendon which fuses with that of the latissimus dorsi. 

Relations. — Laterally, the triceps; medially, the serratus ventralis. The sub- 
scapular vessels lie in a groove between the anterior edge of this muscle and the 
posterior border of the subscapularis; near the shoulder joint the posterior cir- 
cumflex artery and the axillary nerve emerge between the two muscles. The 
medial face of the muscle is crossed by the thoracic branches of the brachial plexus, 
and by the artery which supplies the latissimus dorsi. 

Blood-supply. — Subscapular artery. 

Nerve-supply.- — Axillary nerve. 

3. Coraco-brachialis.^ — This muscle lies on the medial surface of the shoulder 
joint and the arm. 

Origin. — The coracoid process of the scapula. 

Insertion. — (1) A small area above the teres tubercle of the humerus; (2) the 
middle third of the anterior surface of the humerus. 

Action. — To adduct the arm and to flex the shoulder joint. 

Structure. — The long tendon of origin emerges between the subscapularis and 
the medial branch of the supraspinatus. It passes over the terminal part of the 
subscapularis and is provided with a synovial sheath. The belly spreads out and 
divides into two parts. The small, short part is inserted into the proximal third of 
the medial surface of the shaft of the humerus ; the large, long part is inserted into 
the middle third of the humerus, in front of the teres tubercle and the medial head of 
the triceps. 

^ Also termed the coraco-humeralis. 



THE MUSCLES OF THE SHOULDER 



301 



Relations. — Laterally, the subscapularis, the brachialis, the tendon of insertion 
of the latissimus dorsi, and the humerus; medially, the deep pectoral; in front, 
the biceps brachii. The anterior circumflex artery and the nerve to the biceps 
pass between the two parts, or between the muscle and the bone, and the brachial 
vessels lie along the posterior border of the muscle. 



Subscdpularis 

Ankrior deep pectoral 



Latissimus dorsi 



Teres major 



Tensor fascice antihrachii. 



Deep fascia of forearm 




"ipraspmatus 

Posterior deep 
pectoral 



Cora co-brach ialis 
Biceps brachii 



Extensor carpi radialis 

Brachialis 

Long medial ligament of elbow 



Fig. 277. — Muscles of Shoulder and Arm op Horse; Medial View. 
1, Long head of triceps brachii; 2, medial head of triceps; 3, distal end of humerus. 



Blood-supply. — Anterior circumflex artery. 
Nerve-supply. — Musculo-cutaneous nerve. 

4. Capsularis.^ — This is a very small muscle, which lies on the flexion surface 
of the capsule of the shoulder joint. 

1 Also known as the scapulo-humeralis posticus s. gracilis. 



302 FASCIA AND MUSCLES OF THE HORSE 

Origin. — The scapula, close to the rim of the glenoid cavity. 

Insertion. — The posterior surface of the shaft of the humerus, a short distance 
below the head. 

Action. — It has been held that it tenses the capsule of the shoulder joint and 
prevents its being pinched during flexion, but there does not appear to be any 
attachment of the muscle to the joint capsule. 

Structure. — It is fleshy and usually about the breadth of a finger. It may, 
however, consist of only a few bundles of fibers ; sometimes it is double. It passes 
through the brachialis muscle to reach its insertion. 

Relations. — Laterally, the teres minor and triceps muscles; medially, the teres 
major and subscapularis muscles, and the capsule of the joint. 

Blood-supply. — Posterior circumflex artery. 

Nerve-supply. — Axillary nerve. 



m. THE MUSCLES OF THE ARM 
This group consists of five muscles (Mm. brachii) which are grouped around the 
humerus. They arise from the scapula and the humerus, and are inserted into the 
forearm. They act on the elbow joint and the fascia of the forearm. 

1. Biceps brachii.^ — This is a strong fusiform muscle, which lies on the anterior 
surface of the humerus (Fig. 277). 

Origin. — The tuber scapulae. 

Insertion. — (1) The radial tuberosity; (2) the medial ligament of the elbow 
joint; (3) the fascia of the forearm and the tendon of the extensor carpi radialis. 

Action. — To flex the elbow joint; to fix the shoulder, elbow, and carpus in 
standing; to assist the extensor carpi radialis, and to tense the fascia of the fore- 
arm. 

Structure. — The muscle is inclosed in a double sheath of fascia, which is attached 
to the tuberosities and the deltoid ridge of the humerus. The tendon of origin 
is molded on the intertuberal or bicipital groove; it is very strong and dense and 
is partly cartilaginous. Its play over the groove is facilitated by the large inter- 
tuberal or bicipital bursa (Bursa intertubercularis).^ The synovial membrane 
covers not only the deep face of the tendon, but extends somewhat around the edges 
to the superficial face. A well-marked tendinous intersection runs through the belly 
of the muscle and divides distally into two portions. Of these, the short, thick 
one is inserted into the radial tuberosity and detaches fibers to the medial collat- 
eral ligament of the elbow joint. The long tendon (Lacertus fibrosus) is thinner, 
blends with the fascia of the forearm, and ends by fusing with the tendon of the 
extensor carpi radialis; thus the action is continued to the metacarpus. 

Relations. — Laterally, the brachiocephalicus and brachialis muscles; medially, 
the posterior deep pectoral and the superficial pectoral muscles; in front, the an- 
terior deep pectoral muscle; behind, the humerus, the coraco-brachialis muscle, 
the anterior circumflex and anterior radial vessels, and the musculo-cutaneous 
nerve. 

Blood-supply. — Branches of the brachial and anterior radial arteries. 

Nerve-supply. — Musculo-cutaneous nerve. 

2. Brachialis.^ — This muscle occupies the musculo-spiral groove of the humerus. 
Origin.- — The proximal third of the posterior surface of the humerus. 
Insertion. — The medial surface of the neck of the radius (under cover of the 

long collateral ligament) and the transverse radio-ulnar ligament. 
Action. — To flex the elbow joint. 

^ Also known as the coraco-radialis or flexor brachii. 

^ In some cases the bursa communicates with the cavity of the shoulder joint. 

' Also known as the humeralis obliquus s. externus and as the brachialis anticus. 



THE MUSCLES OF THE ARM 303 

Structure. — The peculiar spiral course of this muscle gave rise to the name 
often applied to it— humeralis obliquus. Beginning on the posterior surface of the 
shaft, close to the head of the humerus, it winds over the lateral surface, crosses the 
biceps very obliquely, and finally reaches the medial side of the forearm by passing 
between the biceps and the extensor carpi. It is entirely fleshy, with the exception 
of its relatively slejider tendon of insertion. Some fibers at the proximal end are 
attached to the capsule of the shoulder joint, which may thereby be tensed during 
flexion. 

Relations. — Laterally, the skin and fascia, the teres minor, deltoid, triceps 
(lateral head), and brachiocephalicus muscles. Deeply, the teres major, the bi- 
ceps, and the humerus. The anterior radial artery crosses the deep face of the 
muscle in its distal third, and the radial nerve accompanies the muscle in the distal 
half of the musculo-spiral groove. 

Blood-supply. — Brachial artery. 

Nerve-supply. — Musculo-cutaneous nerve; frequently radial nerve also. 

3. Tensor fasciae antibrachii (Fig. 277). ^ — This is a thin muscle which lies 
chiefly on the medial surface of the triceps. 

Origin. — The tendon of insertion of the latissimus dorsi and the posterior 
border of the scapula. 

Insertion. — (1) The deep fascia of the forearm; (2) the olecranon. 

Action. — (1) To tense the fascia of the forearm and to extend the elbow joint. 

Structure. — The origin consists of a very thin aponeurosis which blends with 
those of the caput longum and the latissimus dorsi. In most cases there is a dis- 
tinct division into anterior and posterior heads. The muscular portion is thin in 
its anterior part, somewhat thicker behind, and is narrower than the aponeurotic 
origin. It is succeeded by an aponeurotic insertion, which ends chiefly by blending 
with the fascia of the forearm a little below the elbow. There is, however, a small 
but constant tendinous attachment to the olecranon. 

Relations. — Laterally, the cutaneus, triceps (long and medial heads), the medial 
and middle flexors of the carpus, and the ulnar vessels and nerve; medially, the 
latissimus dorsi, serratus ventralis, and posterior pectoral muscles. 

Blood-supply. — Subscapular, ulnar, and deep brachial arteries. 

Nerve-supply. — Radial nerve. 

4. Triceps brachii (Figs. 267, 268, 277).— This, together with the preceding 
muscle, constitutes the large muscular mass which fills the angle between the pos- 
terior border of the scapula and the humerus. It is clearly divisible into three 
heads. 

(a) Long head (Caput longum tricipitis).' — This, the largest and longest of 
the three heads, is a powerful, thick, triangular muscle, which extends from the 
posterior border of the scapula to the olecranon. 

Origin. — The posterior border of the scapula. 

Insertion. — The lateral and posterior part of the summit of the olecranon. 

Action. — (1) To extend the elbow joint; (2) to flex the shoulder joint. 

Structure.— The muscle arises by a wide, strong aponeurosis from the posterior 
border of the scapula. From this the bundles of the fleshy portion converge to 
the short, strong tendon of insertion. A careful examination will show that the 
muscle is penetrated by a tendinous intersection from which many fibers take origin 
obliquely. The superficial face is covered by an aponeurosis which is specially 
developed at its distal part. A small bursa occurs under the tendon of insertion. 

1 M'Fadyean and Vaughan term this muscle the scapulo-ulnaris, while Arloing and Lesbre 
term it "Ancone accessoire du grand dorsal." The above name seems to agree best with the 
chief insertion and action, although it certainly arises largely from the tendon of insertion of the 
latissimus dorsi. 

* Also known as the anconaeus longus or caput magnum. 



304 FASCI.E AND MUSCLES OF THE HORSE 

Relations. — Laterally, the cutaneus, deltoid, infraspinatus, teres minor, and 
the lateral head; medially, the tensor fasciae antibrachii, teres major, latissimus dorsi 
and posterior deep pectoral muscles, and the subscapular vessels; in front, the 
brachialis and the medial head, the deep brachial and posterior circumflex vessels, 
and the axillary and radial nerves; behind, the skin and fascia. 

J5/ood-SMpp??/.— Subscapular and deep brachial arteries. 

Nerve-supply. — Radial nerve. 

(b) Lateral head (Caput laterale tricipitis).' — This is a strong, quadrilateral 
muscle, which lies on the lateral surface of the arm. Its proximal third is covered 
by the deltoid and teres minor muscles, the remainder only by the thin cutaneous 
muscle and the skin. 

Origin. — (1) The deltoid tuberosity and the curved rough line which extends 
from it to the neck of the humerus; (2) the strong fascia which extends from the 
deltoid tuberosity to the lateral surface of the elbow joint. 

Insertion. — (1) A small prominent area on the lateral surface of the olecranon; 
(2) the tendon of the long head. 

Action. — To extend the elbow joint. 

Structure. — The origin consists of short tendinous fibers. The belly is thick, 
and is composed of parallel bundles which are directed obliquely downward and 
backward. They are inserted partly into the tendon of the long head and partly 
into the olecranon below and in front of that tendon. 

Relations. — Laterally, the deltoid, teres minor, and cutaneus muscles ; medially, 
the long and medial heads and the brachialis muscle. Branches of the circumflex 
vessels and axillary nerve emerge between the posterior edge of the muscle and the 
long head. The deep face of the muscle is related to the branches of the deep bra- 
chial artery and of the radial nerve. 

Blood-supply. — Posterior circumflex and deep brachial arteries. 

Nerve-supply. — Radial nerve. 

(c) Medial head (Caput mediale tricipitis) (Fig. 277). ^ — This is much the small- 
est of the three heads. It is situated on the medial surface of the arm, and extends 
from the middle third of the humerus to the olecranon. 

Origin. — The middle third of the medial surface of the shaft of the humerus, 
behind and below the teres tubercle. 

Insertion. — The medial and anterior part of the summit of the olecranon, be- 
tween the insertion of the long head and the origin of the ulnar head of the deep 
digital flexor. 

Action. — To extend the elbow joint. 

Structure. — The muscle is fleshy except at its insertion, where it has a flat ten- 
don, under which a small bursa may be found. 

Relations. — Laterally, the humerus, brachialis, anconeus, and the lateral head; 
medially, the posterior deep pectoral, coraco-brachialis, teres major, latissimus dorsi, 
and tensor fascise antibrachii muscles, the brachial and deep brachial vessels, and 
the median and ulnar nerves; behind, the long head, branches of the deep brachial 
vessels, and the radial nerve. 

Blood-supply. — Deep brachial and ulnar arteries. 

Nerve-supply. — Radial nerve. 

5. Anconeus. — This is a small muscle which covers the olecranon fossa and 
is covered by the triceps. It is somewhat difficult to separate from the lateral head. 

Origin. — The distal third of the posterior surface of the humerus. 

Insertion. — The lateral surface of the olecranon. 

Action. — To extend the elbow joint, and to raise the capsule of the joint and 
prevent its being pinched during extension. 

* Also known as the anconi3eiis lateralis s. externus or caput medium. 
2 Also known as the anconjeus mediahs s. internus or caput parvum. 



FASCIA AND MUSCLES OF THE FOREARM AND MANUS 



305 



Structure. — It is almost entirely fleshy. The deep face is adherent to the joint 
capsule. 

Relations. — Superficially, the triceps muscle; deeply, the humerus and the 
elbow joint. 

Blood-supply. — Deep brachial artery. 

Nerve-supply. — Radial nerve. 



-Ul 



•Deep flexor tendon 

■•Distal end of small metacarpal bone 
•'Suspensory ligament 



Branch of superficial flexor tendon 
Distal digital annular ligament 
Upper border of cartilage 
of third phalanx 



IV. FASCIA AND MUSCLES OF THE FOREARM AND MANUS 
(FASCIA ET MUSCULI ANTIBRACHII ET MANUS) 

The forearm is covered on three sides by the muscles of this group, leaving 
the medial surface of the radius for the most part subcutaneous. The extensors of 
the carpus and digit lie on the 
dorsal and lateral parts of the 
region, while the flexors oc- 
cupy the volar surface. 

The fascia of the fore- 
arm (Fascia antibrachii) 
forms a very strong and com- 
plete investment for all the 
muscles of the region. The 
superficial fascia is thin, and 
blends at the carpus with the 
deep fascia ; it furnishes inser- 
tion to the posterior super- 
ficial pectoral muscle. The 
deep fascia is very strong and 
tendinous in character. It 
furnishes insertion at its 
proximal and medial part to 
the tensor fasciae antibrachii 
muscle; at its proximal anter- 
ior and lateral part to the 
brachiocephalicus and biceps. 
It is attached at the elbow to 
the lateral tuberosities of the 
humerus and radius, to the 
ulna, and to the collateral 
ligaments. On ' the medial 
surface of the forearm it 
blends with the periosteum 
on the subcutaneous surface 

of the radius. It is closely adherent to the surface of the extensor muscles, but is 
rather loosely attached to the flexors; near the carpus it blends with the tendons 
attached to the accessory carpal bone. From its deep face are detached intermus- 
cular septa, which form sheaths for the muscles and are attached to the underlying 
bones. The principal septa are: (a) One which passes between the common digital 
extensor and the lateral extensor and ulnaris laterahs; (h) one between the com- 
mon extensor and the extensor carpi radialis; (c) one between the medial and middle 
flexors of the carpus. 

The carpal fascia (Fascia carpi) is a direct continuation of that of the forearm. 
It is attached chiefly to the tuberosities at the distal end of the radius, to the ac- 
cessory carpal bone, and to the carpal collateral ligaments. In front it forms the 
so-called dorsal annular ligament of the carpus (Lig. carpi dorsale), bridging over 
20 




Fia. 278. — Digit of Horse; Volar View. 
14, Deep flexor tendon; 15, superficial flexor tendon; 16, volar an- 
nular ligament of fetlock; 17, proximal digital annular or vaginal liga- 
ment; 11, cartilage of third phalanx; 34, digital cushion. (After Ellen- 
berger-Baum, Anat. fiir Kiinstler.) 



306 FASCIA AND MUSCLES OF THE HORSE 

the grooves and binding down the extensor tendons and their synovial sheaths. Be- 
hind it is greatly thickened and forms the volar annular or transverse ligament of 
the carpus (Lig. carpi transversum) . This stretches across from the accessory car- 
pal bone to the medial collateral ligament and the proximal extremity of the medial 
metacarpal bone. It thus completes the carpal canal (Canalis carpi), in which lie 
the flexor tendons, the carpal synovial sheath, the common digital artery, and 
the medial volar nerve. 

The superficial fascia of the metacarpus and digit presents no special features, 
but the deep fascia (Fascia metacarpea et digitalis) is complicated by the existence 
of several annular ligaments. In the metacarpus it is hardly distinguishable from 
the periosteum in front. On the proximal part of the volar surface it forms a strong 
and close sheath for the flexor tendons, and is attached to the metacarpal bone 
on each side. Lower down and between the annular ligaments it is thin. On the 
flexion surface of the fetlock joint it is much thickened by fibers passing transversely 
from one sesamoid bone to the other, forming the volar annular ligament of the fet- 
lock, which binds down the flexor tendons in the sesamoid groove and converts the 
latter into a canal. Distal to this is a second thick quadrilateral sheet, the prox- 
imal digital annular ligament (Lig. vaginale), which covers and is adherent to the 
tendon of the superficial flexor. It is attached on either side by two bands to the 
ends of the borders of the first phalanx, thus firmly binding down the flexor tendons. 
A little further down a crescentic fibro-elastic sheet, the distal digital annular liga- 
ment, covers the terminal expansion of the deep flexor tendon. It is attached 
on either side by a strong band to the side of the first phalanx about its middle; its 
superficial face is largely covered by the digital cushion and its deep surface is in 
great part adherent to the deep flexor tendon. It is also connected with the so- 
called tendon or ligament of the ergot (Fig. 572). This is a thin and narrow 
fibrous band, which begins in the fibrous basis of the ergot, as the mass of horn at the 
fetlock is called. It descends to the side of the pastern joint, crossing over the 
digital artery and nerve; here it widens out and blends with the fibro-elastic sheet 
just described. 

A. Extensor Division 

1. Extensor carpi radialis (M. radialis dorsalis).^ — This is the largest muscle 
of the extensor division, and lies on the dorsal surface of the radius. 

Origin. — (1) The lateral condyloid crest of the humerus; (2) the coronoid 
fossa; (3) the deep fascia of the arm and forearm and the intermuscular septum 
between this muscle and the common extensor. 

Insertion. — The metacarpal tuberosity. 

Action. — To extend and fix the carpal joint and to flex the elbow joint. 

Structure. — The tendon of origin blends with that of the common extensor 
and is adherent to the capsule of the elbow joint. The belly of the muscle is rounded 
and runs out to a point at the distal third of the forearm. The tendon, which runs 
nearly the whole length of the fleshy portion, appears on the surface of the latter 
about its middle; here the muscle shows a distinctly pennate arrangement. The 
tendon passes through the middle groove at the distal extremity of the radius and 
over the capsule of the carpal joint, bound down by the dorsal annular ligament and 
invested with a synovial sheath. The latter begins three to four inches (ca. 8- 
10 cm.) above the carpus and extends to the middle of the carpus. Distal to this 
the tendon is attached to the joint capsule, but there is usually a small bursa at the 
level of the third carpal bone. In the distal half of the forearm the deep fascia 
blends with the tendon, and here the latter is joined by the long tendon of the biceps. 

Relations. — Superficially, the skin, fascia, and the oblique extensor; deeply, 
the capsule of the elbow joint, the short biceps tendon, the radius, the carpal joint 

1 Also commonly termed the extensor metacarpi magnus. 



EXTENSOR DIVISION 307 

capsule, the anterior radial artery, and the radial nerve; laterally, the common ex- 
tensor; medially, at the elbow, the brachialis and biceps. 

Blood-supply. — Anterior radial artery. 

Nerve-supply. — -Radial nerve. 

2. Common digital extensor (M. extensor digitalis communis). ^ — This muscle 
lies lateral to the foregoing, which it resembles in general form, although less bulky. 

Origin. — (1) The front of the distal extremity of the humerus, in and lateral 
to the coronoid fossa; (2) the lateral tuberosity on the proximal extremity of the 
radius, the lateral ligament of the elbow, and the lateral border of the radius at the 
junction of its proximal and middle thirds; (3) the lateral surface of the shaft of 
the ulna; (4) the fascia of the forearm. 

Insertion. — (1) The extensor process of the third phalanx; (2) the dorsal sur- 
face of the proximal extremities of the first and second phalanges. 

Action. — To extend the digital and carpal joints, and to flex the elbow joint. 

Structure. — The muscle is a compound one, representing the common extensor, 
together with vestiges of the proper extensors of the digits. Usually at least two 
heads may be distinguished, although the division is always more or less artificial 
so far as the muscular part is concerned. The humeral head (Caput humerale), 
which constitutes the bulk of the muscle, arises from the front of the lateral epi- 
condyle of the humerus in common with the extensor carpi; the tendon of origin 
is adherent to the capsule of the elbow joint. Its belly is fusiform, and terminates 
in a point near the distal third of the radius. The tendon appears on the surface 
of the muscle about the middle of the belly, the arrangement being pennate. The 
tendon passes downward through the outer of the two large grooves on the front of 
the distal end of the radius, and over the capsule of the carpal joint. Passing down 
over the front of the metacarpus, it gradually inclines medially, reaching the middle 
line of the limb near the fetlock. A little below the middle of the first phalanx it 
is joined by the branches of the suspensory ligament, and the tendon thus becomes 
much wider. Two synovial membranes facilitate the play of the tendon. The 
proximal one is a synovial sheath which begins about three inches (ca. 7-8 cm.) 
above the carpus, and terminates at the proximal end of the metacarpus. At the 
fetlock a bursa occurs between the tendon and the joint capsule, but otherwise 
the two are adherent. The smaller head, arising chiefly from the radius and ulna, 
is often divisible into two parts (Fig. 568). The larger of these is the radial head 
(Caput radiale) ;- it arises from the lateral tuberosity and border of the radius, and 
from the lateral ligament of the elbow joint. The flat belly is succeeded by a deli- 
cate tendon, which accompanies the principal tendon over the carpus (included in 
the same sheath), and then passes outward to fuse with the tendon of the lateral 
extensor, or it may continue downward between the common and lateral extensor 
tendons to the fetlock. Usually a slip is detached which is inserted on the prox- 
imal extremity of the first phalanx, or ends in the fascia here. The smaller and 
deeper division is the ulnar head (Caput ulnare) f it is usually somewhat difficult 
to isolate. It arises from the ulna close to the interosseous space. It has a small 
rounded belly and is provided with a deficate tendon which may fuse with the 
principal tendon or may be inserted into the joint capsule and the fascia in front of 
the fetlock joint. 

Relations. — The chief relations of the belly of the muscle are : superficially, the 
skin and fascia; deeply, the elbow joint, the radius and ulna, the extensor carpi 
obliquus, and the anterior radial vessels and radial nerve; in front and medially, 

^ Termed also the anterior extensor of the phalanges or extensor pedis. 

2 This (formerly called the muscle of PhilUps) is considered to represent the part of the 
common extensor for the fourth and fifth digits. 

' Martin considers that this muscle (formerly termed the muscle of Thiernesse) represents 
the extensor indicis proprius and the part of the common extensor for the second digit. 



308 



FASCIA AND MUSCLES OF THE HORSE 



the extensor carpi radialis; behind, the lateral extensor and the interosseous 
vessels. 

Blood-supply. — Radial and interosseous arteries. 

Nerve-supply. — Radial nerve. 

Lesbre reports that he has found in one case a brachioradialis muscle in the horse. It 
was a delicate fleshy bundle, superposed on the medial border of tlie common extensor, and ex- 
tended from the lateral condyloid crest to the distal part of the medial border of the radius. 



Extensor carpi obliquus 



Metacarpal tuberosity -^ ' H 
Tendon from common to lateral extensor '^' 



Lateral small metacarpal hone 



Branch of suspensory ligament to 
extensor tendon 




Olecranon 
Ulnar head of deep flexor 



Lateral extensor 
Deep flexor {humeral head) 

Tendon of ulnaris lateralis 
Accessory carpal bone 



Check ligament 

Suspensory ligament 
Flexor tendons 




Flexor tendons 
Cartilage of tJiird j)halanx 



Fig. 279. — Muscles of Left Thoracic Limb of Horse from Elbow Downward; Lateral View. 

O, Extensor carpi radialis; g, brachialis; g', anterior superficial pectoral; c, common digital extensor; e, ulnaris la - 

eralis. (After EIlenberger-Baum, Anat. fiir Kiinstler.) 

3. Lateral digital extensor (M. extensor digitalis lateralis s. digiti quinti pro- 
prius).^— This muscle is much smaller than the preceding, behind which it is situated. 
Origin.— The lateral tuberosity of the radius and the lateral ligament of the 
^ Also known as the lateral extensor of the phalanges. 



EXTENSOR DIVISION 



309 



elbow joint, the shaft of the uhia, the lateral border of the radius, and the inter- 
muscular septum. 

Insertion. — An eminence on the front of the proximal extremity of the first 
phalanx. 

Action. — To extend the digit and carpus. 

Structure.— TliG: muscle is pennate, and is enclosed in a sheath formed by the 
deep fascia, from which many fibers arise. The belly is thin and fusiform and 
terminates at the distal third of the forearm. From here the tendon (at first 
small and round) passes downward through the groove on the lateral tuberosity 
of the distal end of the radius, then over the carpus, and, gradually inclining toward 



Intermuscular septum 



Common digital extensor 

Extensor carpi obliquus 

Intermuscular septum 

Lateral digital extensor 
Intermuscular septum 



Deep digital flexor 
{humeral head) 

Ulnaris lateralis 



Deep digital flexor 
{ulnar head) 




Extensor carpi radialis 



Cutaneous branch of mv 
culo-cutaneous nerve 
Cephalic vein 



Median nerve 
Flexor carpi radialis 



Flexor carpi ulnaris 



Ulnar vessels and nerve 



Superficial digital flexor 



Fig. 280. — Cross-section of Left Forearm of Horse. 

Section is cut a little above middle of region and the figure is a proximal view. 

1, Median artery and satellite veins; 2, 3, branches of deep brachial and anterior radial vessels; 4, dorsal interosseous 

vessels. 



the front, but not reaching the middle line of the limb, it passes over the meta- 
carpus and fetlock to its insertion. Two synovial membranes occur in connection 
with the tendon. A synovial sheath envelops the tendon, beginning about three 
inches (ca. 6-8 cm.) above the carpus, and reaching to the proximal end of the 
metacarpus. At the fetlock a small bursa lies between the tendon and the joint 
capsule, but otherwise the tendon is adherent to the capsule. The tendon becomes 
flat and much larger below the carpus, having received the tendon of the radial 
head of the common extensor and a strong band from the accessory carpal bone. 

Relations. — Superficially, the skin and fascia; deeply, the lateral face of the 
radius and ulna; in front, the common extensor, the oblique extensor, and the 



310 FASCIiE AND MUSCLES OF THE HORSE 

interosseous artery; behind, the lateral flexor of the carpus and the deep flexor of 
the digit. 

Blood-supply. — Interosseous artery. 

Nerve-supply. — Radial nerve. 

4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis 
brevis).^ — This is a small muscle which curves obliquely over the distal half of the 
radius and the carpus. 

Origin. — The lateral border and adjacent part of the dorsal surface of the 
radius (the attachment area begimiing at a point above the middle of the bone and 
extending down to its distal fourth). 

Insertion. — The head of the medial (second) metacarpal bone. 

Action. — To extend the carpal joint. 

Structure. — The muscle is pennate and has a flat belly which curves downward, 
forward, and medially over the distal part of the radius. The tendon continues 
the direction of the muscle, and passes over the tendon of the extensor carpi radialis ; 
it then occupies the oblique groove at the distal end of the radius, and crosses the 
medial face of the carpus. It is provided with a sjmovial sheath. 

Relations. — Superficially, the skin and fascia, the lateral extensor, and the 
common extensor; deeply, the radius, the extensor carpi radialis, the carpal joint 
capsule, and the medial ligament of the carpus. 

Blood-supply.- — Interosseous and anterior radial arteries. 

Nerve-supply. — Radial nerve. 

B. Flexor Division 

1. Flexor carpi radialis (or medial flexor of the carpus).- — This muscle lies on 
the medial surface of the forearm, behind the border of the radius. 

Origin. — The medial epicondyle of the humerus, below and behind the col- 
lateral ligament. 

Insertion. — The proximal end of the medial (second) metacarpal bone. 

Action. — To flex the carpal joint and to extend the elbow. 

Structure. — The muscle has a short tendon of origin, which is succeeded by a 
somewhat flattened, fusiform belly. The tendon of insertion begins near the distal 
fourth of the radius and descends in a canal in the transverse carpal ligament. It 
is provided with a synovial sheath which begins two or three inches (ca. 5-8 cm.) 
above the carpus and extends almost to the insertion of the tendon. 

Relations. — Superflcially, the skin and fascia, the posterior superficial pectoral, 
and the tensor fasciae antibrachii; deeply, the elbow joint, the radius, the deep 
flexor, the flexor carpi ulnaris, the median vessels, and the median nerve. At the 
elbow the artery and nerve lie in front of the muscle, but below they dip beneath it. 

Blood-supply. — Median artery. 

Nerve-supply. — Median nerve. 

On removing the deep fascia on the medial surface of the elbow the student may notice a 
small muscle lying along the collateral ligament. This is the pronator teres, which is usually 
not present or a mere vestige in the horse. It arises by a small, flat tendon from the medial epi- 
condyle of the humerus, and is inserted into the medial ligament of the elbow. On account of its 
small size and the fact that the forearm is fixed in the po.sition of pronation, the muscle can have 
no appreciable function. It is usually represented by a tendinous band. 

2. Flexor carpi ulnaris (or middle flexor of the carpus).^ — This muscle lies on the 
medial and posterior aspect of the forearm, partly under, partly behind, the preced- 
ing muscle. It arises by two heads — humeral and ulnar. 

1 Also known as the extensor metacarpi obliquus. 

2 Also known as the flexor carpi s. metacarpi internus or radialis volaris. 

2 Also known as the flexor carpi (s. metacarpi) medius or ulnaris medialis. 



FLEXOR DIVISION 



311 



Origin. — (1) The medial epicondyle of the humerus just behind the preceding 
muscle; (2) the medial surface and posterior border of the olecranon. 



Long head of triceps 
Medial head of triceps 

Olecranon 
Ulnar head of deep flexor 



Flexor carpi idnaris 
Flexor carpi radialis 



Accessory carpal bone 
Medial ligament of carpus 



Superficial flexor tendon 

Deep flexor tendon 
Suspensory ligament 

Distal end of Mc. II 
Annular ligament 

Superficial flexor tendon 
Deep flexor tendon 




Biceps brachii 



Extensor carpi radialis 
Long tendon of biceps 
Brachialis 

Long medial ligament 



Radius 



Tendon of extensor carpi 
obliquus 



Metacarpal tuberosity 



Mc. in 



Fetlock joint 

E.vtensor branch of suspensory 
ligament 

Common extensor tendon 

Pastern joint 

Cartilage of third phalanx 



Fig. 2S1. — Muscles of Left Thoracic Limb of Horse from Elbow Downward; Medial View. 
The fascia and the ulnar head of the flexor carpi ulnaris have been removed. 1, Distal end of humerus; 2, median 



Insertion. — The proximal edge of the accessory carpal bone. 
Action. — To flex the carpal joint and to extend the elbow. 



312 



FASCIiE AND MUSCLES OF THE HORSE 



Structure. — The humeral head is much the larger, constituting, in fact, the 
bulk of the muscle. It is flattened, curved, and tapers at both ends. The ulnar 
head, much smaller and very thin, is covered by an aponeurosis from which many of 
its fibers arise. It joins the large head a little above the middle of the forearm. 



Ulnar head of deep flexor 
Stump of flexor carpi radialis 

Stump of flexor carpi idnaris 



Superficial digital flexor 
Deep digital flexor 

Tendon of ulnar head 

Radial head of superficial flexor 
Insertion of flexor carpi idnaris 
Accessory carpal bone 



Deep flexor tendon 
Superficial flexor tendon 

Check ligament 
Suspensory ligament 




Biceps brachii 

Brachialis 

Long medial ligament 

Extensor carpi radialis 



Radius 



Annular ligament 



Deep flexor tendon 
Cartilage of third phalanx 




Tendon of flexor carpi radialis 
Tendon of extensor carpi obliquus 



Mc. Ill 



Fetlock joint 

Extensor branch of suspensory 
ligament 



Fig. 282. — Muscles of Left Thoracic Limb of Horse, fhom Elbow Downward; Medial View. 
Parts of superficial muscles have been removed, carpal canal opened up, and flexor tendons drawn backward. 



The tendon of insertion is short and strong; it blends with the posterior annular 
ligament of the carpus. 

Relations. — Superficially, the tensor fascise antibrachii, superficial pectoral, and 
flexor carpi radialis, the skin and fascia, and cutaneous branches of the ulnar 
nerve; deeply, the superficial and deep flexors of the digit. In the cUstal half of 



FLEXOR DIVISION 313 

the forearm the ulnar vessels and nerve lie between the lateral edge of this muscle 
and the lateral flexor of the carpus. 

Blood-supply. — Ulnar and median arteries. 

Nerve-supply. — Ulnar and median nerves. 

3. Ulnaris lateralis (or lateral flexor of the carpus).^ — This muscle lies on the 
lateral face of the forearm, behind the lateral extensor of the digit. 

Origin. — The lateral epicondyle of the humerus, behind and below the lateral 
ligament. 

Insertion. — (1) The lateral surface and proximal border of the accessory carpal 
bone ; (2) the proximal extremity of the lateral (fourth) metacarpal bone. 

Action.- — To flex the carpal joint and to extend the elbow. 

Structure.- — The belly of the muscle is flattened and is intersected by a good 
deal of tendinous tissue. There are two tendons of insertion. The short tendon 
is inserted into the accessory carpal bone. The long tendon is detached just above 
the carpus; it is smaller and rounded; it passes downward and a little forward 
through a groove on the lateral surface of the accessory carpal bone, enveloped by 
a synovial sheath, to reach its insertion on the lateral metacarpal bone. A synovial 
pouch lies under the origin of the muscle at the elbow joint, with the cavity of 
which it communicates. 

Relations. — Superficially, the skin, fascia, and cutaneous branches of the ulnar 
nerve; deeply, the elbow joint, the ulna, and the flexors of the digit; in front, the 
lateral extensor of the digit; behind, the middle flexor of the carpus, the ulnar head 
of the deep flexor, and the ulnar vessels and nerve. 

Blood-supply. — Interosseous, ulnar, and median arteries. 

Nerve-supply. — Radial nerve. 

4. Superficial digital flexor- (M. flexor digitalis superficialis) . — This muscle is 
situated in the middle of the flexor group, chiefly under cover of the middle flexor 
of the carpus. 

Origin. — (1) The medial epicondyle of the humerus; (2) a ridge on the pos- 
terior surface of the radius, below its middle and near the medial border. 

Insertion. — (1) The eminences on the proximal extremity of the second phalanx, 
behind the collateral ligaments; (2) the distal extremity of the first phalanx, also 
behind the collateral ligaments. 

Action. — To flex the digit and carpus and to extend the elbow. 

Structure. — The fleshy part of the muscle is the humeral head (Caput humerale) ; 
it takes origin from the humerus. The radial head (Caput tendineum) consists of 
a strong fibrous band, usually termed the radial or superior check Ugament, which 
fuses with the tendon near the carpus. The belly of the muscle is intersected by 
tendinous strands, and fuses more or less with that of the deep flexor, from which 
it is therefore somewhat difficult to separate. Near the carpus it is succeeded by a 
strong, thick tendon which passes down through the carpal canal and is enveloped 
by a synovial sheath, in common with the deep flexor. This, the carpal sheath 
(Vagina carpea), begins three or four inches (8-10 cm.) above the carpus, and ex- 
tends downward nearly to the middle of the metacarpus. Below the carpus the 
tendon becomes flattened and broader and at the fetlock it widens greatly. Near 
the fetlock it forms a ring through which the tendon of the deep flexor passes (Fig. 
286) . Here the two tendons are bound down in the sesamoid groove by the volar 
annular ligament, which fuses more or less with the superficial flexor tendon. At 
the distal end of the first phalanx the tendon divides into two branches which di- 
verge to reach their points of insertion, and between these branches the tendon of 

1 Also known as the flexor carpi (s. metacarpi) externus or extensor carpi ulnaris. Morpho- 
logically it belongs to the extensor group. 

2 Also commonly known as the flexor perforatus or superficial flexor of the phalanges. 



314 



FASCIA AND MUSCLES OF THE HORSE 



the deep flexor emerges (Fig. 278). A second synovial membrane, the digital 
synovial sheath (Vagina digitalis), begins at the distal fourth of the metacarpus, 





183. — Synovial Sheaths and Burs^ of Distal 
Part op Right Fore Limb of Horse; Medial 
View. 



Fig. 284. — Synovial Sheaths and Burs^ of Distal 
Part of Right Fore Limb op Horse; Lateral 
View. 
The synovial sheaths (colored yellow) and the joint capsules (colored pink) are injected. 



a. Sheath of extensor carpi obliquus; b, sheath 
of flexor carpi radialis; c, carpal sheath; d, d', d", d'", 
digital sheath; e, bursa under common extensor ten- 
don; /, capsule of fetlock joint; 1, extensor carpi ra- 
dialis; 2, tendon of extensor carpi obliquus; 3, flexor 
carpi radialis; 4> flexor carpi ulnaris; 5, superficial 
flexor tendon; 6, deep flexor tendon; 7, suspensory liga- 
ment; 8, small metacarpal bone; 9, large metacarpal 
bone; 10, volar annular ligament of fetlock; 11, 
proximal digital annular ligament; 12, radius; 13, 
radiocarpal joint; 14, fetlock joint; 1.5, cartilage of 
third phalanx; 16, band from first phalanx to cartilage. 
(After Ellenberger, in Leisering's Atlas.) 



a, Sheath of extensor carpi radialis: b, sheath 
of common extensor; c, sheath of lateral extensor; d, 
sheath of outer tendon of ulnaris lateralis; e, e', carpal 
sheath; /, /', /", digital sheath; g, bursa under com- 
mon extensor tendon; h, bursa under lateral extensor 
tendon; i, capsule of fetlock joint; 1, extensor carpi 
radialis; 3, common digital extensor; 3, lateral digital 
extensor; 4. ulnaris lateralis; 4'< 4", tendons of 4; 5, 
superficial flexor tendon; 6, deep flexor tendon; 7, 
suspensory ligament; 8, lateral metacarpal bone; 9, 
large metacarpal bone; 10, volar annular ligament 
of fetlock; 11, digital annular ligament; 12, fetlock 
joint; 13, cartilage of third phalanx; 14, band from 
first phalanx to cartilage. (After Ellenberger, in 
Leisering's Atlas.) 



two or three inches (ca. 5-8 cm.) above the fetlock, and extends to the middle of 
the second phalanx. 

Relations. — The belly of the muscle is related superficially to the ulnar head 
of the deep flexor, the flexor carpi ulnaris, and, at its origin, to the ulnar vessels 



FLEXOR DIVISION 



315 



and nerve; deeply, to the humeral head of the deep flexor. The tendon is re- 
lated superficially to the skin and fascia; deeply, to the deep flexor tendon. 

Blood-supply. — Median artery. 

Nerve-supply. — Ulnar and median nerves. 

5. Deep digital fiexori (M. flexor digitaUs profundus). — The fleshy part of 
this muscle lies on the posterior surface of the radius, and is almost entirely under 
cover of the preceding muscles. It is the largest muscle of the flexor group. 

Origin. — (1) The medial epicondyle of the humerus; (2) the medial surface of 
the olecranon; (3) the middle of the posterior surface of the radius and a small ad- 
jacent area of the ulna. 

Insertion. — The semilunar crest and the adjacent surface of the cartilage of 
the third phalanx. 

Action. — -To flex the digit and carpus and to extend the elbow. 

Structure. — This muscle consists of three heads. The humeral head (Caput 
humerale) constitutes the bulk of the muscle. It is marked by tendinous inter- 
sections, and is separable into three secondary heads. A synovial pouch from the 
elbow joint descends under its 



Tendon of 
lateral extensor 



Tendon of 
common extensor 



origin about two inches. The 
ulnar head (Caput ulnare) is 
much smaller, and is at first 
superficially situated between 
the lateral and middle flexors 
of the carpus. The radial head 
(Caput radiale) is the smallest, 
and is not always present; it 
is situated on the distal two- 
thirds of the posterior surface 
of the radius, under the humer- 
al head. Each of these heads 
is provided with a tendon. The 
principal tendon — that of the 
humeral head — begins about 
three or four inches (8-10 
cm.) above the carpus and is 
joined at the carpus by the 
tendons of the other two heads. 
The conjoined tendon passes 
downward through the carpal 

canal, being included in the carpal synovial sheath with the superficial flexor ten- 
don, as previously described. The tendon is at first broad and three-sided, but 
becomes narrower and rounded below. Continuing downward, it is joined about 
the middle of the metacarpus by a strong fibrous band, the so-called inferior or 
subcarpal check ligament (Caput carpale s. tendineum).^ This is a direct continua- 
tion of the posterior ligament of the carpus. Below this the tendon passes through 
the ring formed by the superficial flexor tendon, then in succession over the sesa- 
moid groove, the chstal sesamoidean ligaments, and the flexor surface of the distal 
sesamoid, to its insertion (Figs. 241 and 242). At the fetlock it widens consider- 
ably, narrows again in the middle of the digital region, again widens at the pulley 




Tendon of superficial flexor 
Fig. 285. 



Cross-sectiox of Distal Part of Lej 
Horse, Just Above Sesamoids 



Intersesamoi- 
dean ligament 

Digital vein 
Digital artery 
Digital nerve 



Tendon of deep flexor 

Metacarpus of 



1 Also commonly knowTi as the flexor perforans or deep flexor of the phalanges. 

- This might appropriately be termed the carpal head (caput carpale) or tendinous head 
(caput tendineum). At its upper end it is broad, occup>ang the entire width of the space between 
the small metacarpal bones; below it becomes narrower and thicker. It is related in front to 
the suspensory ligament, and its posterior face, which is related to the deep flexor tendon, is 
covered by the deep layer of the carpal sheath. 



316 



FASCIA AND MUSCLES OF THE HORSE 



of the second phalanx, and forms a terminal fan-like expansion. At the pulleys 
of the digit the tendon contains cartilage and is thickened. From the distal fourth 
of the metacarpus to the distal end of the second phalanx it is inclosed in the dig- 
ital synovial sheath described in connection with the superficial flexor. The bursa 
podotrochlearis or navicular bursa is found between the tendon and the distal sesa- 
moid or navicular bone. The terminal part of the tendon is bound down by the 
distal digital annular ligament described with the fascia. 

Relations. — The belly of the muscle is related posteriorly to the superficial 



Extensor tendon 



Proximal end of capside of fetlock 
joint 

Bursa 

Collateral ligament of fetlock joint — ^ "^ ' 

Fascia 



Branch of suspc7isory ligament- 



Lateral volar ligament of pastem 
joint 



\ ^"l" 



^hl\ 



Superficial flexor tendon 
Deep flexor te?idon 
Suspensory ligament 
.Lateral interosseus tendon 

' Proximal end of digital sheath 
' Ring of superficial flexor tendon 
• Intersesamoidean ligame7it 
Posterior annular ligament {cut) 



. .Collateral sesamoidean ligament 
ij'/l Superficial distal sesamoidean 
ligament 
Middle distal sesamoidean ligament 

> Attachments of proximal digital 
' annular ligament 



Pouch of digital sheath 





llti^^rff^ 


^ ^Cartilage 


Suspensory ligament of navicidar 
bone 

Ba?id from cartilage to extensor 

tendon 
Collateral ligament of coffin joint -{- 

i 




> 



Fig. 286. — Ligaments and Tendons or Distal Part of Limb of Horse. 

Mc. Ill, Large metacarpal bone; Ph. I, first phalanx; Ph. II, second phalanx; Ph. III. third phalanx; 1, deep flexor 

tendon; 2, band from first phalanx to digital cushion. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



flexor and to the middle flexor of the carpus; medially, to the flexor carpi radialis, 
the radial check ligament, and the median vessels and nerve; laterally, to the 
ulnaris lateralis; anteriorly, to the radius and ulna and branches of the median 
artery and nerve. Below the carpus the tendon is accompanied by the vessels and 
nerves of the digit. It may also be noted that the muscle is not entirely covered 
by the other flexors; it comes in contact with the skin and fascia on the postero- 
lateral aspect of the proximal half of the forearm, and also on the lateral aspect of 
the distal fourth. 

Blood-supply. — Median and ulnar arteries. 



FASCIA AND MUSCLES OF THE PELVIC LIMB — THE FASCIA 317 

Nerve-supply. — Median and ulnar nerves. 

The five muscles of the metacarpus and digit are either reduced to vestiges or 
modified greatly in structure. 

1, 2. Lvimbricales (medialis et lateralis). — These are two very slender fusiform 
muscles which lie on either side of the flexor tendons above the fetlock. They arise 
from the deep flexor tendon, and end in the fibrous tissue which lies under the nod- 
ule of horn at the fetlock which is known as the ergot (Fig. 572). Their action is 
inappreciable. The size of these muscles is subject to much variation. Often very 
little muscular tissue can be foimd, but the small tendon is constantly present. 

Blood-supply. — Volar metacarpal arteries. 

Nerve-supply. — Median and ulnar nerves. 

3, 4, 5. Interossei. — These are three in number in the horse, and are situated 
chiefly in the metacarpal groove. Two, the medialis and lateralis, are very small 
muscles, each of which arises from the corresponding small metacarpal bone near 
its proximal extremity, and is provided with a delicate tendon which is usually lost 
in the fascia at the fetlock (Fig. 240). They have no appreciable action. Their 
blood- and nerve-supply is the same as that of the preceding muscles. 

The interosseus medius is so much modified that it is usually termed the 
suspensory or superior sesamoidean ligament. It contains little muscular tissue, 
being transformed very largely into a strong tendinous band (Tendo interosseus), 
bifurcate below, and having for its chief function the supporting of the fetlock. It 
has been described, in deference to common usage, with the ligaments. 



Fascle and Muscles of the Pelvic Limb 
The FASCiiE 

The iliac fascia (Fascia iliaca) covers the ventral surface of the iliacus and psoas 
muscles, over which it is tightly stretched (Fig. 575). It is attached medially to 
the tendon of the psoas minor; laterally it is attached to the tuber coxae and blends 
with the deep layer of the lumbo-dorsal fascia. Its anterior part is thin. Pos- 
teriorly it is continuous with the inguinal ligament and the pelvic fascia. It fur- 
nishes surfaces of origin for the sartorius, cremaster externus, and transversus ab- 
dominis muscles. 

The pelvic fascia (Fascia pelvis) lines the cavity as the parietal layer and 
at the pelvic outlet is reflected on the viscera to form the visceral layer. Laminae 
are detached from it to strengthen the various peritoneal folds. 

The superficial fascia of the gluteal region is thin and is closely adherent to 
the deep fascia. A subcutaneous bursa may be found on the tuber coxae. The 
gluteal fascia (Fascia glutea) covers the superficial muscles of the region, and de- 
taches intermuscular septa, which pass between the muscles. It is attached to the 
sacral spines, the dorsal sacro-iliac ligament, and the tubera of the ilium, and is con- 
tinuous in front with the lumbo-dorsal fascia, behind with the coccygeal fascia. 
Its deep face gives origin to fibers of the superficial and middle glutei, the biceps 
femoris, and the semitendinosus, so that care is necessary in dissecting it off these 
muscles. The chief intermuscular septa are: (1) One which passes between the 
superficial gluteus and the biceps femoris; (2) one between the biceps and semi- 
tendinosus, from which a lamella is detached which passes between the middle and 
posterior parts of the biceps and is attached to the tuber ischii; (3) one between the 
semitendinosus and semimembranosus, which is attached to the sacro-sciatic liga- 
ment and tuber ischii; it furnishes origin for fibers of the long head of the semi- 
membranosus. 

The superficial fascia of the thigh presents no exceptional features, but the deep 



318 FASCIA AND MUSCLES OF THE HORSE 

fascia is very thick and strong on the front and lateral surface. This part, the 
fascia lata (Fig. 267), is continuous mth the gluteal fascia; it is tendinous in char- 
acter, and easily separable from the underlying muscles. It furnishes insertion to 
the tensor fascise latse and to the biceps femoris (in part), by both of which it is 
tensed. At the stifle it is attached to the patella and the lateral and medial patellar 
ligaments. Medially it is continuous with the medial femoral fascia. It furnishes 
the following intermuscular septa: (1) One which passes between the vastus lat- 
eralis and biceps femoris to be attached to the third trochanter of the femur; (2) 
two which pass between the three branches of the biceps femoris; (3) a fourth be- 
tween the biceps femoris and semitendinosus. The medial femoral fascia (Fascia 
femoralis medialis) covers the superficial muscles on the medial surface of the thigh. 
At its upper part it is joined by the femoral lamina of the aponeurosis of the external 
oblique muscle (Fig. 575). The posterior part is thin. It is continuous with the 
fascia lata in front and the fascia cruris below. At the stifle it fuses with the ten- 
dons of the sartorius and gracilis. 

The fascia cruris, or fascia of the leg, consists of three layers. Two of these 
invest the entire region and may, therefore, be termed the common fasciae. The 
superficial layer is a continuation of that of the thigh, while the second layer may be 
regarded chiefly as a continuation of the tendons of the superficial muscles of the 
hip and thigh (biceps femoris, semitendinosus, tensor fascise latse, sartorius, and 
gracilis). The two layers frequently fuse, and are attached chiefly to the medial 
and lateral patellar ligaments and the crest and medial surface of the tibia. About 
the middle of the leg the two layers unite behind the deep flexor of the digit and 
form a strong band which passes dowTiward in front of the tendons of the gastroc- 
nemius and superficial flexor, to be attached with the latter to the anterior and 
medial part of the tuber calcis. This constitutes a tarsal tendon of insertion of the 
biceps femoris and semitendinosus. A strong band, about two inches in width, 
arises from the lateral supracondyloid crest, descends over the lateral head of the 
gastrocnemius, and blends with the foregoing and the superficial flexor tendon. 
The third layer forms sheaths for the muscles, furnishing origin in part to their 
fibers. Two important intermuscular septa are detached, viz.: (1) One which 
passes between the long and lateral digital extensors to be attached to the fibula 
and the lateral border of the tibia; (2) one between the lateral digital extensor and 
the deep digital flexor. 

The tarsal fascia (Fascia tarsi) fuses with the ligaments and bony prominences 
of the region. It is strong and tendinous in front, and joins the tendon of the long 
extensor below the joint. On the sides it is thin and fuses with the ligaments. 
Posteriorly it is very thick and strong, forming an annular ligament which stretches 
from the medial ligament to the fibular tarsal bone and the plantar ligament. This 
converts the groove at the back of the hock into a canal, in which are the deep flexor 
tendon with its synovial sheath and the plantar vessels and nerves. In this vicinity 
there are three annular ligaments (Ligamenta transversa). The proximal one binds 
down the tendons of the long extensor, peroneus tertius, and tibialis anterior on 
the distal end of the shaft of the tibia. The middle one stretches from the fibular 
tarsal bone to the lateral tendon of the peroneus tertius, forming a loop around the 
tendon of the long extensor. The distal band stretches across the proximal ex- 
tremity of the large metatarsal bone and incloses the tendons (and sheaths) of the 
two extensors of the digit. 

The metatarsal and digital fasciae do not differ materially from those of the 
corresponding regions of the thoracic limb. 



THE MUSCLES THE SUBLUMBAR MUSCLES 319 

The Muscles 1 

I. THE SUBLUMBAR MUSCLES (Figs. 287, 575) 
The muscles of this group are not confined to the sublumbar region, but ex- 
tend beyond it both before and behind. Their chief function is to flex the hip 
joint. Two, however, — the psoas minor and the quadratus lumborum,^ — have not 
this action. 

1. Psoas minor. — This is a fusiform, flattened, pennate muscle, which lies 
along the ventro-lateral aspect of the bodies of the last three thoracic and the 
lumbar vertebrae. 

Origin. — The bodies of the last three thoracic and first four or five lumbar 
vertebrae, and the vertebral ends of the sixteenth and seventeenth ribs. 

Insertion. — The psoas tubercle on the shaft of the ilium. 

Action. — To flex the pelvis on the loins, or to incline it laterally. 

Structure. — The muscle arises by a series of digitations which pass backward 
and outward to join the tendon at an acute angle. The latter lies along the lateral 
border of the fleshy portion and is flattened. It appears on the surface of the mus- 
cle at the third lumbar process and increases gradually in width until it reaches the 
pelvic inlet, where it becomes narrower. 

Relations. — The ventral surface of the thoracic part of the muscle is related 
to the pleura, crura of the diaphragm, and sympathetic and splanchnic nerves. 
In the abdomen the chief ventral relations are the peritoneum, the vena cava 
(right side), the aorta and left kidney (left side), the sympathetic nerves, and the 
ureters. Dorsally, the chief relations are the vertebrae, the psoas major, and lum- 
bar nerves. The lumbar arteries pass through the medial edge. Near its insertion 
the tendon is crossed medially by the external iliac artery, and laterally by the fem- 
oral nerve. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

2. Psoas major. — This is much larger than the preceding muscle, by which it 
is partly covered. It is triangular, with the base anterior. 

Origin. — The ventral surfaces of the transverse processes of the lumbar ver- 
tebrae and the last two ribs. 

Insertion. — The trochanter minor of the femur, by a common tendon with 
the iliacus. 

Action. — To flex the hip joint and to rotate the thigh outward. 

Structure. — The origin of the muscle is fleshy, the belly being in general flat- 
tened, thick in its middle, thin at its edges. The thoracic part is small, the abdom- 
inal part much thicker and wider, extending laterally beyond the extremities of the 
lumbar transverse processes. From the lumbo-sacral articulation it lies in a deep 
groove formed in the iliacus (with which it is partly united), becomes smaller and 
rounded, and passes downward and backward to terminate by a strong tendon 
common to it and the iliacus. On account of the intimate union between the psoas 
major and iliacus they are frequently considered a single muscle, to which the name 
ilio-psoas is applied ; some anatomists include the psoas minor also under this term. 

Relations. — Dorsally, the last two ribs and thoracic vertebrae, the lumbar 
vertebrae, the internal intercostals, quadratus lumborum, longissimus dorsi, and 
iliacus, and the lumbar vessels and nerves; ventrally, the pleura and peritoneum, 
the iliac fascia, inguinal ligament, the diaphragm, psoas minor and sartorius, 
and the circumflex iliac vessels. 

^ On account of the very slight mobihty of the sacro-iUac articulation, the muscles of the 
pelvic girdle are much reduced, and almost all of those which might be included in this group 
extend to the femur or even to the leg. It seems undesirable, therefore, to attempt a morpho- 
logical grouping. 



320 FASCIA AND MUSCLES OF THE HORSE 

Blood-supply. — Lumbar and circumflex iliac arteries. 
Nerve-supply. — Lumbar and femoral nerves. 

3. Iliacus. — This muscle covers the ventral surface of the ilium lateral to the 
sacro-iliac articulation, and extends beyond the lateral border of the bone, under- 
neath the middle gluteus. 

Origin. — The ventral surface of the ilium lateral to the ilio-pectineal line, the 
ventral sacro-iliac ligament, the ^\^ng of the sacrum, and the tendon of the psoas 
minor. 

Insertion. — The trochanter minor of the femur, by a common tendon with 
the psoas major. 

Action. — To flex the hip joint and to rotate the thigh outward. 

Structure.- — The belly of the muscle is so deeply grooved for the psoas major 
as to give the appearance of being completely divided into medial and lateral parts. 
When the psoas is removed, it is seen, however, that the two heads are not entirely 
separated. The lateral, larger head arises from the wing of the ilium chiefly; the 
medial, smaller head arises chiefly from a small area on the shaft of the ilium, be- 
tween the psoas tubercle and the depression for the medial tendon of the rectus 
femoris, and from the tendon of the psoas minor. The two parts inclose the psoas 
major in front of the hip joint. 

Relations. — Dorsally, the ilium, sacrum, sacro-iliac articulation, the gluteus 
medius, the ilio-lumbar and external circumflex vessels; ventrally, the iliac fascia, 
inguinal ligament, the psoas major, sartorius, and abdominal muscles. At the 
level of the hip joint the chief relations are: medially, the femoral vessels, the fem- 
oral nerve, and the sartorius muscle ; laterally, the rectus femoris and tensor fasciae 
latse; in front, the abdominal muscles; behind, the hip joint. 

Blood-supply. — Lumbar, circumflex iliac, and deep femoral arteries. 

Nerve-supply. — Lumbar and femoral nerves. 

4. Quadratus lumborum. — This thin muscle lies on the lateral part of the ven- 
tral surfaces of the lumbar transverse processes. 

Origin. — The ventral surface of the upper part of the last two ribs and the 
lumbar transverse processes. 

Insertion. — The ventral surface of the wing of the sacrum and the ventral 
sacro-iliac ligament. 

Action. — Acting together, to fix the last two ribs and the lumbar vertebrae; 
acting singly, to produce lateral flexion of the loins. 

Structure. — The muscle is pennate, and is curved with the convexity lateral. 
It is thin, largely mixed with tendinous fibers, and is, in general, little developed in 
the horse in comparison with some of the other animals (e. g., dog, sheep). 

Relations. — Ventrally, the psoas major and the last thoracic and first three 
lumbar nerves; dorsally, the last two ribs, the lumbar transverse processes, and 
the lateral branches of the lumbar arteries. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

5. Intertransversales lumborum.^ — (See p. 279.) 



11. THE LATERAL MUSCLES OF THE HIP AND THIGH 

Under this head the muscles of the lateral surface of the pelvis and thigh, and 
those which form the posterior contour of the latter, will be described. 

1. Tensor fasciae latae (Fig. 267). — This is the most anterior muscle of the 
superficial layer. It is triangular in form, with its apex at the tuber coxae. 

Origin. — The tuber coxae. 

Insertion. — The fascia lata and thus indirectly to the patella, the lateral patel- 
lar ligament, and the crest of the tibia. 



THE LATERAL MUSCLES OF THE HIP AND THIGH 321 

Action. — To tense the fascia lata, flex the hip joint, and extend the stifle joint. 

Structure. — The muscle arises by a rather small head, about two inches (ca. 
5 cm.) wide, on the antero-inferior eminence of the tuber coxae. Below this the 
belly spreads out and terminates in the aponeurosis about midway between the 
point of the hip and the stifle. Many fibers arise from an intermuscular septum 
between this muscle and the superficial gluteus; this septum is attached to the lat- 
eral border of the ilium. The aponeurosis fuses with the fascia lata, which may be 
regarded practically as the tendon of insertion; it detaches a lamina which passes 
with the tendon of insertion of the superficial gluteus to the lateral border of the 
femur. 

Relations. — Laterally, the skin and fascia; medially, the obliquus abdominis 
externus, the iliacus, superficial gluteus, rectus femoris, and vastus lateralis, branches 
of the circumflex iliac, ilio-lumbar, and iliaco-femoral arteries, and the anterior 
gluteal nerve; anteriorly, the prefemoral lymph-glands. A considerable quantity 
of connective tissue is found between the deep face of the muscle and the abdominal 
wall. 

Blood-supply. — Circumflex iliac, ilio-lumbar, and iliaco-femoral arteries. 

Nerve-supply.- — Anterior gluteal nerve. 

2. Gluteus superficialis (Fig. 267). — This muscle lies behind and partly 
underneath the tensor fasciae latse. It is triangular and consists of an anterior and 
a posterior head united by the gluteal fascia. 

Origin. — (1) The tuber coxae and the adjacent part of the lateral border of 
the ilium; (2) the gluteal fascia. 

Insertion. — The third trochanter of the femur. 

Action. — To abduct the limb, flex the hip joint, and tense the gluteal fascia. 

Structure. — The anterior head of the muscle is not completely separable (ex- 
cept artificially) from the tensor fasciae latse, since both muscles are attached to an 
intermuscular septum. The attachment to the border of the ilium is by means of 
an intermuscular septum, which passes beneath the thick lateral border of the 
gluteus medius and furnishes origin to fibers of both muscles. The posterior head 
arises from the deep face of the gluteal fascia, and so indirectly from the dorsal 
sacro-iliac ligament. The two heads unite and terminate on a strong flat tendon, 
which is inserted into the edge of the third trochanter of the femur, under cover of 
the biceps femoris. 

Relations. — Superficially, the skin, fascia, and biceps femoris; deeply, the 
gluteus medius, iliacus, rectus femoris, and branches of the iliaco-femoral vessels; 
in front, the tensor fasciae latae; behind, the biceps femoris. 

Blood-supply. — Gluteal and iliaco-femoral arteries. 

Nerve-supply. — Anterior gluteal nerve. 

3. Gluteus medius (Figs. 268, 580).— This is a very large muscle which covers 
the gluteal surface of the ilium and the greater part of the lateral wall of the pelvis, 
and extends forward also on the lumbar part of the longissimus dorsi. 

Origin. — (1) The aponeurosis of the longissimus dorsi, as far forward as the 
first lumbar vertebra; (2) the gluteal surface and tubera of the ilium; (3) the dorsal 
and lateral sacro-iliac and sacro-sciatic ligaments, and the gluteal fascia. 

Insertion. — (1) The summit of the trochanter major of the femur; (2) the crest 
below the trochanter; (3) the lateral aspect of the trochanteric ridge. 

Action.— To extend the hip joint and abduct the limb. By its connection 
with the longissimus a muscular mass is formed which is one of the chief factors in 
rearing, kicking, and propulsion. 

Structure. — The anterior extremity of the muscle is narrow and thin, and lies 

in a depression on the surface of the longissimus, from the strong aponeurosis of 

which the fibers take origin. The pelvic portion of the muscle is very voluminous, 

and forms the bulk of the muscular mass which gives the haunch its rounded con- 

21 



322 FASCIA AND MUSCLES OF THE HORSE 

tour. This part of the muscle is intersected by several tendinous sheets. One of 
these is particularly distinct, and is attached to the gluteal line on the ilium. This 
divides the muscle incompletely into superficial and deep strata. The superficial 
part is inserted by a strong tendon into the summit of the great trochanter, and 
by a pointed fleshy mass with a tendinous border into the lateral surface of the 
trochanteric ridge. The deep part is termed the gluteus accessorius ; it is smaller, 
and arises entirely from the ilium between the gluteal line and the tuber coxae (Fig. 
580). It has a strong flat tendon which passes over the anterior part or convexity 
of the trochanter to be inserted into the crest below it. The trochanter is covered 
here A\dth cartilage, and the trochanteric bursa (Bursa trochanterica) is interposed 
between the tendon and the cartilage.^ 

Relations. — Superficially, the skin, lumbo-dorsal and gluteal fasciae, the tensor 
fasciae latse, gluteus superficialis, and biceps femoris; deeply, the longissimus, the 
ilium, sacro-iliac and sacro-sciatic ligaments, the gluteus profundus, iliacus and 
rectus femoris, the iliaco-femoral vessels, the gluteal and internal pudic vessels and 
nerves, and the great sciatic nerve. 

Blood-supply. — Gluteal, ilio-lumbar, lumbar, and iliaco-femoral arteries. 

Nerve-supply.— Gluteal nerves. 

4. Gluteus profundus.^^ — This much smaller quadrilateral muscle lies under 
the posterior part of the preceding muscle, and extends over the hip joint, from the 
superior ischiatic spine to the anterior part of the trochanter major (Fig. 580). 

Origin. — The superior ischiatic spine and the adjacent part of the shaft of the 
ilium. 

Insertion. — The edge of the anterior part or convexity of the trochanter major 
of the femur. 

Action. — To abduct the thigh and to rotate it inward. 

Structure. — The muscle is short and thick and contains numerous tendinous 
intersections. The fibers are directed almost transversely outward over the capsule 
of the hip joint and converge at the convexity of the trochanter. 

Relations.- — Superficially, the gluteus medius and branches of the gluteal vessels 
and nerves; deeply, the shaft of the ilium, the hip joint, and the rectus femoris 
and capsularis. 

Blood-supply.- — Gluteal artery. 

Nerve-supply. — Anterior gluteal nerve. 

5. Biceps femoris.^ — This large muscle lies behind and in part upon the super- 
ficial and middle glutei. It extends in a curved direction from the sacral and 
coccygeal spines to the lateral surface of the stifle and leg (Figs. 267, 292, 580). 

Origin.-^{l) The dorsal and lateral sacro-iliac ligaments, the gluteal and 
coccygeal fasciae, and the intermuscular septum between this muscle and the semi- 
tendinosus; (2) the tuber ischii. 

Insertion. — (1) A rough eminence on the posterior surface of the femur near 
the trochanter tertius; (2) the free (anterior) surface of the patella and the lateral 
patellar ligament; (3) the tibial crest; (4) the crural fascia and the tuber calcis. 

Action. — The action is somewhat complex, because the muscle is composed 
of three parts, has several points of insertion, and acts on all the joints of the 
limb except those of the digit. The general action is to extend the limb, as in pro- 
pelling the body, rearing or kicking, and to abduct it. The anterior part, by its 
attachment to the posterior surface of the femur and to the patella, would extend 

^ By most anatomists the portion inserted into the crest is termed the gluteus accessorius, 
but Lesbre considers this to be the deep gluteus, homologous with the gluteus minimus of man. 
The portion inserted into the trochanteric ridge apparently represents the piriformis of man. 

^ Lesbre considers this to be the scansorius. 

* Apparently the muscle represents the biceps, together with part of the gluteus super- 
ficialis of man. Hence the names, gluteo-biceps and paramero-biceps have been suggested. 



THE LATERAL MUSCLES OF THE HIP AND THIGH 323 

the stifle and hip joints and abduct the hmb. The middle part, being inserted 
chiefly on the tibial crest and the lateral patellar ligament, would extend the hip, 
and may, with the semitendinosus, flex the stifle. The posterior part, by virtue 
of its attachment to the tuber calcis, assists in extending the hock. It is to be noted, 
however, that extension of the hock joint can occur only when the stifle is also ex- 
tended, and vice versa. 

Structure. — The muscle has two heads of origin. The long or vertebral head 
arises chiefly from the dorsal and lateral sacro-iliac ligaments, the coccygeal fascia, 
and the intermuscular septum. There is often a large bursa between this head and 
the trochanter major. The short or ischiatic head arises by a strong tendon from 
the ventral spine on the tuber ischii, which also furnishes origin to part of the semi- 
tendinosus. They unite, and a short tendon, detached from the deep face of the 
muscle, is inserted into the posterior surface of the femur near the third trochanter; 
here a bursa is interposed between the tendon and the bone. The muscle then 
divides into three parts, which terminate on a strong aponeurosis over the 
junction of the thigh and leg. The anterior part is directed toward the patella, 
the middle one toward the tibial crest, while the posterior one assists in the forma- 
tion of the posterior contour of the limb. The aponeurosis blends with the deep 
layer of the fascia cruris, as already described. A synovial bursa occurs under the 
patellar insertion, and in some cases there is also one between the muscle and the 
third trochanter. 

Relations. — Superficially, the sldn and fascia; deeply, the sacro-iliac and sacro- 
sciatic ligaments, the coccygeal fascia, the femur, the gluteus medius, obturator, 
gemellus, quadratus femoris, adductor, semimembranosus, vastus lateralis, and 
gastrocnemius muscles, branches of the lateral sacral, gluteal, obturator, femoral 
and deep femoral vessels, the great sciatic, tibial, peroneal, and posterior gluteal 
nerves; in front, the superficial and middle glutei; behind and medially, the semi- 
tendinosus. 

Blood-supply. — Gluteal, obturator, and posterior femoral arteries. 

Nerve-supply. — Posterior gluteal and great sciatic nerves. 

6. Semitendinosus. — This is a long muscle which extends from the first two 
coccygeal vertebrae to the proximal third of the medial surface of the tibia. It lies 
at first behind the biceps, then passes downward on the back of the thigh, between 
that muscle and the semimembranosus (Figs. 268, 288, 580). It has two heads of 
origin. 

Origin. — (1) The transverse processes of the first and second coccygeal ver- 
tebrae, the coccygeal fascia, and the intermuscular septum between this muscle and 
the biceps femoris; (2) the ventral surface of the tuber ischii. 

Insertion. — (1) The tibial crest; (2) the crural fascia and the tuber calcis. 

Action. — To extend the hip and hock joints, acting wdth the biceps and semi- 
membranosus in propulsion of the trunk, rearing, etc.; also to flex the stifle and ro- 
tate the leg inward.^ 

Structure. — The long or vertebral head is small at its origin, but becomes larger 
by the accession of fibers arising on the intermuscular septum. Below the tuber 
ischii it unites mth the short head, which arises partly by fleshy fibers, partly by a 
common tendon with the biceps. The muscle then passes downward on the back 
of the thigh, and terminates on a wide tendon on the medial surface of the proximal 
third of the leg. A distinct band passes forward to be inserted on the tibial crest 
(a bursa lying between the tendon and the tibia), part fuses with the fascia of the 
leg, while the remainder joins the biceps tendon and concurs in the formation of the 
tendinous band, which, as before described, terminates on the tuber calcis (Fig. 
583) . A bursa may occur under the long head where it passes over the tuber ischii. 

1 It should be remembered, however, that the stifle can be flexed only when the hock is also 
flexed and vice versa. 



324 



FASCIiE AND MUSCLES OF THE HORSE 



Relations. — Laterally, the skin and fascia, the biceps, and the medial head 
of the gastrocnemius; medially, the coccygeal fascia, the sacro-sciatic ligament, 
the semimembranosus; anteriorly, the biceps femoris, branches of the femoral 
artery, and the great sciatic nerve. 

Blood-supply. — Posterior gluteal, obturator, and posterior femoral arteries. 

Nerve supply. — Posterior gluteal and great sciatic nerves. 



Origin of obhquus ab- 
dominis internus 
Inguinal ligament (part 
removed) 

Iliacus 

Tensor facice latoe -- 

Rectus femoris 




Vastus medialis ^B* 

Sartorius 

Gracilis 



Patella 



Medial patellar ligament _ 
Tendon of sartorius ^ 

Tendon of gracilL 



Fascia cruris 



Fig. 287. — Muscles of Pelvis and Thigh of Young Horse, Right Side; Medial View. 
1, Psoas minor, and 1', its insertion; 2, psoas major; 3, 3', h3ads of obturator internus; 4, sacro-coccygeus ven- 
tralis; 5, coccygeus; 6, retractor ani (cut) ; 7, sacro-sciatic ligament; 8, lesser sciatic foramen; 9, semimembranosus; 
10, lumbo-sacral plexus; 11, obturator nerve and vessels (cut); 12, femoral vessels (origin); 13, pubis; 14, prepubic 
tendon; 15, deep inguinal lymph glands; 16, opening for external pudic vein. Vertebrae are numbered by regions. 



7. Semimembranosus^ (Figs. 276, 287, 288, 576).— This very large, three- 
sided muscle lies on the medial surface of the preceding muscle and the gastroc- 
nemius, and has two heads of origin. 

Origin. — (1) The posterior border of the sacro-sciatic ligament; (2) the ventral 
surface of the tuber ischii. 

1 This muscle was incorrectly designated the adductor magnus by Percivall and Strange- 
ways. Its name, however, is not at all descriptive of its structure in the domesticated animals. 



THE MEDIAL MUSCLES OF THE THIGH 325 

Insertion. — The medial epicondyle of the femur, behind the collateral ligament. 

Action. — To extend the hip joint and to adduct the limb. 

Structure.— The long head, small and pointed above, extends toward the root 
of the tail, fusing with the sacro-sciatic ligament. Passing downward, it becomes 
larger and covers in part the posterior aspect of the tuber ischii. A bursa may be 
found here. Below this it joins the short head, which is larger. The large belly 
so formed passes downward and forward, covered in great part by the gracilis, and 
terminates on a short, flat tendon of insertion at the distal end of the femur. 

Relations. — The upper part of the muscle concurs with the sacro-sciatic liga- 
ment in forming the lateral boundary of the pelvic outlet. It is related posteriorly 
and laterally to the skin and fascia and the semitendinosus ; medially, to the anus 
and its muscles, the vulva in the female, and the internal pudic artery and nerve 
(Figs. 577, 578). Below the pelvis the chief relations are: laterally, the semi- 
tencUnosus, biceps, and gastrocnemius, branches of the obturator, femoral, and 
posterior femoral arteries, and the great sciatic nerve and its chief branches; 
medially, the crus penis and ischio-cavernosus muscle (in the male) and the 
gracilis; in front, the adductor and the femoral vessels; behind, the skin and fascia. 

Blood-supphj. — Obturator and femoral arteries. 

Nerve-supply. — Great sciatic nerve. 



m. THE MEDIAL MUSCLES OF THE THIGH 

The muscles of this group are arranged in three layers. 

First Layer 

1. Sartorius (Figs. 287, 288, 576). — This long and rather narrow muscle is the 
most anterior one of the first layer. It extends from the posterior part of the sub- 
lumbar region to the lower and medial part of the stifle, and is directed downward 
and somewhat backward. 

Origin. — The iliac fascia and the tendon of the psoas minor. 

Insertion. — The medial patellar ligament and the tuberosity of the tibia. 

Action. — To flex the hip joint and adduct the limb. 

Structure. — The muscle is thin at its origin, but becomes thicker, narrower, 
and three sided distally. It terminates near the stifle joint on an aponeurosis which 
blends with that of the gracilis and with the fascia of the leg. 

Relations. — Medially, the inguinal ligament, the abdominal muscles, the skin 
and fascia; laterally, the ilio-psoas, quadriceps femoris, and femoral nerve. It 
forms the anterior boundary of the femoral canal, in which the femoral artery and 
vein and the deep inguinal lymph glands are situated (Fig. 576). 

Blood-supply.- — Femoral artery. 

Nerve-supply. — Saphenous nerve. 

A rare variation is the existence of a small accessory head which arises from the anterior 
border of the pubis or from the prepubic tendon and joins the normal muscle near the middle of 
the thigh. 

2. Gracilis (Figs. 276, 287, 575). — This is a wide, quadrilateral muscle, 
which is situated behind the sartorius, and covers the greater part of the medial 
surface of the thigh. 

Origin. — The middle third of the pelvic symphysis, the prepubic tendon and 
accessory ligament, and the ventral surface of the pubis behind the prepubic ten- 
don. 

Insertion. — The medial patellar hgament, the medial surface of the tibia in 
front of the medial femoro-tibial ligament, and the crural fascia. 

Action. — To adduct the limb. 

Structure. — The muscle arises by a strong tendon, chiefly in common with the 



326 FASCIA AND MUSCLES OF THE HORSE 

opposite muscle. Its direct attachment to the ventral surface of the pelvis is not 
so extensive as a superficial inspection would suggest. The tendon of origin pre- 
sents anteriorly a foramen for the passage of the external pudic vein. The belly- 
is composed of parallel bundles, and is marked by a superficial furrow which, how- 
ever, does not indicate a muscular division. It terminates on the medial surface 
of the stifle on a thin wide tendon which blends in front with that of the sartorius, 
below with the crural fascia. 

Relations. — Superficially, the skin and fascia, the penis or mammary gland, 
and the saphenous vessels and nerve; deeply, the pectineus, adductor, semimem- 
branosus and semitendinosus, and, at the middle of the femur, the femoral vessels; 
anteriorly, the sartorius. In the proximal third of the thigh the sartorius and gracili 
are separated by a triangular interval (femoral triangle), in which lie the deep in- 
guinal lymph glands and the femoral vessels. 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Obturator nerve. 

Second Layer 

1. Pectineus (Figs. 276, 288, 576). — This muscle is fusiform and extends from 
the anterior border of the pubis to the middle of the medial border of the femur. 

Origin. — The prepubic tendon, the accessory ligament, and the anterior border 
of the pubis. 

Insertion. — The middle of the medial border of the femur, near the nutrient 
foramen. 

Action. — To adduct the limb and flex the hip joint. 

Structure. — The belly is cylindrical and contains little fibrous tissue. Its 
origin is perforated by the accessory ligament — from which many fibers arise — 
and is thus divided into two unequal parts. The large upper part arises largely 
from the prepubic tendon — only a small part gaining direct attachment to the 
pubis. The small lower part does not reach the bone. The insertion is pointed 
and tendinous. 

Relations. — Medially, the gracilis; laterally, the femur, the vastus medialis, 
the terminal part of the psoas major and iliacus, and the deep femoral artery; an- 
teriorly, the sartorius, the femoral vessels, the saphenous nerve, and the deep in- 
guinal lymph glands; posteriorly, the adductor and obturator externus, and the 
obturator nerve (anterior division). 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Obturator nerve. 

The femoral canal is exposed in the dissection of the preceding muscles (Figs. 
288, 290). It is bounded anteriorly by the sartorius, posteriorly by the pectineus, 
and laterally by the ilio-psoas and vastus medialis. Its medial wall is formed by 
the femoral fascia and the gracilis. Its upper or abdominal opening, the femoral 
ring (Lacuna vasorum), lies behind the medial part of the internal inguinal ring and 
is bounded anteriorly by the inguinal ligament, posteriorly by the anterior border 
of the pubis, and laterally by the tendon of the psoas minor. The canal termi- 
nates below at the insertion of the pectineus. It contains the deep inguinal lymph 
glands, the femoral artery and vein, and the saphenous nerve. 

2. Adductofi (Figs. 276, 288, 576).— This fleshy, prismatic muscle lies behind 
the pectineus and vastus medialis. It extends downward and forward from the 
ventral surface of the pelvis to the medial epicondyle of the femur. 

Origin. — The ventral surface of the pubis and ischium and the tendon of ori- 
gin of the gracilis. 

1 It has been customary to describe two adductors — a parvus or brevis, and a longus or 
magnus. This division is partly artificial, and has been abandoned in the new nomenclature — 
a return to the views of Bourgelat and Girard. 



THE MEDIAL MUSCLES OF THE THIGH 



327 



Insertion. — (1) The posterior surface of the femur from the level of the third 
trochanter to the groove for the femoral vessels; (2) the medial epicondyle of the 
femur and the medial ligament of the stifle joint. 

Action. — To adduct the limb and extend the hip joint. It also rotates the fe- 
mur inward. 

Structure. — It is almost entirely fleshy, and is composed of parallel bundles 



Psoas minor 
Sartorius (origin) 

Iliopsoas 

Tensor JascivE latce 

Rectus fetnoris 




Semimembranosus 
Adductor 



Vastus medialis 



Patella 



Middle patellar ligament ^^ 
Medial patellar ligament --'^^^ 
Tendon of sartorius 

Tendon of gracilis 



Tibial insertion of semitendinosus 



Semitendinosus 



Medial head of gastroc- 
nemius 
Tibial nerve 



Fig. 288. — iMuscles of Pelvis and Thigh of Horse, Right Side; Medial View. 
Figure represents deeper dissection of specimen shown in preceding figure. 
1, Tendon of insertion of psoas minor; 2, lumbo-sacral plexus; 3, 3', heads of obturator internus; 4, sacro-coccy- 
geus ventralis; 5, coccygeus; C, retractor ani (origin) ; 7, sacro-sciatic hgament; 8, lesser sciatic foramen; 9, femoral 
nerve; 10, femoral vessels; 11, 11, pectineus; 12, accessory ligament; 13, external pudic vein; 14, pubis; 15, femoro- 
patellar joint capsule; 16, distal end of femur; 17, medial meniscus; 18, medial ligament of stifle joint; 19, medial 
femoro-patellar ligament. 



united rather loosely. It is usually possible to separate from the principal mass a 
small anterior short part/ which is inserted into the femur behind the pectineus. 
The principal mass- is perforated just below the insertion of the pectineus by an 
opening for the femoral vessels (hiatus adductorius), and is thus divided into two 

^ This has been termed by various authors the adductor parvus or brevis. 
2 Termed by various authors the adductor magnus or longus. 



328 FASCIA AND MUSCLES OF THE HORSE 

branches. The lateral branch is inserted into the back of the femur with the short 
portion, while the medial branch is attached to the medial epicondyle and col- 
lateral ligament. There is often a superficial slip which ends partly on the femoro- 
patellar joint capsule and may reach the accessory cartilage or medial ligament of 
the patella. Some fibers pass under the collateral ligament and end on the tendon 
of the semimembranosus. 

Relations. — Medially, the gracilis, and branches of the femoral artery and 
of the obturator nerve; laterally, the femur, the obturator extern us, quadratus 
femoris, biceps femoris, and the femoral, deep femoral, and obturator arteries; an- 
teriorly, the pectineus, vastus medialis, and a large branch of the obturator nerve; 
posteriorly, the semimembranosus and the great sciatic nerve. 

Blood-supply. — Femoral, deep femoral, and obturator arteries. 

Nerve-supply. — Obturator nerve. 

3. Semimembranosus. — Described on p. 324. 

Third Layer 

1. Quadratus femoris.^ — This is a narrow, three-sided muscle, which lies under 
cover of the upper part of the adductor (Fig. 581). 

Origin. — The ventral surface of the ischium, just in front of the semimembrano- 
sus. 

Insertion. — An oblique line on the posterior surface of the femur, near the 
lower part of the trochanter minor. 

Action. — To extend the hip joint and to adduct the thigh. 

Structure. — It is composed of parallel bundles of fibers directed do\\Tiward, 
forward, and outward. 

Relations. — Postero-medially, the adductor, semimembranosus, and the ob- 
turator vessels; antero-laterally, the obturator externus and biceps femoris, the 
deep femoral vessels, and the great sciatic nerve. 

Blood-supply. — Deep femoral and obturator arteries. 

Nerve-supply.- — Great sciatic nerve. 

2. Obturator externus (Fig. 581). — This is a pyramidal muscle which extends 
across the back of the hip joint from the ventral surface of the pelvis around the 
obturator foramen to the trochanteric fossa. 

Origin. — The ventral surface of the pubis and ischium, and the margin of the 
obturator foramen. 

Insertion. — The trochanteric fossa. 

Action. — To adduct the thigh and to rotate it outward. 

Structure. — It is almost entirely fleshy, the muscle-bundles being rather loosely 
connected. The insertion is pointed, flattened, and partly tendinous. The origin 
is perforated by the obturator vessels and nerve. 

Relations. — Medially, the adductor and quadratus femoris and the deep 
femoral vessels; laterally, the gemellus, the tendon of the obturator internus, the 
biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus, 
and the external pudic vein. 

Blood-supply. — Deep femoral and obturator arteries. 

Nerve-supply. — Obturator nerve. 

3. Obturator internus (Fig. 288). — This arises within the pelvic cavity by two 
heads, the tendon emerging through the lesser sciatic foramen. 

Origin. — (1) The pelvic surface of the pubis and ischium around the obturator 
foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum. 
Insertion. — The trochanteric fossa. 
Action. — To rotate the femur outward. 

1 Also known as the ischio-femoralis. 



ANTERIOR MUSCLES OF THE THIGH 329 

Structure. — The ischio-pubic head Ues on the pelvic floor and covers the ob- 
turator foramen. It is thin and fan-shaped. The iliac head extends along the 
lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both 
terminate on a flat tendon which passes outward through the lesser sciatic fora- 
men to be inserted into the trochanteric fossa. The tendon furnishes insertion to 
fibers of the gemeflus. A synovial bursa facilitates the play of the tendon over the 
lateral border of the ischium.^ 

Relations. — The pelvic surface is covered by the pelvic fascia and in part by 
the peritoneum. The obturator vessels and nerve lie between the two heads, and 
the internal pudic vessels and nerve lie along the dorsal edge of the iliac head. The 
tendon is crossed by the great sciatic nerve. 

Blood-supply. — Obturator and internal pudic arteries. 

Nerve-supply. — Great sciatic nerve. 

4. Gemellus- (Fig. 580).— This is a thin, triangular muscle, which extends 
from the lateral border of the ischium to the trochanteric fossa and ridge. 

Origin. — The lateral border of the ischium near the ischiatic spine. 

Insertion. — The trochanteric fossa and ridge. 

Action. — To rotate the femur outward. 

Structure. — The thin tendon of origin is attached to a line on the lateral border 
of the ischium, which begins just below the posterior end of the superior ischiatic 
spine. Many superficial fibers are inserted into the tendon of the obturator in- 
ternus. 

Relations. — Superficially, the biceps femoris, the tendon of the obturator in- 
ternus, the gluteus medius, and the great sciatic nerve; deeply, the obturator ex- 
ternus and the hip joint. 

Blood-supply. — Obturator artery. 

Nerve-supply. — Great sciatic nerve. 



IV. ANTERIOR MUSCLES OF THE THIGH 

This group consists of the sartorius, quadriceps femoris, and capsularis. 

1. Sartorius. — This is described on p. 325. 

2. Quadriceps femoris (Figs. 268, 289, 291). — This constitutes the large mus- 
cular mass which covers the front and sides of the femur. It has four heads, one 
of which, the rectus, arises from the ilium; the other three arise from the femur. 
All are inserted into the patella. 

(1) Rectus femoris. — This is fusiform and rounded. It arises by two tendons. 

Origin. — Two depressions on the shaft of the ilium above and in front of the 
acetabulum. 

Insertion. — The base and anterior surface of the patella. 

Action. — To extend the stifle joint and to flex the hip joint. 

Structure. — It has two short strong tendons of origin; beneath the lateral one 
is a bursa. The belly is rounded and rests in a groove formed by the other portions 
of the quadriceps. Its sides are covered by a strong tendinous layer which fur- 

1 The iliac head has been described as a separate muscle, and termed the piriformis. This 
does not seem desirable, especially since it is probable that the homologue of the piriformis of 
man is that portion of the middle gluteus which is inserted into the trochanteric ridge. 

^ The name is based on the arrangement in man, in whom the muscle usually consists of two 
fascicuh forming a groove between them for the tendon of the obturator internus. In the horse 
it is usually undivided at its origin, but toward the insertion the upper part is separated from the 
rest of the muscle or is readily isolated. The muscle is subject to much variation in size. When 
well developed, the insertion extends from the proximal end of the trochanteric fossa to a point 
just above the femoral attachment of the biceps femoris; in such cases the upper part, which 
occupies the space behind the hip joint between the gluteus profundus and obturator externus, 
is much thicker than the remainder, which covers the latter muscle. The gemellus may be re- 
garded as the extrapelvic head of the obturator internus (Gegenbaur). 



330 



FASCIA AND MUSCLES OF THE HORSE 



nishes insertion to fibers of the vasti. The tendon of insertion is formed by the 
union of these tendinous layers on the lower part of the muscle. The lower portion 
of the muscle is pennate, the fibers on either side converging on the tendon at an 
acute angle. 

Relations. — Medially, the iliacus, sartorius, and vastus medialis; laterally, 
the tensor fasciae latae, glutei, and vastus lateralis; posteriorly, the hip joint and 
the vastus intermedins; anteriorly, the fascia lata and the skin. The anterior 
femoral artery and branches of the femoral nerve descend into the interspace be- 



\' Shaft of ilium 
y Medial tendon of origin 
-^ of rectus femoris 



Gluteus profundus 

Vastus lateralis 
Rectus femoris 




Prepubic tendon (ir, 
median section) 
Obturator externus 

Iliopsoas {insertion) 
Adductor 

Vastus medialis 



Medial femoro-tibial ligament 
Medial vieniscus 



Lateral patellar ligament 



Tuberosity of tibia 



Fig. 289. — Muscles of Right Thigh of Horse, Deep Dissection. The Preparation is Viewed fro.m in Front 

AND Somewhat Medially. 

1, Accessory ligament of hip joint; 2, transverse ligament of same; 3, head of femur; 4, patella; 5, trochlea of femur; 

6, 7, middle and medial patellar ligaments. 



tween the upper part of the rectus and the vastus medialis; similarly, the iliaco- 
femoral artery dips in between the rectus femoris and vastus lateralis. 

Blood-supply. — Femoral and iliaco-femoral arteries. 

Nerve-supply. — Femoral nerve. 

(2) Vastus lateralis. — This lies on the lateral surface of the femur, extending 
from the great trochanter to the patella. It is wide in its middle, smaller at each end. 

Origin. — The lateral border and surface of the femur, from the trochanter 
major to the supracondyloid fossa. 



ANTERIOR MUSCLES OF THE THIGH 



331 



Insertion.— (1) The lateral part of the anterior surface of the patella; (2) the 
tendon of the rectus femoris. 

Action. — To extend the stifle joint. . 

Structure.— The fibers are directed downward and forward, many being in- 
serted into the tendinous sheet which covers the side of the rectus. A bursa is 
usually present between the distal end and the patella. 

i^e/a«ions.— Laterally, the fascia lata and skin, tensor fascia lata, superficial 



Fold of flank 
Tensor fasci(r latcB 



Vastus lateralis 

]■ T v^^^^^- oV Tl^^^^^^x ^ Vastus intermedium 

Vastus mediahs * ^i— i ■■ ow »^^^^^^^ ^ 

Sartorius 
Saphenous vein —-.^^jM 
Saphenous nerve ''^ 
Femoral artery 
Gracilis 



Peroneal nerve 
Tibial nerve 



SemitendinosH 



Fig. 290.— Cross-section of Middle of Right Thigh of Horse. 

gluteus, and biceps femoris; medially, the femur and femoro-patellar joint capsule, 
the rectus femoris, vastus intermedins, and the iliaco-femoral artery. 

Blood-supply.— llisico-iemoral artery. 

Nerve-supply.— Femoral nerve. j r „ :„ „ oir,. 

(3) Vastus mediaUs.— This resembles the preceding muscle, and lies m a sim- 
ilar position on the medial side of the femur. , ^ ^u r +„i +i.;rri 

Onom.-The medial surface of the femur, from the neck to the distal third. 

Insertion.-{l) The medial border of the patella and its cartilage, and the 




332 



FASCIA AND MUSCLES OF THE HORSE 



proximal part of the medial patellar ligament. (2) The tendon of the rectus 
femoris. 

Action. — To extend the stifle joint. 

Structure. — This is very similar to that of the vastus lateralis. It is, how- 
ever, more difficult to separate from the intermedins, because many fibers of the 
latter arise on the tendinous sheet which covers the contact surface- of the medial 



Shaft of ilium 



Gluteus profundus 



Trochanter major 
{anterior part) 



Vastus lateralis 
Vastus intermedium 

Rectus femoris 

Vastus lateralis 

Biceps femoris 

Patella 



Lateral femoro-tibial 
ligament 
Lateral patellar ligament 



Prepubic tendon 
Obturator externum 




Vastus medialis 



Adductor 



r Medial femoro-tibial ligament 
Medial meniscus 
Middle patellar ligament 

Tuberosity of tibia 



Fig. 291. — Mi s. i.ks <>f Right Thigh of Horse; Deep Dissection. 
The preparation is viewed from tiie front and somewhat medially. Most of rectus femoris and vastus lateralis 
has been removed. 1, Stump of origin of rectus femoris; 2, capsularis; 3, accessory ligament; 4, cotyloid ligament; 
5, head of femur; 6, trochlea of femur. 



vastus. Its insertion into the patella is chiefly by means of a broad, strong tendon. 
From the deep face fleshy fibers are inserted also into the femoro-patellar joint cap- 
sule. 

Relations. — Medially, the skin and fascia, the iliacus, sartorius, pectineus, and 
adductor, the femoral vessels, and saphenous nerve; laterally, the femur, femoro- 
patellar joint capsule, rectus femoris, and vastus intermedins, the anterior femoral 
artery, and branches of the femoral nerve. 



THE MUSCLES OF THE LEG AND FOOT 333 

Blood-supply. — Femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

(4) Vastus intermedius. — This muscle is deeply situated on the anterior face 
of the femur, and is entirely covered by the preceding heads. 

Origin.— {1) The anterior surface of the femur, from the proximal to the distal 
fourth; (2) the tendinous covering of the vastus medialis. 

Insertion. — (1) The base of the patella; (2) the femoro-patellar joint capsule. 

Action. — (1) To extend the stifle joint; (2) to tense (raise) the femoro-patellar 
capsule during extension of the joint. 

Structure.- — The muscle is usually quite difficult to isolate from the other vasti, 
so that many since Glinther have declared it an artefact.^ It is entirely fleshy, and 
is small at its proximal end, but when traced downward increases in bulk by the 
accession of fibers arising on the femur and the tendinous covering of the vastus 
medialis. The terminal part is intimately adherent to the femoro-patellar joint 
capsule, where the latter bulges above the level of the patella. 

Relations. — Medially, the vastus medialis; laterally, the vastus lateralis; 
anteriorly, the rectus ; posteriorly, the femur and femoro-patellar capsule. 

Blood-supply. — Iliaco-femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

The patellar ligaments are to be regarded as tendons of the quadriceps which communicate 
the action of the latter to the tibia, the patella being intercalated as a sesamoid bone. 

3. Capsularis (Fig. 291). ^ — This is a small fusiform muscle (scarcely as large 
as one's finger), which arises by a thin tendon on the ilium immediately above the 
outer tendon of the rectus femoris. Its delicate tendon of insertion dips in between 
the vastus intermedius and lateralis and is attached to the proximal third of the 
anterior surface of the femur. It passes over the outer side of the hip joint, to the 
capsule of which some fibers are attached. Sometimes the muscle has two dis- 
tinct heads, in which case the additional head arises between the two tendons of 
origin of the rectus femoris. Its action may be to raise the capsule during flexion 
of the joint. It is related laterally to the gluteus profundus and vastus lateralis, 
medially to the rectus femoris and vastus intermedius and the hip joint. 



V. THE MUSCLES OF THE LEG AND FOOT 
The muscles of this region cover almost all of the tibia except its medial face, 
which is largely subcutaneous. As in the forearm, the muscles fall into two groups, 
a dorso-lateral and a plantar. The muscles of the first group are extensors of the 
digit and flexors of the hock, those of the second have the opposite action. 

A. Dorso-lateral Group 

1. Long digital extensor (M. extensor digitalis longus).^ — This muscle is sit- 
uated superficially on the dorso-lateral aspect of the leg, and is provided with a long 
tendon which passes dowTi over the front of the tarsus, metatarsus, and digit. 

Origin.— The extensor fossa of the femur. 

Insertion.— {1) The extensor process of the third phalanx; (2) the dorsal sur- 
face of the proximal extremities of the first and second phalanges. 

Action.- — To extend the digit and flex the hock. It also assists in fixing the 
stifle joint. 

^ While it is true that the separation of the intermedius is never entirely a natural one in the 
horse, it varies in individual cases, and is usually clear on cross-sections. In some subjects it is 
possible to separate another slip which may represent the articularis genu of man. 

^ Also known as the rectus parvus. 

3 Also termed the extensor pedis or the anterior extensor of the phalanges. 



334 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — The origin is by means of a strong tendon in common with the 
peroneus tertius, on which also many fibers arise. The common tendon passes 
downward in the groove between the lateral condyle and the tuberosity of the tibia, 

f 



Patella - — 



\ 



Crest of tibia 

Long digital extensor 
Lateral digital extensor ■ 



Proximal annular ligament - 
Lateral malleolus 



Middle annular ligament 

Distal annular ligament 

Tendon of long extensor 

Tendon of lateral extensor 



Branch of suspensory ligament to 
extensor tendon 



~ Gastrocnemius, lateral head 
Soleus 
\,\ Tendon of gastrocnemius 

- Tarsal tendon of biceps femoris 

- Deep flexor 



Superficial 
flexor tendon 




Superficial flexor 
teridon 



Deep flexor tendon 



Suspensory 
ligament 



Fig. 292. — Muscles of Lower Part of Thigh, Leg, and Foot of Horse; Lateral View. 

</, Faacia lata; g, g', g", biceps femoris; r, semitendinosus; .27', lateral condyle of tibia. The extensor brevis is visible 

in the angle between the long and lateral extensor tendons, but by an oversight it is not marked. (After EUen- 

berger-Baum, Anat. fiir Ktinstler.) 



where a pouch from the femoro-tibial capsule descends three or four inches (ca. 
7.5 to 10 cm.) beneath the tendon. The belly is fusiform and somewhat flattened. 
The long tendon of insertion begins in the belly about its middle, and is clear of the 



THE MUSCLES OF THE LEG AND FOOT 335 

fleshy part near the tarsus. It passes downward over the front of the hock, bound 
down by the three annular ligaments already described (see tarsal fascia), and en- 
veloped by a sjmovial sheath which begins a little above the level of the lateral 
malleolus, and extends nearly to the junction with the lateral extensor tendon. 
This union occurs usually about a hand's breadth below the tarsus. In the angle 
of union the extensor brevis also joins the principal tendon. Beyond this point 
the arrangement is the same as in the fore limb. 

Relations. — Superficially, the skin and fascia; deeply, the femoro-tibial joint, 
peroneus tertius, and tibialis anterior; behind, the lateral extensor and the super- 
ficial and deep peroneal nerves. In front of the tarsus the anterior tibial artery 
crosses the deep face of the tendon (Fig. 585). 

Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 

2. Lateral digital extensor (M. extensor digitalis lateralis).^ — This muscle lies 
on the lateral surface of the leg, behind the preceding one. 

Origin. — The lateral ligament of the stifle joint, the fibula, the lateral border 
of the tibia, and the interosseous ligament. 

Insertion.— The tendon of the long extensor, about a third of the way down 
the metatarsus. 

Action. — To assist the long extensor. 

Structure. — The belly is fusiform, flattened, and pennate. The tendon runs 
through the entire length of the belly and becomes free from it at the distal fourth 
of the tibia. It descends through the groove on the lateral malleolus, bound down 
by an annular ligament, and, inclining forward, blends (usually) with the tendon 
of the long extensor. It is provided with a synovial sheath, which begins about 
an inch (ca. 2 to 3 cm.) above the lateral malleolus and ends about one and one- 
half inches (ca. 3 to 4 cm.) above the junction. Sometimes the fusion does not 
occur; the tendon then descends alongside of that of the long extensor, and is in- 
serted into the first phalanx like the corresponding muscle of the thoracic limb. 

Relations.— Laierally, the skin and fascia and the superficial peroneal nerve; 
medially, the tibia and fibula; anteriorly, the intermuscular septum, the long 
extensor, and the tibialis anterior; posteriorly, the deep digital flexor and the soleus. 

Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 

3. Peroneus tertius (Tendo f emoro-metatarseus) .^ — This consists in the horse 
of a strong tendon which lies between the long extensor and the tibialis anterior. 

Origin. — The extensor fossa (between the lateral condyle and the trochlea 
of the femur), in common with the long extensor. 

Insertion. — (1) The proximal extremity of the large (third) metatarsal bone 
and the third tarsal bone ; (2) the fibular and fourth tarsal bones. 

Action.- — Mechanically to flex the hock when the stifle joint is flexed. 

Structure. — It is entirely tendinous. The proximal end and the underlying 
prolongation of the synovial membrane of the femoro-tibial joint have been men- 
tioned in the description of the long extensor. The superficial face gives origin 
to fibers of the long extensor in the upper part of the leg, and the deep face is fused 
with the tibialis anterior except at either end of the region. At the distal end of the 
tibia the tendon is perforated for the emergence of the tendon of the tibialis anterior 
and divides into two branches. The anterior branch is attached to the third tarsal 
and third metatarsal bones, while the lateral one curves outward, bifurcates, and 

^ Also known as the peroneus or the lateral extensor of the phalanges. Lesbre considers it 
to be the homologue of the peroneus brevis of man and other pentadactyls. 

2 It seems inadvisable to retain the old term, tendinous part of the flexor metatarsi, since it 
is inapphcable to other domesticated animals in which the muscle is well developed (e. g., pig). 
Schmaltz uses the term tendo femoro-tarseus, and Varaldi and Lesbre designate it the femoro- 
metatarsal cord. The name peroneus anterior has also been proposed. 



336 



FASCIA AND MUSCLES OF THE HORSE 



is inserted into the fibular and fourth tarsal bones. The lateral tendon gives off 
a branch which forms a loop around the long extensor tendon (Fig. 293). 

Relations. — Superficially, the long extensor; deeply, the tibialis anterior. The 
anterior tibial vessels cross the deep face of the outer branch. 



Lateral ridge of trochlea of femur 
Lateral femoro-tibial ligament 

Lateral meniscus 
Lateral condyle of tibia "^ 

Long extensor (stump) 

Peroneus tertius 
Tibialis anterior 
Lateral extensor 



Tendinous loop 
Extensor brevis 



Tendon of lateral extensor 
Tendon of long extensor 




Medial ridge of trochlea of femur 



Medial meniscus 

Medial femoro-tibial ligament 



Tendon of long extensor 
Annular ligament 
Peroneus tertius 

Medial tendon of tibialis anterior 

Anterior tendon of tibialis anterior 
Anterior tendon of peroneus tertius 

Annular ligament 
Ml. Ill 



Fig. 293. — Muscles of Right Leg of Horse; Front View. 
The greater part of the long extensor has been removed. \, 2, 3, Stumps of patellar ligaments; 4, tuberosity of tibia. 



4. Tibialis anterior.^ — This lies on the dorso-lateral face of the tibia; it is wide 
and flattened above, pointed below. 

Origin. — The lateral condyle and border of the tibia and a small area on the 
lateral surface of the tuberosity. 

^ This is also known as the muscular part of the flexor metatarsi. 



THE MUSCLES OF THE LEG AND FOOT 



337 



Insertion. — (1) The ridge on the front of the proximal end of the large meta- 
tarsal bone; (2) the first and second tarsal bones. 

Action. — To flex the hock joint. 

Structure. — The origin is fleshy, and forms a groove in which lie the common 
tendon of the long extensor and peroneus tertius and a synovial pouch which de- 
scends from the femoro-tibial joint. Many superficial fibers arise from the deep 
fascia at the proximal part of the leg and thus from the tibial crest. Passing down- 
ward on the tibia, the belly is united by tendinous and fleshy fibers with the per- 
oneus tertius, and terminates close to the tarsus in a point on the tendon of inser- 




FiG. 294. — Injected Synovial Sheaths and Burs.*; 

OF Tarsal Region of Horse; Medial View. 

a, Synovial sheath of peroneus tertius and tibialis 
anterior; h, bursa under medial (cunean) tendon of 
tibiahs anterior; c, synovial sheath of flexor longus; 
d, tarsal sheath of deep flexor; e, e', bursa under 
superficial flexor tendon; /, /', tibio-tarsal joint capsule; 
1, long extensor; 2, tibialis anterior; 2', medial (cun- 
ean) tendon of 2; 3, flexor longus; 4, deep digital 
flexor; o, superficial flexor tendon; 6, gastrocnemius 
tendon; 7, tibia; S, tarsus; 9, tuber calcis; 10, large 
metatarsal bone; 11, medial small metatarsal bone; 
12, 12', fascial bands. (After Ellenberger, in Leisering's 
Atlas.) 




Fig. 295. — Injected Synovial Sheaths and Burs« 
OF Tarsal Region of Horse; Lateral View. 
o, Synovial sheath of long digital extensor; 6, 
synovial sheath of lateral digital extensor; c, c', bursa 
under superficial flexor tendon; d, capsule of hock joint; 
1. long extensor; 2, lateral extensor; 3, 3, 3, annular 
ligaments; 4, deep digital flexor; 5, tendon of gastroc- 
nemius; 6, superficial flexor tendon; 7, tibia; 8, tarsus; 
9, tuber calcis; 10, metatarsus. (After Ellenberger, 
in Leisering's Atlas.) 



tion. The latter emerges between the branches of the peroneus tertius and bi- 
furcates, the anterior branch being inserted into the large metatarsal bone, the 
medial one into the first tarsal bone. The tendon is provided with a s3aiovial sheath 
at its emergence, and a bursa is interposed between the medial branch and the 
medial ligament of the hock.^ 

Relations. — Superficially, the long and lateral extensors, the peroneus tertius, 
and the deep peroneal nerve; deeply, the tibia, the deep flexor, and the anterior 
tibial vessels. 

^ In surgical works the medial branch is termed the cunean tendon; it is sometimes resected 
for the relief of bone spavin. 
22 



338 



FASCIAE AND MUSCLES OF THE HORSE 



Blood-supply. 
Nerve-supply. 



-Anterior tibial artery 
-Peroneal nerve. 



third of the femur to the point of the hock. 



Sluifl of fcmu 



Medial head of 
gastroc7ierniits 



Fascial hand 



Latind head of 
(jdst roc tic till us 



B. Plantar Group 
1. Gastrocnemius (Fi^s. 268, 292, 296).^This muscle extends from the distal 

It arises by two heads. 

Origin. — (1) Lateral head, 
from the lateral supracondj^- 
loid crest (margin of the supra- 
condyloid fossa); (2) medial 
head, from the medial supra- 
condyloid crest. 

Insertion. — The posterior 
part of the tuber calcis. 

Action. — To extend the 
hock and to flex the stifle 
joint; these two actions, how- 
ever, cannot occur simulta- 
neously. 

Structure. — The two bel- 
lies are thick, fusiform, and 
somewhat flattened. They 
are covered by a strong apo- 
neurosis and contain tendinous 
intersections. They terminate 
toward the middle of the leg 
on a common tendon, which at 
first lies posterior to that of the 
superficial flexor, but, by a 
twist in both, comes to lie in 
front of the latter. The deep 
fascia blends with the tendon 
throughout its length, and the 
soleus muscle is inserted into 
its anterior edge. A small 
bursa (Bursa tendinis m. gas- 
trocncmii) lies in front of the 
insertion on the tuber calcis, 
and a large bursa (calcanea 
subtendinea) is interposed be- 
tween the two tendons from 
the twist downward to the 
middle of the hock. The super- 
ficial digital flexor lies between 
the two heads and is adherent 
to the lateral one (Fig. 584). 
The term tendo calcaneus or 
tendo Achillis is a convenient 
designation for the aggregated 
tendons in the distal part of the 
leg which are attached to the 
tuber calcis. 
Rclations.—Antoviorly, the stifle joint, the superficial digital flexor, popliteus, 
deep digital flexor, popliteal vessels, and tilnal nerve; medially (above), the semi- 




Soleiis 



Ural cxlcn- 
sor 

■.ror }i<dlucis 

Tendon of (/os- 
trocnctniua 



Snpcrficiid 
Jlcvor tendon 



A 

Tendon of deep flexor 
Fig. 20G. — Musci.es op Right Leo of Horse: PosTEnioR View 



Tendon of long 
digital flexor 



THE MUSCLES OF THE LEG AND FOOT 339 

tenclinosus, semimembranosus, and adductor, (below) the fascia and skin; laterally 
(above), the biceps femoris and peroneal nerve, (below) the fascia and skin. The 
popliteal lymph lands lie on the upper part of the nmscle. 

Blood-supply. — Popliteal artery, 

Nerve-iiupph). — Tibial nerve. 

2. Soleus (Fig. 29G). — This muscle is very small in the horse. It lies along 
the lateral border of the gastrocnemius under the common deep fascia, on the prox- 
imal half of the lateral surface of the leg. 

Origin. — The head of the fibula. 

Insertion. — The tendon of the gastrocnemius, about the middle of the leg. 

Action. — To assist the gastrocnemius. 

Structure. — It is a thin, fleshy band, usually about an inch (ca. 2 to 3 cm.) in 
width, and terminates on a thin tendon which fuses with that of the gastrocnemius.^ 

Relations. — Superficially, the skin, fascia, and peroneal nerve; deeply, the 
lateral extensor and deep flexor. 

Blood-supply. — Posterior tibial artery. 

Nerrc-supply. — Ti])ial nerve. 

3. Superficial digital flexor (M. flexor digitalis pedis superficialis) (Figs. 292, 
296, 297).- — The proximal part of this muscle lies between and under cover of 
the two heads of the gastrocnemius. It consists almost entirely of a strong tendon, 
the belly being very little developed. 

Origin. — The supracondyloid fossa of the femur. 

Insertion. — (1) The tuber calcis; (2) the eminences on each side of the prox- 
imal extremity of the second phalanx, and the distal extremity of the first phalanx 
behind the collateral ligaments of the pastern joint. 

Action. — To flex the digit and extend the hock joint. On account of the ex- 
ceedingly small amount of muscular tissue the action is to be regarded chiefly as a 
mechanical effect which results from the action of other muscles on the stifle joint. 

Structure. — The origin is by means of a strong round tendon which is incom- 
pletely covered with fleshy fibers as far as the upper third of the leg. Here it is 
intimately attached to the gastrocnemius, especially to the lateral head. At the 
distal third of the tibia it winds around the medial surface of the gastrocnemius 
tendon, and then occupies a position behind the latter. At the point of the hock 
it witlens out, forming a sort of cap over the tuber calcis, and detaches on either side 
a strong band which is inserted into the tuber calcis with the tarsal tendons of the 
l)iceps and semitendinosus. It then passes downward over the plantar ligament, 
l)ecomes narrower, and is arranged distally as in the thoracic limb. A large syno- 
vial bursa (B. calcanea su])tcndinea) lies untler the t(»ndon from the distal fourth of 
the tibia to the middle of the tarsus. A subcutaneous bursa (B. calcanea su])cu- 
tanea) is sometimes present on the wide part of the tendon at the point of the hock. 

Relations. — Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the 
femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels; 
medially, the tibial nerve. 

Blood-supply. — Posterior femoral artery. 

Nerve-supply. — Til^ial nerve. 

4. Deep digital flexor (M. flexor digitalis pedis profundus) (Figs. 292, 298).^ — 
The belly of this nuiscle lies on the posterior surface of the tibia, and is divisible 
into three heads, which, however, finally unite on a common tendon of insertion. 

Origin. — (1) The posterior edge of the lateral condyle of the tibia; (2) the 
border of the lateral condyle of the tibia, just behind the facet for the fibula; (3) 

^The soleus is sometimes included with the two heads of the gastrocnemius under the 
name triceps suric. 

2 This is also known as the flexor pedis perforatus or superficial flexor of the phalanges. 
' This muscle is also commonly termed the flexor pedis perforans. 



340 



FASCIA AND MUSCLES OF THE HORSE 



the middle third of the posterior surface and the upper part of the lateral border of 
the tibia, the posterior border of the fibula, and the interosseous ligament. 

Insertion. — The semilunar crest and the adjacent surface of the cartilage of 
the third phalanx. 

Action. — To flex the digit and to extend the hock joint. 

Structure. — (1) The medial head is termed the long digital flexor (M. flexor 
digitalis longus s. flexor accessorius) ; it is easily isolated (Figs. 298, 584). It has a 
fusiform belly, which crosses the leg obliquely and lies in a groove formed by the 

Peroneus tertius 



Long digital 
extensor 



Superficial -peroneal 




Tibialis ayiterior 



Cutaneous branch of 
enous nerve 



Saphenous vessels 
' nerve 



Lateral head of gastroc- 
nemius 

Recurrent tarsal vein 



Flexor digitalis longus 
Vein 

Tibial nerve 
Superficial digital flexor 

Medial head of gastroc- 
nemius 



Fig. 297. — Cross-ssction of Left Leg of Horse. 
The section is cut about the junction of the proximal and middle thirds of the region. 1, .\nterior tibial vessels; 
2, deep peroneal nerve; 3, fibula; 4, posterior tibial vessels; 5, recurrent tibial vessels. A cutaneous branch of the 
saphenous nerve is shown medial to the popliteus, but is not marked. 



other heads and the popliteus. This terminates near the lower third of the tibia 
on a round tendon which descends in a canal in the medial ligament of the hock, 
and joins the common tendon about a third of the way down the metatarsus. In 
its course over the medial surface of the hock the tendon is provided with a S3mo- 
vial sheath which extends from the distal fourth of the tibia to the junction with 
the principal tendon. (2) The superficial head is the tibialis posterior (M. tibialis 
posterior); it is only partially separable from the deep head. It has a flattened 
belly, terminating near the distal third of the tibia on a flat tendon which soon fuses 



THE MUSCLES OF THE LEG AND FOOT 



341 



with the principal tendon. (3) The deep head, the flexor haUucis (M. flexor 
hallucis longus), is much the largest. It lies on the posterior surface of the tibia, 
from the popliteal line outward and downward. The belly contains much tendi- 
nous tissue, and terminates behind the distal end of the tibia on a strong round ten- 



Shaft of femur - 

Medial head of gastrocnemius - 

Medial condyle of femur. 

Medial femoro-tibial ligament-.^ 
Medial meniscus. 
Medial condyle of tibia. 

PopliteuS- 
Flexor digitalis longus_ 



'Lateral head of gastrocnemius 
'Superficial digital flexor 

-Lateral condyle of femur 
Lateral femoro-tibial ligament 
Lateral condyle of tibia 

■ Tibialis posterior 
-Lateral digital extensor 



Flexor hallucis 



Pouch of joint capsule 



Deep flexor tendon . 
Tendon of flexor digitalis longus 



Tendon of gastrocnemius 



Superficial flexor tendon 



Fig. 298.— Muscles of Right Leg or Horse, Deep Dissection; Posterior View. 

don The latter receives the tendon of the tibialis posterior, descends in the tarsal 
groove, bound do^vn by the strong plantar annular ligament (Ligamentum lacmi- 
atum) and enveloped in a synovial sheath, receives the tendon of the medial head 
below the hock, and, a little further down, the so-called check ligament (Caput 
tendinemn). The tendon is partly cartilaginous where it plays over the hbular 



342 



FASCIA AND MUSCLES OF THE HORSE 



tarsal bone. The tarsal sheath (Vagina tarsea) begins two to three inches (ea. 
5 to 7.5 cm.) above the level of the medial malleolus, and extends about one-fourth 
of the way dowTi the metatarsus. The check ligament resembles that of the fore 
limb, except that it is longer and very much weaker; it may be absent.^ The re- 
mainder of the tendon is arranged like that of the thoracic limb. 




Tarsal sheath 



Tibial tarsal bone 



Medial tendon of 
tibialis anterior 



Joint canty 
Dorsal ligament 
Central tarsal bone 
Third tarsal bone 

Mt. in 



Superficial flexor 
tendon- 



Joint capsule {tarso- 
metatarsal ligament) 

Fourth tarsal 
Perforating tarsal vein 
Check ligament 
Suspensory ligament 



Fig. 299. — Sagittal Section of Right Hock of Horse. 
through the middle of the groove of the trochlea of the tibial tarsal bone 



The section 

of cavity of hock joint; 3, thick part of joint capsule over which deep flexor tendon play 
tentaculum). A large vein crosses the upper part of the joint capsule (in front of 1). 



1, 2, Proximal ends 
4, fibular tarsal bone (sus- 



Relations.- — Anteriorly, the tibia and fibula, the popliteus, lateral extensor, 
tibialis anterior, and the tibial vessels; posteriorly, the gastrocnemius, superficial 
flexor, and the tibial nerve; laterally, the fascia, skin, and the soleus; medially, 
the fascia and skin. 



1 This might well be called the tarsal (tendinous) head of the deep flexor. 



MUSCLES OF THE METATARSUS AND DIGIT 343 

Blood-supply. — Posterior tibial artery. 

Nerve-supply. — Tibial nerve. 

5. Popliteus (Fig. 298). — This thick, triangular muscle lies on the posterior 
surface of the tibia above the popliteal line. 

Origin. — A small depression on the lateral epicondjde of the femur, close to 
the articular surface and under the lateral ligament. 

Insertion. — A triangular area on the posterior surface of the tibia, proximal and 
medial to the popliteal line; also the proximal half of the medial border and a 
narrow adjacent part of the medial surface of the tibia. 

Action. — To flex the femoro-tibial joint and to rotate the leg inward. 

Structure. — The strong tendon of origin lies at first under the lateral ligament, 
and curves backward and inward over the lateral condyle of the tibia in contact 
with the lateral meniscus; it is invested by a reflection of the synovial membrane 
of the joint (Fig. 584). The tendon is succeeded by a thick triangular belly, the 
fibers of which are directed medially in the proximal part, but incline downward 
below. 

Relations. — Superficially, the fascia and skin, semitendinosus, gastrocnemius, 
superficial flexor; deeply, the femoro-tibial joint, the tibia, the popliteal vessels 
and their divisions. The saphenous vessels and nerve lie along the medial border 
of the muscle, separated from it, however, by the deep fascia. 

Blood-supply. — Popliteal and posterior tibial arteries. 

Nerve-supply. — Tibial nerve. 

MUSCLES OF THE METATARSUS AND DIGIT 

Extensor digitalis brevis. — This small muscle lies in the angle of union of the 
tendons of the long and lateral extensors of the digit. (Fig. 293.) 

Origin. — The lateral tendon of the peroneus tertius, the middle annular liga- 
ment, and the lateral ligament of the hock. 

Insertion. — The tendon of the long extensor. 

Action. — To assist the long extensor. 

Structure. — It is principally fleshy, having a superficial origin from the annular 
ligament, and a deep one (by a thin tendon) from the lateral tendon of the peroneus 
tertius. The insertion is by a thin tendon. 

Relations. — Superficially, the skin and fascia and the tendons of the long and 
lateral extensors; deeply, the tarsal joint capsule, the great metatarsal artery, and 
the deep peroneal nerve. 

Blood-supply. — Great metatarsal artery. 

Nerve-supply. — Deep peroneal nerve. 

The interossei and lumbricales are arranged like those of the thoracic limb, 
the only noticeable difference being the greater development of the lumbricales in 
the pelvic limb. 



THE MUSCLES OF THE OX 
Muscles of the Face 

The cutaneus is much more developed than in the horse, presenting as a special 
feature the extensive frontalis muscle, which covers the frontal and nasal regions. 

The orbicularis oris does not form a complete ring, the defect being in the 
middle of the upper lip. 

The levator nasolabialis is extensive, thin, and not very distinct from the 



344 



THE MUSCLES OF THE OX 



frontalis; it divides into two layers, between which the levator labii superioris 
proprius and the lateral dilator of the nostril pass. The superficial layer ends in 
the nostril and upper lip, the deep layer on the accessory (lateral) nasal cartilages 
and on the nasal process of the premaxilla. 

The levator labii superioris proprius arises on and before the facial tuberosity 
and terminates by several tendons in the muzzle. It passes between the two layers 
of the preceding muscle, blending in part with the deep layer. 

The zygomaticus is much stronger than in the horse. It arises on the masse- 
teric fascia, and ends chiefly in the upper lip. 




Fig. 300. — Muscles of Head of Ox; Lateral View. 
o, Levator labii superioris proprius; b, levator nasolabialis; c, trapezius; c', brachiocephalicus; d, d', sterno- 
cephalicus; e, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; y', malaris; h, buccinator; i, depressor labii 
inferioris; k, orbicularis oris; to, masseter; n, parotido-auricularis ; o', zygomatico-auricularis and scutulo-auricularis 
superficialis inferior; o", scutulo-auricularis superfioialis superior; o'", scutulo-auricularis superficialis accessorius; 
p, p', soutularis; u, frontalis; w, mylo-hyoideus; 1, concha; 2, 3, posterior and anterior borders of 1; 8, scutiform 
cartilage; 9, zygomatic arch; 2S', ramus of mandible; 37, external maxillary vein; 3S, jugular vein; 39, facial vein; 
44, parotid gland; 50, 51', mandibular gland; dotted line at 50 indicates position of atlantal lymph gland, and the 
parotid lymph gland lies partly under parotid gland, just in front of 44; 58, medial palpebral ligament; 69, laryngeal 
prominence. (After Ellenberger-Baum, Anat. fiir Kunstler.) 



The depressor labii superioris arises just in front of the facial tuberosity, and 
divides usually into two branches, which terminate in a number of tendons that 
form a network in the muzzle and upper lip. 

The incisivus inferior is a small, rounded muscle, which arises on the body of 
the mandible below the second and third incisors, and ends in the lower lip, blending 
with the orbicularis. 

The depressor labii inferioris is thin, and does not extend as far backward 
as in the horse; only the anterior end is distinct from the buccinator. 



MUSCLES OF THE FACE 



345 



The buccinator shows no marked variation, but its superficial layer is well 
developed. 

The dilatator naris lateralis arises in front of the facial tuberosity, passes for- 
ward between the branches of the levator nasolabialis, and terminates in the lat- 
eral wing of the nostril. 

The dilatator naris apicalis is situated in the muzzle and joins its fellow at a 
median raphe. It arises on the border and upper surface of the body of the pre- 




FiG. 301. — Muscles op Head of Ox; Dorsal View. 
a, a'. Levator labii superioris propriiis; h, levator nasolabialis; /, dilatator naris lateralis; g', malaris; o, zygo- 
matico-auricularis and scutulo-auricularis superficialis inferior; o", scutulo-auricularis superficialis superior; o'", 
scutulo-auricularis superficialis accessorius; p, scutularis; u, frontalis; z, orbicularis oculi; 1, concave surface of 
concha; 3, 2, anterior and posterior borders of concha; 8, scutiform cartilage; 34, parietal cartilage; 39, facial vein; 
49, muzzle; 58, medial palpebral ligament. (/Vfter EUenberger-Baum, Anat. filr Kunstler.) 



maxilla, the fibers passing obliquely upward and outward to the medial wing of the 
nostril. 

The dorsal part of the lateralis nasi arises from the alar cartilage of the nostril 
and ends in the medial wing of the nostril. 

The ventral part of the lateralis nasi consists of two layers which arise on the 
nasal process of the premaxilla and the lateral nasal cartilage and end in the lateral 
^\^ng of the nostril. 

The orbicularis oculi is well developed. 

The corrugator supercilii is not present as a separate muscle, its place and 
function being taken by the frontalis. 

The malaris is broad, and spreads out below on the fascia over the buccinator 
and masseter; it is divided into two parts. 



346 



THE MUSCLES OF THE OX 



MANDIBULAR MUSCLES 

The masseter is not so large as in the horse; a considerable part of it arises 
on the facial tuberosity and is directed obliquely backward and downward, so that 
it would draw the lower jaw forward as well as upward. 

The temporalis conforms to the temporal fossa, and is therefore longer and 
entirely lateral in position. 

The pterygoideus medialis arises from the lateral surface of the perpendicular 
part of the palatine bone and from the pterygoid process. Since the origin is nearer 




Fig. 302. — Muscles of Head of Ox; Ventral View. 
d, d', Sterno-cephalicus; e, omo-hyoideus; 5, zygomaticus; A, buccinator; i, depressor labii inferioris; ^•, orbicularis 
oris; m, masseter; n, parotido-auricularis; o', zygomatico-auricularis; w, mylo-hyoideus; 1, concha, convex surface; 
2, anterior border of concha; 30', angle of jaw; 39, facial vein; 44, parotid gland; 43, lower lip; 48, angle of mouth; 
60, 50', mandibular gland; 69, larynx; X, wing of atlas. (After EUenberger-Baum, Anat. fur Kunstler.) 

the median plane and the insertion further from it than in the horse, the muscle pro- 
duces more marked lateral movement of the mandible. 

The pterygoideus lateralis is flattened transversely, wide and thin in front, 
narrower and thicker behind. It has an extensive origin in the pterj^go-palatine 
fossa, where it is partly covered by the pterygoideus medialis. 

The occipito-mandibularis is absent. 

The digastricus has a tendinous origin on the paramastoid process of the 
occipital bone; its bellies are short and thick. The intermediate tendon is round and 
thick; it does not perforate the stylo-hyoideus. The anterior bellies are connected 
beneath the root of the tongue by a layer of transverse muscle-fibers termed the 
transversus mandibulse. 



MUSCLES OF THE NECK — VENTRAL GROUP — LATERAL GROUP 347 



HYOm MUSCLES 

The mylo-hyoideus is thicker and more extensive than in the horse. 

The stylo-hyoideus has a long, slender tendon of origin which is attached to the 
muscular angle of the great cornu of the hyoid bone. The insertion is fleshy and 
is not perforated by the digastricus. 

The genio-hyoideus is much more developed than in the horse. 

The kerato-hyoideus has an additional attachment on the middle cornu of the 
hyoid bone. 

The hyoideus transversus is bifid. 

The stemo-thyro-hyoideus has no intermediate tendon and is thicker. 

The omo-hyoideus arises as a thin band from the fascia over the third and 
fourth cervical vertel^rse. It blends here with the rectus capitis ventralis major. 

The occipito-hyoideus is thick. Its large lateral part entirely covers the para- 
mastoid process (from which it arises) and is inserted into the muscular angle of 
the great cornu. The smaller medial part arises from the ventral end of the para- 
mastoid process and ends on the medial face of the great cornu below the dorsal 
end. 



Muscles of the Neck 
a. ventral group 

The cervical cutaneus is absent. 

The stemo-cephalicus consists of two muscles. They arise from the manu- 
brium sterni and first rib. The superficial muscle is the stemo-mandibularis ; it 
is inserted on the anterior border of the masseter, the ramus of the mandible, and 
the buccal fascia. The deep muscle is the stemo-mastoideus ; it crosses under the 
preceding and ends on the mastoid processes, the mandible, and, in common with 
the rectus capitis ventralis major, on the basilar part of the occipital bone. 

There are two scaleni. The scalenus ventralis (s. primse costse) arises from 
the transverse processes of the third to the seventh cervical vertebrae and ends on 
the first rib. It is traversed by the roots of the brachial plexus, which divide it 
into bundles. The emerging brachial artery separates a narrow part below from 
the main mass. The scalenus dorsalis (s. supracostalis) arises usually on the 
transverse processes of the fourth, fifth, and sixth cervical vertebrae. Its wide 
posterior part lies on the ventral part of the serratus thoracis; it is attached to the 
third rib and to the serratus thoracis. 

The rectus capitis ventralis major arises on the third to the sixth cervical 
transverse processes, and blends at its insertion with the sterno-mastoideus and 
the cleido-mastoideus. 

The rectus capitis ventralis minor is larger than in the horse. 

The rectus capitis lateralis and longus colli resemble those of the horse. 

The intertransversales are large. From the sixth cervical vertebra forward 
they form a muscular mass (M. intertransversarius longus) which is inserted into 
the wing of the atlas. 

B. LATERAL GROUP 
The splenius is thin. It arises directly from the first three or four thoracic 
spines, and ends by a thin tendon on the occipital bone, the wing of the atlas, 
and the transverse process of the axis, blending with the brachiocephalicus, longis- 
simus capitis, and omo-transversarius. The remaining muscles present no very 
marked differential features. 



348 



THE MUSCLES OF THE OX 




MUSCLES OF THE THORAX — ABDOMINAL MUSCLES 349' 



Muscles of the Thorax 

The levatores costarum number ten or eleven pairs. 

The external intercostal muscles are thick; they terminate at the costo- 
chondral junctions. The internal intercostals are specially thick in relation to the 
cartilages of the sternal ribs; here there exist bundles (comparable to the levatores 
costarum) which are attached in front to the sternum, behind to a costal cartilage. 
The interosseous part thins toward the upper end of the spaces. 

The diaphragm presents several important differential features. Its slope is 
much steeper and its width is greater than in the horse. The upper limit of the 
costal attachment extends almost in a straight line from the last rib about a hand- 
breadth above its middle to the junction of the eighth rib with its cartilage, and 
along the latter to the sternum. The midline slopes from the twelfth thoracic 
vertebra obliquely as far as the foramen vense cavae, beyond which it is almost 
vertical. The right crus divides into two branches, which circumscribe the hiatus 
oesophageus, unite below, and then spread out in the tendinous center. The left 
crus is small. The hiatus a?sophageus is situated about four to five inches (10 to 
12 cm.) below the eighth thoracic vertebra, a little to the left of the median plane. 
The foramen vense cavae is a little more ventral and almost in the median plane. ^ 

In the sheep the costal attachment differs from that of the ox. The upper 
limit of the attachment extends in a gentle curve (convex ventrally) from the 
last rib about the junction of its middle and ventral thirds to the ventral end of 
the ninth rib. 

MUSCLES OF THE BACK AND LOINS 

The serratus dorsalis anterior is very thin. It is inserted on the fifth to the 
eighth ribs when fully developed, but it may be reduced to two or three digitations 
or may be absent. The serratus dorsalis posterior is inserted on the last three or 
four ribs. 

The longissimus costarum has a distinct lumbar portion which is attached to 
the lumbar transverse processes and the tuber coxae. 

The longissimus dorsi resembles that of the horse, but it is more fleshy anter- 
iorly, and the spinalis dorsi is clearly distinguishable from the common mass. In 
the lumbar region the tendons meet across the summits of the spines. 

Intertransversales are present in the back, and interspinales in the back and 
loins. 

Muscles of the Tail 

These resemble in general those of the horse; the coccygeus is, however, much 
more developed. 

Abdominal Muscles 

The obliquus abdominis extemus is somewhat thinner and has a less extensive 
origin, which begins at the lower part of the fifth intercostal space and ends on 
the last rib above its middle. The direction of the fibers in the flank is horizontal, 
and they do not reach to the tuber coxae, nor as high as the lumbar transverse proc- 
esses. (In this region the abdominal tunic has a strong attachment to the point 

1 The sternal part is clearly separable from the costal part. The costal attachment is much 
higher posteriorly than in the horse, thus diminishing the capacity of the thorax in comparison 
with that animal. The last digitation is thus some seven or eight inches (ca. 18 to 20 cm.) above the 
corresponding digitation of the transversus abdominis. There are small intermediate digitations- 
at the last two intercostal spaces. 



350 



THE MUSCLES OF THE OX 



of the hip and the lumbo-dorsal fascia.) The aponeurosis is intimately united with 
the abdominal tunic, and does not detach a femoral lamina. 

The obliquus abdominis intemus is more developed and has an additional 
origin from the lumbo-dorsal fascia. The aponeurosis blends with that of the 
external oblique near the linea alba, and detaches a layer which assists in the for- 
mation of the internal sheath of the rectus. 

The rectus abdominis arises on the lateral border of the sternum as far for- 
ward as the third costal cartilage. The two muscles are separated, except near 
the pelvis, by an interval varying from two to four inches (ca. 5 to 10 cm.), so that 
this part of the abdominal wall is entirely fibrous. (The umbilicus is in a trans- 
verse plane through the third lumbar vertebra.) There are five tendinous inscrip- 
tions, at the third of which is a foramen for the passage of the subcutaneous ab- 
dominal vein. The prepubic tendon has, in addition to lateral branches inserted 




Fig. 304. — Deeper Muscles of Neck, Shoulder, and Thorax op Ox. 
c', Cleido-oceipitalis muscle; d, sterno-cephalicus; /, /', long and lateral heads of triceps; g, superficial pectoral 
muscle; h, h', deep pectoral muscle; i, i', serratus ventralis; k, latissimus dorsi; I, obliquus abdominis externus; »', 
biceps brachii; w, splenius; x, rhomboideus; y, longissimus capitis et atlantis; z, supraspinatus ; z', infraspinatus; 
z", tendon of insertion of z'; 1', cartilage of scapula; 2, tuberosity of spine of scapula; S, acromion; 5, lateral tuberosity 
of humerus; 6, deltoid tuberosity; S, olecranon; £6, transverse processes of cervical vertebrae; 27, posterior auricular 
muscles: X, wing of atlas. (After EUenberger-Baum, Anat. fiir Kunstler.) 

into the ilio-pectineal eminences, a strong attachment to the median common ten- 
don of the adductors of the thigh, so that the abdominal wall is strongly retracted 
and almost vertical at its junction with the pubis. 

The transversus abdominis presents no striking differential features. The 
transversalis fascia is strong and distinct except over the diaphragm. 



Muscles of the Thoracic Limb 
i. muscles of the shoulder girdle 

The trapezius is much thicker and broader than in the horse, and is undivided. 
It arises on the ligamentum nuchae and supraspinous ligament, from the atlas to 
the twelfth thoracic vertebra. 



MUSCLES OF THE SHOULDER — MUSCLES OF THE ARM 351 

The omo-transversarius arises on the wing of the atlas, and, inconstantly, 
the transverse process of the axis, and is inserted into the scapular spine and fascia. 

The rhomboideus is clearly divided into cervical and thoracic parts, the latter 
extending further than in the horse. 

The latissimus dorsi has a broad tendon of origin, which blends with the 
lumbo-dorsal fascia; it is also attached to the eleventh and twelfth ribs and the 
fascia over the external intercostal and oblique abdominal muscles. The anterior 
fibers end on the tendon of the teres major, the middle part on an aponeurosis on 
the medial surface of the caput longum, and the posterior part on a tendon which is 
common to this muscle and the deep pectoral. 

The brachiocephalicus has two distinct parts. The dorsal division, the cleido- 
occipitalis, arises on the occipital bone and the ligamentum nuchas. The ventral 
part, the cleido-mastoideus, is smaller and arises by a round tendon on the mastoid 
process and the rectus capitis ventralis major, and by a thin tendon on the mandible. 

The superficial pectoral muscle is thinner than in the horse and its two parts 
are not so clearly separal^le. 

The deep pectoral muscle arises as far forward as the second rib and is un- 
divided. However, the scapular portion may be considered to be represented by a 
small branch which arises from the anterior part of the sternum and the first rib 
and passes upward to end on the deep face of the brachiocephalicus in front of the 
shoulder joint. ^ A tendon detached from the dorsal edge blends with the latissimus 
dorsi and coraco-brachialis. 

The serratus ventralis is clearly divided into cervical and thoracic parts. 
The former is large and extends from the third (or second) cervical vertebra to 
the fifth rib, being overlapped behind by the thoracic part. It is inserted on a 
large triangular area on the antero-superior part of the costal surface of the scapula. 
The thoracic part is relatively thin and is covered by a very strong aponeurosis; 
it is attached to the fourth to the ninth ribs by six digitations, and is inserted by a 
flat tendon which insinuates itself between the middle and posterior parts of the 
subscapularis to end on a rough line — equivalent to the posterior serratus area of 
the horse — and also on the cartilage of the scapula in continuity with this line. 



n. MUSCLES OF THE SHOULDER 

The deltoid is clearly divided into acromial and scapular parts. The former 
(Pars acromialis) arises on the acromion, the latter (Pars scapularis) on the posterior 
border of the scapula and the aponeurotic covering of the infraspinatus. The 
scapular part of the muscle is largely inserted into the fascia covering the triceps. 

The supraspinatus, infraspinatus, and teres minor do not differ materially 
from those of the horse. 

The subscapularis consists of three parts with a common tendon of insertion. 

The teres major and coraco-brachialis resemble those of the horse. 

The capsularis is absent. 

m. MUSCLES OF THE ARM 

The biceps is smaller and less tendinous, and is situated more medially than 
in the horse. The tendon of origin is flat, and is bound down in the intertuberal or 
bicipital groove by a fibrous band. The tendon to the extensor carpi radialis is 
less distinct than in the horse. (In the sheep the tendon of origin is round and is 
invested by the synovial membrane of the shoulder joint. The tendon of inser- 
tion bifurcates; one branch ends on the tuberosity of the radius, the other on the 
ulna.) 

1 According to Meckel and Lesbre, this is the homologue of the subclavius of man. 



352 



THE MUSCLES OF THE OX 



The medial head of the triceps is more developed than in the horse, and ex- 
tends up to the neck of the humerus. 

The tensor fasciae antibrachii is a slender muscle which lies along the posterior 

border of the triceps and is not 
';j connected with the latissimus 

I dorsi. 

IV. MUSCLES OF THE FOREARM 

AND MANUS 

A. Extensor Division 
The extensor carpi radialis 

is like that of the horse. There 
is sometimes a small muscle 
lying along its medial border, 
which may represent the exten- 
sores pollicis. 

There are three digital ex- 
tensors: 1. The common digital 
extensor (M. extensor digitalis 
communis) arises by two heads 
from the lateral epicondyle of 
the humerus and from the ulna. 
The heads fuse about the middle 
of the forearm, and terminate 
soon on a tendon which passes 
over the carpus and metacarpus, 
gradually inclining forward. At 
the fetlock joint it divides into 
two branches, each of which is 
inserted into the extensor pro- 
cess of the corresponding third 
phalanx. 2. The medial digital 
extensor (M. extensor digiti ter- 
tii proprius) arises on the lateral 
epicondyle, and is inserted by 
two branches into the second 
and third phalanges of the me- 
dial digit. The tendon receives 
two reinforcing slips from the 
suspensory ligament. 3. The 
lateral digital extensor (M. 
extensor digitalis lateralis s. 
digiti quarti proprius) is stronger 
than that of the horse; it arises 
from the lateral ligament of the 
elbow joint, the lateral tuber- 
osity of the radius, and the 
ulna. The tendon terminates 
like that of the preceding 
muscle. "^ 
the horse. 

^ It may be remarked that, in addition to the extension action, the common extensor approxi- 
mates the digits, while the others tend to abduct them. 





Fig. 305. — Muscles of Antibr.\- 

CHIUM AND MaNUS OF Ox; 

Lateral View. 

o. Extensor carpi radialis; b, 
extensor digiti tertii; c, extensor 
digitalis communis; d, extensor 
digiti quarti; e, ulnaris lateralis; 
/, extensor carpi obliquus; /', ul- 
nar head of flexor carpi ulnaris; g, 
brachialis; h, interosseus mediug 
or suspensory ligament; i, flexor 
tendons; i', branch of h, to super- 
ficial flexor tendon; 8, olecranon; 
11, accessory carpal bone; 12', 
metacarpal tuberosity. (After 
EUenberger-Baum, Anat. fur 
Kiinstler.) 



Fig. 306. — Muscles of Anti- 

BRACHIUM AND MaNUS OF 

Ox; Medial View. 

a. Extensor carpi radialis; 
b, tendon of extensor digiti ter- 
tii; /, tendon of extensor carpi 
obliquus; s, brachiaUs; A, inter- 
osseus medius or suspensory 
ligament; i, flexor tendons; i', 
branch of h; k, flexor carpi radi- 
alis; /, flexor carpi ulnaris; m, 
superficial digital flexor. (After 
Ellenberger-Baum, Anat. fur 
Kiinstler.) 



The extensor carpi obliquus resembles that of 



MUSCLES OF THE FOREARM AND MANUS 



353 



The extensor tendons are bound down at the carpus by an annular ligament, 
and are furnished with synovial sheaths (Figs, 307, 308). 

B. Flexor Division 

The three flexors of the carpus are like those of the horse, but the long tendon 
of the lateral flexor ends on the large metacarpal bone, not on the small one. The 
tendon of the medial flexor naturally ends on the medial part of the large meta- 
carpal bone. 

The superficial digital flexor is somewhat blended at its origin with the middle 
flexor of the carpus. It divides into two bellies, superficial and deep, terminating 




Fig. 307. — Right Cahpus or Ox with Burs^ and Fig. 308. — Right Carpus of Ox with Burs^ and 

Synovial Sheaths Injected; Lateral View. Synovial Sheaths Injected; Medial View. 

1, Extensor carpi radialis, with synovial sheath (/') and bursa (/"); ^. extensor carpi obliquus, with synovial 
sheath (2') and bursa {2"); 3, extensor digiti tertii proprius; 4< extensor digitalis communis; S', common synovial 
sheath of 3 and 4; 5, extensor digiti quarti proprius, with synovial sheath (5') ; 6, 6', ulnaris lateralis, with bursa 
(6"); 7, flexor carpi radialis, with synovial sheath; S, deep digital flexor, with synovial sheath {8'); 9, flexor carpi 
ulnaris; 10, superficial digital flexor, with synovial sheath, 10'; a, radius; 6, carpus; c, metacarpus; d, cut edge of 
annular ligament. (After Schmidtchen.) 



on tendons at the distal part of the forearm. The superficial tendon passes over 
the posterior annular ligament (Lig. carpi transversum), perforates the metacarpal 
fascia, and joins the deep tendon about the middle of the metacarpus. The deep 
belly is connected with the deep flexor by a strong fibrous band. Its tendon passes 
under the annular ligament of the carpus in a groove on the deep flexor, from which 
it receives fibers. The conjoined tendon soon bifurcates, each branch receiving a 
reinforcing band from the suspensory ligament, and forming near the fetlock a 
ring for the corresponding branch of the deep flexor tendon. Passing under two 
digital annular ligaments, they are inserted into the volar surfaces of the second 
phalanges by three slips, 
23 



354 THE MUSCLES OF THE OX 

The deep digital flexor has the same heads as in the horse, the humeral head, 
as before mentioned, being connected ^\^tll the deep part of the superficial flexor. 
The tendon, which is not reinforced by a check ligament as in the horse, divides 
near the distal end of the metacarpus into two branches which are inserted into the 
volar surfaces of the third phalanges. 

The synovial sheaths at the carpus present the following special features: 
One is found in connection with the tendon of the superficial part of the superficial 
flexor of the digits. There is a common sheath for the tendons of the common ex- 
tensor and the medial extensor. 

Bursse may occur under the tendons of the proper extensors of the digits at the 
fetlock; they are constant only in old animals (Schmidtchen). The branches of 
the tendon of the common extensor are provided with synovial sheaths from their 
origin to the middle of the second phalanx. There are two digital synovial sheaths 
for the flexor tendons; they may communicate at their upper part, and they ex- 
tend from the distal third of the metacarpus nearly to the distal sesamoids. Bursse 
occur between the latter and the branches of the deep flexor tendon. 

A feeble pronator teres is present on the medial surface of the elbow along the 
medial collateral ligament. 

The fascia on the volar face of the metacarpus and digit is very thick. It is 
continuous above with the ligamentum carpi transversum, and is attached on either 
side to the metacarpal bone. At the fetlock it forms the fibrous basis for the small 
claws, and below this it detaches two strong bands which diverge to be inserted into 
the second and third phalanges, blending with the collateral ligaments. 

The lumbricales are absent, unless we regard as such the muscular bundles 
which arise on the deep flexor and are inserted into the superficial flexor tendon at 
the carpus. 

The interosseus medius, or suspensory ligament, is somewhat more muscular 
than in the horse; indeed, in the young subject it may be almost entirely fleshy. 
Its arrangement is somewhat complex. Single at its origin, it detaches about the 
middle of the metacarpus a band which joins the tendon of the superficial flexor 
and concurs near the fetlock in the formation of the ring for the deep flexor tendon. ^ 
A little lower down it divides into three and then into five branches. The abaxial 
branches (two pairs) are attached to the corresponding sesamoids and tendons of 
the proper extensors, while the middle branch passes through the sulcus at the distal 
end of the metacarpus and bifurcates, each division fusing with the tendon of the 
corresponding proper extensor. 



The Muscles of the Pelvic Limb 
l the sublumbar muscles 

The psoas minor begins at the disc between the twelfth and thirteenth thoracic 
vertebrae. 

The psoas major has a fleshy origin on the posterior border of the last rib, and 
a thin tendon attached to the twelfth rib; it is relatively narrower than in the horse 
and does not entirely cover the quadratus lumborum. 

The iliacus begins under the body of the sixth lumbar vertebra, and is more 
closely united with the psoas major than in the horse. 

The quadratus lumborum extends as far forward as the body of the tenth or 
eleventh thoracic vertebra. It is wider than in the horse and extends beyond the 
lateral border of the psoas major. 

' Lesbre regards this band as the subcarpal check ligament, which on this basis is blended 
with the suspensory hgament above. 



LATERAL MUSCLES OF THE HIP AND THIGH 



355 



II. LATERAL MUSCLES OF THE HIP AND THIGH (Figs. 303, 309) 

The tensor fasciae latae is large, and the fleshy part extends further down than 
in the horse. 

Tlie gluteus superficialis is not present as such; apparently its anterior part 
has fused with the tensor fascise latae and its posterior part with the biceps femoris. 

The gluteus medius is small, the lumbar part being insignificant and extend- 
ing forward only to the fourth lumbar vertebra. Its deep portion (gluteus ac- 
cessorius) is easily separable, and its strong tendon is inserted into the femur below 
the trochanter major, under cover of the upper 
part of the vastus lateralis. 

The gluteus profundus is thin, but exten- 
sive, arising as far forward as the tuber coxae, 
and from the lower part of the sacro-sciatic liga- 
ment. The fibers converge on a broad, strong 
tendon which passes under the upper part of 
the vastus lateralis, and is inserted into a tu- 
bercle a short distance below the great tro- 
chanter. 

The biceps femoris is very wide at its 
upper part, having apparently absorbed the 
posterior part of the superficial gluteus. It 
arises from the sacral spines, sacro-sciatic liga- 
ment, and tuber ischii. It is divided by a 
fi])ro-elastic septum in the thigh into two por- 
tions, which end in front and below on a wide 
aponeurosis; the latter is attached to the patella 
and its lateral ligament and blends with the fas- 
cia cruris and fascia lata. There is no femoral 
attachment. A large bursa occurs between the 
muscle and the great trochanter in the adult. 
The part of the tendon which fuses with the 
lateral patellar ligament presents a fibro-cartil- 
aginous thickening, and an extensive bursa is 
interposed between it and the lateral condyle 
of the femur. 




A layer derived from the fascia lata is intimately 
adherent to the deep face of the muscle, and cases occur 
in which this fascials ruptured by the trochanter major, 
thus fixing the muscle behind the trochanter. 



Fig. 309. — Gluteal, Femor.\l, and Crural 
Regions of Ox, After Removal op 
Superficial Muscles. 
p. Gluteus medius; r, semitendinosus; u, 
coccygeus; 28, vastus lateralis; 28', rectus fe- 
moris; 29, semimembranosus; 30, gastrocnemi- 
us; 31, sacro-sciatic ligament: 16, tuber coxae; 
17, tuber ischii; 19, trochanter major; 20, patel- 
la; 21', lateral condyle of tibia. (After Ellen- 
berger-Baum, Anat. fiir Kiinstler.) 



The semitendinosus and semimembrano- 
sus arise on the ischium only. The latter is very large and has a branch attached 
to the medial condyle of the tibia. 



III. ANTERIOR MUSCLES OF THE THIGH 

The quadriceps femoris reseml)les that of the horse; but the vasti (and es- 
pecially the medial one) are not so thick, and the vastus intermedins is more clearly 
separable, and consists of two parts. Bursae occur under the insertions of the 
medial and lateral vasti, and often under the end of the rectus in the adult. 

The articularis genu is a small muscle which lies under the distal part of the 
vastus intermedins, and is partly inserted on the sui^rapatellar cul-de-sac of the 
synovial membrane of the stifle joint. 

The capsularis is absent. 



356 THE MUSCLES OF THE OX 

IV. MEDIAL MUSCLES OF THE THIGH 

The sartorius arises by two heads, one from the tendon of the psoas minor 
and the ihac fascia, the other from the shaft of the ihum. The femoral vessels 
pass between them. 

The gracilis is more extensively united with its fellow at its origin than in the 
horse. 

The pectineus is large, and arises by a single head from the pubis and prepubic 
tendon. It divides into two branches, one of which is inserted as in the horse, 
while the other extends to the medial epicondyle of the femur. 

The adductor resembles that of the horse, but does not reach to the medial 
condyle of the femur. 

The quadratus femoris and obturator extemus resemble those of the horse. 

The obturator intemus has no iliac head, and its tendon passes through the 
obturator foramen. 

The gemellus is large; some of its fibers of origin join the obturator internus 
through the lesser sciatic foramen. 

V. MUSCLES OF THE LEG AND FOOT 

A. DORSO-LATERAL GrOUP 

There are four digital extensors, two of which are fused with each other and 
the peroneus tertius in the upper third of the leg. 

1. The long digital extensor (M. extensor digitalis longus) arises in common 
with the peroneus tertius and the medial extensor in the extensor fossa of the femur, 
and separates from the other muscles near the middle of the leg. At the distal 
end of the tibia it terminates on a tendon which passes down over the hock (bound 
down by two annular ligaments) and ends like that of the thoracic limb. 

2. The medial digital extensor (M. extensor digiti tertii proprius) arises in com- 
mon with the preceding muscle and the peroneus tertius, and is covered by them 
to the distal third of the tibia. Its tendon passes under the annular ligaments 
between those of its cogeners and ends on the second phalanx of the medial digit. 

3. The lateral digital extensor (M. extensor digitahs lateralis s. digiti quarti 
proprius)^ arises on the lateral ligament of the stifle joint and the lateral condyle of 
the tibia. Its tendon passes over the lateral surface of the hock, and terminates 
on the dorsal surface of the second phalanx of the lateral digit. 

The reinforcing bands from the suspensory ligament are arranged as in the 
forelimb. 

4. The short digital extensor (M. extensor digitalis brevis) resembles that of 
the horse ; it is inserted on the tendon of the long extensor. 

The peroneus longus (not present in the horse) is situated in front of the lateral 
extensor. It arises on the lateral condyle of the tibia and the fibrous band which 
represents the shaft of the fibula. Its tendon passes downward and backward 
over the lateral surface of the hock, crosses over that of the lateral extensor and 
under the lateral ligament, and ends on the first tarsal bone and the proximal end 
of the large metatarsal bone. It is enveloped by a synovial sheath. It would ap- 
parently act as an inward rotator at the hock joint. 

The peroneus tertius is a well-developed muscle which arises on the common 
tendon with the long and medial extensors. It has a large, fusiform belly, which 
is superficially situated on the front of the leg. Close to the tarsus it ends on a 
flat tendon, which is perforated by that of the tibialis anterior, and ends on the 
proximal end of the large metatarsal and second and third (fused) tarsal bones. 

^ Lesbre regards this muscle as the homologue of the peroneus brevis of man and other 
pentadactyls. 



MUSCLES OF THE LEG AND FOOT 



357 



The tibialis anterior is smaller, and arises by two heads. The larger head 
springs from the lateral surface of the tuberosity and crest of the tibia; the lateral, 
smaller one (M. extensor hallucis longus), arises from the upper part of the lateral 




Fig. 310. — Muscles of Left Leg and Foot of Ox; 
Antekiok View. 
o, Peroneus tertius; a', tibialis anterior; 6, long 
digital extensor; b', extensor digiti tertii; c, peroneus 
longus; d, extensor digiti quarti; i, i, annular liga- 
ments; k, lateral ligament of hock joint; I, branch of 
suspensory ligament; 20, patella; SI', lateral condyle 
of tibia; 28, tuberosity of tibia. (After Ellenberger- 
Baum, Anat. fiir Kunstler.) 



Fig. 311. — Muscles of Left Leg and Foot of Ox; 
Later.^l View. 
a, Peroneus tertius; a', tibialis anterior; 6, long 
digital extensor; b' , tendon of 6; c, peroneus longus; 
d, extensor digiti quarti; e, deep digital flexor; e', ten- 
don of e; e", branch of interosseus medius or suspen- 
sory ligament; /, gastrocnemius (the soleus lies just in 
front of /) ; /', tendon of superficial digital flexor; h, in- 
terosseus medius or suspensory ligament; i, i, annular 
ligaments; 20, patella; 21', lateral condyle of tibia; 
28, tuberosity of tibia. (After Ellenberger-Baum, Anat. 
fur Kunstler.) 



l)order of the tibia and the fibrous band which replaces the shaft of the fibula. The 
tendon perforates that of the preceding muscle, passes to the medial face of the 
hock, and ends on the metatarsal and second and third tarsal bones. 



358 



THE MUSCLES OF THE OX 



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THE MUSCLES OF THE PIG — MUSCLES OF THE FACE 359 

B. Plantar Group 

The gastrocnemius and soleus resemble those of the horse. 

The superficial flexor is more fleshy than in the horse. Its tendon termi- 
nates as in the forelimb. 

The deep flexor in general resembles that of the horse, but the tibialis poste- 
rior (superficial head) is distinct and is larger than in the horse. The flexor digitahs 
longus (medial head) is also larger, while the flexor hallucis longus (deep head) is 
smaller. The common tendon ends like that on the forelimb. 

The synovial sheaths and bursse of the muscles of the leg and foot are shown in 
Figs. 312-315. 



THE MUSCLES OF THE PIG 
Muscles of the Face 

The facial cutaneus is pale, thin, and difficult to separate from the skin. 

The orbicularis oris is little developed. 

The levator nasolabialis is thin and pale, and is undivided. 

The levator labii superioris proprius may well be termed the levator rostri. 
It has a large pennate belly, which arises in the preorbital fossa. The tendon ends 
on the anterior part of the os rostri. A muscular slip connects it with the premaxilla. 

The zygomaticus arises on the fascia over the masseter and ends at the angle 
of the mouth. 

The depressor labii inferioris separates from the buccinator only near the 
angle of the mouth; it ends by a number of tendinous branches in the lower lip. 

The dilatator naris lateralis is well developed. It arises under the levator 
rostri and ends by a tendinous network around the nostril. 

The transversus nasi is represented only by a few fibers which cross over the 
OS rostri. 

The depressor rostri arises on the facial crest. It has a long strong tendon 
which passes below the nostril and turns dorso-medially to meet the tendon of the 
opposite side and end in the skin of the snout. It depresses the snout and con- 
tracts the nostril. 

The malaris is absent, and the other palpebral muscles present no special 
features. 

MANDIBULAR MUSCLES 

The masseter is thick. 

The pterygoideus medialis is wide at its insertion. 

The pterygoideus lateralis is large and distinct. 

The digastricus has only one belly and has no connection with the hyoid bone. 
It ends on the medial and lower surface of the mandible, in front of the groove for 
the facial vessels. 

HYOID MUSCLES 

The mylo-hyoideus consists of two more or less distinct layers, the superficial 
one being the transversus mandibulse. 

The occipito-hyoideus and kerato-hyoideus are small. 

The hyoideus transversus is absent. 

The omo-hyoideus and stemo-hyoideus are referred to in connection with the 
muscles of the neck. 



THE MUSCLES OF THE PIG 



Muscles of the Neck 



The cutaneus consists of two layers which cross each other obhquely. The 
fibers of the superficial layer are directed nearly vertically, those of the deep layer 
toward the face, on which they are continued to form the facial portion. 

The brachiocephalicus is described with the other muscles of the shoulder girdle. 

The stemo-cephalicus arises on the sternum and is inserted by a long round 
tendon on the mastoid process. 

The thyroid part of the stemo-thyro-hyoideus has a peculiar arrangement. 
It arises (separately from the opposite muscle) on the manubrium sterni. About 
the middle of the neck it has an oblique tendinous intersection, beyond which it 




Fig. 316. — Superficial Muscles or Pig, After Removal op M. Cut.vneus. 
a. Levator nasolabialis; 6, levator labii superioris proprius; h', fleshy slip of h which comes from premaxilla; c, 
dilatator naris lateralis; d, depressor rostri; e, orbicularis oris; /, depressor labii inferioris; s, zygomaticus; /i, masseter; 
i i', i", brachiocephalicus (cleido-occipi talis, cleido-mastoideus, pars clavicularis deltoidei) ; k, stemo-cephalicus; I, 
sterno-hyoideus; m, omo-transversarius; n, n', trapezius; o, anterior deep pectoral; p, latissimus dorsi; g, lumbo- 
dorsal fascia ; r, obliquus abdominis externus; r', aponeurosis of r; s, serratus dorsalis; /, serratus ventralis; m, posterior 
deep pectoral; v, supraspinatus; w, w', deltoideus; x, long head of triceps; y, lateral head of triceps; z, tensor fasciae 
antibrachii; 1, brachialis; S, extensor carpi radialis; 3, extensor digiti quarti; 4, extensor digiti quinti; 5, extensor 
carpi ulnaris; 6, ulnar head of deep flexor; 7, gluteus medius; 8, tensor fasciae latse; 9, 10, 10', biceps femoris; 11, 
semitendinosus; 13, semimembranosus; 13, caudal muscles; H, panniculus adiposus in section. (After EUenberger, 
in Leisering's Atlas.) 



divides into two branches: one of these is inserted in the usual fashion, the other 
ends on the laryngeal prominence. The hyoid part is well developed. 

The omo-hyoideus is thin. It arises as in the horse, but has no connection 
with the brachiocephalicus nor with the opposite muscle. 

The omo-transversarius arises on the first or second cervical vertebra (under 
cover of the brachiocephalicus), and is inserted into the lower part of the scapular 
spine. 

There are two scaleni. The scalenus ventralis (s. primse costse) resembles 
that of the ox, is attached to the last four cervical vertebrse, and is perforated by 
the nerves of the brachial plexus. The scalenus dorsalis (s. supracostalis) arises 
on the transverse processes of the third to the sixth cervical vertebra, and ends 
on the third rib. 

The ventral muscles of the head present no special features. 

The longus colli is separated from the opposite muscle, so that part of the 
bodies of the cervical vertebrae is exposed as in man. 



MUSCLES OF THE THORAX — MUSCLES OF THE BACK AND LOINS 361 

The intertransversales resemble those of the ox. 

The splenius is thick and extensive. It ends in three parts on the occipital, 
the temporal, and the wing of the atlas (inconstant) . 

The longissimus capitis et atlantis is small, and its atlantal part is blended 
with the longissimus cervicis. 

The complexus is large, and is clearly divided into two parts: the dorsal part 
(Biventer cervicis) is marked by several tendinous intersections; the ventral part 
is the complexus proper. 

The obliquus capitis posterior is relatively thin. 

The recti capitis dorsales are thick and more or less fused. 

Muscles of the Thorax 

The levatores costarum and rectus thoracis present no special features. 

The external intercostal muscles are absent under the serratus dorsalis and the 
digitations of the external oblique. 

The internal intercostals are thick between the cartilages of the sternal ribs. 

The retractor costae and the transversus thoracis resemble those of the horse ; 
the latter extends back to the eighth cartilage and fuses with the transversus ab- 
dominis. 

The diaphragm has seven costal digitations on each side, the posterior ones 
being attached to the ribs at some distance (ca. one-third to one-fourth of rib- 
length) from the costo-chondral junction.^ The line of attachment reaches the 
latter at the tenth rib, and passes along the eighth cartilage to the xiphoid process. 
The tendinous center is more rounded than in the horse. The crura are well 
developed. The right crus is very large, and is perforated by the extensive slit- 
like hiatus oesophageus, which is median in position, and lies about two and one- 
half to three inches (ca. 6 to 8 cm.) below the twelfth thoracic vertebra. The hiatus 
aorticus is between the crura. 



Abdominal Muscles 

The abdominal tunic is little developed. 

The obliquus abdominis extemus has an extensive fleshy portion and a cor- 
respondingly narrow aponeurosis; the latter does not detach a femoral lamina, 
but is reflected in toto to form the inguinal ligament. 

The obliquus abdominis intemus resembles that of the ox; a small fusiform 
muscle, which crosses the inguinal canal obliquely and is attached on the abdominal 
surface of the inguinal ligament, is apparently a detached slip of the internal 
oblique. 

The rectus abdominis is extensive and thick. It has seven to ten inscriptions. 
Its tendon of insertion fuses largely with the common tendon of the graciles, and 
does not give off an accessory band to the head of the femur. 

The fleshy part of the transversus abdominis is well developed. It blends 
in front with the transversus thoracis. 

The cremaster extemus is present in the female as well as in the male. 



Muscles of the Back and Loins 

The serratus dorsalis anterior is inserted into the fifth to the eighth ribs 
inclusive, the serratus dorsalis posterior into the last four or five ribs. There are 
usually no digitations attached to the ninth and tenth ribs. 

1 It is interesting to note that the diaphragm has no attachment to the fifteenth rib, which is 
often present and well developed. 



362 THE MUSCLES OF THE PIG 

The longissimus costarum extends to the wing of the atlas. 

The spinalis et semispinalis can be separated without much difficulty from 
the longissimus dorsi, the division from the common mass of the loins beginning 
about the first lumbar vertebra. 

The multifidus resembles that of the horse. 

Interspinales are present, as well as distinct intertransversales of the Imck 
and loins. 



Muscles of the Tail 

The dorsal and lateral sacro-coccygei arise as far forward as the last lumbar 
vertebra. Gurlt explains the twist of the tail as being due to the spiral arrangement 
of the insertions of the tendons. 



Muscles of the Thoracic Limb 
muscles of the shoulder girdle 

The trapezius is very wide, its line of origin extending from the occipital bone 
to the tenth thoracic vertebra. There is no clear division between its two parts, 
which are both inserted into the scapular spine. 

The omo-transversarius resembles that of the ox. 

The rhomboideus consists of three parts. The cervical part (Rhomboideus 
cervicalis) is greatly developed, its origin extending from the second cervical to the 
sixth thoracic vertebra. The cephalic part (Rhomboideus capitis) arises with the 
splenius on the occipital bone, and is inserted with the cervical part. The thoracic 
part (Rhomboideus thoracalis) extends as far back as the ninth or tenth thoracic 
vertebra. 

The latissimus dorsi is attached to the four ribs preceding the last. It is 
inserted into the medial tuberosity of the humerus. 

The brachiocephalicus divides into two parts, the cleido-mastoideus and 
cleido-occipitalis, which arise on the mastoid process and nuchal crest respectively, 
and unite at the fibrous vestige of the clavicle. 

The anterior superficial pectoral muscle is thin. The posterior superficial pec- 
toral muscle is divided into two parts, one of which ends on the humerus, the other 
on the fascia of the forearm. The anterior deep pectoral muscle resembles that of 
the horse, but its origin does not extend behind the first two chondro-sternal joints. 
The posterior deep pectoral muscle is very long. 

The cervical part of the serratus ventralis is greatly developed, its origin ex- 
tending from the wing of the atlas to the upper part of the fifth rib, and passing 
under the thoracic part; the latter resembles that of the ox. 

MUSCLES OF THE SHOULDER 

The deltoid is undivided; it arises from the aponeurosis covering the infra- 
spinatus, and it ends largely on the deltoid ridge, but partly on the fascia of the arm. 

The supraspinatus is large ; it has a small attachment to the medial tuberosity 
and ends chiefly on the lateral tuberosity of the humerus. There is a bursa between 
the tendon and the anterior part of the lateral tuberosity. 

The infraspinatus is wide ; it is inserted into a depression below the posterior 
division of the lateral tuberosity. There is a bursa between the tendon and the 
tuberosity. 

The teres minor is large and rounded; it ends on a tubercle between the 
lateral and deltoid tuberosities of the humerus. 



MUSCLES OF THE ARM MUSCLES OF THE FOREARM AND MANUS 363 

The subscapularis is very broad at its upper part. It extends posteriorly up 
to the dorsal angle of the scapula, but anteriorly only about two-thirds of the way 
up to the vertebral border. 

The teres major presents nothing remarkable. 

The coraco-brachialis is short, wide, and undivided. There is a bursa between 
its broad tendon of origin and the tendon of insertion of the subscapularis. 

The capsularis is variable; it may be half an inch wide or very small and 
is frequently absent. 

MUSCLES OF THE ARM 

The biceps brachii is fusiform and not greatly developed. Its tendon of origin 
is rounded and the underlying bursa communicates so freely with the shoulder joint 
as to be regarded as an evagination of the synovial membrane of the latter. A small 
band binds down the tendon in the bicipital groove. The tendon of insertion di- 
vides into two branches. One branch passes back across the medial surface of the 
neck of the radius to end on the proximal extremity of the ulna. The other is 
attached to the radius under cover of the brachialis tendon. 

The brachialis is large. Its tendon of insertion divides. The small branch is 
inserted into the medial border of the radius distal to the biceps tendon. The large 
branch crosses the medial border of the radius and ends on the medial surface of the 
ulna distal to the biceps tendon; there is a bursa under this tendon. 

The tensor fasciae antibrachii resembles that of the horse, but is very wide and 
bends around the posterior border of the triceps. 

The long head of the triceps is inserted into the summit of the olecranon by two 
tendons, between which there is a synovial bursa. The lateral head is inserted into 
a crest on the lateral surface of the olecranon by a thin tendon, under which there 
is a bursa. The medial head arises from the proximal third of the medial surface 
of the humerus; it is inserted into the medial surface of the olecranon by a short 
tendon, under which there is a small bursa. 

There are two anconei. 



MUSCLES OF THE FOREARM AND MANUS 

The extensor carpi radialis is a strong, fleshy muscle, the tendon of which is 
inserted into the proximal end of the third metacarpal bone. It may be divided 
into two parts (M. extensor carpi radialis longus, brevis). 

The extensor carpi obUquus is well developed ; it arises from the distal two-thirds 
of the lateral surface of the radius and ulna and ends on the second metacarpal bone. 

The common digital extensor (M. extensor digitalis communis) arises on the 
lateral epicondyle of the humerus and the lateral ligament of the elbow, and divides 
into three parts. The tendon of the medial head ends chiefly on the third digit, 
but commonly sends a small branch to the second. The tendon of the middle head 
divides lower down into two branches for the third and fourth (chief) digits; above 
this bifurcation it detaches a small branch to the second digit, which usually unites 
with the tendon of the extensor digiti secundi. The tendon of the deep head di- 
vides into two l)ranches, the medial one joining the tendon of the middle head, while 
the lateral one ends on the fifth digit. 

The extensor of the second digit (M. extensor digiti secundi proprius) is covered 
by the preceding muscle, with which it is partially fused. It arises on the ulna. 
Its delicate tendon usually unites with the tendon of the middle head of the common 
extensor which goes to the second digit. 

The lateral digital extensor (M. extensor digitalis lateralis) consists of two dis- 
tinct parts: (1) The large dorsal muscle is the extensor digiti quarti proprius; it 
has a long tendon which ends on the fourth digit, and often sends a slip to the fifth 



364 



THE MUSCLES OF THE PIG 



digit. (2) The small volar muscle is the extensor digiti quinti proprius; it ends by 
a long tendon on the lateral aspect of the fifth digit. 

The supinator, when present, is a pale, thin muscular slip which arises on the 

lateral border of the radius just above the interosseous space, extends medially and 

downward across the dorsal surface of the bone to its medial 

border, where it blends with the radial head of the deep 

flexor. 

The pronator teres is a delicate, fusiform muscle which 
lies along the medial surface of the elbow and proximal part 
of the forearm. It arises from the medial epicondyle and 
collateral ligament of the elbow and is inserted by a thin 
tendon to the medial border of the radius about its middle. 
The flexor carpi radialis is well developed. It arises 
on the medial epicondyle of the humerus, and is inserted 
into the third metacarpal bone. 

The flexor carpi ulnaris is narrow and has no ulnar 
head. It runs obliquely down the back of the forearm in 
the furrow between the superficial and deep flexors of the 
digit. It arises from the medial epicondyle of the humerus 
and ends on the accessory carpal bone. 

The ulnaris lateralis (M. extensor carpi ulnaris) is 
covered by a tendinous band, which is a thickened part 
of the fascia of the forearm and extends from the lateral 
epicondyle to the accessory carpal bone and lateral aspect 
of the carpus. The belly of the muscle is round : its ten- 
don of insertion perforates this band in the distal part of 
the forearm and ends on the proximal end of the fifth 
metacarpal bone. 

The superficial digital flexor arises from the medial 
epicondyle of the humerus and consists of two parts. The 
tendon of the superficial head passes down behind the pos- 
terior annular ligament of the carpus (bound down by a 
special annular ligament), forms a ring at the fetlock for a 
tendon of the deep flexor, and ends by two branches on the 
second phalanx of the fourth digit. It receives a small 
band from the accessory carpal bone. The tendon of the 
deep head, after detaching a strong branch to the tendon 
of the deep flexor, passes down with the latter (for which 
it forms a ring), and ends on the third digit. 

The deep digital flexor has three heads — humeral, 
ulnar, and radial. The humeral head is very large and 
forms the greater part of the contour of the volar face of 
the forearm. It consists of two parts — a large superficial 
part, and a much smaller deep part which arises with the 
superficial flexor. Each ends at the distal part of the fore- 
arm on a short tendon. These unite and receive the ten- 
dons of the radial and ulnar heads and a branch from the 
superficial flexor tendon. The ulnar head has a short, 
thick, prismatic belly which arises from the medial surface of the proximal 
part of the ulna. Its long, thin tendon passes down on the humeral head and 
joins the tendon of the latter at the level of the accessory carpal bone. The 
radial head is small. It arises from the upper part of the medial border of the 
radius and from the deep fascia, and its tendon joins that of the humeral head at 
the distal end of the forearm. The common tendon divides into four branches, 




Fig. 317. — Muscles of Anti- 

BRACHIUM AND MaNUS 

OF Pig; Dorso- lateral 

View. 

a, a', Extensor carpi 
radialis; b, extensor carpi 
obliquus (s. abductor pollicis 
longus) ; c, d, e, common dig- 
ital extensor; c', c", tendons of 
insertion of c; d', d", tendons 
of d; e', e", tendons of e; f, 
tendon of extensor digiti se- 
cundi; ff, extensor digiti quarti ; 
h, extensor digiti quinti; /(', 
tendon of h; i, tendinous, and 
k, fieshy, part of ulnaris later- 
alis; k', tendon of k; I, ulnar 
head of deep digital flexor; m, 
superficial digital flexor; n, 
brachialis. (After EUenberger, 
in Leisering's Atlas.) 



MUSCLES OF THE HIP AND THIGH 365 

the larger central pair ending on the third phalanges of the principal digits, the 
smaller abaxial pair on the accessory digits. The latter are bound down by a 
peculiar spiral band. There is no subcarpal check ligament. The carpal sheath 
envelops the tendon of the deep flexor and that of the deep part of the superficial 
flexor. It extends from the distal third of the forearm to the distal third of the 
metacarpus. At the proximal part of the metacarpus a small muscular band ex- 
tends from the deep flexor tendon to the tendon of the deep part of the superficial 
flexor. Another muscular bundle passes from the deep flexor tendon to the second 
digit. 

The liimbricales are represented by bundles which extend from the deep flexor 
tendon to the tendon of the deep head of the superficial flexor. 

The third and fourth interossei are present. Each sends two slips to the cor- 
responding sesamoid bones and extensor tendon. 

There are flexors, adductors, and abductors of the second and fifth digits. 



Muscles of the Pelvic Limb 
sublumbar muscles 

The psoas minor is intimately united with the psoas major in front, and has a 
long small tendon which ends on the psoas tubercle. It has no thoracic part. 

The psoas major is large and rounded. It begins at the last rib. 

The quadratus lumborum is well developed, and extends to the last three or 
four thoracic vertebrae. 



MUSCLES OF THE HIP AND THIGH 

The tensor fasciae latae is broad, and its fleshy part reaches almost to the patella. 

The gluteus superficialis has a sacral head only; it blends with the biceps 
femoris. 

The gluteus medius has a small lumbar part which does not extend so far 
forward as in the horse. The deep part (Gluteus accessorius) is pretty clearly 
marked. 

The gluteus profundus is extensive, reaching nearly to the tuber coxae. 

The biceps femoris has a narrow origin from the sacro-sciatic ligament and 
tuber ischii. It ends below like that of the ox. 

The semitendinosus has two heads like that of the horse. 

The semimembranosus arises from the tuber ischii and has two insertions as 
in the ox. 

The sartorius has two heads of origin, between which the external iliac vessels 
are situated. The medial one arises from the tendon of the psoas minor, the lat- 
eral one from the iliac fascia. 

The graciles are united at their origin even more than in the ox. 

The pectineus is well developed and is flattened from before backward. 

The adductor shows no division and is partially fused with the gracilis. It 
ends on the femur just above the origin of the gastrocnemius. 

The quadratus femoris is large. 

The obturator extemus resembles that of the horse. 

The obturator intemus is extensive and strong; its tendon emerges through 
the obturator foramen. 

The gemellus is fused in part ^vith the obturator intemus. 

The quadriceps femoris is more clearly divided than in the horse, and its 
action is transmitted by a single patellar ligament. 

The capsularis is absent. 



366 



THE MUSCLES OF THE PIG 



MUSCLES OF THE LEG AND FOOT 
The peroneus tertius is a well-developed muscle which is in great part super- 
ficially situated on the front of the leg. It covers the long digital extensor, with 
which it is united except in the distal third of the leg. It arises from the extensor 
fossa of the femur by a common tendon with that muscle, 
a synovial pouch from the femoro-til)ial joint extending 
down under the origin. 

This sac is an inch and a half or more (ca. 3 to 4 cm.) in length 
in large subjects and extends around the hiteral edge of the tendon 
to its superficial face, so as to make a partial sheath and underlie 
the origin of the peroneus longus also. 

The muscle is continued at the distal end of the leg 
by a strong tendon which passes over the flexion surface of 
the hock, between the tendon of the long extensor (lateral) 
and that of the tibialis anterior (medial), all three being 
bound down by a strong annular ligament which extends 
across from one malleolus to the other. It ends by two 
or more branches on the first and second tarsal and third 
metatarsal bones. Not rarely there is a thin tendon in- 
serted into the fourth metatarsal bone. The tendon usu- 
ally receives a small branch from that of the tibialis an- 
terior at the annular ligament. 

The tibialis anterior is smaller than the preceding. It 
arises from the lateral surface of the tuberosity and lateral 
condyle of the tibia. At the distal end of the leg the ten- 
don passes under the annular ligament mentioned above 
(where it detaches a small branch to the peroneus tertius), 
and ends on the second tarsal and the proximal end of the 
second metatarsal bone. The terminal part passes under a 
superficial layer of the medial ligament of the hock, and is 
provided with a bursa. 

The peroneus longus descends in front of the fibula and 
the lateral extensor. It arises chiefly from the lateral con- 
dyle of the tibia. The tendon of insertion descends through 
a groove on the lateral malleolus, crosses over the tendons 
of the lateral extensor, then under the lateral ligament to 
the plantar surface of the hock, to end on the first tarsal 
bone. There is a bursa under the tendon where it lies in 
the groove on the fourth tarsal. The muscle is a flexor of 
the hock. 

The long digital extensor arises in common with the 
peroneus tertius, by which it is largely covered and with 
which it is united to the distal third of the leg. Three ten- 
dons appear at the proximal annular ligament and extend 
downward and a little medially over the flexion surface of 
the hock. Here they are bound down by an annular liga- 
ment given off from the tendon of the peroneus tertius and attached laterally 
to the distal end of the fibular tarsal bone. The tendons gradually diverge as 
they descend the metatarsus. The central one divides at the distal end of the 
metatarsus into two branches which end on the third phalanges of the chief 
(third and fourth) digits. This tendon is joined before bifurcating by the tendon 
of the extensor digitalis brevis. The medial tendon ends on the second and third 
phalanges of the medial chief (third) digit. It receives a branch from the inter- 




FiG. 318. — Muscles of Leg 
.\ND Foot of Pig; Dorso- 
L.\TER,\L View. 
a. Tibialis anterior; a', 
tendon of preceding; b, pero- 
neus tertiu.s; b\ tendon of b; 
c, long digital extensor; d, e, f, 
/', /", tendons of c; g, peroneus 
longus; g', tendon of g; h, 
extensor digiti quarti; h', 
tendon of h, which receives //' 
from the interosseus medius; 
i, extensor digiti quinti; k, deep 
digital flexor; I, soleus; m, 
gastrocnemius; n, extensor dig- 
italis brevis. (After Ellenber- 
ger, in Leisering's Atlas.) 



MUSCLES OF THE LEG AND FOOT 367 

osseus at the distal end of the first phalanx, and may detach a tendon to the second 
digit. The lateral tendon is smaller. Its branches end on the third phalanges of 
the accessory (second and fifth) digits and on the lateral chief (fourth digit) ; there 
may be a branch to the third digit, and the branch for the fourth may go to the 
corresponding branch of the central tendon. Other variations occur. 

The synovial sheath for the tendons of the extensor longus and peroneus tertius at the hock 
extends nearly half an inch (ca. 1 cm.) above the proximal annular ligament and an inch or more 
(ca. 2 to 3 cm.) below the distal annular ligament in a large adult. 

The lateral digital extensor lies on the lateral face of the leg, behind the per- 
oneus longus. It arises from the lateral surface of the fibula, the lateral femoro- 
tibial ligament, and the intermuscular septum between this muscle and the deep 
digital flexor. It consists of two parts. The larger anterior muscle (extensor 
digiti quarti) has a tendon which appears a little distal to the middle of the leg, de- 
scends on the grooved lateral surface of the fibula, inclines forward, crossing under 
the tendon of the peroneus longus, and ends on the extensor process of the third 
phalanx of the lateral chief (fourth) digit. It receives an interosseus tendon at 
the first phalanx. The tendon of the posterior muscle (extensor digiti quinti) 
accompanies that of the anterior one to the tarsus and descends to the lateral ac- 
cessory (fifth) digit. 

The two tendons are bound down at the lateral malleolus by an annular ligament. The 
anterior tendon may receive a branch of the long extensor tendon and send a tendon to the fifth 
digit. The posterior tendon may send a reinforcing branch to the tendon of the long extensor for 
the fifth digit. There may be a third small head which arises from the middle of the fibula and 
sends a delicate tendon to join that of the posterior head. 

The extensor hallucis longus is a small, fusiform muscle which is covered by the 
extensor longus and peroneus longus. It arises from the proximal end of the fibula 
and its delicate tendon descends at first under that of the peroneus tertius, inclines 
medially at the hock, and ends on the medial accessory (second) digit. 

The extensor digitalis brevis is a well-developed muscle which lies on the dor- 
sal face of the distal part of the tarsus and on the chief metatarsal bones. It arises 
from the neck of the tibial tarsal and the body of the fibular tarsal bone, and is 
partially divided into three parts. The tendon of the superficial part joins that of 
the long extensor for the chief digits. The deep part has two tendons which join 
those of the long extensor for the accessory digits. 

The gastrocnemius has short but wide and thick heads. The lateral one is 
the larger and is united with the superficial digital flexor to the distal third of the 
leg. The tendon forms a groove for the superficial flexor tendon above the hock 
and is inserted chiefly into the prominences on each side of the notch of the tuber 
calcis. 

The soleus is thick and wide and blends with the lateral head of the gastroc- 
nemius. It arises from the lateral epicondyle of the femur and the deep fascia 
at the stifle. Its tendon joins that of the gastrocnemius. 

The popliteus presents nothing remarkable. 

The superficial digital flexor has a belly of considerable size. It arises with the 
lateral head of the gastrocnemius, with which it is fused to the distal third of the 
leg. The tendon is almost entirely enclosed by the twist of the gastrocnemius in 
the lower part of the leg. At the tuber calcis it is thick and largely cartilaginous, 
and is molded on the groove and ridges of the bone. It is attached by a strong 
band to each side of the tuber calcis. A large bursa under the tendon extends up- 
ward in the groove formed by the gastrocnemius almost to the muscular part and 
downward to the middle of the fibular tarsal bone. The tendon divides distally 
into two branches which go to the chief digits. It also detaches from its plantar 
surface two bands which join the fascia of the accessory digits. 

The deep digital flexor presents three distinct heads: (1) The tibialis pes- 



368 THE MUSCLES OF THE DOG 

terior is the smallest. It has a fusiform belly in the proximal half of the leg and 
arises from the grooved plantar surface of the fibula. The tendon joins that of the 
flexor hallucis at the distal end of the leg. (2) The flexor digitalis longus is much 
larger and has a fusiform, pennate belly which extends obliquely across the prox- 
imal two-thirds of the leg. It arises from the proximal end of the fibula, the pop- 
liteal line, the middle third of the medial part of the plantar surface of the tibia, and 
the intermuscular septum between this muscle and the flexor hallucis. The ten- 
don (which has a synovial sheath) descends in a groove behind the medial malleolus, 
bound down by an annular ligament, inclines laterally on the joint capsule, and 
joins the tendon of the flexor hallucis. (3) The flexor hallucis has a large fusiform 
belly which extends almost to the distal end of the leg. It arises from the greater 
part of the plantar surface of the tibia, the medial surface and plantar border of 
the fibula, and the interosseous membrane. The tendon descends in the tarsal 
canal, receiving the tendons of the other heads, and ends like the corresponding 
one of the forelimb. The tarsal synovial sheath begins at the distal end of the 
muscular part and extends to the middle of the metatarsus. 

The lumbricales are absent, but there are four interossei. Rudimentary 
adductors of the second and fifth digits may be found. 



THE MUSCLES OF THE DOG 
Muscles of the Face 

The cutaneus of the face is well developed. Most of it is a continuation of the 
cervical cutaneus; the bundles extend forward over the lower part of the lateral 
surface of the face to the angle of the mouth and the upper lip. Other bundles ex- 
tend upward; some of these spread out on the cheek and lateral nasal region, and 
a thin la3^er passes toward the lower eyelid, blending with the orbicularis oculi and 
constituting a malaris muscle. Another stratum is attached to the scutiform carti- 
lage and spreads out on the masseter. 

The orbicularis oris is poorly developed. In the upper lip it is divided cen- 
trally, and in the lower lip it is distinct only near the angles of the mouth. 

The levator nasolabialis is wide and undivided. It has an extensive origin on 
the frontal and nasal bones. The fibers run downward and forward to the lateral 
wing of the nostril and the upper lip. 

The levator labii superioris proprius arises behind the infraorbital foramen, 
runs forward under the preceding muscle, and ends in numerous small tendons 
which are in part inserted around the nostril, in part blend with those of the oppo- 
site side. 

The zygomaticus is narrow and very long; it arises on the scutiform cartilage, 
and ends at the angle of the mouth. 

The depressor labii inferioris is absent. 

There are no special nasal muscles. The homologue of the lateral dilator is 
triangular; it is small at its origin just ventral to the levator labii superioris pro- 
prius, and ends almost entirely in the upper lip. 

The buccinator is wide and very thin, and the two planes of fibers cross each 
other. 

The palpebral muscles present no very noteworthy special characters. Two 
small muscles act on the upper eyelid. One of these, the corrugator supercilii, 
arises from the fascia on the frontal bone and ends near the medial canthus. The 
other arises from the zygomatic arch and ends near the lateral canthus. 



MUSCLES OF THE FACE 



369 




Fig. 319. — Muscles op Head of Dog. 
o, Scutularis; b, c, anterior auricular muscles; rf, helicis; e, antitragicus; /,/, zygomaticus, out of which a portion 
is cut; g, stump of cutaneus attached to scutiform cartilage; h, parotido-auricularis; i, masseter; k, malaris; I, 
levator nasolabialis; m, levator labii superioris proprius; ra, dilatator naris lateralis; o, p, buccinator (buccalis. molaris) ; 
q, retractor angulioris (from cutaneus); r, occipito-mandibularis; s, mylo-hyoideus; /, base of concha; S, parotid 
gland; 2', parotid duct; 3, mandibular gland; 4. mandibular lymph glands; S, buccal glands; 6, zygomatic arch; 
7, maxilla; 8, dorsum nasi; 9, parotid lymph gland. (Ellenberger-Baum, Anat. d. Hundes.) 





Fig. 320. — Superficial Muscles of Dog, After Removal of M. cutaneus. 
Levator nasolabialis; 2, levator labii superioris proprius; 3, dilatator naris lateralis; 4, 4'i buccinator; 5, 



tractor anguli oris; e, zygomaticus; 7, malaris; 5, masseter; 9, occipito-mandibularis, /O, scutularis; /i, other auric- 
ular muscles; 12, parotido-auricularis; 13, mjlo-hyoideus; 14< sterno-hyoideus; IS, sterno-thyroideus; 16, spienius; 
17, lumbo-dorsal fascia; 18, rectus abdominis; 19, obliquus abdominis externus; 19', aponeurosis of preceding; 20, 
intercostal muscle; 21. sacro-coccygeus accessorius; 22, sacro-coccygeus dorsalis; 23, sacro-coccygeus ventralis; 24i 
great trochanter; ^-5, jugular vein; a, 6, c, brachiocephalicus; d, clavicle; e, /, trapezius; a, serratus cervicis; A, omo- 
transversarius; i, latissimus dorsi; k, posterior deep pectoral; I, supraspinatus; to, to', deltoid; re, infraspinatus; o, 
triceps, long head; o', triceps, lateral head; p, brachialis; q, extensor carpi radialis; r, gluteus medius; s, gluteus 
superficiaUs; <,«', tensor fasciae latae; u, sartorius; n, biceps femoris; i', fascia lata; t/), semitendinosus; z, semimem- 
branosus; y, sartorius; z, gracilis; 26, pronator teres; 27, flexor carpi radialis; 28, flexor carpi ulnaris; 29, tibialis 
anterior; 30, popliteus; 5/, 3/', deep digital flexor; 3^, superficial digital flexor; 33, gastrocnemius; 34, spine of scap- 
ula; a, parotid gland, with a', its duct; fi, mandibular gland; S, mandibular lymph glands; rj, parotid lymph gland; 
f, inferior buccal glands. (After EUenberger, in Leisering's Atlas.) 
24 



370 



THE MUSCLES OF THE DOG 



MUSCLES OF THE MANDIBLE 
The masseter is thick and its superficial face is strongly convex. It arises 
from the zygomatic arch, and extends beyond the branch of the jaw below and be- 
hind. Three partly separate strata may be recognized in its structure. 

The temporalis is very large and 
strong, and contains much tendinous 
tissue. It arises from the temporal 
fossa and the orbital ligament and 
ends on the coronoid process of the 
mandible. It blends in part with 
the masseter. 

The pterygoideus lateralis is 
not distinct from the medialis. 

The digastricus is absent. 

The occipito-mandibularis is a 
strong, round, fleshy muscle, which 
arises on the paramastoid process 
and is inserted into the border and 
medial surface of the ramus of the 
mandible at the level of the last 
molar teeth; it sometimes has a 
tendinous intersection. 



HYOID MUSCLES 

The mylo-hyoideus is well de- 
veloped. 

The stylo-hyoideus is very slen- 
der, and is inserted into the body of 
the hyoid bone. 

The hyoideus transversus and 
omo-hyoideus are absent. 

The stemo-thyro-hyoideus is 
large and arises chiefly on the first 
costal cartilage. It is clearly di- 
vided into stemo-thyroideus and 
stemo-hyoideus. 




Fig. 321. — Ventral Muscles of Head, Neck, and Thorax 
OF Dog. 
a, Mylo-hyoideus; 6, occipito-mandibularis; c, sterno- 
hyoideus; c', sterno-thyroideus ; d, sterno-cephalicus; e, brachio- 
cephalicus; /, subscapularis; g, superficial pectoral; h, deep pec- 
toral; i, rectus abdominis; k, obliquus abdominis externus; I, 
long head of triceps; m, medial head of triceps; n, biceps 
brachii; o, brachialis; 1, 1', 1", mandibular lymph glands; 2, 
thyroid gland; 3, external jugular vein. (EUenberger-Baum, 
Anat. d. Hundes.) 



Muscles of the Thoracic Limb 

The trapezius is thin, and is 
divided into cervical and thoracic 
portions by a narrow aponeurotic 
part. Its line of origin extends from 
about the middle of the dorsal bor- 
der of the neck to the ninth or tenth thoracic spine, the right and left muscles 
meeting (except at their posterior part) on a median fibrous raphe. It is inserted 
into the entire length of the spine of the scapula. 

The omo-transversarius arises by a tendon on the lower part of the spine of 
the scapula (where it is often partially blended with the trapezius) , and is inserted 
into the wing of the atlas. 



MUSCLES OF THE THORACIC LIMB 371 

The rhomboideus consists of three parts. The rhomboideus thoracalis is 
small ; it arises from the fourth to the sixth or seventh thoracic spine, and is inserted 
into the medial surface (chiefly) of the dorsal angle of the scapula. The rhom- 
boideus cervicalis arises from the ligamentum nuchge as far forward as the second 
or third cervical vertebra, and is inserted into the medial surface of the cervical 
angle of the scapula. The rhomboideus capitis is a narrow band which is given off 
laterally from the preceding; it is inserted into the nuchal crest. 

The latissimus dorsi is extensive ; it has an attachment to the last two ribs and 
also to the upper part of the spine of the scapula in addition to the origin from the 
lumbo-dorsal fascia. Its lower edge blends near the shoulder with the cutaneus. 

The brachiocephahcus contains in front of the shoulder a tendinous intersec- 
tion and a fibrous mass in which the clavicle is embedded. Anterior to this it sepa- 
rates into two diverging parts. The dorsal part is the cleido-cervicaUs, which 
widens above and is attached to the median raphe of the neck and to the occipital bone. 
The ventral part is the cleido-mastoideus ; it is narrow and is attached to the mas- 
toid process. The common mass posterior to the clavicle and the fibrous inter- 
section, which is attached to the humerus, is homologous with the clavicular part 
of the deltoid of man. 

The superficial pectoral muscle is small. It arises on the sternum from the 
manubrium as far back as the third costal cartilage, and is inserted into the humerus 
at the border between the medial and anterior surfaces. A superficial slip detached 
from it is inserted into the fascia of the forearm. The deep pectoral has no scapular 
part. It arises on the sternum and costal cartilages from the second costal to the 
xiphoid cartilage, and from the aponeurosis of the obliquus abdominis externus. 
It is inserted chiefly into the medial tuberosity of the humerus, but also Ijy small 
slips into the lateral tuberosity and the fascia of the arm. 

The serratus ventralis shows no clear division into cervical and thoracic parts. 
It arises from the last five cervical vertebrae and the first eight ribs, and is inserted 
into the upper part of the costal surface of the scapula. 

The deltoid is clearly divided into scapular and acromial parts. The scapular 
part is triangular and arises from almost the entire length of the spine of the scapula; 
it is inserted largely into the fascia on the lateral surface of the arm. The acromial 
part is short, thick, and fusiform; it arises from the lower edge of the acromion, 
and ends on the deltoid tuberosity. 

The supraspinatus is large ; it ends chiefly on the lateral tuberosity of the hu- 
merus, but has a small attachment to the medial tuberosity also. 

The infraspinatus is bipennate. The tendon of insertion passes in a groove on 
the lateral tuberosity of the humerus, to end on a well-defined mark on the same; a 
large bursa lies under the tendon. 

The teres minor is short and fusiform ; it arises on a tubercle on the posterior 
border of the scapula, just above the glenoid cavity, and is inserted into a tubercle 
on the upper part of the deltoid ridge. 

The subscapularis is wide and is multipennate in structure, being intersected 
by fibrous septa which are attached to the rough lines on the costal surface of the 
scapula. It is inserted into the medial tuberosity of the humerus. 

The teres major is thick. It arises on the upper part of the posterior border 
of the scapula and on the subscapularis, and is inserted into an eminence (tuber- 
ositas teres) on the proximal third of the medial surface of the humerus by a com- 
mon tendon with the latissimus dorsi. 

The coraco-brachialis has a short and undivided belly. It arises from a small 
depression on the medial surface of the tuber scapulae, and ends on the proximal 
third of the humerus, just medial to the brachialis. The tendon of origin has a syno- 
vial sheath. 

The capsularis is absent. 



372 



THE MUSCLES OF THE DOG 



The biceps brachii lies almost entirely on the medial surface of the humerus. 
It is long and fusiform. The tendon of origin is round, and is bound down in the 
intertuberal groove by an annular ligament. It is enveloped by an extension of 
the synovial membrane of the shoulder joint. The tendon of insertion is bifid; 



( 

Teres major 1 

Latissimus dorsi -.^^^^K\ ^ 'ir'/ 

Lot^g head of triceps _^ ^ '^ 

Tensor fascice antibrachii ... ||i'|, 

-II r/ #/^ 

Medial head of triceps —MMLI^^^ / m// 

Flexor carpi ulnar is -ll|'i \l \^ 

Flexor car pi radialis IIL-Vi \ ' 

Superficial digital flexor %- ^ 

Deep digital flexor «»,xM 1^ \\ 

JW 

'I 





~ Subscaj}ularis 
- Supra spinatus 



Coraco-brachialis 
Accessory head of triceps 



Biceps brachii 



Humerus 



Extensor carpi radialis 
Pronator teres 



Radius 

Radial head of deep 
digital flexor 



[uscLEs OF Thoracic Limb of Dog; Medial View. CEllenberger-Baum, Anat. des Hundes.) 



one branch is attached to a rough mark on the lateral surface of the ulna, just below 
the semilunar notch; the other branch ends on a distinct mark on the postero- 
medial aspect of the proximal part of the shaft of the radius, one to two inches be- 
low the head. 



MUSCLES OF THE THORACIC LIMB 



373 



The brachialis is very little curved. Its tendon of insertion passes over the 
medial ligament of the elbow and under the ulnar tendon of the biceps and ends 
just proximal to the latter. The tendon of the biceps forms a partial sheath for 
that of the brachialis. 

The tensor fasciae antibrachii is thin and narrow. It arises on the tendon and 
lateral surface of the latissimus dorsi, and ends on the 
olecranon and the fascia of the forearm. 

The triceps has an additional deep head (Caput 
accessorium), which arises just below the head of the 
humerus. The medial head is very long; it arises from 
a mark on the proximal fourth of the medial surface of 
the humerus, just behind the insertion of the teres major 
and latissimus dorsi. A bursa lies on the olecranon in 
front of the common tendon of insertion. 

The brachioradialis is a long, narrow, delicate mus- 
cle, situated superficially on the dorsal surface of the 
forearm. It arises with the extensor carpi on the crest 
above the lateral epicondyle of the humerus, and is in- 
serted into the distal part of the medial border of the 
radius. It is often much reduced, and is sometimes ab- 
sent. It rotates the forearm and paw outward. 

The extensor carpi radialis arises on the lateral con- 
dyloid crest and divides into two parts. The larger lat- 
eral part, the extensor carpi radialis brevis, ends on the 
proximal end of the third metacarpal bone. The medial 
and more superficial part, the extensor carpi radialis 
longus, ends on the second metacarpal bone. (A ten- 
don to the fourth metacarpal ma}^ occur.) 

The extensor carpi obliquus or abductor pollicis 
longus arises from the lateral border and dorsal surface 
of the ulna, the interosseous ligament, and the proximal 
part of the lateral border of the radius. It is inserted 
into the first metacarpal bone by a tendon which con- 
tains a small sesamoid bone. It abducts the first digit. 

There are three (or four) extensors of the digits. 

1. The common digital extensor (M. extensor digi- 
talis communis) arises on the lateral epicondyle of the 
humerus and the lateral ligament of the elbow joint. 
It has four bellies, each of which has a tendon of inser- 
tion. These end on the third phalanges of the second, 
third, fourth, and fifth digits. 

2. The extensor of the first and second digits (M. 
extensor pollicis longus et extensor indicis proprius) is 
small, and is covered by the common and lateral ex- 
tensors. It arises on the proximal half of the ulna. Its 
tendon descends with that of the common extensor and 
divides into two branches. The delicate medial branch 
ends on the first digit, while the larger lateral one ends 
with the tendon of the common extensor for the second 
digit. 

3. The lateral digital extensor (M. extensor digitalis lateralis) consists of two 
muscles which are not rarely fused. They arise on the lateral epicondyle of the 
humerus and the lateral ligament of the elbow joint. The larger superficial muscle 
is the extensor of the third and fourth digits (M. extensor digiti tertii et quarti); 




Fig. 323. — Muscles of Antibra- 

CHIUM AND MaNUS OF DoG; 

Lateral View. 

a, Triceps brachii; 6, brachi- 
alis: c, extensor carpi radialis; d, 
common digital extensor; d', d", 
d'", d"", tendons of preceding; e, 
lateral digital extensor; e', /, ten- 
dons of preceding; g, ulnarid 
lateralis; h, ulnar head, h', hu- 
meral head of flexor carpi ulnaris; 
t, extensor carpi obliquus (s. ab- 
ductor pollicis longus) ; k, inter- 
ossei; I, branches from preceding 
to extensor tendons; 1, olecranon; 
2, radius; 3, lateral epicondyle of 
humerus. (After EUenberger, in 
Leisering's Atlas.) 



374 



THE MUSCLES OF THE DOG 



its tendon divides at or near the carpus into two branches, which are inserted into 
the third phalanges of the third and fourth digits, blending with the corresponding 
tendons of the common extensor. The posterior muscle is the extensor of the fifth 
digit (M. extensor digiti quinti) ; its tendon fuses with that of the common extensor 
for the fifth digit. 

The ulnaris lateralis or extensor carpi ulnaris is a large flat muscle which lies 
on the lateral surface of the ulna. It arises on the lateral epicondyle of the humerus, 
and is inserted into the proximal end of the fifth metacarpal and the accessory carpal 
bone. It is chiefly an abductor of the paw. 

The flexor carpi ulnaris consists of two quite distinct heads. The larger 
humeral head arises on the medial epicondyle, while the smaller, 
superficial ulnar head arises on the posterior border of the ulna. 
The tendons of the two end on the accessory carpal bone and 
have a bursa between them. 

The flexor carpi radiaHs arises on the medial epicondyle of 
the humerus and is inserted by a bifid tendon into the second 
and third metacarpal bones. 

The tendons of the foregoing eight muscles are provided 
with synovial sheaths at the carpus. 

The pronator teres is a fusiform muscle, which is situated 
superficially on the proximal part of the medial border of the 
radius. It arises on the medial epicondyle of the humerus, and 
is inserted into the dorsal surface and medial border of the radius 
almost half way to the carpus. It is related deeply to the radial 
vessels, the median nerve, and the tendon of the biceps. Its 
action is to flex the elbow and rotate the forearm inward (pro- 
nation). 

The superficial digital flexor is situated superficially on 
the medio-volar surface of the forearm. It arises on the medial 
epicondyle of the humerus and terminates near the carpus on a 
tendon which passes dowTiward outside of the carpal canal and 
receives below the carpus two reinforcing bands, one from the 
accessory carpal, the other from the sesamoid bone at the medial 
side of the carpus. It divides distally into four branches, which 
are inserted into the second phalanges of the second, third, 
fourth, and fifth digits. 

The deep digital flexor has humeral, ulnar, and radial 

heads; the radial head arises from the medial border of the 

radius. They unite on a common tendon which passes down 

through the carpal canal, gives off a branch to the first digit, 

and divides into four branches. These perforate the tendons 

of the superficial flexor and are inserted into the third phalanges 

of the second to the fifth digits. The tendons are provided with 

synovial sheaths from the middle of the metacarpus downward, 

and are held in place by three digital annular ligaments. 

The palmaris longus^ is a small muscle which arises from the deep digital 

flexor below the middle of the forearm, and ends by two tendons which unite with 

those of the superficial flexor for the third and fourth digits. 

The supinator is a short, flat, fusiform muscle which arises from the front of 
the lateral epicondyle of the humerus with the lateral ligament, and from the lateral 
prominence of the head of the radius, and is inserted into the proximal fourth of the 

1 The homology here is doubtful. Sussdorf regards the ulnar head of the deep digital flexor 
as the homologue of the palmaris longus of man, while Alexais considers that the latter is repre- 
sented by the superficial digital flexor. 




Fig. 324. — Volar Mus- 
cles OF Left Fore- 
Paw OF Dog. 
o, Abductor pol- 
licis brevis et opponens 
poUicis; b, flexor poUi- 
cis brevis; c, adductor 
poUicis; d, adductor 
digiti secundi; e, ad- 
ductor digiti quinti; /, 
flexor digiti quinti 
brevis; g, abductor 
digiti quinti; h, in- 
terossei; 1, accessory 
carpal bone; S, first 
digit; 3-6, sesamoids 
of metacarpo-phalan- 
geal joints. (Ellen- 
berger-Baum, Anat. d. 
Hundes.) 



MUSCLES OF THE THORACIC LIMB 375 

dorsal surface