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Full text of "A text-book of veterinary anatomy"

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Webster Famyy UDrary ot Veterinary Iviedicine 
Cummings School of Veterinary Medicine at 
Tufts University 
200 Westboro Road 
North Grafton, MA 01 535 



A TEXT-BOOK 



of 



VETERINARY ANATOMY 



BY 

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

PROFESSOR OF COMPARATIVE ANATOMY IN OHIO STATE UNIVERSITY, COLUMBUS, OHIO 
MEA\BER OF THE AMERICAN ASSOCIATION OF ANATOMISTS 



WITH 588 ILLUSTRATIONS 
MANY IN COLORS 



PHILADELPHIA AND LONDON 

W. B. SAUNDERS COMPANY 

191 1 



\0 



Copyright, 1910, by W. B. Saunders Company 



Reprinted July, 1911 



PRINTED IN AMERICA 



TO 

KATHERINE OLDHAM SISSON 

ESf GRATEFUL RECOGNITION OF CONSTANT 

INSPIRATION AND ENCOURAGEMENT 

THIS BOOK IS DEDICATED 

By THE Author 



PREFACE 

The lack of a modern and well-illustrated book on the structure of the i)rinci- 
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 lal)oratory 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 clinical 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 l)elieved 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 English- 
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 sul)stantial adoption of this terminology, but considered it 
desirable to offer a sort of transitional stage at ]:)resent. 

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 publishers 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 l)e 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 eft'ort of the pul)lishers 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 pagk 

The Skeleton 19 

Structure of Bones -f> 

Development and Growth of Bone 22 

Composition and Physical Properties of Bone 23 

Descriptive Terms 23 

The Vertebral Column 24 

The Ribs and Costal Cartilages 25 

Costal Cartilages 26 

The Sternum 2G 

The Thorax 27 

The Skull 27 

Bones of the Thoracic Limb 27 

Bones of the Pelvic Limb 29 

Skeleton of the Horse 31 

Vertebral Column 31 

Ribs. 43 

Sternum -^^ 

Bones of the Skull -i" 

Cranium -1" 

Face ^7 

The Skull as a Whole 65 

The Cranial Cavity 69 

The Nasal Cavity "1 

The Paranasal Sinuses '2 

Bones of the Thoracic Limb ' -i 

Bones of the Pelvic Limb 92 

Skeleton of the Ox 112 

Vertebral Column 112 

Ribs 11-1 

Sternum 1 1 -^ 

Bones of the Skull 115 

The Skull as a Whole 123 

Bones of the Thoracic Limb 127 

Bones of the Pelvic Limb 131 

Skeleton of the Pig 136 

Vertebral Column 136 

Ribs 138 

Sternum 139 

Bones of the Skull 139 

The Skull as a Wliole 144 

Bones of the Thoracic Limb 146 

Bones of the Pelvic Limb 148 

Skeleton of the Docj 150 

Vertebral Column 150 

Ribs 153 

11 



12 CONTENTS 

PAGE 

Sternum 153 

Bones of the Skull 153 

The Skull as a Whole 159 

Bones of the Thoracic Limb 162 

Bones of the Pelvic Limb 165 

ARTHROLOGY 

Synarthroses 169 

DiARTHROSES 170 

Amphiarthroses 172 

Articulations of the Horse 172 

Joints and Ligaments of the Vertebra^ 172 

Atlanto-occipital Articulation 176 

Costo-vertebral Articulations 177 

Costo-chondral Articulations 178 

Chondro-sternal Articulations 178 

Sternal Joints and Ligaments 178 

Articulations of the Skull 179 

Articulations of the Thoracic Limb 180 

Articulations of the Pelvic Limb 190 

Articulations of the Ox, Pig, and Dog 203 



THE MUSCULAR SYSTEM— MYOLOGY 

The Muscles and Accessory Structures 211 

Fasci.« and Muscles of the Horse 213 

Panniculus carnosus 213 

Fascise and Muscles of the Head 213 

Fasciae and Muscles of the Neck 224 

Fasciae and Muscles of the Back and Loins 235 

Fasciae and Muscles of the Tail 238 

Muscles of the Thorax 240 

Muscles of the Abdomen 245 

Muscles of the Thoracic Limb , 250 

Fasciae and Muscles of the Pelvic Limb 273 

Muscles of the Ox 295 

Muscles of the Pig 311 

Muscles of the Dog 318 

SPLANCHNOLOGY— THE DIGESTIVE SYSTEM 

Digestive System of the Horse 330 

The Mouth 330 

The Tongue 335 

The Teeth 338 

The Salivary Glands 346 

The Pharynx 348 

The oesophagus 350 

The Abdominal Cavity 352 

The Peritoneum 353 

The Pelvic Cavity 354 

The Stomach 357 

The Small Intestine 360 

The Large Intestine 363 

The Pancreas 371 

The Liver 373 

The Spleen 377 

The Peritoneum 379 



CONTENTS 13 



PAGE 



Digestive System of the Ox 382 

Digestive System of the Sheep 405 

Digestive System of the Pig 410 

Digestive System of the Dog 423 



THE RESPIRATORY SYSTEM 

Respiratory System of the Horse 436 

The Nasal Cavity 43G 

The Larynx 440 

The Trachea 448 

The Bronchi 450 

The Thoracic Cavity 450 

The Pleune 451 

The Lungs 453 

The Thyroid Gland of the Horse 457 

The Thymus of the Horse 458 

Respiratory System of the Ox 458 

Respiratory System of the Pic; 464 

Respiratory System of the Dot; 466 



THE UROGENITAL SYSTEM 

Urinary Organs of the Horse 469 

The Kidneys 469 

The Ureters 475 

The Urinary Bhxdder 475 

The Adrenal Bodies 477 

Urinary Organs of the Ox 478 

Urinary Organs of the Pig 481 

Urinary Organs of the Dog 483 



THE MALE GENITAL ORGANS 

Male Genital Organs of the Horse 485 

The Testicles 485 

The Scrotum 487 

The Vas Deferens 488 

The Spermatic Cord 489 

The Tunica Vaginalis 489 

Descent of the Testicles 490 

The VesicuUr Seminales 491 

The Prostate 493 

The Uterus Masculinus 493 

The Bulbo-urethral Glands 493 

The Penis 494 

The Prepuce 496 

Male Genital Organs of the Ox 500 

Male Genital Organs of the Pig 504 

Male Genital Organs of the Dog 506 



THE FEMALE GENITAL ORGANS 

Genital Organs of the Mare 508 

The Ovaries 508 

The Uterine or Fallopian Tubes 511 

The Uterus 511 

The Vagina 514 



14 CONTENTS 

P\GE 

The Vulva 514 

The Urethra 515 

The Mammary Glands 516 

Genital Organs of the Cow 517 

Genital Organs of the Sow 521 

Genital Organs of the Bitch 522 



ANGIOLOGY 

The Organs of Circflation 524 

Blood-vascular System of the Horse 525 

The Pericardium 525 

The Heart 526 

The Pulmonary Artery 535 

The Systemic Arteries 535 

The Coronary Arteries 537 

The Brachiocephalic Trunk or Anterior Aorta 537 

Arteries of the Thoracic Limb 556 

Branches of the Thoracic Aorta 565 

Branches of the Abdominal Aorta 566 

Arteries of the Pelvic Limb 578 

The Veins 585 

The Pulmonary Veins 585 

The Systemic Veins 585 

The Anterior Vena Cava and its Tributaries 586 

The Posterior Vena Cava and its Tributaries 595 

The Lymphatic System 599 

Lymphatic System of the Horse 600 

The Lymph Glands and Vessels of the Heatl and Neck 601 

The Lymph Glands and Vessels of the Thorax 603 

The Lymph Glands and Vessels of the Abdomen and Pelvis 604 

The Lymph Glands and Vessels of the Thoracic Limb 605 

The Lymph Glands and Vessels of the Pelvic Limb 606 

The Foetal Circulation 606 

Blood-vascular System of the Ox 608 

The Pericardium and Heart 608 

The Arteries 609 

The Veins 621 

Ly'mphatic Sy'stem of the Ox 623 

Circulatory System of the Pig 626 

The Pericardium and Heart 626 

The Arteries 627 

The Veins 630 

Lymphatic System of the Pig 630 

Circulatory System of the Dog 632 

The Pericardium and Heart 632 

The Arteries 633 

The Veins 641 

Lymphatic System of the Dog 643 

NEUROLOGY.— THE NERVOUS SYSTEM 

General Considerations 644 

Nervous System of the Horse 648 

The Spinal Cord 648 

The Brain 652 

The Cranial Nerves • t)7() 

The Spinal Nerves. 692 



CONTENTS 15 

PAGE 

Sympathetic Nervous System of the Hokse 710 

Nervous System of the Ox 715 

Nervous System of the Pig 720 

Nervous System of the Dog 724 



^STHESIOLOGY 

The Sense Organs and Skin of the Horse 734 

The Eye 734 

The Ear 747 

The Skin 761 

The Olfactory and Gustatory Apparatus 772 

The Sense Organs and Skin of the Ox 772 

The Sense Organs and Integument of the Pig 777 

The Sense Organs and Integument of the Dog 770 



Index 783 



VETERINARY ANATOMY 



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 gross or macroscopic 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. 

This 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 wliich it has undergone as disclosed by the geological record. 

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 details 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 
2 17 



18 VETERINARY ANATOMY 

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 

2. Arthrology 

3. Myology 

4. Splanchnology 

(1) Digestive System 

(2) Respiratory System 

(3) Urogenital System 

(a) Urinary Organs 

(b) Genital Organs 

5. Angiology 

6. Neurology 

7. ^Esthesiology 

(1) Sense Organs 

(2) Common Integument. 

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 orcUnary standing position. 
The surface directed toward the plane of support (the ground) is termed inferior 
or ventral, and the opposite surface is superior or dorsal ; 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 median plane is internal or medial to it, and an object or surface which is further 
than another from the median plane is external or lateral 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 head end of the body is termed anterior, cephalic, or cranial ; and the 
tail end posterior or caudal ; relations of structures with regard to the longitudinal 
axis of the body are designated accordingly. Certain terms are used in a special 
sense as applied to the limbs. Proximal and distal express relative distances of 
parts from the axis of the body. The anterior face of the thoracic limb from the 
elbow downward is also 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 internal or medial 
and external or lateral in the animals with which we are concerned. 

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 ca\aties 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. 



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 which 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 tlie shells and cliitinous co\'crings 
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 chiefly from the mesoderm, but includes the notochord or primi- 
tive 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 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 foetus 
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 
somewliat similar dimensions in length, breadth, and thickness. Their chief func- 
tion appears to be that of diffusing concussion. Sesamoid bones, which are 
developed 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. This group would include bones of irregular shape, 
such as the vertebne 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. 

19 



20 



OSTEOLOGY 



STRUCTURE OF BONES' 

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

The architecture of bone can be studied best by means of longitudinal and 
cross-sections. These show that the bone consists of an external shell of dense 
compact substance, within which is the more loosely arranged spongy substance. 





Fig. 1. — Frontal Skction of Large Metatarsal Fig. 2. — Sagittal Section of Large Metatarsal 

Bone of Horse, Posterior Part. Bone of Horse. 

iS'.C, Compact substance; S.s., spongy substance; Cm., medullary cavity; F.n., nutrient foramen. Note the 
greater thickness of the compact substance of the inner and anterior parts of the shaft. 

In typical 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 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. 



' Only tho fi;ross structure is discussed here, 
be made to iiistological works. 



For the microscopic structure reference is to 



STRUCTURE OF BONES 21 

The spongy substance (Substantia spongiosa) consists of delicate bony plates 
and spicules which run in various directions and intercross. These plates are 
definitely arranged with regard to mechanical requirements, so that systems of 
pressure and tension plates can be recognized, in conformity with the lines of pres- 
sure and the pull of tendons and ligaments respectively. The intervals (marrow 
spaces) between the plates are occupied by marrow. The spongy substance forms 
the bulk of short bones and of the extremities of long bones; in the latter it is not 
confined to the ends, but extends a variable distance along the shaft also. Some 
bones (Ossa pneumatica) contain air-spaces or sinuses within the compact sub- 
stance instead of spongy bone and marrow. 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 even 
undergo absorption, producing an actual deficiency. 

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

The periosteum is the membrane which invests the outer surface of bone, 
except where it is covered with cartilage. It consists of an outer protective fibrous 
layer, and an inner cellular osteogenic layer. During active growth 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 activity of the periosteum. 

The marrow (Medulla ossium) occupies the interstices of the spongy 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 
rubra), 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 substance, while the yellow is practically ordinary acUpose tissue. 

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. 

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 
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 bones and supply the spongy bone and 
marrow in them. In the case of the larger bones — and especially the long bones — • 
the large medullary or nutrient artery enters at the so-called nutrient 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 they are destitute of valves. 

The lymph-vessels form perivascular channels in the periosteum and the 
Haversian canals of the compact substance. Lymph-spaces exist at the periphery 
of the marrow. 

The nerves appear to be distributed chiefly to the blood-vessels. Special 
nerve-endings (Vater-Pacini corpuscles) in the periosteum are to be regarded as 
sensory, and probably are concerned in mediating the muscle sense (Kopsch), 



22 



OSTEOLOGY 



DEVELOPMENT AND GROWTH OF BONE' 
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 development the process begins at a definite center of 
ossification where the cells (osteoblasts) surround themselves with a deposit of 

bone. The process extends from this center to the 
periphery of the future bone, thus producing a net- 
work of bony trabeculse. The trabeculse 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 periosteal bone are formed 
by osteoblasts until the bone attains its definitive 
thickness. 

In endochondral ossification the process is funda- 
mentally the same, but not quite so simple. Osteo- 
blasts emigrate from the deep face of the perichon- 
drium or primitive periosteum into the cartilage and 
cause calcification of the matrix or ground-substance 
of the latter. Vessels extend into the calcifying area, 
the cartilage cells shrink and disappear, forming 
primary marrow cavities which are occupied by pro- 
cesses of the osteogenic tissue. There is thus formed 
a sort of scaffolding of calcareous trabeculse on which 
the bone is constructed by the osteoblasts. At the 
same time perichondral bone is formed by the osteo- 
blasts of the primitive periosteum. The calcified 
cartilage is broken dowm and absorbed through the 
agency of large cells called osteoclasts, and is re- 
placed 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, 
one for the diaphysis or shaft and one for each epiphysis or extremity. Many 
bones have secondary centers from which processes or apophyses develop. 

The foregoing outline accounts for the growth 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 
growing cartilage — the epiphyseal cartilage — which intervenes between the diaph- 

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




Fig. 3. — Left Femur of Young Pig, 
External View, to Show Di- 
vision OF A Long Bone into 
Shaft (s) and Extremities. 
Proximal extremity consi.sts of 
two parts, head (A) and trochanter 
major (t. m.), which have separate 
centers of ossification. Distal extrem- 
ity consists of trochlea (/) and condyles 
(c); e.I., epiphyseal cartilages; s./., 
supracondyloid fossa. 



CHEMICAL COMPOSITION OF BONE — DESCRIPTIVE TERMS 23 

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 ossifica- 
tion, 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. 

After the bones have reached their full size, the periosteum l^ecomes 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 healing of fractures and the occurrence of bony enlarge- 
ments. 

CHEMICAL COMPOSITION OF BONE 

Dried bone consists of organic and inorganic matter in the ratio of 1 : 2 
approximately. 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 animal matter when boiled 
yields gelatin. The following table represents the composition in 100 parts of ox 
bone of average quality: 

Gelatin 33.30 

Phosphate of lime 57.35 

Carbonate of hme 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. 

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 shar}) ritlge. 

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. 



24 



OSTEOLOGY 



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 or antrum is an air-cavity. 

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



VERTEBRAL COLUMN 

The vertebral column (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 (Vertebra? immobiles), as 
distinguished from the movable or "true" 
vertebrae (Vertebrae mobiles). 

The column is subdivided for descrip- 
tion into five regions, which are named ac- 
cording to the part of the body in which 
they are placed. Thus the vertebrae are 
designated as cervical, thoracic (or dorsal), 
lumbar, sacral, and coccygeal or caudal 
(Vertebrae cervicales, thoracales, lumbales, 
sacrales, coccygeae). The number of verte- 
brae in a given species is fairly constant in 
each region except the last, so that the ver- 
tebral formula may be expressed (for the 
horse, for example) as follows: 
CyTigLgSjCyjj.^j. 
The vertebrae in a given region have 
special characters by which they may be 
distinguished from those of other regions, and individual vertebrae have characters 
which are more or less clearly recognizable. All typical vertebrae have a common 
plan of structure, which must first be understood. The parts of which a vertebra 
consists are the body or centrum, 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 vertebrae 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 
laterally, and is in relation to various muscles and viscera. In the thoracic region 
the body presents two pairs of demifacets (Foveae costales) at the extremities for 
articulation with the heads of two pairs of ribs. 

The arch (Arcus vertel^rae) 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 pedicles form the lateral parts of the arch, and are 

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




Trojisv. 



fiuief 



Fig. 4. — First Thoracic Vertebr.e of Horse 
To illustrate plan of structure of vertebrje. 



THE RIBS 25 

cut into in front and behind by the vertebral notches (Inoisura vertebraHs cranialis, 
caudaUs). The notches of two adjacent vertebra' form intervertebral foramina 
for the passage of the spinal nerves and vessels ; in some vertebrae, however, these 
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 vertebral rings, together with the ligaments 
which unite them, inclose the vertebral canal (Canalis vertebralis), which con- 
tains the spinal cord and its coverings and vessels. 

The articular processes, two anterior and two posterior (Processus articulares 
craniales, caudales), project from the borders of the arch on either side. They 
present joint surfaces adapted to those of adjacent vertebrae, and the remaining 
surface is roughened for muscular and ligamentous attachment. 

The spinous process (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 side 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 or haemal spine. 

Mammillary processes (Processus mammillares) are found in most animals on 
the last thoracic and anterior lumbar vertelirae between the transverse and anterior 
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 
which 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 
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 bodj^ 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 areas). In the horse 
and ox the body and arch are usually fused at Ijirth, but the epiphyses do not fuse till growth is 
complete. In the pig, sheep, and dog the body and arch are united at birth by cartilage (neuro- 
central 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 Avhich usually corre- 
spond in number to the thoracic vertebrae. Each articulates dorsally with the spine 
and is continued ventrally by a costal cartilage. Those which articulate with the 
sternum by means of their cartilages are termed sternal or "true" ribs (Costse 
sternales s. verae); the remainder are asternal or "false" ribs (Costa? asternales s. 
spurise). Ribs at the end of the series which have their ventral ends free in the 
abdominal wall are named floating ribs (Costae fluctuantes). The intervals be- 
tween the ribs are termed intercostal spaces (Spatia intercostalia). 

A typical rib^ consists of a shaft and two extremities. The shaft (Corpus costae) 

' 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. 



26 OSTEOLOGY 

is band-like and varies much in length, breadth, and curvature. In the case of 
some ribs the curvature is not uniform, but is most 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 almost vertical, while the remainder slope backward 
in increasing degree. The external surface is convex, and the internal flattened 
from edge to edge; on the latter, close to the posterior border, is the costal groove 
(Sulcus costalis), which fades out ventrally. It contains the intercostal vein. 
The anterior and posterior borders 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 costse) 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 outer surface is rough, its inner smooth. The tubercle (Tuberculum 
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 has a rough depression in which the costal cartilage is embedded. 

Development. — The ribs are ossified in cartilage from three centers — one each 
for the shaft (and sternal end), head, and tubercle; the third center does not occur 
in the last two ribs. 

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 the remainder 
overlap and are attached to each other to form the costal arch (Arcus costalis). 



THE STERNUM 

The sternum or breast-bone is a median segmental bone which completes the 
skeleton of the thorax ventrally, and articulates with the cartilages of the sternal 
ribs laterally. It consists of six to eight bony segments (Sternebrae) connected by 
intervening cartilage in the young subject. Its form varies with that of the thorax 
in general and with the development of the clavicles in animals in which they are 
present. Its anterior extremity, the manubrium stem! or presternum, is specially 
affected by the latter factor, being broad and strong when the clavicles are well 
developed and articulate with it (as in man), relatively small and laterally com- 
pressed when 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 mesostemum 
(Corpus sterni) presents laterally, at the junction of the segments, concave facets 
(Incisurae costales) for articulation with the cartilages of the sternal ribs. The 
posterior extremity or metasternum presents the xiphoid (or ensiform) cartilage 
(Processus xiphoideus) ; this is thin and plate-like, as in the horse and ox, or narrow 
and short, as in the pig and dog. 

Development. — The cartilaginous sternum is formed by the fusion medially 
of two lateral l)ars which unite the ventral ends of the first eight or nine costal 
cartilages, and is primitively unsegmented. 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 



THE THORAX — THE BONES OF THE THORACIC LIMB 27 

cartilage will he 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 very 
vascular. 

THE THORAX 

The skeleton of the thorax comprises the thoracic vertebrae dorsally, the ribs 
and their cartilages laterally, and the sternum ventrally. The thoracic cavity 
(Cavum 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 aperture (Apertura thoracis cranialis) is 
bounded by the first thoracic vertebra dorsally, the first pair of ribs and their 
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 between the thoracic 
and abdominal cavities) 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 understood to include all of the bones of the head. 
The head consists of the cranium and the face, and it is therefore convenient to 
divide the bones into cranial and facial groups. 

The cranial bones (Ossa cranii) inclose the brain with its membranes and 
vessels and the essential organs of hearing. They concur with the facial bones in 
forming the orbital and nasal cavities, in which the peripheral organs of sight and 
of smell are situated. 

The facial bones (Ossa faciei) form the skeleton of the oral and nasal cavities, 
and also support the larynx and the root of the tongue. 

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 cartilage bones. Only 
two form permanent movable joints with other parts of the skull. The mandible 
or lower jaw-bone forms diarthrodial joints with the temporal bones, and the hyoid 
bone is attached to the latter by bars of cartilage. The other bones form immov- 
able 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 lines 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 consists of four chief segments, viz., the shoulder girdle, 
the arm, the forearm, and the forefoot or manus. 

The shoulder girdle (Cingulum extremitatis thoracicse), 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, 
fiat 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 mastoido- 
humerahs 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 mammals 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 limb. Thus in typical quadrupeds, 



28 OSTEOLOGY 

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 limbs for grasping, burrowing, climbing, etc. 
(e.^.,man, apes, moles), have well-developed clavicles which connect the scapula with the sternum. 

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

In the forearm (Antibrachium) are two long bones, the radius and ulna. 
These vary in relative size and mobility. In the horse and ox the two bones are 
fused, and the lower 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 upper 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 forefoot or hand (Manus) consists of three subdivisions, 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 (Ossa carpi). These are typically 
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 outw^ard), 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 variety of terms borrowed from human anatomy and 
based on the form of the bones in man. The following table of synonyms in common use is ap- 
pended for comparison. The Latin terms and abbreviated notations are given in parenthesis. 

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, C2) Trapezoid 

Third carpal (Os carpale tertium, C3) Os magnum 

Fourth carpal (Os carpale quartum, C4) Unciform 

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

The metacarpus contains typically five metacarpal bones (Ossa metacarpalia 
I-V), one for each digit; they are long bones and are designated numerically from 
within outward. This arrangement occurs in the dog, although the first meta- 
carpal 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 metacarpal bone and carries the single 
digit, while the second and fourth are nmch reduced. 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 Equida? illustrate in a most complete man- 
ner the reduction which has occurred in this respect. The earhest known ancestor of the horse, 
Eohippus or Hyracotherium of the Lower Eocene, had four well developed metacarpal bones, 
each of which carried a digit; the first metacarpal bone was small. Eleven intermediate stages 
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 BONES OF THE PELVIC LIMB 29 

the weight, while the second and fifth are reduced. The existing horse has a single 
digit, the third of his polydactyl ancestors. The skeleton of each fully developed 
digit consists of three phalanges and certain sesamoid bones. The first or proximal 
phalanx (Phalanx prima) articulates with the corresponding metacarpal bone above 
and with the second or middle phalanx (Phalanx secunda) below. The third 
or distal 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 the flexor tendons or in the joint capsules. Two proximal 
sesamoids (Ossa sesamoidea phalangis primae) occur at the flexor side of the meta- 
carpo-phalangeal joint and form a pulley for the flexor tendon. The distal 
sesamoids (Ossa sesamoidea phalangis tertiae) are similarly placed l^etween the 
deep flexor tendon and the joint between the second and third phalanx; they are 
absent in the dog, which has a small sesamoid on the extensor side of the meta- 
carpo-phalangeal joints, 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 appears to be inherited. 



THE BONES OF THE PELVIC LIMB 

The pelvic limb, like the thoracic, consists of four segments, viz., the pelvic 
girdle, thigh, leg, and the hind foot or pes; the last is subdivided into tarsus, 
metatarsus, and digits. 

The pelvic girdle (Cingulum extremitatis pelvina) consists of the os coxae or 
hip bone, which joins its fellow of the opposite side ventrally at the symphysis 
pelvis, and articulates very firmly with the sacrum dorsally. The two coxal bones, 
together with the sacrum and the first two or three coccygeal vertebrae, constitute 
the bony pelvis. The os coxae consists originally of three flat bones, the iUum, 
ischium, and pubis, which meet at the acetabulum, a large cotyloid cavity that 
articulates with the head of the femur. These three parts are fused before growth 
is complete, but are considered separately for convenience of description. The 
ilium (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 large, 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 below with the tibial tarsal bone. The fibula is situated 
along the outer 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 (Ossa tarsi) numbering 
five to seven in the different animals. The proximal or crural row consists of two 
bones, the tibial and fibular tarsals ; the former is situated at the inner or tibial 
side, and has a trochlea for articulation with the distal end of the tibia; the latter, 
situated externally, 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 



30 



OSTEOLOGY 



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 inta 
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 caleis 

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

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

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

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. 




Fig. 5. — Skeleton of Horse, with Outline 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; 6.L., sixth lumbar vertebra; K, sacrum; I.S., first coccygeal vertebra; 
16.S., sixteenth coccygeal vertebra; 6.R., sixth rib; 6.K., costal cartilage; 18.R., last rib; 1, scapula; 1', cartilage 
of scapula; 2, spine of .scapula; 4, humerus; 4' external epicondyle of humerus; 5, external tuberosity of humerus; 
6, deltoid tuberosity; 7, shaft of ulna; 8, olecranon; 9, radius; 10, carpus; 11, accessory carpal bone; 12, meta- 
carpus; 1.3, digit; 14, sternum; 14", xiphoid cartilage; 15, ilium; 16, 16', external and internal angles of ilium; 
17, ischium; 18, femur (shaft); 19, trochanter major; 27, trochanter minor; 28, trochanter tertius; 20, patella; 
21, tibia (shaft); 21', external condyle of tibia; 23, fibula; 22, tarsus; 24, tuber caleis; 25, metatarsus; 26, digit. 
(After Ellenberger-Baum, Anat. fiir Kunstler.) 



THE SKELETON OF THE HORSE 



31 



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 vertebra^ is taken to be 18, the tem- 
poral and OS coxa> are not divided into parts, the usual number of carpal and tarsal elements is 
taken, and the sesamoids are included. 



The Vertebral Column 

The vertebral formula of the horse is C7TjsLgS5Cyj5.2^. 




^Anterior articu- 
lar process of 
axis 



\-- — Anterior part of 
* transverse pro- 

cess 
Posterior part of 
transverse pro- 
cess 
Dorsal crest 



^': 



Fossa atlantis 



Ventral crest 



Trans- 
verse 
pro- 
cess 



Anteri- 
or part 
Posteri- 
or part 



lk\ 



Basi-occipital 
Occipital condyle 
J'(ir<ini(istoid {styl- 
oid) process 




Posterior articu- 
lar process 

Anterior articu- 
lar process 



Fig. 6. — Cervical Vertebra of Horse, Fig. 7. — Cervical Vertebr.e of Horse, Ventral View. (After 
Dorsal View. (After Schmaltz, Schmaltz, Atlas d. Anat. d. Pferdes.) 

Atlas d. Anat. d. Pferdes.) 



32 THE SKELETON OF THE HORSE 

THE CERVICAL VERTEBRAE 

These are quadrangular, massive, and longer than the vertebrae of other regions; 
they decrease in length from the second to the last. The third, fourth, and fifth 
are typical, and have the following characters: 

1. The bodies are long as compared with those of other vertebrae. Each 
presents a median ventral spine or crest, which becomes more prominent as it is 
traced backward, and is tuberculate at its posterior end. The lateral aspect is 
concave. The dorsal surface has a flat central area which is narrow in the middle 
of the vertebrae, and wide at either end; it gives attachment to the superior com- 
mon ligament. On either side of this area is a groove which lodges the longitudinal 
spinal vein. These lateral grooves are connected at the middle of the surface by 
a transverse furrow, in which there are several foramina through which veins 
emerge from the spongy substance of the body. The anterior extremity presents 
a head which has an oval articular surface, strongly convex, and wider above than 
below. The posterior extremity is larger and has a nearly circular cotyloid cavity. 

2. The arches are large and strong. They are perforated on either side by a 



Anterior articular process 



Head 




Articular cavity 
Transverse process 

Facet for tubercle of first rib 
Facets for head of first rib 

Fig. 8. — Last Cervical and First Thoracic Vertebr.e of Horse, Lateral View. (After Schmaltz, Atlas d. 

Anat. d. Pferdes.) 

foramen which communicates with the foramen transversarium. The verte])ral 
notches are large. 

3. The articular processes are large. Their articular surfaces are extensive, 
oval in outline, and slightly concave; the anterior ones are directed upward and 
inward, the posterior downward and outward. The remaining surface is mainly 
roughened for ligamentous and muscular attachment. A crest connects 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 
transversarium, through which the vertebral artery passes. The process divides 
externally into anterior and posterior branches, which are thickened and rough for 
muscular attachment. 

5. The spinous process is represented by a 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 



THE ATLAS 



33 



articular processes are shorter, thicker and further apart; they are connected with 
the anterior ones by a tliicls; ridge. The spinous process is less rudimentary; it 
is half an inch or more (ca. 1.5 cm.) in height. Tlie transverse processes have 
three branches; the third part is a thick, almost sagittal plate, which forms with 
its fellow and the body a wide ventral groove on the posterior part of the vertebra ; 
the oth(>r l^ranches correspond to those of the typical vertebra;, but are short and 
thicker. The foramen transversarium is large; below its posterior end is a fossa. 
The ventral crest is small and is less prominent posteriorly. 

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

The seventh cervical vertebra is readily distinguished l)y the following charac- 
ters : It is shorter and wider than the others. The body is flattened dorso-ventrally 
and wide, especially liehind ; here it has a demifacet on either side for articulation 
with ])art of the head of the first ril). 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 transversarium. The ventral crest is replaced 
by a pair of tubercles. 

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



both. 



Dorsal arch 



Anterior 

articular 

cavity 




Intervertebral 
foramen 



Vertebral 
foramen 



Foramen 

trans ver- ~ . 

sarin m Ventral 
arch 



Fossa 

atlantis 




Fig. 9. — Atlas of Horse, Anterior View. 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



Fig. 



10. — Atlas of Horse, Posterior View. 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



(After 



The Atlas 

This vertebra is decidedly atypical in form and structure. The body and 
spinous process are absent. It has the form of a strong ring, from which two 
ciu'vetl plates, the wings, project laterally. The ring incloses a very large vertebral 
foramen, and consists of two lateral masses connected by dorsal and ventral arches. 

The lateral masses (Mass* laterales) present two deep oval anterior articular 
cavities (Fovese articulares craniales) whicli receive the occipital condyles; they are 
separated by a wide notch al)ove and a narrow one below. The outer margin is also 
notched, and a triangular non-articular depression cuts into the inner part of each 
cavity. The posterior articular surfaces (Facies articulares caudales) are some- 
what saddle-shaped; they are confluent on the ventral arch below^ but are widely 
separated above, and do not conform in shape to the corresponding surfaces of the 
axis. 

The dorsal arch (Arcus dorsalis) presents a. median dorsal tubercle (Tubercu- 
lum dorsale) and is concave below. It is perforated on either side near its anterior 
margin by the intervertebral foramen. The anterior border is deeply notched, and 
the posterior is thin and concave. 

The ventral arch (Arcus ventralis) is thicker, narrower, and less curved than 
3 



34 



THE SKELETON OF THE HORSE 



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 (Fovea dentis), on 
which the dens or odontoid process of the axis rests. In front of this is a transverse 
rough excavation for the attachment of the odontoid ligament. 

The wings (Alse) are modified transverse processes. They are extensive curved 
plates which project outward, downward, 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. Two foramina perforate 
each wing. The anterior one, the foramen alare, is connected with the interverte- 
bral foramen by a short groove. The posterior one is the foramen transversarium. 

Development. — The atlas ossifies from three or four centers, one or 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. 
These parts are usually fused at about six months. 



Axis 



Atlas 



?qrr^ 




I ntervertebral for. 
Post, artic. process 
! A7it. artic. process 
Dorsal crest 



Post, artic. 
process 



1 7iter vertebral ' 

foramen Furanun 

transversarium 




I ntrr vertebral 
foramen Foramen 

transversarium 
Ventral crest 



Fig. 11. 



-First Three Cervical Vertebra of Horse, Lateral View. 

Pferdes.) 



Ventral en s! ■"""'^^ * 

(After Schmaltz, Atlas d. Anat. d. 



The Axis 

The axis (Epistropheus) is the longest of the vertebrae, and is characterized 
by the presence of the odontoid process, which projects from the anterior part of 
the body. 

The body has a median ventral crest which terminates in a tubercle behind. 
The anterior extremity presents centrally the odontoid process (Dens) ; 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 odontoid ligament dorsally. 
Flanking this on either side are the modified anterior articular processes, which 
have saddle-shaped articular surfaces confluent below with that of the dens. The 
posterior extremity has the usual cavity. 

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 usually ossifies later. 
The posterior border has the usual notches. 

The posterior articular processes are typical. 

Tlie transverse processes are small, single, and project backward. The 
foramen transversarium 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. 



THE THORACIC VERTEBRAE 



35 



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 l)y Lesbre to be the head of the axis. 



Occipital crest 



Median crest 



Paramastoid process I, /„,„./v'a^ 



Dorsal arch of atlas 



Anterior articular process of axis 




Intervertebra I for a m e n 



Foramen transversarium 



Post, articular processc 
Ant. articular processe 



Transverse process 
Dorsal crest — 



For a me n tra ns versa ri um 
Post, articular processes 

Fig. 12. — Occipital Bone and First Three Cervical Vertebr.e of Horse, Dorsal View. (After Schmaltz, 

Atlas d. Anat. d. Pferdes.) 



THE THORACIC VERTEBRA 

These (Vertebrae thoracales) are usually eighteen in number in the horse, but 
there are sometimes nineteen, rarely seventeen. As regional characters we note 
the surfaces for articulation with the ribs and the length and form of the spinous 



36 



THE SKELETON OF THE HORSE 



processes. Those in the middle of the series are the most typical and present the 
following features: 

1. The bodies are short and constricted in the middle. The ends are expanded 
and have articular surfaces which are not strongly curved. On the upper part of 
each side are anterior and posterior costal facets (Fovea costalis cranialis, cau- 
dalis), which, with those of adjacent vertebrae, form sockets for the heads of 
the ribs. 

2. The arches are small. Their posterior notches are relatively large and are 
often converted into foramina. 

3. The articular processes are small. The anterior pair are in fact represented 



Anterior nrticidar process 




Posterior articular process 
Transverse processes 



Facets for tubercles of ribs 



Facets for heads of ribs 
Intervertebral foramina 



Facet for head of rib ^«cc< for tubercle of rib 



Fig. 13. — Third, Fourth, and Fifth Thoracic Vertebr.e op Horse, Lateral View. (After Schmaltz, Atlas 

d. Anat. d. Pferdes.) 



only by two oval facets on the anterior part of the laminae which face almost directly 
upward. The posterior pair 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 tuberosity of the 
rib which has the same serial number. 

5. The spinous process is large, narrow, and slopes upward and backward. 
The anterior l)or(k"r is thin, the posterior wider and furrowed. The summit is 
expanded and rough. 

The first thoracic vertebra is easily recognized by the following specific charac- 
ters: The body is wide and flattened dorso-ventrally. In front it has a head like 



THE THORACIC VERTEBRA 



37 



the cervical vertcbne, and behind a cavity somewhat deeper than any other thoracic 
vertebra. Two costal facets are found on either side, and a well-marked spine 
ventrally. The arch is large and strong, and has large notches. The articular 
processes are much larger than those of other thoracic vertebne, and resemble a 
good deal those of the seventh cervical in form. The transverse processes are 
short and thick, and each has on its ventral aspect a large concave facet for articu- 
lation 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.). It 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 gradually 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 



(i 



Spine ■ 



A n terior articu lar 
processes 



Facet for 

tubercle 

of rib 



Facet for head 
of rib 




nsvcrse process 



Tubercle 
of rib 
Neck 
of rib 



Body of rib -^ 



Facets for 
heads of ribs 




Articular cavity 
of body 



Fig. 14. — Third Thoracic Vertebr.e axd Upper Part 
OF Rib of Horse, Anterior View. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



Fig. 15. — Lower Part of Ninth Thoracic Verte- 
bra OF Horse, Posterior View. (After 
Schmaltz, Atlas d. Anat. d. Pferde.s.) 



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 separates to 
form the mammillary process. (3) The spinous processes increase in length to 
the third and fourth, antl 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, 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. 



38 



THE SKELETON OF THE HORSE 



THE LUMBAR VERTEBRAE 
The lumbar vertebrae (Vertebrae lurnbales) 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 triangular on cross-section, and present a 



Spine 
Anterior articular processes 



Arch 

Transverse process 
Facet for head of first rib 




ns verse process 



/ 
Body 



first rib ^"y^ 



Fig. 16. — First Thoracic Vertebra a.nd Upper Part of First Rib of Horse, Anterior View, (.\fter 

Schmaltz, Atlas d. Anat. d. Pferdes.) 

distinct ventral crest. From the fourth backward they become wider and flatter 
and the ventral crest fades out. 

The arches of the first two or three are about equal in size and similar to that 
of the last thoracic; from the fourth they decrease noticeably in breadth and height. 

The anterior articular processes are fused with the mammillary processes, and 



Mammillary processes 



Facet for head of rib' 
Facet for tubercle of rib 

Intervertebral foramina 




Posterior articular processes 



Tubercle of rib 
Head of rib 



Fig. 17. 



-Last Two Thoracic and First Lumbar Vertebr.e of Horse, Lateral View. 
Atlas d. Anat. d. Pferdes.) 



(After Schmaltz, 



present superiorly 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 sur- 
faces, which fit into the grooved surfaces of the anterior pair of the next vertebra. 
The transverse processes are large plates, flattened dorso-ventrally, which 
project outwartl and usually curve slightly downward; their length increases to 



THE SACRUM 39 

the third and 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 inner part of the posterior border 
for articulation with the sixth process; the latter has a corresponding convex 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 inner part of the sixth process is 
thick, the outer part thinner, narrower, and curved forward. The inner part of 
the fifth is also somewhat thickened. 

The spinous processes resemble those of the last two thoracic vertebrae. 
They are usually al)out 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) 
has been proposed. The occurrence of a lumbar rib in connection with the transverse process of 
the first lumbar is not rare. Reduction of the number to five has been observed frequently, and 



MamiuiUory processes -'=^'rj 
Anterior arlicular processes '^' 




Transverse 
process 



Ventral spine N^tefca^jj^ Body 
Fig. 18. — Secoxd Lumbar Vertebra ok Horse, Anterior View. (After Schmaltz, .\tlas d. Anat. d. Pferdes.) 

may or may not be compensated by an additional thoracic vertebra. This variation is not more 
common in certain races as Sanson and others have maintained. Very few cases are recorded of 
seven lumbar vertebrae — 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 

The sacrum (Os sacrum) is formed by the fusion of five vertebrae usually, and 
is conveniently 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 presents centrally the five sacral spines, which are directed 
upward and backward, and have (with the exception of the first) tuberous summits 
which are sometimes bifid. 

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

On either side of the spines is a groove, in which are the four dorsal sacral 



40 



THE SKELETON OF THE HORSE 



foramina (Foramina saoralia dorsalia); the dorsal branches of the sacral nerves 
emerge through them. 

The ventral or pelvic surface (Facies pelvina) is concave in its length, wide in 
front, narrow behind. It is marked by four more or less distinct transverse lines 
(Lineffi transversa), which indicate the demarcation of the bodies of the vertebra^. 
At the ends of these lines are the ventral sacral foramina (Foramina sacralia 
ventralia), 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 comnmnicate with the sacral canal and are 
together equivalent to the usual intervertebral foramina. 




Fig. 19. — S.\crum of Horse, Dorso-later.\l View. 
C, Body of first sacral vertebra; ^1, arch of first vertebra; Cs, sacral canal; P.s. 1-5, sacral spines; P.t., 
wings of sacrum; 1, 1', surfaces for articulation with transverse processes of last lumbar vertebra; F.a., auricular 
surface; 2, 2', articular processes; 3-6, dorsal sacral foramina; 7, interarcuate space; 8, lateral border; h, apex. 
(Struska, Anat. d. Haustiere.) 



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). 
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 internally for articulation with those of the last lumbar vertebra. On 
each side of these is a smooth notch which is converted into a foramen by apposition 
with the last lumbar. The lateral parts of the base, the wings or alae (Ala? sacrales), 



THE COCCYGEAL VERTEBR.B 41 

are strong prismatic masses with pointed ends, which result from the fusion of the 
first with part of the second transverse process. Each has in front a large, oval, 
slightly convex surface for articulation with the transverse process of the last lum- 
bar. Posteriorly there is an elongated oval area which faces upward, backward, 
and outward. This is the auricular surface (Facies auricularis), which articulates 
with the ilium; it is slightly concave in its length, and somewhat rough and irregu- 
lar. The rest of the dorsal surface of the wing is roughened for ligamentous attach- 
ment, 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 about twice its height. Traced 
backward it is seen to diminish in size rapidly, and the posterior opening is quite 
small and triangular. 

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



Vertebral canal 




Spine 

-process Spine --\ 



Transverse _ 
Transverse process 



Body Posterior end of body 



Fig. 20. — First CocrvGEAL Vertebra of Horse, Fig. 21. — First Coccygeal Vertebra of Horse, 
Left View. (After Schmaltz, Atlas d. Anat. Dorsal View. (After Schmaltz, Atlas d. Anat. 

d. Pferdes.) d. Pferdes.) 

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 
behind till near adult age. 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 
These (Vertebrae coccyges) 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 bodies only. The 
first three have bodies which are somewhat flattened dorso-ventrally, constricted 
in the middle, and have at the ends slightly convex, elliptical, articular surfaces. 
The ventral surface has a median groove for the coccygeal artery. The arch is 
small and triangular; it is formed of two fiat 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, open above, and soon disappears; the transverse processes 



42 THE SKELETON OF THE HORSE 

gradually fade out, and the vertebrae are reduced to cylindrical rods of diminishing 
size. The last one has a pointed end. 

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 vertebrse, 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 lumbar; 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, diminishes from the sixth or seventh 
to the fifteenth or sixteenth, which is vertical and is termed the anticlinal or 
diaphragmatic vertebra. Behind this they are inclined a little forw^ard 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 laminae 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 may be remarked that a line 
through the summits of the spines does not correspond to these curves formed by 
the bodies. 

The vertebral canal, of course, corresponds in curvature to the bodies. Its 
caliber varies greatly at different points. The greatest diameter (ca. 5 cm.) 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 (ca. 2.5 cm. wide, 3 cm. high). It widens considerably at the junction of the 
cervical and thoracic regions to accommodate 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 correlated with the small size of the spinal cord and the 
very limited movement of the spine. At the middle of the lumbar region it again 
widens 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 complete at the fourth coccygeal vertebra. 

The articular processes are very large and wide apart in the neck, greatly 
reduced and nmcli 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 outer 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- 



THE RIBS 



43 



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 vertebrte. 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 260 to 265 cm. (ca. 8 feet 8 inches to 8 feet 10 inches). The relative lengths 
of the various regions appear to vary most in the neck and back. 

The table below gives the measurements in centimeters in a trotting stallion of medium size 
and in an adult Percheron stallion. The percentages are in round numbers. 





Trotter 


Percheron 


Cervical 


60.0 
98.0 
31.5 
20.0 
54.0 


22.7% 
37.2% 
12.0% 
7.6% 
20.5% 


74.0 
100.0 
36.5 
22.5 
58.0 


25.4% 


Thoracic 

Lumbar 

Sacral 

Coccygeal 


34.4% 

12.5% 

7.7% 

20.0% 




263.5 


100.0 


291.0 


100.0 



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 or "true" ribs, the remainder 
asternal or "false." 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 A 
typical rib has the following characters: 

The shaft or body (Corpus costie) is elongated, relativel}^ 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 outer 
surface on the table, the ventral end is raised. The external surface is convex in 
its length and also transversely; its anterior part is, however, grooved longitudin- 
ally. A di.stinct 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 often 
applied, however, to a corresponding rough elevation which gives attachment to the 
ilio-costaUs muscle; it is most distinct on the fourth to the eighth inclusive. The 
internal surface is smooth, concave in its length, and rounded from side to side; 
the costal groove, situated posteriorly, is very distinct above and fades out about 
the middle. 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 costs?), composed of two convex facets, anterior and posterior, 
separated by a groove for the attachment of the conjugal ligament. It articulates 
with the cavity formed by facets on the bodies of two adjacent thoracic vertebrae 



44 



THE SKELETON OF THE HORSE 



Tubercle 



Head 



and the intervertebral fibro-cartilage. The neck (Collum costae) is roughened 
above and in front. The tubercle (Tuberculum eostse) is placed above and behind 
the junction of neck and shaft; it has a small surface (Facies articularis tuberculi 
costae) for articulation Avith the transverse process of the corresponding thoracic 
vertebra. 

The sternal extremity (Extremitas sternalis) is somewhat expanded, and is 
continued by the costal cartilage. 

The first rib is easily distinguished. It is the shortest and least curved. At 
the lower part of the anterior border there is a smooth impression where the brachial 
vein curves around it; above this is usually the scalene tubercle. The costal 

groove is absent. The head is large and 
has two facets of unequal extent which 
meet at an acute angle in front; the smaller 
one faces forward and articulates with the 
last cervical vertebra; the larger one is 
directed inward and articulates with the 
first thoracic verte]:)ra. The neck is thick 
and very short. The tubercle is larger than 
that of any other rib and has an extensive 
articular surface which is convex in its 
length. The sternal end is larger than that 
of any other rib; it is thick and ver}' wnde, 
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 usual on the 
seventeenth also, and not rare on the six- 
teenth.) 

The serial position of the other ribs may 
be determined approximately by the follow- 
ing 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 external 
groove is distinct on the fourth to the eighth 
inclusive. The curvature increases in de- 
gree rapidly from the first to the seventh, 
remains about the same to the sixteenth, and 
then decreases very noticeably. In regard 
to dorso-ventral direction, the first rib inclines a little forward, the second is about 
vertical, while behind this they slope backward in increasing degree, so that a 
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 lies almost directly outward from 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 is formed between the neck and the transverse process. 

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




Fig. 22. — Left Seventh Rib of Horse, Anteho- 
EXTERNAL ViEW. (After Schmaltz, Atlas 
d. Anat. d. Pferdes.) 



THE COSTAL CARTILAGES — THE STERNUM 45 

Variations. — A nineteenth rib on one side or both is not rare. It is usually imperfectly 
developed and tiuite variable. In some cases it is a mere strip of cartilage connected by ligament 
with the first lumbar transverse process; in other cases it is ossified, ancl may be fused with the 
process; in others again it is coiuiected with an additional presacral vertebra which may be 
thoracic or lumbar or ambiguous in character. It is commonly floating, but may be attached to 
the eighteenth. Reduction in number is uncommon. Fusion of adjacent ribs sometimes occurs. 

THE COSTAL CARTILAGES 

The first costal cartilage is an inch or more (2.5 to 3 cm.) in length. The upper 
part 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 
expanded 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 the 

iL _ Cariniform cartilage 

'A 

Ventral border "^Bw^' 

Costal cartilages.' "' Iff ^' Uios 



Xiphoid cartilage 

Fig. 2.3.— Sternum and Cost.\l C.\rtil.\ges of Horse, Ventr.^l View. (After Ellenberger-Baum, Anat. f. 

Kiinstler.) 

longest, and is very firmly attached to the eighth; behind this they diminish pro- 
gressively in size, and are attached to each other by elastic tissue. 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 decreases in obtuseness 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. 

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

The dorsal surface has the form of a very narrow isosceles triangle with the 
apex in front. It is concave longitudinally, flattened transversely. 

The lateral surfaces are convex above, slightly concave Ijolow, and diminish 
in extent behind. Each presents on its upper part seven articular cavities (Fovese 
costales), which receive the sternal ends of the second to the eighth costal cartilages 
inclusive. These cavities are situated in series at the intersternebral junctions. 



46 



THE SKELETON OF THE HORSE 



The first four are elliptical in outline with the long diameter vertical, and are sep- 
arated 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. 




annifornt 
Cartilage 



Fig. 24. — Steenum of Horse, Lateral View. 
The sternebrse are designated by Roman numerals and the costal facets by ordinary figures. 



First 
thoracic 
vertebra 



First rib 



The dor so-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. 

The anterior extremity or manubrium 
sterni^ can be distinctly felt in the central 
furrow of the breast. It consists of a laterally 
compressed cartilaginous prolongation, commonly 
called the cariniform cartilage. Its lateral surfaces 
are flat and furnish attachment to muscles of the 
breast and neck. The ventral border is rounded, 
and is continued l)ackward on the body of the 
bone. The dorsal border is concave and has an 
articular cavity for the first pair of costal cartil- 
ages. 

The posterior extremity is formed by the 
xiphoid or ensiform cartilage (Processus xiphoi- 
deus). 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 laterallj^ Its dorsal surface is 
concave, and gives attachment to the diaphragm. 
The ventral surface is convex. The free margin 
is very thin. 

Development. — At birth the sternum of the 
horse consists of seven bony segments or sternebrse 
united by intersternebral cartilages. The last two 
sternebrse 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 com- 
pact substance. The adult sternum thus con- 
sists to a very considerable extent of persisting 

cartilage, viz., the intersternebral cartilages, the ventral keel, and the extremities; 

in old age these undergo partial ossification. 

'The manubrium stprni of man is equivalent, strictly speaking, to the cariniform cartilage 
+ the first osseous segment of the horse. 




Cariniform 
cartilage of 
sternum 



Fig. 25. — Anterior Aperture of Tho- 
rax OF Horse. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



THE THORAX — THE OCCIPITAL BONE 



47 



THE THORAX 
The bony thorax of the horse is remarkably compressed laterally in its anterior 
part, but widens greatly behind. The anterior aperture is oval and very narrow 
below; in a horse of medium size its greatest witltii is about 4 inches (10 cm.), and 
its height 7 to 8 inches (ca. 18 to 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 to 100 
cm.) long. The height from the last segment 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 divergence of the roof and floor. The greatest width of the pos- 
terior aperture is about 20 to 24 inches (50 to 60 cm.). The intercostal spaces 
increase in width from tlie first to the seventh or eighth, and then diminish. Their 
average width is about 1J<4 to \}/2 inches (3 to 3.5 cm.). 



The Bones of the Skull 
(A) bones of the cranium 

The bones of the cranium (Ossa cranii) are the Occipital, Sphenoid, Ethmoid, 
Interparietal, Parietal, Frontal, and Temporal. The first four are single, the others 
paired. 

Occipital crest ^^\,Suprnoccipital 
Occipital condyle £ -^y External auditory meatus 

Glenoid cavity of squamous temporal 

/ I'arictal 

Orbited wing of sphenoid 
r^ei ''^ ' ^ Frontal crest 




Vascula 



Mental foramen 



Jncisor 
teeth 



Fig. 26. — Skull, Atlas, and Axis of Horse, Lateral View. 
8, Body of mandible; 28', horizontal (molar) part of ramus; 30, vertical part of ramus; 9, zygomatic 
process of squamous temporal; 11, coronoid process of mandible; 12, supraorbital process; 13", paramastoid 
(styloid) process of occipital; 19, orbit; 20, malar bone; 21, lacrimal bone; 22, nasal bone; 23, premaxilla; 
23', nasal process of i>remaxilla; 25, 29, canine teeth; 26, maxilla; 27, facial crest; 31, condyle of mandible; 
32, atlas; 33, axis; x, wing of atlas; e, naso-maxillary notch, (.\fter EUenberger-Baum, Anat. far Kiinstler.) 



The Occipital Bone 
The occipital bone (Os occipitale) is situated at the posterior part of the cra- 
nium, of which it forms the posterior wall and part of the ventral wall or base/ 
'The long axis of the skull is considered to be horizontal in these descriptions. 



48 



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 brain and spinal 
cord join. The foramen is bounded laterally and dorsally by the lateral parts of 
the bone, and ventrally by the basilar part or process. 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 (Condyli 
occipitales), which articulate with the atlas. The condyles are oblicjuely placed, 
wide apart dorsally, and separated by a small interval ventrally. The articular 
surface is curved so sharply in the dorso-ventral direction as to form a blunt ridge 



Occipital crest 
Upper border of 

Foramen magnum 

Hypoglossal foramen 
For. lacerum posterius 
Stylo-mastoid foramen 

Hyoid process 

Mxiscular process --xCs 

For. lacerum anterius , 

Tubercles at spheno- _ 
occipital junction 

Alar foramen . 

Pterygoid process 
of sphenoid 
Pterygoid bone . 

Vomer (alee) . 
Pterygoid process of 
palate bone 

Palate bone {perpcn- 

dicular part) 
Alveolar tuberosity 

Posterior narcs 
Last molar tooth 




- Median crest for lig. nuchoe 
' Occipital condyle 

— Paramastoid process 

— Condyloid fossa 

— Mastoid process 

— Bidln ossea 
Postglenoid process 

Glenoid cainty 

Temporal condyle 
Zygomatic process 
Infratemporal fossa 



Zygomatic process of 
malar 

^ Ptery go-palatine fossa 

- Maxillary hiatus 

- Maxillary tuberosity 

- Facial crest 
-. Hamulus of pterygoid 

Vomer 

Palate bone {horizon- 
tal part) 
Ant. palatine foramen 

Palatine groove 

Palatine process of 

maxilla 

Fig. 27. — Lixe Dr.\wing of Posterior H.vlf of B.\se of Skull of Horse, Without M.\ndible. (Key to 

Fig. 28.) 
1, Incisura carotica; 2, incisura ovali.s; .3, incisura spinosa; 4, external orifice of parieto-temporal canal; 
5, Eustachian canal; 6, petro-tympanic fissure; 7, external auditory canal; 8, hyoiil process; 9, Vidian groove; 
10, supraorbital process; A, basilar part of occipital; B, body of sphenoid; C, temporal wing of sphenoid; D, 
squamous temporal bone; E, petrous temporal bone; F, orbital part of frontal bone. 



externally. The cranial surface is concave and smooth. External to the condyle is 
the paramastoid or styloid process (Processus jugularis), a strong flattened bar of 
bone which projects downward and backward; its external surface is convex and 
roughened for muscular attachment. Between the root of this process and the 
condyle is a smooth depression, the condyloid fossa (Fossa condyloidea inferior) ; 
in this is the hypoglossal foramen (Foramen hypoglossi), which transmits the nerve 
of like name. 

The basilar part or process (Pars basilaris) is a strong, somewhat prismatic 
bar which extends forward from the ventral margin of the foramen magnum. It 



THE OCCIPITAL BONE 



49 



is much narrower in front than behind. The ventral surface is rounded. The 
cranial surface is concave and smooth; its posterior part supports the medulla, 
and its anterior part has a shallow cavity on which the pons rests. The lateral 
borders are thin and sharp, and form the inner margin of the foramen lacerum 
(Foramen lacerum et jugulare). The anterior end has, in the young subject, a 




Fig. 28. — Ventral Htri ack op Skui.i. of Hor.se, Po.sterior Half Without Mandible. 
The skull is inclined slightly. (Notation on key Fig. 27.) 

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 tubercles for the attachment of the ventral straight muscles of 
the head. 

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



50 THE SKELETON OF THE HORSE 

situated above the lateral portions, from which it remains distinct till the second 
year. The outer surface is crossed by a very prominent ridge, the occipital crest ; 
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 unecjual parts; the small anterior area (Planum parietale) 
presents a median ridge which is the posterior part of the external sagittal crest; 
the large area below the crest (Planum nuchale) also has a central eminence, the 
external occipital protuberance, on the sides of which the funicular part of the 
ligamentum nuchic is attached. The internal surface is concave and presents a 
deep central depression and two shallower lateral ones which adapt it to the surface 
of the cerebellum. 

The occipital bone is connected by suture with the interparietal, two parietals, 
and two temporals, and by synchondrosis with the sphenoid; the condyles articu- 
late with the atlas. 

Development. — The occipital ossifies in cartilage from four centers, and con- 
sists at birth of four pieces as described above." The lateral parts unite with the 
basilar 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 temporo-occipital 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 a cen- 
tral part, the body, two pairs of wings, and two pterygoid processes. 

The body (Corpus) is a cylindrical bar, flattened dorso-ventrally, and wider 
in front than behind. Its ventral surface (Facies externa) is convex in the trans- 
verse direction; and its anterior part is concealed to a large extent by the vomer 
and pterygoid bones. The cerebral surface (Facies cerebralis) presents the fol- 
lowing features: (1) In front is a raised, flattened part which is subdivided by a 
median elevation into two slightly concave lateral areas; this part has a posterior, 
thin, free margin (Limbus sphenoidalis), which overlies the entrance to the optic 
foramina. (2) Just behind this and at a lower level is a smooth transverse de- 
pression, the optic groove (Sulcus chiasmatis), on which the optic chiasma rests. 
(3) From each end of this groove the optic foramen passes forward and outward to 
terminate in the posterior part of the orbital fossa. '^ (4) Near the posterior end 
is a central depression, the hypophyseal or pituitary fossa (Fossa hypophysea), 
which lodges the hypophysis cerebri or pituitary body. On each side of this is an 
ill-defined groove for the internal carotid artery and the cavernous sinus. The an- 
terior end is expanded, and 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 
complete septum which is not always median.^ The posterior end is fiat and is 

' The occipital crest of this description is equivalent to the external occipital protuberance 
and superior nuchal line of man. A curved line a little lower down, which is continued on the 
paramastoid process, represents the inferior nuchal line of man. 

-Other terms for these parts are basioccipital (basilar part), cxoccipitals (lateral parts), 
and supraoccipital (squamous part). It should be noted, however, that the lines between the 
basioccipital and cxoccipitals pass through the lower part of the condyles. 

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

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



THE SPHENOID BONE 51 

joined to the basilar part of the occipital; at the line of junction there is 
dorsally a transverse elevation, the spheno-occipital crest (Crista spheno- 
occipitalis). 

The orbital wings (Alte orbitales) curve upward and soinewliat outward from 
the sides of the body of the pre-sphenoid. Their inner or cerebral surfaces are 
concave, and are marked b>' digital impressions (Impressiones digitate) for the gyri 
of the cerebrum. The external surface is convex and is largely concealed by the 
overlapping temporal wing and the squamous temporal and frontal bones; a 
narrow part of it (Facies orbitalis) is uncovered on the innei- wail of the orbital 
cavity at the sphenoidal notch of the frontal bone. The dorsal border unites with 
the frontal bone at the spheno-frontal suture. The anterior border joins the eth- 
moid at the spheno-cthmoidal suture; at its lower part it concurs with the frontal in 
the formation of the ethmoidal (or internal orbital) foramen. The posterior border 
is overlapped by the temporal wing and the sc^uamous temporal. The root of the 
wing is perforated by the optic foramen. Immediately below and behind the latter 
(i. e., beneath the root) is the foramen lacerum orbitale or orbital fissure. Below 
this, and separated from it usually by a thin plate, is a larger opening, the foramen 
rotundum, which is bounded externally by the root of the pterygoid process. Be- 
hind these foramina is the pterygoid crest (Crista pterygoidea), which is continued 
downward and forward on the pterygoid process; on its upper part may be found 
the small and inconstant trochlear (or pathetic) foramen. Just behind the crest 
is the temporal foramen (For. alare parvum), through which the anterior deep 
temporal artery emerges from the alar canal of the pterygoid process. 

The temporal wings (Alae temporales) extend outward and somewhat upward 
from the body of the post-sphenoid; they are irregularly quadrilateral in outline. 
The external surface (Facies temporalis) enters into the formation of the infra- 
temporal fossa, and bears the pterygoid process on its anterior part; at the junction 
with the body there is a small groove for the pterygoid nerve. The internal 
surface (Facies cerebralis) presents, at the junction with the body, two longitudinal 
grooves (Sulci nervorum).' The outer groove is the larger, and leads forward to 
the foramen rotundum; it contains the maxillary nerve. The inner groove con- 
ducts to the orbital fissure, and contains the third, sixth, and ophthalmic nerves. 
The outer groove is bounded externally 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 
wing. The posterior border forms the anterior boundary of the foramen lacerum; 
it presents three notches, which are (from within outward) the carotid, oval, and 
spinous (Incisura carotica, ovaUs, spinosa). The angle of junction 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 
transmits the internal maxillary artery. From this canal a branch leads upward 
and forward to open at the temporal foramen. The external surface is concave, and 
is marked by lines for muscular attachment. The internal surface is largely con- 
cealed by the overlapping palate and pterygoid bones, with which it concurs in the 
formation of the pterygoid or Vidian canal. 

Development. — The sphenoid is ossified in cartilage, and consists in early life 
of two distinct parts, the pre-sphenoid and post-sphenoid. 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. 

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



52 



THE SKELETON OF THE HORSE 



Variation. — The dorsal border of the orbital wing may come 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 (Os ethmoidale) is situated in front of the body and orbital wings 
of the sphenoid. It projects forward between the orbital plates 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 per- 
pendicular plate. 

The cribriform plate (Lamina cribrosa) is a sieve-like partition between the 
cranial and nasal cavities. Its margin joins the orbital wings of the sphenoid 
laterally, and the cranial plate of the frontal bones dorsally. Its cranial surface 
is divided into two parts by a median ridge, the crista 
i _ galli, which is the intracranial portion of the perpendicu- 

^^^^^■^ lar plate. Each half forms a deep oval cavity, the eth- 

moidal or olfactory 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. 

The lateral masses or labyrinth project forward from 
the cril)riform plate into the posterior part of the nasal 
cavity, which they nearly fill. Each mass is somewhat 
conical in shape, with the base attached to half of the 
cribriform plate. The inner surface is separated by a 
narrow space from the perpendicular plate. The outer 
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 papyracea. The mass consists of a large 
number of delicate, scroll-like plates of bone, termed 
ethmo-turbinals or ethmoidal cells. These are attached 
to the lamina papyracea, and are separated by narrow 
intervals termed ethmoidal meatuses, which communicate with the nasal cavity. 
In the living animal the ethmo-tur]:)inals are covered with mucous membrane. 

The lateral mass is a very complex structure, the arrangement of which may be studied on 
cross-sections of decalcified specimens with the mucous membrane retained. Each mass consists 
of six turbinals which extend almost to the perpendicidar plate and are termed endoturbinals. 
These diminish in size from above downward; the largest is attached to the nasal bone, and is 
hence usually called the naso-turbinal or superior turbinal; the second is much smaller, and is very 
commonly termed the great ethmoid cell. Between the endoturbinals are twenty-one small 
ectoturbinals, and all are beset with secondary and tertiary coiled lamellae. 

The perpendicular plate or mesethmoid (Lamina perpendicularis) is median, 
and forms the posterior jjart of tlie septum nasi. Its lateral surfaces are nearly 
plane, but are marked below l)y 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 ])rojects into the cranial cavity as a 
ridge, the crista galli. The dorsal border joins the frontal bones at their line of 
junction — the frontal suture. The ventral border is received into the groove of 
the vomer. 

Development. — The ethmoid develops in cartilage from five centers, two for 

' 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 
skull. 




Fig. 29. — Cross-section of 
Lateral Mass of 
Ethmoid Bone of 
Horse. 



THE INTERPARIETAL BONE 



53 



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 entirely cartilaginous. By the time ossification is complete the ethmoid has 
united with surrounding Ijones to such an extent that it cannot be separated intact 
for study. 

Occipital crest 

Supraoccipital 



Temporal crest 



Zygomatic process 

Supraorbital foramen 

Orbit 



Malar bone 
Facial crest 

Infraorbital foramen 




Curonoid process 



Nasal process of premaxiUa 



Canine tooth 
Foramen incisivum 



Fig. 30. — Skull of Horse, Dorsal View. 
12, Supraorbital process; 14, parietal bone; 14', external sagittal crest; 15, frontal bone; 15', frontal 
crest; 21, lacrimal bone; 22, nasal bone; 26, maxilla; 24, incisor teeth. (After EUenberger-Baum, Anat. fiir 
Kiinstler.) 



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 sometimes distinctly 
paired in skulls of young foals. 

The external surface (Facies externa) is quadrilateral and is flat and 



54 THE SKELETON OF THE HORSE 

smooth in the very yoiins foal; later it presents the median external sagittal 

crest. 

The internal surface (Facies cerebralis) presents the internal occipital pro- 
tuberance, 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 Iwrders which form part of the tentorium 

osseum. 

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

bones. 

Development. — Tlie interparietal ossifies in membrane from two chief lateral 
centers.^ It fuses first with the parietals, somewhat later with the occipital, but 
the period at which this union takes place is ciuite variable. 

The Parietal Bones 

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

The external surface (Facies parietalis) is convex, and is marked by a more or 
less prominent curved line, the external sagittal crest ; this is median in its posterior 
part, and is continuous with the crest of like name on the occipital bone; in front 
it curves outward and is continuous with the frontal crest. The surface external 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 or cerebral surface (Facies cerebralis) is concave. It presents 
numerous digital impressions (Impressiones digitatse) which correspond to the gyri 
of the cerebrum. There are also furrows (Sulci vasculosi) for the meningeal arte- 
ries. Along the inner 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 
coronalis). 

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

The internal border is thick and serrated. It joins its fellow at the sagittal 
suture, and (in the young subject) meets the interparietal at the interparietal suture. 
The line of junction is marked internally by the internal sagittal crest (Crista 
sagittalis interna). 

The external border is beveled and is overlapped l)y the squamous temporal 
bone, forming the parieto-temporal suture (Sutura parieto-squamosa). The angle 
of junction of the external and posterior ])orders articulates with the posterior 
angle of the temporal wing of the sphenoid. 

Development. — Each parietal bone ossifies in membrane from a single center. 
In the young foal the central ])art of the bone is much more convex than in the 
adult and forms a prominence similar to the pronounced fuller parictale of the 
young child; the external sagittal crest is not present, and the external surface is 
smooth. 

The sagittal sutures is usually closed at four years, the parieto-occipital at five years, and the 
parieto-temporal at twelve to fifteen years. 

' According to Martin, there arc originally foiu- centers, two anterior and two posterior 
(smaller) ones, which fuse in a variable manner. 



the frontal bones — the temporal bones 55 

The Frontal Bones 

The frontal bones (Ossa frontalia) are situated on the limits of the cranium 
and face, betwcM'u the parietals l;)ehind and the nasal bones in front. Each is 
irregularly (luadrilateral, and consists of frontal, orl)ital, and temporal parts. 

The frontal part (Pars naso-frontalis) forms the basis of the forehead. Its 
external surface (Facies frontalis) is nearly flat, and is smooth and subcutaneous; 
it is separated from the temporal part ])y 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, or presents instead a notch on its anterior 
border; its upper surface is convex, while the lower or orbital surface is concave 
and smooth, forming a shallow fossa for the lacrimal gland (Fossa glandulae lacri- 
malis). The internal surface enters into the formation of the cranial cavity and 
the frontal sinus. The cranial surface presents digital impressions for the cerebral 
gyri. The two plates of the bone separate and diverge in front, and thus inclose 
a large air-space which is part of tlie frontal sinus. The cranial plate curves down- 
ward and articulates with the cribriform })late of the ethmoid bone; the facial plate 
extends forward and joins the nasal and lacrimal bones. 

The orbital part (Pars orbitalis) forms the major part of the inner wall of the 
orbital cavity. It is separated from the frontal part by a prominent ridge which is 
part of the orl)ital margin. Its external or orbital surface 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 or internal orbital foramen. The internal surface faces 
into the frontal sinus and gives attachment to the lateral mass of the ethmoid. 

The temporal part is separated from the orbital part by the deep sphenoidal 
notch (Incisura sphenoidalis), which is occupied by the orbital wing of the sphenoid. 
Its external surface forms part of the inner wall of the temporal fossa. The 
internal surface is largely covered l;)y the orbital wing of the sjihenoid 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 inner border joins its 
fellow at the frontal suture. (2) The anterior Ijorder meets the nasal and lacrimal at the naso- 
frontal and fronto-lacrimal sutures. (3) Laterally it forms the spheno-frontal suture with the 
orbital wing of the sphenoid, and also joins the palate bone and maxilhi. (4) Posteriorly it 
meets the parietal at the parieto-frontal (or coronal) suture, and articulates below this with the 
squamous temporal. (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 cartilagin- 
ous margin 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 craniuuL It is situated between the occipital behind, the parietal above, 
the frontal in front, and the sphenoid below. It consists of two distinct parts, 
squamous and petrous. 

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

The internal surface (Facies cerebralis) is largely overlapped by the surround- 
ing bones, l)ut its central part is free and presents digital impressions and vascular 
grooves. 



56 THE SKELETON OF THE HORSE 

The external surface (Facies temporalis) is convex, and enters into the forma- 
tion of the temporal fossa. From its lower part there springs the zygomatic 
process (Processus zygomaticns), which forms the external l^oundary of the tem- 
poral fossa. It is at first directed outward, and is wide and flattened dorso-ven- 
trally. It then turns forward, becomes narrower, and is twisted so that its surfaces 
are internal and external. Its anterior end is pointed and joins the zygomatic 
process of the malar bone, with which it forms the zygomatic arch (Arcus zygo- 
maticus). The narrow anterior part has a convex outer surface and a concave 
inner one. Its upper border has a rough area for articulation with the supraorbital 
process of the frontal. Its lower 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 (Tuberculum 
articulare), behind which is the glenoid fossa (Fossa mandibularis). The fossa is 
limited behind by the post-glenoid process, the anterior surface of which is articu- 
lar. Behind this process is a fossa in which is the external opening of the parieto- 
temporal canal. The dorsal surface is concave and forms the outer boundary of 
the temporal fossa. The superior border is sinuous and is continuous behind with 
the temporal crest. 

The posterior process (Processus posterior) springs from the posterior part of 
the squama. Its external surface is crossed by the temporal crest, which forms 
here the outer limit of the temporal fossa. The internal surface forms the outer 
boundary of the parieto-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 
auditory process and overlaps the mastoid process. 

The superior border of the squamous temporal articulates with the parietal, 
forming the parieto-temporal suture. The inferior border joins the temporal wing 
of the sphenoid at the spheno-squamous suture. The anterior border unites with 
the frontal l)one, and the posterior with the parietal. 

2. The petrous temporal (Os petrosum) is placed between the occipital behind 
and the parietal in front, and is largely overlapped externally by the squamous 
temporal. It has the form of a four-sided pyramid, the base of which is ventral. 

The external surface is mainly concealed by the squamous temporal, but two 
features are visible. A short tube of bone, the external auditory process, protrudes 
from the lowest part through the notch of the squamous temporal. The process is 
directed outward, upward, and a little forward. It gives attachment to the annular 
cartilage of the ear. Its lumen, the external auditory 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 membrane in the natural state. The 
mastoid process projects ventrally in the interval between the posterior process 
of the squamous temporal and the root of the paramastoid (or styloid) process of 
the occipital bone; its outer surface is crossed by a curved groove which leads to 
the parieto-temporal canal. 

The internal surface faces into the cerebellar fossa of the cranium. It is con- 
cave and smooth but irregular. In its lower part is the entrance to a short canal, 
the internal auditory meatus, which transmits the seventh and eighth cranial nerves. 

The fundus of the meatus is divided by a crest into a superior and an inferior fossa. In the 
superior one is the origin of the facial canal, which curves through the bone and opens exter- 
nally at the stylo-mastoid foramen; it transmits the facial (seventh cranial) nerve. The in- 
ferior fossa presents small foramina for the passage of fibers of the auditory (eighth cranial) 
nerve. 

Behind the meatus and near the posterior margin of the surface is the slit-like 
opening of the aquaeductus vestibuli, covered by a scale of bone. Below this is a 
narrow fissure, the orifice of the aquaeductus cochleae. 



BONES OF THE FACE 57 

The anterior surface looks iijiward and forward. The outer part articulates 
with the parietal bone and the inner part faces into the cerebral fossa of the cranium. 
A sharp border, the petrosal crest (Crista petrosa), separates this surface from the 
inner one. 

The posterior surface joins the lateral part of the occii)ital bone. 

The base forms the outer Ijoundary of the foramen laccn-um Ijasis cranii. It 
is very irregular and presents a number of important features. The hyoid process 
is a short rod which projects downward and forward below the base of the external 
auditory process, inclosed in a bony tube ; it is connected by a bar of cartilage with 
the hyoicl bone. The stylo-mastoid foramen is situated between the root of the 
hyoid process and the mastoid process; it is the external opening of the facial canal, 
through which the facial nerve emerges. The bulla ossea is a considerable emi- 
nence situated centrally; it is thin-walled and incloses a cavity which is part of the 
tympanum. The muscular process' is a sharp spine which projects downward 
and forward from the anterior part of the base; it gives origin to the tensor and 
levator ]ialati muscles. External to the root of the preceding is the small petro- 
tympanic or Glaserian fissure (f^issura petro-tympanica) for the passage of the 
chorda tympani nerve. The osseous Eustachian tube is a semicanal at the inner 
side of the root of the muscular process; it leads to the tympanum. At the inner 
side of the preceding is the slit-like orifice of the petrosal canal, which communicates 
with the facial canal. 

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

Development. — The petrous temporal may be regarded as consisting of petro- 
mastoid and tympanic parts. The latter includes the external auditory process, 
the bulla ossea, and the muscular process; it is developed in membrane. The 
petro-mastoicl is developed in the cartilaginous ear capsule. Its petrous part 
consists of verj^ dense bone which contains the labyrinth or internal ear and forms 
the inner wall of the tympanum. 

The parieto-temporal canal (Meatus temporalis) is a continuation of the trans- 
verse groove which extends outward from the base of the tentorium osseum. It 
is directed downward, forward, and somewdiat outward, and opens externally in 
front of the root of the auditory process. It is bounded by the squamous temporal 
externally, the petrous behind, and the parietal in front and internally. 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 (Foramen lacerum et jugulare) is a large 
irregular opening in the cranial base, bounded internally l)y the basilar part of the 
occipital bone, externally by the petrous temporal, and in front by the temporal 
wing of the sphenoid. It consists of a large anterior part (Foramen lacerum an- 
terius), and a narrow posterior part (Foramen lacerum posterius s. jugulare). 
It transmits the internal carotid artery, the middle meningeal artery, the mandi- 
bular, ninth, tenth, and eleventh cranial nerves, and the inferior 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 
(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, Superior Turbinal, Inferior Turbinal, Vomer, 

Mandible, and Hyoid. The last three are single, the others paired. 

1 This is commonly termed the styloid process. It is not the homologue of the styloid process 
of man. 



58 the skeleton of the horse 

The Maxillae 

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 
with 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. 

The body (Corpus maxillee) presents two surfaces, two borders, and two ex- 
tremities. The external or facial surface (Facies lateralis) is somewhat concave 
in front and convex behind. On its posterior part is a horizontal ridge, the facial 
or zygomatic 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 by a corresponding ridge on the malar Ijone. About two inches 
(5 cm.) al)ove and a little in front of the anterior end of the crest is the infra- 
orbital foramen (Foramen infraorbital) ; this is the external opening of the infra- 
orbital canal. 

In the young horse the anterior part of the surface is convex over the embedded parts of the 
teeth. As the latter are extruded the surface flattens and becomes concave in old subjects. 

The internal 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 with that on the inner 
surface of the lacrimal bone. Below the groove is the inferior turbinal crest 
(Crista conchalis inferior), to which the inferior turl:)inal bone is attached. Lower 
down and parallel with the turl)inal crest is the palatine process, which projects 
inward like a shelf. Behind this the surface is rough for articulation with the palate 
bone; this area is crossed i^y a groove which concurs with a furrow on the palate 
bone in the formation of the palatine canal. The posterior part of the bone is 
excavated to form part of the maxillary sinus. 

The superior border is irregular and scaly. Its anterior part is grooved and 
its posterior part Ijeveled for articulation with the nasal process of the premaxilla 
and the nasal and lacrimal l)ones. 

The inferior or alveolar border (Processus alveolaris) is thick, and presents six 
large cavities, the alveoli, for the cheek teeth. The alveoli are separated by trans- 
verse interalveolar septa. There is often a small alveolus for the first premolar 
("wolf tooth") close to the first large one. Further forward the border is narrow 
and forms part of the interdental or interalveolar space (]\Iargo interalveolaris). 
Behind the last alveolus is a rough area, the alveolar tuberosity. 

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

The posterior extremity forms a rounded prominence, the maxillary tuberosity 
(Tuber maxillare). Internal to the tuberosity is a deep cavity, the maxillary 
hiatus, in which are three foramina. The upper one, the maxillary foramen, leads 
into the infraorl)ital canal. The lower one, the posterior palatine foramen, is the 
entrance to the palatine canal. The spheno-palatine foramen perforates the inner 
wall of the hiatus and opens into the nasal cavity. 

The zygomatic or temporal process (Processus temporalis) projects backward 
above and external to the tul)crosity; it is overlapped by the corresponding part 
of the malar and also articulates with the zygomatic process of the temporal. A 
small curved plate extends inward from it and joins the frontal and palate bones, 
forming part of the floor of the orbit. 

The palatine process (Processus palatinus) is a plate which projects horizon- 
tally inward from the lower part of the inner surface of the body. It forms the 



THE PREMAXILL^ 



59 



greater part of the basis of the hard palate. Its superior or nasal surface is 

smooth and concave transversely; on its anterior part, close to the inner border, 

is a siuillow groove in which the organ of Jacobson is situated. The inferior or 

palatine surface is slightly concave from side to side, and presents along its outer 

part the palatine groove (Sulcus palatinus). The groove is a continuation of the 

palatine canal, and contains the palatine arterj- and nerve. The internal border 

unites with its fellow to form the 

median palatine suture; its nasal 

aspect bears the nasal crest, which 

forms, with that of the opposite 

proct^ss, a groove for the vomer. 

The posterior border unites with 

the horizontal part of the palate 

bone at the transverse palatine 

suture. 

The infraorbital or superior 
dental canal extends almost hori- 
zontally from the maxillary fora- 
men 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 pre- 
maxilla, carrying vessels and 
nerves to the teeth there. 

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

The Premaxillae 

The premaxillae (Ossa incis- 
iva) form the anterior part of the 
upper jaw and carry the incisor 
teeth. Each consists of a body 
and two processes, nasal and pala- 
tine. 

The body is the thick an- 
terior part which carries the in- 
cisor teeth. Its labial or superior 
surface is convex and smooth, and 
is related to the uj^per lip. The 

palatine or inferior surface is concave and presents a foramen a little behind its 
middle.' The internal surface is rough, and joins the opposite bone; it is marked 
by a curved groove, which forms with that on the opposed surface, the incisive 

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




Fig. 31. — Upper J.\w of Horse About Four and a Half 
Years Old, Ventral View. 
1, 1, Posterior nares; 2, vomer; 3, horizontal part of 
palate bone; 4, anterior palatine foramen; 5, palatine groove; 
6, transverse palatine suture; 7, median palatine suture; 8, 
palate process of maxilla; 9, palate process of premaxilla; 10, 
foramen incisivum; 11, malar bone; 12, maxilla; 13, anterior 
end of facial crest; 14, interalveolar space; I. 1-3, inci.sor 
teeth; C, canine tooth; I'\, first premolar or "wolf" tooth. 



60 THE SKELETON OF THE HORSE 

foramen (Foramen incisivum). The alveolar border (Limbus alveolaris) separates 
the palatine and labial surfaces; it is curved antl tliick, and presents three alveoh 
for the incisor teeth; behind the third alveolus it is rounded and free, forming part 
of the interalveolar space. 

The nasal process (Processus nasalis) projects l^ackward and upward from the 
body, forming here the lateral wall of the nasal cavity. The two surfaces, facial 
and nasal, are smooth and rounded. The superior border is free, thick, and smooth. 
The inferior 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 
extremity fits into the interval between the nasal bone and the maxilla. 

The palatine process (Processus palatinus) is a thin plate which forms the an- 
terior part of the basis of the hard palate. Its nasal or superior surface has a 
longitudinal ridge which forms with that of the other side a groove for the septal 
cartilage. The palatine or inferior surface is flat. The internal border is serrated 
and meets its fellow at the median palatine suture. The external border is sep- 
arated from the maxilla and the nasal process by the palatine cleft (Fissura pala- 
tina). The posterior extremity fits into the interval between the vomer and the 
palatine process of the maxilla. 

Development. — The premaxilla ossifies from a single center. Fusion of the 
two bones is complete at the end of the third or the beginning of the fourth year. 

The Palatine Bones 

The palatine bones (Ossa palatina) are situated on either side of the posterior 
nares, and form the posterior margin of the hard palate. Each is twisted so as to 
form a horizontal and a perpendicular part. 

The horizontal part (Pars horizontalis) is a narrow plate which forms the pos- 
terior part of the hard palate. It presents smooth nasal and palatine surfaces. 
The internal border meets its fellow at the mechan palatine suture, on the nasal 
aspect of which is the nasal crest. The anterior border joins the palate process of 
the maxilla at the transverse palatine suture, antl forms with it the anterior pala- 
tine foramen. The posterior border is concave and free; it gives attachment to 
the aponeurosis of the soft palate. 

The perpendicular part (Pars perpendicularis) is more extensive and forms the 
outer boundary of the posterior nares. The nasal or internal surface is in the 
greater part of its extent concave and smooth ; it is marked by a narrow rough area 
to which the pterygoid bone is attached. Below this the bone curves outward, 
forming the pterygoid process. The maxillary or external surface (Facies max- 
illaris) presents three areas for consideration. The largest articulates with the 
maxilla; it is rough and is crossed by a groove which enters into the formation of 
the palatine canal. Behind this is a smooth part which assists in forming the 
pterygo-palatine fossa. The rough area below this is overlapped by the pterygoid 
process of the sphenoid bone. The superior border is perforated by the spheno- 
palatine foramen. Behind the foramen the two plates of the lione separate to 
inclose part of the spheno-palatine sinus. The inner plate curves inward to articu- 
late with the vomer. The outer plate joins the maxilla and frontal and the orbital 
wing of the sphenoid. 

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 internal surface is smooth, and forms part of the boundary of the posterior 

nares. The external surface articulates with the palatine, vomer, and sphenoid, 

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



THE NASAL BONES — THE LACRIMAL BONES 61 

concun-ing with the last in the formation of the pterygoid or Vidian canal. The 
anterior extremity is free, turned shghtly outward, and forms the hamulus, 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, a base, and an apex. 

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

The internal or nasal surface is smooth and concave from side to side. About 
in its middle it presents the superior turbinal crest (Crista conchalis dorsalis), 
which is parallel with the inner border, and has the superior turbinal bone attached 
to it. Most of this surface faces into the nasal cavity, but its posterior part enters 
into the formation of the frontal sinus; the latter area is marked off by an oblique 
ridge. 

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

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

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

The apex is pointed and thin. 

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 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 external aspect is clearly divided into orbital and facial parts by the orbital 
margin. The orbital surface (Facies orbitaHs) is triangular in outhne, smooth and 
concave; it forms part of the inner and front wall of the orbit. Near the orbital 
margin it presents a funnel-like fossa for the lacrimal sac (Fossa sacci lacrimalis), 
which is the entrance to the osseous lacrimal canal. 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, situated nearly an inch (ca. 2 cm.) from the 
orbital margin. 

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

The orbital margin (Margo orbitalis) is concave, rough above, smooth below. 

The circumference articulates above with the frontal and nasal bones, below 
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. 



62 the skeleton of the horse 

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, a base, and an apex. 

The facial surface is smooth, slightly convex, wide in front, and narrow behind. 
At its lower part it presents the facial or zygomatic crest, which is continuous 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 separated from the facial surface by the concave orbital 
margin. 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 considerable part of it articulates with the maxilla. 

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

The inferior border and the base articulate with the maxilla. 

The apex is beveled above and is overlapped by the zygomatic process of the 
temporal bone. 

Development. — Each ossifies in meml)rane from one or two centers. 

The Turbinal 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, cribriform 
in many places, and covered on both sides with mucous membrane in the fresh 
state. They are arranged in two pairs, superior and inferior. 

The superior or naso-turbinal (Concha dorsalis)^ is somewhat cylindrical in 
form, small at its anterior part, and flattened transversely. It is attached to the tur- 
binal 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 com- 
municates with the middle meatus nasi. The arrangement is best seen on a cross- 
section (Fig. 37) . The posterior part is not rolled, but its lower border is attached to 
the lateral nasal wall, thus helping to inclose a large space which is part of the fron- 
tal sinus. This cavity is separated from that of the scroll-like part by a transverse 
septum. The internal surface is flattened, and is separated from the septum nasi 
by a narrow interval, the common meatus (Meatus nasi communis). Another 
narrow passage, the superior meatus (Meatus nasi superior), separates the upper 
surface from the roof of the nasal cavity. The space between the lower surface 
and the inferior turbinal is the middle meatus (Meatus nasi medius). The anterior 
extremity is prolonged toward the nostril by two small bars of cartilage. 

The inferior or maxillo-turbinal bone (Concha ventralis) is shorter and smaller 
posteriorly than the upper one. It is attached to the inferior turbinal 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 inferior 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 inferior meatus 
(Meatus nasi inferior), which is much larger than the other nasal passages. The 
anterior extremity is prolonged to the nostril by a curved bar of cartilage. 

Development. — Each ossifies in cartilage from a single center. 
' This bone is really a greatly developed first ethmo-turbinal. 



the vomer — the mandible 63 

The Vomer 

The vomer is a median unpaired bone, which assists in forming the lower 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 septi narium) , in w^hich the 
lower part of the perptnidicular ])late of the ethmoid ]:)one 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 in- 
ferior border is thin and free in its posterior third, and divides the posterior nares 
into right and left halves; in the remaind(n- of its extent it is wider and is attached 
to the nasal crest. The anterior extremity lies above the ends of the palatine pro- 
cesses of the premaxillie. The posterior extremity consists of two wings (Alse 
vomeris) which extend outward below the body of the pre-sphenoid ; posteriorly 
they form a notch (Incisura vomeris), and laterally join the palate and pterygoid 
bones. 

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

The Mandible 

The mandible or inferior maxilla (Alandibula) is the largest and the only 
movable bone of the face. The two halves of which it consists at birth unite during 
the second or third month, and it is usually descril)ed as a single bone. It carries 
the lower teeth, and articulates by its condyles with the squamous temporal on 
either side. It consists of a body and two rami.^ 

The body (Corpus mandibuUie) is the thick anterior part which bears the incisor 
teeth. It presents two surfaces and a border. The lingual or superior surface 
(Facies lingualis) is smooth and slightly concave; during life it is covered by mucous 
membrane, and the tip of the tongue overlies it. The labial or 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 
curvetl 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 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) which is expanded 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 external surface is smooth and slightly convex from (>dge 
to edge on the horizontal part; at the junction with the l^ody it presents the mental 
foramen (Foramen mentale), which is the external opening of the mandibular or 
inferior dental canal. On the vertical part it is somewhat concave and presents a 
number of rough lines for the attachment of the masseter muscle. The internal 
surface of the horizontal part is smooth, and presents a shallow longitudinal de- 
pression in its middle; above this there is often a faint mylo-hyoid line for the at- 
tachment 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-glossus 
muscles. On the vertical part the surface is concave, and is marked in its lower and 

' In the Stuttgart Nomenclator Anatomicus (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. 



64 THE SKELETON OF THE HORSE 

posterior part ])y rough lines for tlie attacliment of the internal ]3terygoid muscle. 
In front of its middle is the mandibular or inferior maxillary foramen (Foramen 
mandibulare), which is the posterior orifice of the mandibular or inferior dental 
canal (Canalis mandibular). The canal curves downward and passes forward 
below the cheek teeth, opening externally at the mental foramen; it is continued 
into the body of the bone as a small canal (Canalis alveolaris incisivus), which 
carries the vessels and nerves to the incisor teeth. The superior or alveolar border 
forms anteriorly part of the interalveolar space; here it is thin. Behind this it is 
thick and is excavated 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 inferior 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 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 (Angulus mandi- 
bulfe) ; this part is thick and has two roughened lips, internal and external, sep- 
arated by a considerable intermediate space ; near the condyle it becomes narrower. 
The anterior extremity joins the body. The superior extremity comprises the 
coronoid process in front and the condyle behind, the two being separated by the 
sigmoid notch (Incisura mandibulse), through which the nerve to the masseter 
muscle passes. The coronoid process (Processus coronoideus) is thin transversely 
and curved slightly inward and backward. It projects upward in the temporal 
fossa, and furnishes insertion to the temporal muscle. The condyle (Capitulum 
mandibulse) hes at a much lower level than the end of the coronoid process. It is 
elongated transversely and articulates with the squamous temporal through the 
medium of an articular disc. The part below the condyle is usually termed the 
neck (CoUum mandibuloe); on its antero-internal part is a depression (Fovea 
pterygoidea) for the attachment of the external pterygoid muscle. 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 a median symphysis. 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 large 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; the angle and the 
impression in front of it are more pronounced. 

The Hyoid Bone 

The hyoid bone (Os hyoideum) is situated chiefly between the vertical parts 
of the rami of the mandible, but its upper part extends somewdiat further back. 
It is attached to the petrous temporal bones by rods of cartilage, and supports the 
root of the tongue, the pharynx, and larynx. It consists of a body, a lingual process, 
and three pairs of cornua. 

The body or basihyoid (Basis ossishyoidei) is a short transverse bar, compressed 
dorso-ventrally. The upper surface is concave and smooth in its middle, and pre- 
sents at each end a convex facet or tubercle for articulation with the small cornu. 
The lower surface is slightly roughened for muscular attachment. The anterior 
border carries medially the lingual process. The posterior border is concave and 
smooth in its middle, and carries on either side the thyroid cornu. The body, the 



THE SKULL AS A WHOLE 



65 



lingual process, and the thyroid processes are fused together, and may be compared 
to a spur or a fork with a very short handle. 

The lingual process (Processus lingualis) projects forward medially from the 
body, and is embedded in the root of the tongue during life. It is compressed 
laterally and has a blunt-pointed free end. The lateral surfaces are slightly con- 
cave. The upper border is narrow, the lower thick and irregular. 

The thyroid cornua or thyrohyoids (Cornua laryngea)' extend backward and 
upward from the lateral parts of the body. They are compressed laterally (except 
at their junction with tlie body), and their posterior ends are connected with the 
anterior cornua 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 upper surface of the body. 
Each is somewhat constricted in its middle part and has slightly enlarged ends. 
The lower end has a small concave facet which articulates with the body. The 
upper end articulates with the great cornu, or with the middle cornu when present. 

The great cornua or stylohyoids are much the largest parts of the bone. They 
are directed upwartl and ]>ack\vard, 
and are connected above with the 
base of the petrous temporal l)ones. 
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 external surface is concave 
and smooth. The internal surface 
is convex and smooth. The borders 
are thin. The upper extremity is 
large and forms two angles; the 
upper angle is connected by a rod 
of cartilage with the hyoid process 
of the petrous temporal bone; the 
lower angle is somewhat thickened 
and rough for muscular attachment. 
The lower extremity is small, and 
articulates with the small or the 
middle cornu. 

The middle cornua 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. The latter has primarily two centers (Martin). 




Fig. 32. — Hyoid Boxe of Horse, Viewed from the Side 

.\NU SOMEWH.^T from IN FrONT. 

a. Body; 6, lingual pioce.ss; c, thyroid cornu; c', car- 
tilage of c; d, small cornu; e, middle cornu; /, great cornu; 
/', muscular angle of great cornu; g, cartilage of great cornu. 
(EUenberger-Baum, Anat. d. Haustiere.) 



THE SKULL AS A WHOLE 

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

The superior or frontal surface (Norma frontalis) is formed by the upper part 
of the occipital, the interparietal, parietal, frontal, and nasal bones. It may be 
^ These correspond to the great cornua of man. 



66 



THE SKELETON OF THE HORSE 



divided into parietal, frontal, nasal, and premaxillary regions. The parietal region 
extends from the occipital crest to the parieto-frontal or coronal suture. It is 
marked medially by the external sagittal crest, which bifurcates in front, the 
branches becoming continuous with the frontal crests. The latter curve outward 
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 l)ounded in front l)y the naso- 
frontal suture. On either side of it is the root of the supraorbital process, pierced 




Fig. .33. — Cranial and Orbital Regions of Skull of Horse, Lateral View. The Zygomatic Arch and 
Supraorbital Processes Have Been Sawn Off. 
1, Occipital condyle; 2, condyloid fossa; 3, paramastoid or styloid process; 4, occipital crest; 5, external 
occipital protuberance; 6, external auditory meatus; 7, mastoid process; 8, hyoid process; 9, stylomastoid fora- 
men; 10, muscular process; 11, foramen lacerum anterius; 12, postglenoid process; 13, glenoid cavity; 14, tem- 
poral condyle; 15, Vidian groove; 16, alar canal of pterygoid process indicated by arrow; 17, temporal foramen; 
IS, ethmoidal foramen; 19, optic foramen; 20, .foramen lacerum orbitale; 21, maxillary foramen; 22, spheno- 
jjalatine foramen; 23, posterior palatine foramen; 24, supraorbital foramen (opened); 25, lacrimal fossa; 26. 
depression for origin of obliquus oculi inferior; 27, facial crest; 28. maxillary tuberosity; 29, alveolar tuberosity; 
30, hamulus of pterygoid bone; S.o.. supraoeeipital; P, parietal; S, squamous temporal; B.o., basioccipital; 
5.S., basisphenoid; .4 J., temporal wing of sphenoid; ,4. o., orbital wing of sphenoid; P;. p., pterygoid process of 
sphenoid; P.p., perpendicular part of palate hone; F,F', facial and orbital parts of frontal bone; L,L', orbital 
and facial parts of lacrimal bone; .1/. faci.nl i)art of malar bone; M.x.. maxilla; a. jjarieto-occipital suture; b, 
parieto-temporal or squamous suture; c.cl. siiheno-squamous suture; e, palato-frontal suture; /, fronto-lacrimal 
suture. 



by the supraorbital foramen. The nasal region is convex from side to side, wnde 
behind, narrow in front. Its profile is in some cases nearly straight; in others it 
is undulating, with a varial)ly marked depression about its middle and at the an- 
terior end. The premaxillary region presents the osseous nasal aperture (Apertura 
nasalis ossea) and the foramen incisivum. 

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



THE SKULL AS A WHOLE 67 

The cranial region presents the temporal fossa, the zygomatic arch, and the 
outer part of the i)etrous temporal bone. ^ 

The temporal fossa is bounded internally by the sagittal and frontal crests, 
externally by the temporal crest and the zygomatic arch, and behind by the occipital 
crest. Its upper and middle parts are rough for the attachment of the temporal 
muscle. In its lower posterior part are several foramina which connnunicate with 
the parieto-temporal canal. The fossa is continuous in front with the oi'bital cavity. 

The zygomatic arch is formed by the zygomatic processes of the temporal, 
malar, antl maxilla. Its ventral face presents the condyle and glenoid cavity for 
articulation with the lower jaw, through the medium of the articular disc. Behind 
the glenoid cavity is th(^ post-glenoid process. 

The external auditory process projects outward through a deep notch in the 
lower margin of the sciuamous temporal below the temporal crest. A little 
further back is the mastoid process, crossed in its upper part by a groove for the 
mastoid artery. 

The orbital region conii:)rises the orbit and the pter^'go-palatine fossa. 

The 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 long axis of the cavity, taken from the optic foramen to the middle of 
the inlet, is directed forward, outward, and slightly upward. The inner 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 
extreme anterior part is the fossa for the lacrimal sac. Behind this is a small de- 
pression 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 upper wall (Paries 
superior) is formed l)y 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 lower wall (Paries inferior) is very incomplete, and is formed by the 
malar, the zygomatic process of the temporal, and to a small extent by the maxilla. 
The external boundary (Paries lateralis) is the supraorbital process. At the ex- 
treme posterior part is the orbital group of foramina. Four are situated in front 
of the pterygoid crest. Of these, the uppermost is the ethmoidal or internal 
orbital foramen, which transmits 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 lacerum orbitale, which transmits the 
ophthalmic, third, sixth, and sometimes the fourth nerve; commonly there is a 
very small trochlear or pathetic foramen in the crest for the last named nerve. 
The foramen rotundum is below the foramen lacerum, from which it is separated 
by a thin plate; it transmits the superior maxillary nerve. The alar canal opens 
in common with the foramen rotundum, and the anterior opening of the pterygoid 
or Vidian canal is also found here. The temporal foramen (For. alare parvum) is 
just behind the pterygoid crest and on a level with the foramen lacerum. It is 
the upper opening of a canal which leads from the alar canal, and through it the 
anterior deep temporal artery emerges. The inlet of the orbital cavity (Aditus 
orbitse) is circumscribed by a complete bony ring, which is nearly circular. Its 
antero-inferior part (Margo infraorbitalis) is smooth and rounded; the remainder 
(Margo supraorbitalis) is rough and irregularly notched. During life the cavity is 
completed by the periorbita or ocular sheath, a conical fibrous membrane, the apex 
of which is attached around the optic foramen. 

Below 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 part (maxillary hiatus) contains three foramina. The 
upper one, the maxillary foramen, is the entrance to the infraorbital canal, which 
transmits the infraorl)ital nerve and vessels. The spheno-palatine foramen trans- 



68 THE SKELETON OF THE HORSE 

mits 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 attach- 
ment of the internal pterygoid muscle, but is crossed in front by a smooth groove 
in which the palatine vein lies. 

The maxillary or preorbital region is formed chiefly by the maxilla, but also by 
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 lower margin of the orbit, 
and ends abruptly at a point about an inch and a half (3 to 4 cm.) above the third 
or fourth cheek tooth ;^ its inferior aspect is rough for the attachment of the masse- 
ter 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.) 
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 with 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. 

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

The cranial region (Basis cranii externa) extends forward to the vomer and 
pterygoid processes (Fig. 28) . At its posterior end is the foramen magnum, flanked 
by the occipital condyles. External to the latter is the condyloid fossa, in which 
is the h5rpoglossal foramen, which transmits the hypoglossal nerve and the con- 
dyloid artery and vein. Further outward are the paramastoid or styloid proc- 
esses (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 attach- 
ment of the ventral straight muscles of the head. On either side of the basilar 
part of the occipital is the foramen lacerum basis cranii, bounded externally by 
the base of the petrous temporal bone. In front of these the region becomes very 
wide on account of the lateral extension of the zygomatic processes, bearing on the 
ventral aspect 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 pterygoid or alar foramen, which 
transmits the internal maxillary artery. A little lower is the entrance to the ptery- 
goid (Vidian) canal. 

The guttural region presents the pharyngeal orifice of the nasal cavity. This is 
elliptical and is divided in its depth medially by the vomer into two posterior 
nares or choanae. 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 
bones. 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 

' This relation varies with age; in the young horse the third tooth, in the old subject the 
fourth, lies below the end of the crest. 



THE CRANIAL CAVITY 



69 



of the base of the skull (Fig. 31). The hard palate (Palatum durum) is 
concave from side to side, and in its lengtli also in the anterior part. It 
is formed by the palatine^ processes of the premaxillse and maxillae, and the 
horizontal parts of the palate bones. It is circumscribed in front and 
laterally by the superior alveolar arch, in which the upper teeth are im- 
planted. The interalveolar space (Margo interalveolaris) is that part of the arch 
in which alveoli are not i)r('sent. Behind the last alveolus is the alveolar 
tuberosity, and internal 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 con- 
tinuous at the anterior pala- -2/ 
tine foramen with the palatine 
canal, which is situated be- 
tween the maxilla and the pal- 
ate bone. The palatine cleft 
(Fissura palatina) is the nar- 
row interval along the outer 
margin of the palatine process 
of the premaxilla; it is closed 
in the fresh state by cartilage. 
Scattered along each side of 
the palate are several vascular 
foramina. The transverse 
palatine suture (Sutura pala- 
tina transversa) is about half 
an inch from the posterior bor- 
der. The latter is in a plane 
through the last molar teeth, 
and is concave and free. 

The posterior or nuchal 
surface (Norma occipitalis) is 
formed by the occipital bone. 
It is trapezoidal in outline, 
wider below than above, con- 
cave dorso-ventrally, convex 
transversely. It is separated 
from the superior surface by 
the occipital crest, and from 

the lateral surfaces by the superior curved lines (Linese nucha? superiores). Below 
the crest are two rough areas for the attachment of the complexus muscles. A little 
lower is a central eminence on the sides of which the ligamentum nuchse is attached. 
At the lowest part centrally is the foramen magnum, at which the brain and spinal 
cord meet; this is bounded laterally by the occipital condyles, which are flanked by 
the paramastoid or styloid processes (Processus jugulares). 

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




Fig. 34. — Cranial Cavity of Horse as Seen on Sagittal Sec- 
tion OF Skull. 
O, Frontal sinus; r, sphenoidal sinus; t, cerebral compartment 
of cranium; 1-3, ridges (juga) corresponding to fissures of lateral 
surface of cerebrum; 4, groove for middle cerebral artery; 5, en- 
trance to for. lacerum orbitale; 6, entrance to optic foramen; 7, 8, 
grooves on sphenoid bone; 9, incisura spinosa; 9', groove for middle 
meningeal artery; 10, fossa for pyriform lobe of cerebrum; 11, 
incisura ovalis; 12, incisura carotiea; 13, internal auditory meatus; 
14, foramen lacerum basis cranii; 15, hypoglossal foramen; 16, 
petrous temporal; 17, orifice of atjua'ductus vestibuli; 18, orifice 
of aquaductus cochleie; 19, foramen magnum; 20, petrosal crest; 
21, two plates of frontal bone; 22, supraoccipital; 23, basioccipital; 
24, tentorium osseum; 25, body of sphenoid. (After EUenberger- 
Baum, Top. Anat. d. Pferdes.) 



THE CRANIAL CAVITY 

This cavity incloses the brain, with its membranes and vessels, 
small and is ovoid in shape. 



It is relatively 



70 



THE SKELETON OF THE HORSE 



The superior wall or roof (Calvaria) is formed })y the supraoccipital, inter- 
parietal, parietal, and frontal bones. In the middle line is the internal sagittal 
crest, which joins the crista galli in front, and furnishes attachment to the falx 
cere])ri. Posteriorly the crest is continued by the sharp anterior margin of the 
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 
parieto-temjjoral canals. The 
anterior part of the roof is hol- 
lowed by the frontal sinus. The 
occipital part is very thick and 
strong. 

The lateral walls are formed 
by the occipital, parietal, tem- 
poral, and frontal bones, and in 
part by the orbital wings of the 
sphenoid. Each is crossed oli- 
liquely by the petrosal crest, 
which concurs with the project- 
ing margin of the ]3arietal bone 
and the tentorium osseum in 
dividing the cavity into cerebral 
and cerebellar compartments. 
Behind the crest is a depression 
for the lateral lobe (hemisphere) 
of the cerebellum. Below this 
are the internal auditory meatus 
and the openings of the aquse- 
ductus vesti])uli and aquaeductus 
cochleiB. 

The roof and lateral walls 
are marked by digital impres- 
sions and vascular grooves. 

The inferior wall or floor 
(Basis cranii interna) may be 
regarded as forming three fossae. 
The anterior fossa (Fossa cranii 
anterior) supports the frontal and 
olfactory parts of the cereljrum. 
It is formed chiefly by the pre- 
sphenoid, and lies at a higher 
level than the middle fossa. In 
front the fossa is divided medi- 
ally by the crista galli, lateral to 
which are the deep ethmoidal or 
olfactory fossae for the olfactory 
lobes. The ethmoidal or internal orbital foramen perforates the cranial wall 
at the outer side of these fossse. Further back the central part of the surface 
is slightly elevated, and is flanked by shallow depressions which support the ol- 
factory peduncles. 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 tlui sphenoid may be taken as the line of demarcation between the anterior and 




Fig. 35. — Floor of Cranial Cavity of Horse. 

The roots of the cranial nerves are shown on the left side 
and are designated by number. /, Anterior cranial fossa; //, 
middle cranial fossa; ///, posterior cranial fossa; a, ethmoidal 
fossa; 6, ethmoidal foramen; c, foramen for nasal branch of 
ophthalmic artery; d, orbital wing of sphenoid bone; c, optic 
fossa; /, sella turcica; g, spheno-occipital crest; h, h', clotted line 
indicating contour of pituitary body; h", slight elevation repre- 
senting dorsum sells; i, k, grooves for nerves and cavernous 
sinus; I, depression for pyriform lobe of cerebrum; m, groove 
for middle meningeal artery; n, depression for pons; o, foramen 
lacerum anterius; p, foramen lacerum posterius; q, incisura 
carotica; </, incisura ovalis; (f, incisura spinosa; )•, depression 
for medulla oblongata; s, hypoglossal foramen; t, internal audi- 
tory meatiis; u, foramen magnum; r, frontal sinus; w, zygomatic 
process of temporal bone; x, section of petrous temporal; y, 
section of occipital bone; z, crista galli; 1, 1', 1", dotted lines 
indicating position of olfactory tracts and peduncle. (After 
EUenberger-Baum, Top. Anat. d. Pferdes.) 



THE NASAL CAVITY 



71 



middle fossae. The middle fossa (Fossa cranii media) is the widest part of the 
cavity. It extends backward to the internal sphenooccipital and petrosal crests, 
thus corresponding to the post-sphenoid. In its middle is a small fossa, the sella 
turcica, in wliich the pituitary body, or hypophysis cerebri, is situated. On either 
side are two grooves for nerves; the inner one transmits the ophthalmic, third, 
and sixth nerves to the foramen lacerum orbitale; the outer one leads to the foramen 
rotundum, and lodges the maxillary nerve. External to the grooves is a depression 
for the pyriform lobe of the cerebrum. The posterior fossa (Fossa cranii posterior) 
corresponds to the basilar part of the occipital bone. It contains the medulla, 
pons, and cerebellum. In front is a median depression (Fossa pontis) for the pons. 
The surface behind this is concave transversely and slopes gently downward to the 
foramen magnum; it supports the medulla. On either side are th(^ foramen 
lacerum basis cranii and the hypoglossal foramen. 

The anterior or nasal wall 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. 




Fig. 36. — Medi.w Section of Skull of Horse Without the M.\.vdible. 
The septum nasi is removed, but the mucous membrane on the turbinal bones is retained. a, a', Superior 
turbinal bone, dotted line indicating limit between anterior coiled part and posterior uncoiled part; b, b', .superior 
turbinal folds, inclosing bars of cartilage; c, fold of mucous membrane formed by union of 6 and 6'; d, d', anterior 
coiled and posterior uncoiled part of inferior turbinal, dotted line indicating septum between them; e, f, inferior 
turbinal folds, former (alar fold) inclosing bar of cartilage; g, h, i, .superior, middle, inferior meatus; o, o', frontal 
sinus; partial septum between o and «'; q, nasal part of frontal sinus (nasal sinus); r, lateral mass of ethmoid 
bone; s, sphenoidal sinus; t, cranial cavity; ti, opening made in superior turbinal bone at point where drainage 
of frontal sinus maj- be obtained. (After EUenberger, in Leisering's Atlas.) 



THE NASAL CAVITY 

The nasal cavity (Cavum nasi) is a longitudinal passage which extends through 
the ui)pcr part of the face. It is divided into right and left halves ])y a median 
septum nasi. The lateral walls are formed by the maxilla, premaxilla, and the 
perpendicular part of the palate bones. Attached to them are the turbinal bones, 
which subdivide each nasal fossa into three meatuses (Meatus nasi). This wall 
is crossed obliquely by the canal and groove for the naso-lacrimal duct, and its 
posterior part is perforated by the spheno-palatine foramen. The superior wall 
or roof is formed by the frontal and nasal ])ones. It is concave from side to side, 
and nearly straight longitudinally, except in the posterior part, where it curves 
downward. It presents a median elevation, the nasal crest. The inferior wall 
or floor is formed by the palatine processes of the premaxilla:; and maxilhv, and the 
horizontal parts of the palate bones. It is wider but consideral)ly 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 mecUan groove for the cartilaginous septum, and a furrow for the organ 
of Jacobson on either .side. On either side of the palatine processes of the premax- 
illae is the palatine cleft. 



72 



THE SKELETON OF THE HORSE 



The septum nasi is incomplete in the macerated skull. It is formed by the 
perpendicular plate of the ethmoid behind, and the vomer below. In the fresh 
state it is completed by a plate of cartilage. 

The superior meatus (Meatus nasi superior) is a narrow passage between the 
roof and the superior turbinal bone. It ends at the cribriform plate of the ethmoid. 
The middle meatus (Meatus nasi medius) is the space between the two turbinal 
bones. In its posterior part is the very narrow opening into the maxillary sinus. 
The inferior meatus (Meatus nasi inferior) is the channel along the floor which is 
overhung by the inferior turbinal bone. It is much the largest and is the direct 
path between the anterior and posterior nares. 

The external aperture is bounded by the nasal bones and the premaxillse. 




Fig. .37. — Cross-section of Nasal Region of Skull 
OF Horse; the Section Passes Through 
THE Anterior End of the Facial Crest, 
AND Between the Third and Fourth Cheek 
Teeth. 

a, Superior, b, inferior turbinal bone; c, d, cavi- 
ties of a and b; e, common meatus; /, g, h, superior, 
middle, inferior meatus; t, A', passages to cavities of 
turbinal bones; /, naso-lacrimal duct; m, infraorbital 
canal; n, anterior end of maxillary sinus; o, septal 
cartilage. (After Ellenberger, in Leisering's Atlas.) 



Fig. .38. — 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, Superior, 6, inferior turbinal bone; c, d, cavi- 
ties of a and 6; e, common meatus; /, superior, g, 
middle, h, inferior meatus; (', placed over ridge in 
maxillary sinus; k, communication between outer and 
inner (turbinal) part of maxillary sinus; /, naso- 
maxillary opening; m, naso-lacrimal canal; n, infra- 
orbital canal, (.\fter Ellenberger, in Leisering's Atlas.) 



The posterior extremity or fundus is separated from the cranial cavity by the 
cribriform plate of the etlnnoid, 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 diver- 
ticula, are four pairs of air-sinuses (Sinus paranasales), viz., maxillary, frontal, 
spheno-palatine, and ethmoidal. 

The maxillary sinus (Sinus maxillaris) is the largest. Its external wall is 
formed by the maxilla, the lacrimal, and the malar. It is liounded internally by 
the maxilla, the inferior turbinal, 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 infraorl)ital foramen. Its upper boundary 
corresponds to a line drawn backward from the supraorbital foramen parallel to 
the facial crest. The floor is formed by the alveolar part of the maxilla; it is very 
irregular and is crossed by bony plates running in various directions. The last 



THE PARANASAL SINUSES 



73 



three cheek teeth project up into the cavity to an extent which varies with age; 
they are covered by a thin plate of l^one. The cavity is (hvided into anterior and 
posterior parts by an obUque septum. The outer margin of the septum is commonly 
about one and a half to two inches (ca. 3.5 to 5 cm.) from the anterior end of the 
facial crest; from here it is directed inward, backward, and upward. The upper 
part of the septum (formed by the posterior end of the inferior turbinal bone) is 
very delicate and usually criljriform. 

The position of the septum is quite variable. It is not rare to find it further forward, and 
in some cases it is further back than is stated above. In the recent state, i. c, when covered by 
the mucous membrane on both surfaces, it is nearly always complete, but in very exceptional 
cases there is an opening of varial)le size in the upper part . 

The anterior compartment, often called the inferior maxillary sinus, is partially 
divided by the infraorbital canal into an external maxillary part and an internal 
smaller turbinal part. The latter communicates with the middle meatus by a very 
narrow slit situated at its highest part. The posterior compartment, often called 
the superior maxillary sinus, is also crossed by the infraorlntal canal, internal to 
which it opens freely into the spheno-palatine sinus. It communicates dorsally 




Fig. 39. — Skull of Horse, Lateral View without ^^A^■DIBLE. The Sinuses are Opened up. 

a, Posterior part, 6 and c, anterior part of frontal sinus; d, roof of superior meatus; e, lateral mass of eth- 
moid bone; /, /', naso-lacrimal duct, exposed in its posterior part; g, h, posterior and anterior compartments 
of maxillary sinus (also designated as superior and inferior maxillary sinuses); i, septum between g and h; k, 
lower limit of upper thin and partly membranous portion of septum; /, infraorbital canal; m, turbinal part of 
maxillary sinus; n, bullous prominence of inferior turbinal; o, orbit; p, infraorbital foramen; q, continuation 
of infraorbital canal to premaxilla; r, limit of maxillary sinus. (After Ellenberger, in Leisering's Atlas.) 



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 inner 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 foregoino; statements refer to the arrangement in the average adult animal. In the 
foal the cavity (with the exception of its turbinal part) is largely occupied by the developing 
teeth. In horses five to six years of age the maxillary part of the sinus is still 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 inferior turbinal is smaller than 
usual and leaves a considerable interval, through which the maxillary sinus communicates with 
the nasal cavity. 

The frontal sinus (Sinus concho-frontalis) consists of frontal and turbinal 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 



74 



THE SKELETON OF THE HORSE 



piano through the anterior margins of the orbits, l)ackward to one through the tem- 
poral condyles, and outward into the root of the supraorbital process. It is separ- 
ated from the sinus of the opposite side by a 
complete septum. It is partially subdivided by 
a number of bony plates. The turbinal part is 
situated in the posterior part of the superior tur- 
binal 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. Be- 
hind it is in free communication with the 
frontal part over the lateral mass of the eth- 
moid. It is separated from the nasal cavity 
by the thin turbinal plate. The frontal and 
maxillary sinuses communicate through the 
large opening described above. 

The spheno-palatine sinus (Sinus spheno- 
palatinus) consists of two parts which communi- 
cate under the lateral mass of the ethmoid. 
The sphenoidal (posterior) part is excavated in 
the body of the pre-sphenoid. The palatine (an- 
terior) part is between the two plates of the per- 
pendicular part of the palate 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 Paulli) 
the sphenoidal and palatine parts are separated bj' a trans- 
verse septum, and the sphenoidal part then communicates 
onl}^ with the lower ethmoidal meatuses. 

The term ethmoidal sinus is often applied 
to the cavity of the largest ethmo-turbinal. It 
communicates with the maxillary sinus. 




Fig. 40. — Skull, of Horse, Dorsal View, 
WITH Sinuses Exposed by Re- 
moval OF THE Outer Plate of 
Bone. 

./,• Frontal bone; S, nasal bone; S, 
lacrimal bone; 4, maxilla; a, posterior 
part of frontal sinus; a', middle part of 
frontal .?inu.«; h, anterior (turbinal) part of 
frontal sinus; c, lateral mass of ethmoid 
bone; d, roof of superior meatus; e, froiito- 
maxillary opening; /, naso-maxillary open- 
ing below plate which forms the anterior 
margin of e; g, h, posterior and anterior 
compartments of maxillary .sinus — often 
called the superior and inferior maxillary 
sinuses; i, septum between o and h; k, 
orbit; /, point at which superior turbinal 
bone may be perforated to obtain drainage 
into nasal cavity. (After Ellenberger, in 
Leisering's Atlas.) 



bone, where it gradually subside 
and in great part subcutaneous 



The Bones of the Thoracic Limb 
the scapula 

The scapula is a flat bone, situated on the 
anterior j^art of the lateral wall of the thorax, 
and extending obliquely from the vertebral end 
of the seventh or eighth rib 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 external surface or dorsum (Facies 
lateralis s. dorsalis) is divided into two fossae 
by the spine (Spina scapulae), which extends 
from the vertebral border to the neck of the 
s. The free edge of the spine is thick, rough, 
. A little above its middle is a variable promi- 



THE SCAPULA 



75 



nence, the tubercle of the s]Mnc (Tuber spina^, to which the trapezius muscle 
is attached. The supraspinous fossa (Fossa su])raspinata) is situated in front of 
the spine, and the infraspinous fossa (Fossa infraspinata) behind it. The former 
is much the smaUer 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 the attachment of the teres minor muscle; near the neck is the nutrient foramen, 
and a little lower is a vascular groove. 

The costal surface or venter (Facies costalis) is hollowed in its length by the 



Cervical angle 



Supraspinous fossa 



Anterior border 




Diirsdl angle 



Infraspinous fossa 
Vascular groove 



- Posterior border 



Tubercle of spitic 



Neck 



Tuberosity 




Nutrient foramen 
Vascular groove 



rid cavity 
Fig. 41. — Left Scapula of Horse, External View. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



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 magnus is attached. In the lower third 
there is a vascular furrow with several branches. 

The anterior or cervical border (Margo cranialis) is convex and rough above, 
concave and smooth l)elow. 

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

The superior or vertebral border (Margo dorsalis s. basis) carries the scapular 
cartilage (Cartilago scapulae). In the young subject the edge of the bone is thick, 



76 



THE SKELETON OF THE HORSE 



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 eleva- 
tions of the bone. It thins out toward the free edge, which is convex and lies 
alongside of the upper parts of the vertebral spines. In front it continues the line 
of the scapula, 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 



■■'■^. 



^ 



^^' 



Dorsal angle -^ ,. 

m 



Vascular groove 




Subscapular fossa 
Anterior border 



rosity 



Glenoid cavity 



Coracoid process 



Fig. 42. — Left Scapula of Horse, Costal Surface. — (After Schmaltz, .\tlas d. Anat. d. Pferdes.) 



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; its 
position can be determined readily in the living animal. 

The inferior or articular angle (Angulus glenoidalis) is joined to the body of 
the bone bj^ the neck of the scai)ula (Collum scapuhe). It is enlarged, especially 
in the sagittal cUrection. It bears the glenoid cavity (Cavitas glenoidalis) for articu- 
lation with the head of the hinnerus. The cavity is oval in outline, and its margin 
is cut into in front by the glenoid notch (Incisura glenoidalis), and is rounded off 



THE HUMERUS 



77 



Tuberosity 



Coracoid 
process 



externally; just above its postero-external jiart is a tubercle to which a tendon of 
the teres minor is attached. The bicipital tuberosity or tuber scapulae is the 
large rough prominence in front, to wliicli tlic tendon of origin of the biceps brachii 
is attached; projecting from its inner sitle is the small coracoid process (Processus 
coracoideus), from which the coraco-brachialis muscle arises. 

Development. — The scapula has four centers of ossification, viz., one each 
for the body of the bone, the bicipital and cora- 
coid processes, the anterior part of the glenoid 
cavity, and the tuber spinte. The last ossifies 
after birth and fuses with the spine about the 
third year. The bicipital tuberosity and coracoid 
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 fossae, so that the bone consists here of 
a thin layer of compact substance. Considerable ossifica- 
tion of the cartilage is usual, the borders become much 
rougher, the muscular lines are more pronounced, and a 
medullary cavity may appear in the neck. Much varia- 
tion occurs in dimensions and slope. The average 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 65 
degrees. Exceptionally the coracoid process reaches a 

length of an inch or more ('i^o to 3 cm.), and the chief nutrient foramen may be on the pos 
terior border or in the subscapular fossa. 




Fig. 43. — Distal End of Left Scapula 
OF Horse, End View. (After 
Schmaltz, Atlas d. Anat. d. 
Pferdes.) 



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 
wath the radius and ulna. It is directed obliquely downward and backward, form- 



internal 
tuberosity 



Posterior part-^'. 



Anterior port 




Posterior part 
Anterior part 



L External 
I tuberosity 



Bicipital groove 
Fio. 44.— Proximal End of Left Humerus of Horse, End View. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



ing an angle of about 55 degrees with a horizontal plane. It may be divided into a 
shaft and two extremities. 

The shaft or body (Corpus humeri) is irregularly cylindrical and has a twisted 
appearance. It may be regarded as having four surfaces. The external surface 
is smooth and is spirally curved, forming the musculo-spiral groove (Sulcus musculi 
brachialis), which contains the brachialis muscle; the groove is continuous vnih. the 
posterior surface above and winds around toward the front below. The internal 
surface 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 internal or teres 



78 



THE SKELETON OF THE HORSE 



tubercle (Tuberositas teres), to which the tendon of the latissimus dorsi and teres 
major muscles is attached. The nutrient foramen is in the lower third of this sur- 
face. The anterior surface is triangular, wide and smooth above, narrow and 
roughened below. It is separated from the external surface by a distinct border, 
which bears on its upper part the deltoid tuberosity (Tuberositas deltoidea). 
From the latter a rough line curves upward and backward to the outer surface of 
the neck, and gives origin to the external head of the triceps muscle. Below the 



Internal 
tuberosity , 



Internal 
tubercle 




External 
tuberosity 









Curved line 



Deltoid 
tuberosity 



Internal 

epicondyle ■ Inlcrnal 

condyle 

Fig. 45. — Left Humerus of Horse, In- 
ternal Surface. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



Miisculo-spivdl 
groove 



External con- 
dyloid crest 



Coronoid fossa 



External 
condyle 




Internal 
epicondyle 



Olecranon fossa 



Exttrnal 
epicondyle 



Fig. 



46. — Left Hi'merus of Horse, External Surface 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



tuberosity the border inclines forward, becomes less salient, and ends at the coronoid 
fossa. The posterior surface is rounded from side to side and smooth. 

The proximal extremity consists of the head, neck, two tuberosities, and the 
bicipital 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 (Gollum humeri) is well defined behind, but is prac- 
tically absent elsewhere. The external tuberosity (Tul)erculum majus) is placed 



THE HUMERUS 



79 



antero-externally, and consists of two parts; the anterior part forms the outer 
boundary of the bicipital groove and gives attachment to the external branch of 
the supraspinatus muscle; the posterior part gives attachment to the short inser- 
tion of the infraspinatus, while its outer surface is coated with cartilage, over which 
the chief tendon of the same muscle passes to be inserted into a triangular facet on 
the outer aspect of the anterior part. The internal tuberosity (Tuberculum minus) 
is less salient, and consists of anterior and posterior parts ; the anterior part forms 
the inner Iwundary of the l)icipital groove, and furnishes insertion to the inner 
branch of the supraspinatus above, and the posterior deep pectoral muscle below; 



Biripilal 

ijroucc 



Internal tuhcrosilij 



hiternnl tuhcrde 



Coronoid fossa 
Inkmal epicondyle 




External tuberosity 



Deltoid tuberosity 



-spiral groove 



External condyloid crest 



External condyle 



Irdernal condyle 
Fio. 47. — Left Humerus of Horse, Anterior View. (After Schmaltz Atlas d. Anat. d. Pferdes.) 



the posterior part gives attachment to the subscapularis muscle. The bicipital 
or intertubercular groove (Sulcus intertubercularis) is situated in front; it is 
bounded by the anterior parts of the tuberosities, and is subdivided by an inter- 
mediate ridge. The groove is covered in the fresh state by 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 internal 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- 



80 THE SKELETON OF THE HORSE 

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 
notch of the ulna. The external condyle (Condylus lateraUs) is much smaller and 
is placed somewhat lower and further back, giving the extremity an oblique ap- 
pearance; it is marked by a wide shallow groove. The coronoid fossa (Fossa coro- 
noidea) is situated in front above the groove on the internal condyle; it furnishes 
origin to part of the extensor carpi, and external to it is a rough depression from 
which the anterior or common extensor of the digit arises. Behind and above the 
condyles are two thick ridges, the epicondyles. The internal or flexor epicondyle 
(Epicondylus medialis s. flexorius) is the more salient; it furnishes origin to flexor 
muscles of the carpus and digit, and presents internally a tubercle for the attach- 
ment of the internal lateral ligament of the elbow joint. The external or extensor 
epicondyle (Epicondylus lateralis s. extensorius) bears externally the external 
supracondyloid crest (Crista condyloidea lateralis), which forms here the outer 
boundary of the musculo-spiral groove, and gives origin to the extensor carpi. 
Below this is a rough excavation in which the external lateral ligament is attached. 
The lower border of the epicondyle gives attachment to the flexor carpi externus. 
Between the epicondyles is the deep olecranon fossa (Fossa olecrani). 

Development. — The humerus ossifies from six centers, viz., three primary 
centers for the shaft and epiphyses, and three secondary centers for the external 
tuberosity, the deltoid tuberosity, and the internal condyle. 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 below. It is gently curved, the convexity being anterior. It 
consists of a shaft and two extremities. 

The shaft (Corpus radii) is curved in its length, somewhat flattened from before 
backward, and expanded at its ends. It presents for description two surfaces and 
two borders. The anterior surface (Facies dorsalis) is smooth, slightly convex in 
its length, and rounded from side to side. The posterior surface (Facies volaris) 
is correspondingly concave in its length and is flattened in the transverse direction. 
At its upper part there is a smooth shallow groove, which concurs with the ulna in 
the formation of the interosseous space of the forearm; 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 attached by an interosseous ligament; 
in the adult the two bones are fused here. A variable rough elevation below the 
middle of the surface and close to the internal border gives attachment to the 
superior check ligament. The internal border (Margo medialis) is slightly con- 
cave in its length and is largely sul)cutaneous; 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 internal 
lateral ligament of the elbow-joint. The external border (Margo lateralis) is more 
strongly curved, but presents no special features. 

The proximal extremity or head (Capitulum radii) is flattened from before 
backward and wide transversely. It presents an articular surface (Fovea capituli) 
which corresponds to that on the distal end of the humerus; it is crossed by a 
central sagittal ridge, which has a synovial fossa on its posterior part, and ends in 
front at a prominent lip, the coronoid process (Processus coronoideus). Just 
below the posterior border there are two concave facets for articulation 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 inner side 



THE RADIUS 



81 



of the anterior surface is the bicipital tuberosity (Tu])erositas radii), into which 
the biceps tendon is inserted. The internal tuberosity is continuous with the pre- 
ceding eminence, and furnishes attachment to the short part of the internal lateral 



Processus ..J'^yL^. 
anconccus \^ 

Coronoid 
process \ 



Bicipital 
tuberosity 




I'roxitnal 
I diental 
tuberosity 
of radius 



Proximal ~^ 

external 
tuberosity 
of 7-adius 



Proximal 
internal 
tuberosity 
of radius 



' Interosseous space 



\^ 



Distal external 
tuberosity of 
radius 



\ v/' M 



Fig. 48. — Left Radits axij I i.xa of Horse, Exter- 
nal View. (.A.fter Schmaltz, Atlas d. Anat. d. 
Pferdes.) 



Distal 

external 

tuberosity 

of radius 



\ ,f I 



Fossa 



Distal 
external 
tuberosity 
of radius 



Facet for ulnar 
carpal 



Facet for radial 
carpal 



Fig. 49. — Left Rahius and Ulna of Horse, Pos- 
terior View. (After Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



ligament. The external tuberosity is more salient; it gives attachment to the 
external lateral ligament and to the anterior and lateral extensor muscles of the 
digit. 

The distal extremity is also compressed from before backward. It presents 
6 



82 



THE SKELETON OF THE HORSE 



the carpal articular surface (Facies articularis carpea) which consists of three parts. 
The inner facet is the largest, is quadrilateral, concavo-convex from before back- 
ward, and articulates with the radial carpal bone (or scaphoid) ; the middle one is 
somewhat similar in form but smaller, and articulates with the intermediate carpal 
bone (or semilunar); the outer facet is smaller, is convex, and articulates below 
with the ulnar carpal (or cuneiform) and Ijehind with the accessory carpal (or pisi- 
form). The anterior surface presents three grooves, separated by ridges. The 
middle one is vertical and gives passage to the tendon of the extensor carpi radialis; 
the outer one is similar and contains the tendon of the anterior extensor of the 
digit; the inner one is small and oblique and lodges the tendon of the extensor carpi 
obliquus. The posterior aspect is crossed l)y a rough ridge, below which are three 
depressions. On either side is a tuberosity (Tuberculum ligamenti) to which the 
lateral ligament is attached. The outer 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 outer part 
of the distal end ; the last is morphologically 
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. 




Processus 

(INCOtlCCUS 

Semilunar notch 



Bicipital 
tuberosity 



Interosseou.'i 
space 



Fig. 50. — Upper Half of R.\diu.s and Ulna of 
Horse, Internal View. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



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 below. The anterior 
surface (Facies dorsalis) is applied to the pos- 
terior surface of the radius, and below 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 nutrient foramen, directed 
upward. Above the space it is rough and is 
attached to the radius by an interosseous ligament which is usually permanent. The 
internal surface (Facies medialis) is smooth and slightly concave. The external 
surface (Facies lateralis) is flattened. The internal and external borders are thin 
and sharp, except at the interosseous space. The posterior border is slightly 
concave in its length and is rounded. The lower end is pointed and is usually a 
little below the middle of the radius. It is commonly continued 1)3' a fibrous cord 
to the distal external tuberosity of the radius, but this band may be replaced in 
part or entirely by bone. 

The proximal extremity is the major part of the bone. It projects upward 
and somewhat Ijackward behind the lower end of the humerus, and forms a lever 
arm for the extensor muscles of the elbow. The internal surface is concave and 
smooth. The external surface is convex and is roughened alwve. The anterior 
border bears on its middle a pointed projection, the processus anconaeus or 
"beak," which overhangs the semilunar notch or sigmoid cavity (Incisura semilu- 
naris). The latter is triangular in outline, concave from above downward, and 



THE CARPUS THE INTERMEDIATE CARPAL BONE 



83 



articulates with tlic humerus; in the middle of its lower part is an extensive 
synovial fossa. Just Ijclow the notch are two convex facets which articulate with 
those on the posterior aspect of the proximal end of the radius. The posterior 
border is nearly straight, and is thick and rounded. The free end or summit is 
a rough tuberosity, the olecranon, which gives attachment to the triceps brachii 
and otiier muscles. 

The primitive distal extremity has, as previously 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 lower part of the ": ' 

shaft is usually reduced to a small fibrous band ;• •,■:.,•-. 

or may disappear entirely; in some cases a vari- ^ , 

able remnant of it ossifies. The distal extremity -'' ■ 

fuses early with the radius. The olecranon unites ■ ;. ■ •' 

with the rest of the bone at three to three and a 
half years. A medullary canal appears to occur 
constantly in the adult — contrary to the state- 
ments of some authors. 



•*i''. 









THE CARPUS 

The carpus of the horse consists of seven or 
eight bones (Ossa carpi) arranged in two rows, 
proximal or antibrachial, and distal or metacar- 
pal. The (abbreviated) names and relative posi- 
tions of the l)ones of the left carpus as seen from 
in front are indicated below. 

Proximal Roiv: 
Radial Intermediate Ulnar Accessory 

Distal Row: 
First Second Third Fourth 

The Radial Carpal Bone 
The radial carpal bone (Os carpi radiale, 
scaphoid) is the largest bone of the upper row; it 
is somewhat compressed laterally, and is clearly 
six-sided. The superior or proximal surface is 
convex in front, concave behind, and articulates 
with the inner facet on the distal end of the radius. 
The inferior or distal surface is also convex in front 
and concave liehind; it articulates with the second 

and third carpal bones. The external 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 anterior or dorsal surface is rough and slightly convex. 
The internal surface and the posterior or volar surface are rough and tuberculate. 




Fig. 51. — Sagittal Section of Upper 

Fart of Radius and Ulna of Horse. 

Cm, Medullary cavity of ulna. 



The Intermediate Carpal Bone 
The intermediate carpal bone (Os carpi intermedium, semilunar, lunar) is 
somewhat wedge-shaped, wider in front than behind. The superior or proximal 
surface is saddle-shaped, and articulates with the middle facet on the distal end of 



84 



THE SKELETON OF THE HORSE 



the radius. The inferior or distal surface is smaller, convex in front, concave be- 
hind, and articulates with the third and fourth carpal bones. The internal surface 
has upper and lower facets for articulation with the radial carpal, and l)etween 
these it is excavated and rough. The external surface is similar to the preceding 
and articulates with the ulnar carpal. The anterior or dorsal surface is rough and 
slightly convex. The posterior or volar surface bears a tuberosity on its lower part. 

The Ulnar Carpal Bone 
The ulnar carpal ])one (Os carpi ulnare, cuneiform) is the smallest and most 
irregular l)one of the upper row. The superior or proximal surface is concave, and 
fits the lower part of the outer facet on the distal end of the radius. The inferior 
or distal surface is oblique and undulating for articulation with the fourth carpal 
bone. The internal surface has upper and lower facets for articulation with the 
intermediate. The anterior or dorsal and external surfaces are continuous, convex, 
and rough. The posterior or volar surface is oblique, and bears a concave facet 
for articulation with the accessory carpal bone; below this is a tubercle. 






Fig. 52. — Left Carpal Bones of Horse, with Dip- Fig. 53. — Left Carpal Bones of Horse, -mTH 
TAL End of Radius and Proximal End of Adjacent Ends of Radius and Metacarpus; 

Metacarpus; Internal View. Extern.\l View. 

Ca, Accessory carpal bone; Cr, radial carpal; Ci, intermediate carpal; Cu, ulnar carpal; Cl-4, first to 

fourth carpals; Mc. II, III, IV, metacarpal bones; 1, groove for tendon of extensor carpi obliquus; 2, groove for 

lateral extensor tendon; 3, groove for tendon of flexor carpi externus; 4, metacarpal tubero.sity. (After Schmaltz, 

Atlas d. Anat. d. Pferdes.) 



The Accessory Carpal Bone 
The accessory carpal ]>one (Os carj)i accessorium, pisiform) is situated behind 
the ulnar carpal bone and the outer part of the distal end of the ulna. It is discoid 
and ])resents for description two surfaces and a circumference. The internal 
surface is concave and forms the outer wall of the carpal groove. The external 
surface is convex and rough; a smooth groove for the outer tendon of the flexor 
carpi externus cross(>s its anterior part obliquely downward and slightly forward. 
The anterior border bears two facets; the upper one is concave and articulates with 
the back of the outer facet on the distal end of the radius ; the lower one is convex 
and articulates with the ulnar carpal bone. The remainder of the circumference is 
rounded and rough. 

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 external flexors of the carpus, which 
it enables to act at a meciianical advantage. The posterior l)order furnishes attachment to 
the transverse carpal ligament, which completes the carpal canal for the flexors of the digit. 



THE FIRST CARPAL BONE — THE SECOND CARPAL BONE 



85 



The First Carpal Bone 
The first carpal bone (Os carpale primum, trapezium) is a small inconstant 
bone, commonly about the size and shape of a pea, which is situated in the lower 
part of the internal lateral ligament behind the second carpal bone. 

This bone appears to be absent on both sides in aliout 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 mass 
10 to 12 mm. in length. In exceptional cases it articulates with l)oth the second carpal and the 
second (inner) metacarpal bone, in other cases with the former only, but in the majority of 
specimens no articular facet is present. 



The Second Carpal Bone 
The second carpal bone (Os carpale secundum, trapezoid) is the smallest con- 
stant bone of the lower row, and is irregularly hemispherical in shape. The su- 
perior or proximal surface is a convex 

facet which is continued upon the pos- 2 I 
terior or volar surface and articulates 
with the posterior part of the radial 
carpal. The external surface faces ob- 
liquely outward and forward, and bears 

three facets for articulation with the /"^^ / 

third carpal bone. The anterior or • / / 

dorsal and the internal surface bear a j||j^j|j^ __ , , ,^ 

tuberosity to which the lateral ligament 
attached. The inferior or distal 



IS 





c3 



■J 




Mc. IV 



Fig. 55. — Carpal Articular Surface of Radius 
AND Proximal Articular Surfaces of Car- 
pal AND Metacarpal Bones, Left Side. 
The Accessory and First Carpal Bones are 
NOT Shown. 
Cr, Radial carpal; Ct, intermefliate carpal; Cu, ulnar carpal; C2, C3, C4, second, third, and fourth car- 
pals; Mc.II , second or inner small metacarpal bone; Mc.III, third or large metacarpal bone; Mc.IV, fourth or 
outer small metacarpal bone; 1, 2, grooves for tendons of anterior exten.sor and extensor carpi radialis; .3, meta- 
carpal tuberosity Arrows indicate relations of facets. Short arrow points to facet on ulnar carpal for articu- 
lation with accessory carpal, (.\fter Schmaltz, Atlas, d. Anat. d. Pferdes.) 



Fig. 54. — Carpal Bones of Horse, with Adjacent 
Ends of Radius .and Metacarpus; Anterior 
View. The Accessory and First Carp.\l 
Bones .are Not Shown. 



surface is articular and consists of a large flattened facet for the inner (second) 
metacarpal bone, and a small one for the large (third) metacarpal bone. Some 
specimens have a small facet on the lower part of the posterior surface which 
articulates with the first carpal bone. 



86 the skeleton of the horse 

The Third Carpal Bone 

The third carpal bone (Os carpale tertium, os magnum) is much the largest 
bone of the lower 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 
superior or proximal surface consists of two facets separated by an antero-posterior 
ridge; the inner facet is concave and articulates with the radial carpal; the outer 
facet — for the intermediate carpal — is concave in front and convex behind, where it 
encroaches on the posterior surface. The inferior or distal surface is slightly un- 
dulating, and articulates almost entirely with the large (third) metacarpal bone, 
but it usually bears a small oblique facet at its inner side for the inner (second) meta- 
carpal, and there is commonly a non-articular depression externally. The internal 
surface faces backward and inward, and bears three facets for articulation with 
the second carpal, between which it is excavated and rough. The external surface 
has two facets for articulation with the fourth carpal, and is depressed and rough 
in its middle. The anterior or dorsal surface is convex and is crossed by a rough 
transverse ridge. The posterior or volar surface is relatively small, and is rounded; 
its upper part is encroached upon by the superior articular surface, below which 
it is rough. 

The Fourth Carpal Bone 

The fourth carpal bone (Os carpale quart um, unciform) is somewhat wedge- 
shaped, and is readily distinguished from the second by its greater size and its 
posterior tubercle. The superior or proximal surface articulates with the inter- 
mediate and ulnar; it is convex and curves outward, backward, and downward, 
encroaching on the external and posterior surfaces. The inferior or distal surface 
bears two inner facets for the large (third) metacarpal and an outer one for the ex- 
ternal (fourth) metacarpal bone. The internal surface has two or three facets for 
articulation with the third carpal, between which it is excavated and rough. The 
anterior or dorsal surface is convex and rough. The external surface is small, 
being encroached upon by the superior articular surface. The posterior or volar 
surface bears a tubercle on its lower part.' 

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 antero-posterior 
diameter. The anterior or dorsal surface is convex from side to side, depressed 
along the line of junction of the two rows, and prominent below. The posterior 
or volar surface is in general slightly convex, but very irregular. It forms with the 
accessory the carpal groove (Sulcus carpi), which in the recent state is rendered 
smooth l:)y the posterior ligament; it is converted into the carpal canal (Canalis 
carpi) for the flexor tendons by the transverse carpal ligament, which stretches 
across from the accessory bone to the inner side. The proximal surface is widest in- 
ternally and is elevated in front, concave behind; it is entirely articular and adapted 
to the carpal 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 lower bones usually articulates with two metacarpal bones, but sometimes 
the third does not bear on the inner metacarpal bone. The lateral surfaces are 
both irregular and rough, the internal one lieing the wider. With the excei:)tion of 
the accessory, ulnar, and second, each bone articulates with two l)ones of the other 
row. 

Development. — Each ossifies from a single center. 

1 This bone is probably equivalent to the fourth and fiftli earpals of forms in which five 
carpal elements are present in the lower row. 



THE METACARPUS — THE LARGE METACARPAL BONE 



87 



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 internal and external small metacarpal or "spHnt" bones. 



Tuberosity -^r:^.:^^-'^ 

^f,h 'W^ Head of small 



>^ 



Groove for 

suspensory 
ligament 




metacarpal 
bone 



Nutrient 
foramen 



Distal ends of 
small meta- 
carpal bones 

Sesamoid 
bones 



First phalanx 



Second 
pJialanx 



Fig. 56. — Distal Row of Carpal Bones, Metacar- 
pus, First .\nd Second Ph.\langes, .a.nd 
Proximal Sesamoid Bones of Horse; Pos- 
terior View, Left Side. 
The fourth (external) metacarpal bone is wrongly 

numbered as I. (After Schmaltz, Atlas, d. Anat. d. 

Pferdes.) 



- Metacarpal 
tuberosity 



Head of 
small 
metacar- 
pal bone 



Distal 
ends of 
small 
metacar- 
pal bones 




Second phalanx 



Lateral 
cartilage ' J /- 

Dorsal Wall 

groove sur- 
face of 
third 
phalanx 

Fig. 57. — Left Metacarpal .\xd Digital Bones of 
Horse, Internal View, (.\fter Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



The Large Metacarpal Bone 
This (Os metacarpal tertium) is a very strong long bone, placed vertically 
between the carpus above and the first phalanx below. It consists of a shaft and 
two extremities. 



88 THE SKELETON OF THE HORSE 

The shaft (Corpus) is somieylindrical, and presents two surfaces and two 
borders. The anterior or dorsal surface is smooth, convex from side to side, and 
nearly straight in its length. The posterior or 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 upper two-thirds it is roughened for the 
attachment of the small metacarpal bones. The nutrient foramen occurs at the 
junction of the upper and middle thirds. The lower tliird is wider and flattened. 
The borders are rounded. 

The proximal extremity (Basis) bears an undulating articular surface adapted 
to the lower row of carpal bones. The greater part supports the third carpal l:)one; 
the oblique outer part, separated from the preceding l3y a ridge, articulates with 
the fourth, and a small facet for the second is usually found at the postero-internal 
angle. On either side is a notch separating two small facets which articulate with 
the proximal ends of the small metacarpal bones. Toward the inner side of the 
anterior surface is the metacarpal tuberosity, into which the extensor carpi radialis 
is inserted. The posterior surface is roughened for the attachment of the sus- 
pensory ligament. 

The distal extremity (Trochlea 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 inner condyle is slightly the larger. 
On either side is a small fossa, surmounted by a tubercle, for the attachment of the 
lateral 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 internally. The medullary canal extends further toward the ends 
than in most of the long bones of the horse and there is little spongy bone. 

The Small Metacarpal Bones 

These are situated on either side of the posterior 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 anterior surface is flattened 
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 abaxial surface is 
smooth and rounded from side to side above, grooved below. The axial surface is 
smooth and concave from edge to edge, except below, where it forms a rounded 
edge. 

The proximal extremity or head (Basis) is relatively large. In the case of the 
inner bone it usually bears two facets above which support the second and third 
carpal bones, while the outer bone has here a single facet for articulation with the 
fourth carpal bone. Each has also two facets for articulation with the large meta- 
carpal, and is elsewhere roughened for the attachment of ligaments and nmscles. 
The inner bone may present a small facet behind for the first carpal bone. 

The distal extremity (Capitulum) is usually a small nodule, 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 inner bone is the longer; in other subjects tlio outer 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 varialMe in size and may be a mere point. 

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



THE PHALANGES THE FIRST PHALANX THE SECOND PHALANX 89 

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, situated between the large 
metacarpal bone above and the second phalanx below. 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. 

The shaft (Corpus) is wider and much thicker alcove than below, and presents 
two surfaces and two borders. The anterior or dorsal surface is convex from side 
to side and smooth. The posterior or volar surface is flattened, and bears a triangu- 
lar rough area, bounded laterally l)y ridgc^s which begin at the tuberosities above 
and converge below; this area furnishes attachment to the inferior sesamoiclean 
ligaments. The borders, internal and external, are rounded and have a rough area 
or a tubercle on their middle parts. 

The proximal extremity (Basis) is relatively large. It bears an articular sur- 
face adapted to the distal end of the large metacarpal bone, consisting of two glen- 
oid cavities separated by a sagittal groove; the inner cavity is a little larger than 
the outer one. The posterior angles are formed by buttress-like tuberosities for 
ligamentous attachment. The anterior surface has a slight elevation for the at- 
tachment of the lateral extensor tendon. 

The distal extremity is smaller, especially in its antero-posterior diameter. 
It presents a trochlea for articulation with the second phalanx, consisting of a 
shallow central groove and two lateral convex areas or condyles; the inner area is a 
little the larger. On either side, just above the margin of the articular surface, is a 
depression surmounted by a tubercle, to l)oth of which the lateral ligament is at- 
tached. Behind the tubercle is a distinct facet to which the superficial flexor ten- 
don is attached. 

Development. — The first phalanx ossifies from three centers. The distal end 
unites with the shaft before birth, the proximal end early in the first year. 

The first phalanx contains a small medullary canal in the middle of the shaft. It may be 
remarked that the bone is twisted slightly; when placed volar surface down on the table, it 
touches the latter by three points only, the proximal tuberosities and the internal condyle. 

The Second Phalanx 

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

The upper or proximal surface presents two glenoid cavities separated by a 
low ridge, and articulates with the first phalanx. The middle of the anterior border 
is elevated and roughened in front for the attachment of the anterior or common 
extensor tendon. The posterior border is thick and overhanging; in the fresh 
state its middle part is covered with cartilage, over which the deep flexor tendon 
passes. On either side there is an eminence, to which the lateral ligament and the 
superficial flexor tendon are attached. 

The inferior or distal surface is trochlear, and articulates with the third phal- 
anx and third sesamoid bone. It resembles somewhat the trochlea of the first 
phalanx, but is more extensive and encroaches more on the anterior and posterior 
surfaces. 

The anterior or dorsal surface is convex from side to side and smooth in its 

1 It is also called the large pastern bone or os suffraginis. 
^ This bone is also called the small pastern bone or os coronse. 



90 



THE SKELETON OF THE HORSE 



middle; on its lower part are lateral rough depressions, surmounted by tuberosities, 
to both of which ligaments are attached. 

The posterior or volar surface is smooth, flattened, and slopes obliquely down- 
ward and forward. The borders which separate the anterior and posterior surfaces 
are concave from above downward, rounded from before backward. 

Development. — The second phalanx ossifies like the first, but the proximal 
end unites with the shaft two or three months earlier. 

/♦ Distal border 



Dorsal or wall surface 
. Extensor process 

, '■ Articular surface 
:.i--' Coronary border 
V'-^" Dorsal groove 



Third Phalanx 



Third Sesamoid 



Second Phalanx ^ 




Depression for lateral ligament 



Angle or wing 

Articular surface of third sesamoid or 
navicular bone 



Distal articular surface 
Eminence for lateral ligament 



First Phalanx 




-^ — Dorsal surf ace 

Proximal articular surface 



' — Distal articular surface 

*»-- Eminence for lateral ligament 

Dorsal surface 



" Eminence for extensor tendons 

— Tuberosity 

— Proximal articular surface 

— Intermediate groove 
Fig. 58. — Phalanges and Third Sesamoid of Horse, Dorsal Aspect. 



The Third Phalanx 

The third or ungual phalanx (Phalanx tertia)' is entirely inclosed by the hoof, 
to which it conforms in a general way. It presents for examination three surfaces, 
three borders, and two angles or wings. 

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 posterior border articulates with the third sesamoid. The an- 

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



THE THIRD PHALANX 91 

terior or coronary border forms a central eminence, the extensor (or pyramidal) 
process (Processus extensorius), to the front of which the anterior extensor tendon 
is attached. On either side is a depression for the attachment of the lateral liga- 
ment. 

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. 
Laterally the height diminishes, and the slope becomes steeper, especially on the 
inner 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 
lower border. On either side the dorsal (or preplantar) groove (Sulcus dorsalis) 
passes forward from the wing and ends at one of the larger foramina. In the fresh 
state this surface is covered by the matrix of the wall of the hoof. The inferior or 
distal border is thin, sharp, and irregularly notched; there is commonly a wider 
notch in front. 

The volar or inferior surface (Facies volaris) is arched, and divided into two 
unequal parts by a curved rough line, the semilunar crest (Crista semilunaris). 
The larger anterior area is crescent-shaped, concave, and comparatively smooth; 
it corresponds to the sole of the hoof, and may be termed the sole surface. The 
posterior part is much smaller, and is semilunar; it is related to the deep flexor 
tendon, and is hence called the flexor or tendon surface (Facies flexoria). It 
presents a central prominent rough area, on either side of which is the volar (or 
plantar) foramen (Foramen volare), to which the volar (or plantar) groove (Sulcus 
volaris) conducts from the wing. The foramina lead into the semilunar canal 
within the bone, from which small canals lead to some of the foramina of the wall 
surface. 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 
semihmar 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 wall surface. 

The angles or wings (Anguli) are prismatic masses which project backward on 
either side; the inner 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 vascular 
groove on the side of the wall surface.^ The upper border carries the lateral carti- 
lage. 

The lateral cartilages (Cartilagines ungulse) are rhomboid curved plates, 
which surmount the wings 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 upper border is convex and thin; the 
lower 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 foramina for the passage of 
veins. The central part is mainly hyaline, the periphery mainly fibrous. 

It will be no+ed that the size and form of the wings vary much in different specimens. In 
the new-born foal the wing is a small, pointed projection. Later the process of ossification 
invades the lower part of the cartilage to a varying extent. In some cases the greater part of 
the cartilage is ossified — a condition commonly termed "sidebone." 

Development. — The ossification of the terminal phalanx is peculiar. While 
the proximal articular part is still cartilaginous, a perichondria! 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 

' The upper and lower divisions of the wing are sometimes termed the basilar and retrossal 
processes respectively. 



92 THE SKELETON OF THE HORSE 

vessels, most of which radiate from the semilunar canal to the wall surface; these 
are not canals for nutrient vessels of the bone, but transmit arteries to the matrix 
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 or great sesamoids (Ossa sesamoidea phalangis primse) are 
situated behind the distal end of the large metacarpal bone, and are closely at- 
tached to the first phalanx by strong ligaments. Each has the form of a three- 
sided pyramid. The anterior or articular surface conforms to the corresponding 
part of the distal end of the large metacarpal bone. The posterior or flexor 
surface is flattened and oblique ; in the fresh state it is covered 1 )y a layer of carti- 
lage 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 
posterior surface by a rough everted border. The base faces downward, and 
furnishes attachment to the inferior sesamoidean ligaments. The apex is directed 
upward and is rounded. 

The third sesamoid or navicular bone (Os sesamoideum phalangis tertise) is 
shuttle-shaped, and is situated behind the junction of the second and third phal- 
anges. Its long axis is transverse, and it possesses two surfaces, two borders, and 

two extremities. The articular surface 

... , (Facies articularis) faces upward and 

Articular sur- ) . . „ , . 

face for second forward; it consists 01 a central emi- 
phalanx nence, flanked by concave areas, and 

Articular ^^^^Mce£' '^'^ articulates with the distal end of the 

/^'^ww^'r^^ssaK. r, • , 7 7 7 second lohalanx. The flexor or tendon 

W y'.j:-:i,f>*:rriy^ Distal border /t^. n ■ \ ■ i- , 

— -^« 'i^a » ^" "^ surface (Facies liexoria) is directed 

Fig. 59.— Third Sesamoid or Navicular Bone of downward and backward. It reSCm- 
Horse. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ii,i ,-i c -c i. 

Dies the articular surface m 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 liber) is wide and grooved in its middle, narrower 
and rounded on either side. The distal border (Margo ligamenti) 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 promi- 
nent edge. Tlic extremities are blunt-pointed. 
Development. — It ossifies from a single center. 



The Bones of the Pelvic Limb 

The pelvic girdle consists of the ossa coxae, which unite ventrally at the sym- 
physis pelvis, and articulate with the sacrum dorsally. 



OS COX^ 
The OS coxae (or os innominatum) forms the skeleton of the hip or haunch, and 
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 



93 



THE ILIUM 

The ilium (Os ilium) is the larp;est of tlie three parts. It is irregularly triangu- 
lar and presents two surfaces, three l^orders, and three angles. 

The gluteal surface (Facies glutaea) faces upward, backward, and outward. It 
is wide and concave in front, narrower and convex behind. The wide part is crossed 
by the curved gluteal line (Linea glutiea), which extends from the middle of the 
inner border toward the external angle. This surface gives attachment to the 
middle and deep gluteal muscles. 

The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex, 



Cr.o 1 




Fig. 60. — Ossa Coxardm of Make, Dorsal, View. 
O.iL, Ilium; O.p., pubi.s; O.ls., ischium; A.o.i., wing of ilium; C.o.i., shaft of ilium; Cr.o.i., anterior 
border (crest) of ilium; /, obturator foramen; 2, acetabulum; 3, internal angle of ilium; 4, external angle of 
ilium; -5, gluteal line; 6, psoas tubercle; 7, 8, acetabular and symphyseal branches of pubis; 9, 10, acetabular 
and symphyseal branches of ischium; 12, lesser sciatic notch; 13, ischial arch; 14, great sciatic notch; Id, sym- 
physis pelvis; /7,ilio-pectineal eminence; /S, anterior borders of pubic bones; 79, posterior gluteal line. (Struska, 
Anat. d. Haustiere.) 



and consists of two distinct parts. The inner 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 outer quad- 
rilateral part (Pars iliaca) is in general smooth. It is crossed by the ilio-pectineal 
line (Crista iliopectinea), which begins below the auricular surface and is continued 
on the shaft of the bone to join the anterior border of the pubis. The line 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 external to the iho-pectineal hne. 



94 



THE SKELETON OF THE HORSE 



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

The internal border is deeply concave ; its middle part forms the lower bound- 
ary of the great sciatic foramen, and it is continuous behind with the superior 
ischiatic spine. 

The external border is concave and in great part rough. Its fore part is 
crossed by grooves for the ilio-lumbar vessels, which are continued on the pelvic 
surface. The nutrient foramen is usually situated on or near the posterior part of 
this border. 

The internal or sacral angle (Tuber sacrale) curves upward and a little back- 




Fir,, fll. OSSA COXARUM OF MaRE, VeNTRAL ViEW. 

D, Ilium; .SV/v., jjubis; jS', ischium; a, anterior border (crest) of ilium; b, internal angle of ilium; c' , 
external angle of ilium; d, great sciatic notch; e, external border of ilium; /, iliac surface; </, linea arcuata; /(, 
rough ligamentous area; /, auricular surface; k, ilio-pectineal line; I, psoas tubercle; m, transverse branch, and 
n, symphyseal branch of pubis; o, o', symphysis pelvis; p, anterior border of pubis (pecten); q, tuberculum pubi- 
cum; r, ilio-pectineal eminence; s, tuber ischii; t, ischial arch; u, lesser sciatic notch; i\ acetabular branch, and 
w, symphyseal branch of ischium; x, obturator foramen; y, articvilar surface of acetabulum; z fossa acetabuli; 
1, groove for ilio-lumbar artery; 2, groove for iliaeo-femoral artery; S. subpubic groove; 4< depression for inner 
tendon of origin of rectus femoris; 5, rough area for attachment of adductor muscles. (Ellenberger-Baum, Anat. 
d. HaustiereJ 



ward close to the first sacral spine, and forms here the highest point of the skeleton. 
It is somewhat thickened and rough. 

The external or coxal angle (Tuber coxtr) 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 posterior or acetabular angle meets the other two bones at the acetal)U- 
lum, of which it forms about two-fifths. Its prominent upper border forms part 
of the superior ischiatic spine, which is roughened externally, smooth internally. 
Two depressions above and in front of the acetabulum give attachment to the 



THE ISCHIUM THE PUBIS 95 

tendons of origin of the rectus femoris muscle. This angle is connected with the 
ala or wide part of the bone by a constricted part, often termed the shaft. The 
latter is of three-sided prismatic form. Its external 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 nerves. Its ventral surface is crossed by 
vascular grooves, below which is a rough area, bounded internally by the psoas 
tubercle. 

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. It is irregularly quadrilateral, and may be 
described as having two surfaces, four borders, and four angles. 

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

The inferior surface (Facies externa) 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. 

The posterior border is thick and rough. It slopes obliquely inward and for- 
ward to meet the border of the other side, forming with it the ischial arch (Arcus 
ischiadicus). 

The internal border meets the opposite bone at the symphysis. 

The external border is thick and rounded, but concave in its length; it forms 
the lesser sciatic notch, the lower boundary of the lesser sciatic foramen. 

The antero-internal angle or symphyseal branch (Ramus symphyseos) meets 
the pubis, with which it forms the inner boundary of the obturator foramen. 

The antero-extemal angle or acetabular branch joins the other two bones at 
the acetabulum, of which it forms more than half. Superiorly it bears part of the 
superior ischiatic spine (Spina ischiadica), and internally it is grooved for the ob- 
turator vessels. 

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



THE PUBIS 

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

The superior or 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 urinary bladder rests on it. 

The inferior or ventral surface (Facies externa) is convex, and in great part 
rough for muscular attachment. Near the anterior border it is crossed by the 
subpubic groove, the inner part of which is occupied by a large vein, the outer part 
by the pubo-femoral ligament. 

The anterior border is thin in its inner part (except in the young subject and 
the stallion), forming the pecten ossis pubis. Externally it bears the rough ilio- 
pectineal eminence (Eminentia iliopectinea), beyond which it is continuous with 
the ilio-pectineal line. 

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

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

The internal angle meets its fellow at the anterior end of the symphysis. This 



96 THE SKELETON OF THE HORSE 

part is very thick in the young subject and the stallion, but in the mare, and usually 
in the gelding also, it becomes thin with advancing age. 

The external or acetabular angle joins the ilium and ischium at the acetabu- 
lum. 

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 two l)ranches which 
meet at a right angle; these are termed the transverse or acetabular branch 
(Ramus acetabularis) and the longitudinal or symphyseal branch (Ramus sym- 
physeos). 

The acetabulum is a cotyloid cavity which lodges the head of the femur. It 
faces downward and outward, and consists of an articular and a non-articular part. 
The articular part (Facies lunata) is crescentic, and is cut into internally by the 
non-articular part, Avhich lies at a lower level, and is termed the acetabular fossa 
(Fossa acetabuli). The inner 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 pubo-femoral and round 
ligaments to the head of the femur. 

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- 
externally for the obturator nerve and 
vessels. 

Development. — Each division of the os 
coxae ossifies from one chief center. The 
center for the ilium appears first near the 
acetabulum, followed quickly by one for 
the ischium, and a little later by the 
pubic center. Secondary centers appear 
for the crest and external angle of the 
(^,___^ 'K_>' ilium, the tuber and posterior border of 

the ischium, and the acetabular part of 

Fig. 62. — Ossa Coxarum of Stallion, Dorsal , , . rrii i • i • i • 

View. (After Ellenberger-Baum. Anat. the publS. The publS and ISChmUl are 

fiir Kiin.stier.) United at birth or soon after, but are 

not fused with the ilium 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 montlis, 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 foi' 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 coccygeal vertebrte. The dorsal wall or roof is formed by the sacrum and 
first three coccygeal vertebra?, and tlie ventral wall or floor by the pubic and ischial 
bones. The lateral walls are formed by tlie 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 semimem]3ranosus muscles. 

The anterior aperture or inlet (Apertura pelvis cranialis) is bounded by the 
terminal line (Linea terminalis) or brim, composed of the base of the sacrum dor- 
sally, the ilio-pectineal lines laterally, and the anterior border of the pubis ventrally. 




THE FEMUR 97 

It is almost circular in the mare, semi-elliptical in the stallion, and faces ob- 
liquely downward and forward. It has two principal diameters. Of these, the 
conjugate or sacro-pubic diameter (Conjugata) is measured from the sacral prom- 
ontory to the anterior end of the symphysis. The transverse diameter (Diameter 
transversa) is measured at the greatest width, i. e., just above the psoas tubercle. 

The posterior aperture or outlet (Apertura pelvis caudalis) is much smaller 
and is very incomplete in the skeleton. It is bounded above by the third coccygeal 
vertebra and below by the ischial arch ; in the fresh state it is completed laterally 
by the sacro-sciatic hgament 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 
24 cm.) in the mare, 73^2 inches (ca. 18 to 20 cm.) in the .stallion. The transverse 
diameter of the inlet averages about 9 inches (ca. 22 to 23 cm.) in the mare, and 8 
inches (ca. 20 cm.) in the stallion. The obliquity of the inlet 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 female, 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 stalhon. The pubic part of the floor in the 
female is concave and lies considerably lower than the ischiatic part, which is wide 
and relatively flat. In the stalhon the pubis is very thick centrally, and this part 
of the floor is convex, while the ischial part is relatively narrow, and is concave from 
side to side. The obturator foramina are correspondingly larger in the female. 
The ilium is shorter, and the greater sciatic notch deeper and narrower in 
the male. The pelvis of the gelding, when castration has been performed early, 
resembles that of the mare; otherwise 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 or body (Corpus femoris) is in general cylindrical, but flattened 
behind, and larger above than below. The anterior and lateral surfaces are con- 
tinuous 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. Below this ixu't there is a rough elevation 
externally for the attachment of the femoral tendon of the biceps femoris, and a 
rough line internally to which the quadratus femoris is attached. The middle 
third is narrower, and is rough for the attachment of the adductor muscle. Just 
below this area an oblique groove crosses the surface, indicating the position of the 
femoral vessels. The internal border bears on its proximal part the internal 
trochanter or trochanter minor, a thick rough ridge, to which the ilio-psoas muscle 
is attachetl. From this a rough line curves up to the front of the neck and indicates 
the limit of the attachment of the vastus internus muscle. A narrow rough area 
about the middle gives attachment to the pectineus muscle, and the nutrient 
foramen is usually found just in front of this mark. The supracondyloid crest is 
situated below the groove for the femoral vessels, and gives origin to the inner head 
7 



98 



THE SKELETON OF THE HORSE 



r 



%> 
"^^ 





Il- 



ls^' 



15 





V^ 



\l 



/.S". 





Fig. 



Pos- 



FiG. 65. — Right Fkmur of Horse, In- 
ternal View. 



63. — Right Femur ok Horse, Fig. 64. — Right Femir ok Horse, 

External View. terior \'iew. 

1, Anterior part, 1', p(jsteri(jr part of trochanter major; 2, neck; S, fovea capitis; 4, crest; 5, trochanteric fossa; 6, ex- 
ternal or third trochanter; 7, trochanter minor; 8. eminence for attachment of biceps femoris; 9. internal border; 10, nutrient 
foramen; 11, groove for femoral vessels; 12, supracondyloid crest; IS, supracondyloid fossa; li, trochlea; 15, external epicon- 
dyle; 16, external condyle; 17, extensor fossa; 18, internal condyle; 19, internal epicondyle; 20, intercondyloid fossa. (After 
Schmaltz Atlas d. Anat. d. Pferdes.;* 



THE FEMUR 



99 



1^ 



of the gastrocnemius. The external border is prominent in its upper part, and 
bears at the junction of its proximal and middle thirds the external or third tro- 
chanter (Trochanter tertius); this process is curved forward, and furnishes in- 
sertion to th(^ tendon of the superficial gluteus muscle. At the lower part is found 
the supracondyloid or plantar fossa (Fossa plant aris), in which the superficial 
flexor arises; it is bounded externally by a thick 
rough margin, to which the outer head of the gastroc- 
nemius muscle is attached. 

The proximal extremity (Extremitas proximalis) 
is large and consists of the head, neck, and great tro- 
chanter. The head (Caput femoris) is placed at the 
inner side and is directed inward, upward, and some- 
what forward. It is approximately hemispherical 
and articulates with the acetabulum. It is cut into 
internally by a deep notch, the fovea capitis, in which 
the pubo-f amoral and round ligaments are attached. 
The articular surface is surrounded by a distinct mar- 
gin. The neck (Collum femoris) is most distinct in 
front and internally. The great trochanter (Tro- 
chanter major) is situated externally; it presents 
three features. The anterior part or convexity 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 outer 
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 convex- 
ity. The posterior part or summit is separated from 
the convexity by a notch; it is situated behind the 
plane of the head and rises to a much greater height. 
It furnishes insertion to part of the middle gluteus 
muscle. Its posterior l^order is continued downward 
as the trochanteric ridge, which forms the outer wall 
of the trochanteric fossa. A number of foramina are 
found in the concave area internal to the con- 
vexity. 

The distal extremity (Extremitas distalis) is 
large in both directions and comprises 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 unsym- 
metrical; the inner ridge or lip is much wider, 
more prominent, and extends up higher than the ex- 
ternal one, and the two converge below. The con- 
dyles, internal and external (Condylus medialis, 
lateralis), are separated by the deep intercondyloid 

fossa (Fossa intercondyloidea), and articulate with the condyles of tlie tibia and the 
semilunar cartilages of the stifle joint. A ridge connects each condyle with the lower 
part of the corresponding lip of the trochlea. The intercondyloid fossa lodges the 
spine of the tibia and the crucial 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 external condyle is more strongly convex from side to side 
than that of the inner one, and the ridge which connects it with the trochlea is much narrower. 




Fig. fi6. — Frontal Section of Left 
Femur of Hokse, Anterior 
View. 

The figure shows that the nic- 
(luliary cavity is traversed for the most 
inut by fine bony trabeculae. 



100 



THE SKELETON OF THE HORSE 



The internal epicondyle (Epicondylus medialis) is a rounded prominence on 
the internal surface of the internal condyle, to which the internal lateral ligament 
and the adductor muscle are attached. The corresponding external epicondyle 
(Epicondylus lateralis) is less distinct; it presents a mark where the lateral liga- 
ment is attached, below and behind which there is a depression (Fossa musculi 
poplitei) in which the ]iopliteus muscle arises. Between the external condyle and 
trochlea is the extensor fossa (Fossa extensoria), in which the tendon of origin of 
the anterior extensor 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 great trochanter. The 
edge of the external trochanter 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. 



Trochlea 



Extensor fossa - 

External epicondyle- - 

Depression for origin of^ 
popliteus 

External condyle _ 




- Internal epicondyle 



■Internal condyle 



Intercondyloid fossa 
Fig 67. — Distal Extremity of Right Femur of Horse, End View. 



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 externally with the fibula. It possesses a shaft and two extremities. 

The shaft or body (Corj^us tibiae), large and three-sided above, becomes smaller 
and flattened in the sagittal direction below, but widens a little at the distal end. 
It presents for notice three surfaces and three borders. The internal surface 
(Facies medialis) is broad above, where it furnishes insertion to the internal lateral 
ligament and the sartorius and gracilis muscles; below this it is convex and sub- 
cutaneous. The external surface (Facies lateralis) is smooth and somewhat spiral. 
It is wide and concave in its upper part, below w^iich it becomes narrow'er and 
slightly convex, and winds gradually to the front of the ])one; near the distal end 
it widens a little, becomes flat, and faces forward. The posterior surface (Facies 
posterior) is flattened, and is divided into two parts by the rough popliteal line, 
which runs obliquely from the upper part of the external border to the middle of 
the internal 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 W'hich 
the deep flexor muscle of the digit is attached; the lines fade out below, where the 
surface is smooth and flat. The nutrient foramen is situated on or near the 
popliteal line. The anterior border is very ])n)minent in its upper third, forming 
the tibial crest (Crista tibia?); below it is reduced to a rough line, which ends at a 



THE TIBIA 



101 



small elevation near the distal end of the ])one. The internal border (Alargo medi- 
alis) is rounded in its u})per half, to which th(> popliteus muscle is attached, and a 
tubercle is found on this part. The lower part is a rough line on well-marked bones. 
The external border (Crista interossea) is concave in its upper part and concurs 
with the fibula in the formation of the interosseous space of the leg; a smooth im- 
pression indicates the course of the anterior til)ial vessels through the space to the 



Spine 



External condyle 



Head of fibula 



Vascular impression \--~ 



Shaft of jibula — 
External border of tibia 




T uberosity 

1^ " Groove for tendon of anterior 

extensor and peroneus tertius 



— Groove for lateral extensor tendon 



External malleolus 
Fig. 68. — Right Tibia and Fibula of Horse, External View, 



front of the leg. Lower down the border di\-ides and incloses a narrow triangular 
surface. 

The proximal extremity (Extremitas proximalis) is large and three-sided. It 
bears two lateral eminences, the internal and external condyles (Condylus medialis, 
laterahs). Each presents a somewhat saddle-shaped surface for articulation with 
the condyle of the femur and the semilunar cartilage. The spine or intercondy- 
loid eminence (Eminentia intercondyloidea) is the central prominence, upon which 
the articular surfaces are continued; it consists of a high inner part and a lower 



102 



THE SKELETON OF THE HORSE 



outer part (Tuberculum intercondyloideuni inediale, laterale). On, before, and 
behind the spine are the anterior and posterior intercondyloid fossae, in which 
the anterior crucial Ugament and the semihniar cartilages are attached. The 
condyles are separated behind by the deep popliteal notch (Incisura poplitea), on 
the inner side of which is a tubercle for the attachment of the posterior crucial 
ligament. The external condyle has an overhanging outer margin, below which is 



Spine 



Internal condyle 



Tubercle for posterior crucial ' 
ligament 



Tubercle — 
Nutrient foramen — 




' Fossa for anterior crucial ligament 
Popliteal notch 
f ~ External condyle 

Head of fibula 



Groove for tendon of inner head 

of flexor perforans 

Internal malleolus ' 




' Impression of anterior tibial vessels 
"7 Interosseous si 



space 



ij — Shaft of fibula 
- - Muscular lines 



~ External malleolus 



Fig. 69. — Right Tibia and Fibula of Horse, Posterior View. 



a facet for articulation with the fil)ula. The large anterior eminence is the tu- 
berosity of the tibia (Tuberositas tibiae). It is marked in front by a groove, the 
lower part of which gives attachment to the middle patellar ligament, and the 
groove is flanked by rough areas for the attachment of the internal and external 
patellar ligaments. A semicircular smooth notch (Sulcus muscularis) separates the 
tuberosity from the external condyle, and gives passage to the tendon of origin of 
the anterior extensor and the peroneus tertius. 



THE TIBIA 



103 



The distal extremity (Extremitas distalis) is much smaller than the proximal; 
it is quadrangular in form and larger internally than externally. It presents an 
articular surface (Cochlea tibia3), which is adapted to the trochlea of the til)ial 
tarsal lx)ne (astragalus), and consists of two grooves separated by a ridge. The 
ridge and grooves are directed obliquely forward and outward, and are bounded 
laterally by the malleoli, to which the lateral ligaments of the hock joint are at- 



Spine 



Tuberosity 

Sulcus niusculnris -^ 
External condyle - 

Head of fibula — 

Interosseous space -- 
External surface 
Shaft of fibula — 



External malleolus - 




- Groom far middle patellar ligament 
r — Internal condyle 



Imprint for insertion of gracilis 

Crest 

— Imprint for insertion of semilendi- 
nosus 

Internal surface 



-Internal walleolus 



Fig. 70 — Right Tibia and Fibula of Horse, Axterior View. 



tached. The internal malleolus (Malleolus tibialis) is the more prominent of the 
two, and forms the anterior boundary of a groove for the tendon of the inner 
head of the flexor perforans. The external malleolus (Malleolus fibularis) 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 external malleolus. The latter is 



104 THE SKELETON OF THE HORSE 

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 external articular groove. The 
proximal end unites with the shaft at about three and a half years, and the distal 
end at about two years of age. 



THE FIBULA 

The fibula of the horse is a much reduced long bone, situated along the outer 
side of the tibia. 

The shaft or body (Corpus fibulae) is a slender rod which forms the outer bound- 
ary of the interosseous space; it usually terminates below in a pointed end a]:)out 
one-half to two-thirds of the way down the external border of the tibia. 

The proximal extremity or head (Capitulum fibulae) is relatively large, and is 
flattened transversely. Its internal surface presents a narrow area along the upper 
border for articulation with the tibia. The external surface is rough and gives 
attachment to the external lateral ligament of the stifle joint. It has rounded 
anterior and posterior borders. 

Poplitenl 
Groove for poplitois tendon 't:' ', <^- 



External condijle — 4" 



,^V -' '§ Internal condyle 

Ic Q \ External and internal 

/ tubercles of spine 

Groove for tendon of extensor ^'' 
longits and peroneus tertius 

\ (iroorc for middle patellar ligament 

Tuberosity 

Fig. 71. — Proxi.mal Extremity of Right Tibia of Horse, Exd View. 
I. CM., I.e. p.. Depressions for attachment of anterior and posterior crucial ligaments; I, m, in, depressions for at- 
tachment of semilunar cartilages. 

The distal extremity is fused with the tibia, constituting the external malleolus. 

Development. — This resembles that of the ulna. The embryonic cartilaginous 
fibula extends the entire length of the leg, but does not articulate with the femur. 
The lower part of the shaft is usually reduced to a fibrous band. Three centers of 
ossification appear, one each for the shaft and the extremities. The distal end 
unites early with the tibia, forming the external malleolus. 

It is interesting to note that in some oases the entire shaft of the tibula develops, a reversion 
to the condition in the Miocene ancestors of the present 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 or free surface (Facies libera) is irregularly quadrilateral, convex, 
and rough for muscular and ligamentous attachment. 

The posterior or articular surface is smaller and is triangular in outline. It 
presents a vertical rounded ridge, which corresponds to the groove on the trochlea 
of the femur, and separates two concave areas. Of the latter, the inner cavity is 



THE TARSUS 



105 



much the larger, and is not very well adapted to the inner lip of the trochlea; in 
the fresh state, however, it is completed and rendered more congruent by the 
curved accessory fibro-cartilage. 

The lateral borders converge to the apex below, and 
each forms a prominence or angle at the base. The inner 
angle and the adjacent part of the border give attach- f^ 
ment to the fibro-cartilage of the patella, which increases 
the articular surface. The external border is rounded 
and its angle is less prominent. 

The base (Basis patella') faces upward and back- 
ward, and is convex transversely, concave from before 
backward. 

The apex forms a l)lunt point directed downward. 

Development. — The patella develops as a sesamoid 
bone from a single center in a cartilaginous deposit in 
the tendon of the quadriceps femoris nuiscle. 



THE TARSUS 

The tarsus or hock of the horse usually comprises 
six short bones (Ossa tarsi), but exceptionally seven are 
present. 

The Tibial Tarsal Bone 

The tibial tarsal bone (Os tarsi tibiale, astragalus, 
or talus) is the inner bone of the proximal row. It is 
extremely irregular in form, but may be considered as 
offering six surfaces for description. 

The superior and the anterior or dorsal surface are 
continuous, and form a trochlea for articulation with the 
distal end of the tibia. The trochlea consists of two 
oblique ridges with a deep groove between them, which 
curve spirally forward, downward, and outward. There 
is usually a shallow synovial fossa in the groove. The 
inferior surface is convex from before backward, and 
most of it articulates with the central tarsal; externally 
it has an oblique facet for the fourth tarsal, and a non- 
articular groove cuts into the surface to its middle. The posterior or plantar 
surface is oblique and extremely irregular; it presents four facets for articulation 
with the fibular tarsal bone; the facets are separated by rough excavated areas, and 
the largest fossa (Sulcus tali) forms with a corresponcUng one on the fibular 




C/V 



72. — Frontal Section of 
Right Tibia of Horse, 
Anterior View. 



Base Base 

Accessor!/ Accessory 

cartilage cartilage 



Apex ^:% 




Fig. 73. — Right Patella of Horse, Anterior View. Fig. 74. — Right Patella of Horse, Posterior View. 



tarsal a cavity termed the sinus tarsi. The internal surface bears on its lower part 
a large tul^erosity, and on its upper part a small one for the attachment of the 



106 



THE SKELETON OF THE HORSE 



internal lateral ligament. The external surface is smaller than the internal, and 
is marked by a wide rough fossa in which the external ligament is attached. 

The Fibular Tarsal Bone 
The fibular tarsal bone (Os tarsi fibulare, calcaneum, os calcis) is the largest 
bone of the hock. It is elongated, flattened from side to side, and forms a lever 



Trochlea 
of tibial I 
tarsal I 



Central tarsal 
Third tarsal 

Metatarsal 
tuberosity 
Third yneta- 
tarsal 




Tuber calcis 




*■- Sustentaculum 



Tuberosity 
r i^' for lateral 
ligament 



Fused first 
j^i X iind second 
->-f V^, larsals 



Second 
metatarsal 




Fig. 75.— Right Tarsus and Upper Part of Meta- 
tarsus OF Horse, Internal View. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



Groove for deep 
flexor tendon 



Tibial tarsal 

Centnd 
tarsal 

Fused first 

and second 

tarsals 




Tuber calcis 



Fibular 
tarsal 



Fourth 
tarsal 

Fourth 
metatarsal 



Third 
metatarsal 



Fig. 76. — Right Tarsus and Upper Part of Meta- 
tarsus or Horse, Posterior (Plantar) 
View. (After Schmaltz, Atlas d. Anat. d. 
Pferdes.) 



for the muscles which extend the hock joint. It consists of a body and an inner 
process, the sustentaculum tali. 

The body (Corpus calcanei) is enlarged at its proximal end to form the tuber 



Facets for fibular tarsal 



Groove of trochlea 



Depression 
for external 
lateral liga- 
ment 




S\irfac( for 
central tarsal 



biro'<ity 
for itdirnal 
luttral liga- 
ment 



Fig. 77. — Right Tibial T.\rsal Bone of Horse. 
Anterior View. (After Schmaltz, Atlas d. 
Anat. d. Pferde.s.) 




Fossa 



Depression for 
external lateral 
ligament 

Fig. 78. — Right Tibial Tarsal Bone of Horse, 
External View. (After Schmaltz, Atlas d. 
Anat. d. Pferdes.) 



calcis or "point of the hock." The posterior part of this eminence gives attach- 
ment to the tendon of the gastrocnemius, while in front and laterally it furnishes 
insertion to tendons of the flexor perforatus, biceps, and semitendinosus muscles. 
The inferior extremity l)ears a concave facet for articulation with the fourth tarsal 
bone. The internal surface has on its lower part a strong process, the sustentacu- 
lum tali, which projects inward. The process has a large, oval, slightly concave 



THE TARSUS 



107 



facet in front for articulation with the tibial tarsal, and sometimes a small articular 
surface below for the central tarsal bone. Its plantar surface forms with the smooth 
inner surface of the body a groove for the deep flexor tendon (Sulcus musculi fiexoris 
hallucis longi). Its inner surface has a promineuco on the lower part for the at- 
tachment of the lateral ligament. The external surface of the l)ody is flattened, 
except below, where there is a rough prominence for the attachment of the lateral 




Fossa 




FaccU for tibial 
tarsal bone 

Fig 79. — Right Fibular Tarsal 
Bone of Horse, Anterior 
View. (After Schmaltz, 
Atlas d. Anat.d. Pferdes.) 



Facet for 
tibial tarsal 



Facet for 

central 

tarsal 



Facet for 
central tarsal 



Fig. 80. — Right Fourth Tar- 
sal Bone of Horse, 
Upper Surface. (After 
Schmaltz, Atlas d. Anat. 
d. Pferdes.) 




Surface for 
tibial tarsal 

Fig. 81. — Right Central Tar- 
sal Bone of Horse, 
Upper Surface. (After 
Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



ligament. The anterior or dorsal border is concave in its length, smooth and 
rounded in its upper part. About its midtlle is a blunt-pointed projection (Pro- 
cessus cochlearis) which bears facets on its inner and lower surfaces for articulation 
with the tibial tarsal bone, and is roughened outwardly for ligamentous 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 posterior or plantar border is 




Fused first and 
second tarsals 



Facets for cen- 
tral tarsal 
Facets for central 
tarsal 



Third tarsal 



Fig. 82. — Right First, Second, .\nd Third Tarsal 
Bones of Horse, Upper Surface. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



Second (inter- 
nal) metatar- 
sal 



Fourth (external) 
metatarsal 




/ 
Facets for sec- 
ond and third Facet for third 
tarsals tarscd 



Facets for 
fourth tar- 
sal 



Fig. 83. — Proximal Articular Surfaces of Left 
Metat.\rs.a.l Bones of Horse. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



straight and thick, and widens a little at either end; it is rough, and gives attach- 
ment to the long plantar ligament. 

The Central Tarsal Bone 
The central tarsal bone fOs tarsi centrale, scaphoid, or navicular) is irregularly 
quadrilateral, and is situated between the tibial tarsal above and the third tarsal 
below. It is flattened from above downward, and may be described as having two 



108 



THE SKELETON OF THE HORSE 



surfaces and four borders. The superior surface is concave from before backward, 
and almost all of it articulates with the tibial tarsal; a non-articular depression 
cuts into its outer part, and sometimes there is a facet for the fibular tarsal bone on 
the posterior angle. The inferior surface is convex, and is crossed by a non-articu- 
lar groove, which separates facets for articulation with the third and the first and 



Fourth tarsal 



Groove for great vieta- 
larsal artery 



Fourth {external) tneta- ' ' 
tarsal \ 




Tuber ealcis 
Fibular tarsal 



j^ TrocJilea of tibial tarsal 



Depression for external 
lateral ligament 



Central tarsal 
Third tarsal 



Vascular canal 
Third (large) mctatursal 




Eminence for lateral ligament 



Fig. 84. — Right Tarsal and Metatarsal Bones of Horse, External View. (After Schmaltz, Atlas d. 

A a at. (1. Pferdes.) 

second (fused) tarsals. The anterior or dorsal border and the internal border 
are continuous, convex, and rough. The posterior or plantar border bears two prom- 
inences, separated by a notch. The external border is obli(|ue, and liears anterior 
and posterior facets for articulation with the fourth tarsal, between which it is ex- 
cavated and rough. 



the tarsus 109 

First and Second Tarsal Bones 
The first and second tarsal bones (Os tarsale primum et secundum, cuneiform 
parvum) are usually fused in the horse, forming a bone of very irregular shape, situ- 
ated in the inner and posterior part of the lower row, below the central and behind the 
third tarsal. It is the smallest of the tarsal bones, and may be described as having 
two surfaces, two l)orders, and two extremities. The internal surface faces back- 
ward and inward, and is convex. Its anterior part is ridged, and gives attach- 
ment to the internal lateral ligament, and its posterior part bears an imprint where 
the inner tendon of the tibialis anterior is inserted. The external surface is marked 
by a deep notch which indicates the division between the first and second tarsal 
elements; it bears on its anterior part a large concave facet for the central 
tarsal. The superior border is convex. The inferior border is broad in front, 
where it articulates with the large and inner small metatarsal bones. The 
anterior extremity has a small facet for articulation with the third tarsal, and 
bears internally a ridge or tubercle. The posterior 

extremity is a blunt point. . » „ 

A yiV External 

In some cases the first and second tarsal bones remain V\i^3^%T T' "^'^'^''"' 

separate — a remarkable reversion to the condition in the early iwmm.A. one 

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, y External 

equivalent to the thick anterior part of the bone as described C\ metatarsal 

above, and overlapped by the anterior part of the first tarsal. /^ /|j fto/ig 

The Third Tarsal Bone 
The third tarsal bone (Os tarsale tertium, third or 
great cuneiform) resembles the central, but is smaller 

, . . , . ,,. Ti • -i ill, ii Fig. 85. — Cross-sections of 

and triangular in outline. It is situated between the Metacarp.^l and Met.a.- 

central above and the large metatarsal bone below. It tarsal Bones op Horse. 

possesses two surfaces and three borders. y^^Trf^pf^d*^') ^*'^^ ^ 

The superior 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 inferior surface is 
slightly convex, and rests on the large metatarsal bone; it has an extensive 
central rough excavation. The anterior or dorsal border is convex and bears a 
rounded ridge on its inner part. The internal border is deeply notched and has 
a small facet for the second tarsal on its anterior part. The external border is 
also divided by a notch into two parts, and bears two diagonally opposite facets 
for articulation with the fourth tarsal. In some cases there is a facet for the inner 
small metatarsal bone. 

The Fourth Tarsal Bone 

The fourth tarsal bone (Os tarsale quartum, cuboid) is the outer bone of 
the lower row, and is equal in height to the central and third together. It is 
cuboid in shape and presents six surfaces. 

The superior surface is convex from side to side, and articulates chiefly with 
the fibular tarsal, but to a small extent with the tibial tarsal also. The inferior 
surface rests on the large and external small metatarsal bones. The internal 
surface bears four facets for articulation with the central and third tarsal bones. 
It is crossed from before backward by a smooth groove, which by apposition with 
the adjacent bones forms the canal of the tarsus (Canalis tarsi) for the passage of 
the perforating tarsal vessels. The anterior or dorsal, external, and posterior or 
plantar surfaces are continuous and rough. A tuberosity behind gives attachment 
to the plantar ligament. 




110 



THE SKELETON OF THE HORSE 



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 cen- 
ters, but fusion usually occurs before birth. Each of the other bones ossifies from 
a single center. 



Tuberosity *- 



Ridges for 
attachment 
of middle in- 
ferior sesa- 
moid ligament 

hnprint for 
tendon of _ 
superficial 
flexor 
Condyle ■■' 
Transverse 
prominence - ~ 



Condyle 

Proximal 
border. 

Flexor 
surface ~ 
Wing 

Volar 

graori 

Vdni- 
f Oram I n 
Semilu- 
nar crest 

Flexor 
surface 




^Proximal 
sesanwids 



— s-iSZt 4 Phalanx I 



.^' 



^, Phalanx II 



Third 
sesamoid 
or navic- 
■ ular bone 






Proximal ^_ _ Os 
sesamoids 



Phalanx I 




Phalanx II 



Third sesa- 
moid or na- 
vicular bone 




Foramen 
I N^otch 

! / 



' Phalanx III Phalanx Illy 



Fig. 86. — Digit.\l Bones of Fore Limb of Horse, 
Volar Aspect. 



Fig. 87 



-Digital Bones of Hind Limb of Horse, 
Volar Aspect. 



THE METATARSUS 

The metatarsal bones (Ossa mctatarsalia), three in number, have the same 
general arrangement as the metacarpal bones, but present some important differ- 
ences. Their direction is slightly oblique, downward and a little forward 

The large or third metatarsal bone is about one-sixth longer than the corre- 
sponding metacarpal; in an animal of medium size the difference is about two inches. 
The shaft is more cylindrical, and is almost circular on cross-section, except in its 
lower part. At the upper part of its external surface there is a groove, which is 
directed obliquely downward and backward, and is continued by the furrow formed 
by the apposition of the external metatarsal bone; it indicates the course of the 
great metatarsal artery. A faint impression in a similar place on the inner side 



THE PHALANGES AND SESAMOIDS 111 

marks the position of the corresponding vein. The nutrient foramen is relatively 
higher than on the metacarpal bone. The proximal extremity is much wider from 
before backward than that of the metacarpal bone. Its articular surface is sHghtly 
concave, and is marked by a large central non-articular depression, continued out- 
ward by a deep notch. The greater part of the surface articulates with the third 
tarsal, but there is an outer facet for the fourth, and usually a small facet postero- 
internally 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 outer side behind the 
vascular groove. The distal extremity closely resembles that of the corresponding 
metacarpal bone. 

In some cases the lower part of the shaft is bent backward somewhat. The articular sur- 
face extends a little higher behind than in the case of the metacarpal bone. The large metatarsal 
bone is even more strongly constructed than the metacarpal. The shell of compact substance is 
very thick in the middle of the shaft, especially in front and internally. 

The small metatarsal bones are a little longer than the corresponding meta- 
carpals. The external (fourth) metatarsal is relatively massive, especially in its 
up])er part. The head is large and outstanding, and bears two facets alcove for the 
fourth tarsal, and two in front and internally for articulation with the large meta- 
tarsal; elsewhere it is roughened for attachment. The internal (second) meta- 
tarsal is much more slender than the outer one, especially in its upper part. The 
head bears two facets above for the first and second tarsals, and sometimes one for 
the third tarsal. 



THE PHALANGES AND SESAMOIDS 

The axis of the phalanges of the hind liml) is about five degrees less oblique 
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 wall surface is a 
little (ca. 5 degrees) greater, the sole surface is more concave, and the wings are 
less prominent and closer together. 

The proximal sesamoids are a little smaller, except in thickness. The third 
sesamoid or navicular bone is narrower and shorter. 



112 SKELETON OF THE OX 



SKELETON OF THE OX 

VERTEBRAL COLUMN 

The vertebral formula is C^TjjLgSjCyjg^^o- 

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, quadrilateral and almost sagittal plate, directed downward. The seventh 
transverse process is single, short, and thick, and presents no foramen transversa- 
rium; it is in series with the upper part of the preceding processes. The spinous 
processes are well developed, and increase in height from before backward. They 
are directed upward and forward, with the exception 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 bone is usually bifid. The ventral spines are prominent and thick 
in their posterior 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 trans- 
versarium (posterior foramen) is absent. The cavities for the occipital condyles 
are divided into upper and lower parts by a non-articular area, and are separated 
by a narrow interval below. The posterior articular surfaces are flattened behind 
and are continued into the vertebral canal, forming an extensive area for the odon- 
toid process 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 odontoid 
process (dens) is wide, and its upper surface is deeply concave from side to side. 
The intervertebral 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. 
The bodies are longer and are distinctly constricted in the middle. They bear a 
thin-edged ventral crest. The arches — in addition to the usual notches, which are 
shallow — ^are perforated in the posterior part by a foramen. The transverse 
processes are thick and strong, and bear rounded mammillary processes (except 
at the posterior end of the series) ; the last two, although prominent, do not always 
articulate with the ribs. The spinous processes are long. The first is much higher 
than in the horse, the next two are usually the most prominent, and behind this 
there is a very gradual diminution in height. The backward slope, slight at first, 
increases to the tenth; the last is vertical and lumbar in character. 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 general thin and sharp, but the last three or four some- 
times have thick posterior margins. 

The lumbar vertebrae, six in number, are much longer than in the horse. The 
bodies are much constricted in the middle, expanded at either end, and bear rudi- 
mentary ventral crests. The fourth and fifth are usually the longest. The 
intervertebral foramina are often double in the anterior part of the series, and are 



VERTEBRAL COLUMN 



113 




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114 SKELETON OF THE OX 

very large further back. The articular processes are large, and their facets are 
more strongly curved than in the horse. The transverse processes 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 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 moder- 
ately 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 imited to form a median sacral crest, with a convex thick and rough margin. 
A lateral crest is formed by the fusion of the articular processes. The pelvic 
surface is concave in both directions, and is marked by a central groove, which 
indicates the course of the middle sacral artery. The inferior sacral foramina are 
large. The wings are quadrangular, 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 surface is rough, and 
bears a triangular area below for articulation w4th 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 are concave and 
semi-cylindrical in curvature internally. The lateral borders are thin, sharp, and 
irregular. The apex is wider than in the horse, and the posterior end of the crest 
forms a pointed projection over the opening of the sacral canal. 

The coccygeal vertebrae are longer and better developed 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 articulate), and a pair of ventral 
spines which form a hsemal groove 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 
promontory occurs at the junction of the sacrum and first coccygeal vertebrae. 

Length: The following table gives the lengths of the regions of a shorthorn cow of medium 
size: 

Cervical 47 cm. 

Thoracic 75 cm. 

Lumbar 40 cm. 

Sacral 24 cm. 

Coccygeal 75 cm. 

261 cm. 

Variations: Sometimes fourteen thoracic vertebra? and fourteen pairs of ribs are present; 
reduction to twelve with the normal number of lumbar verteln-a? is very rare. AccorcHng to 
Franck, there are sometimes seven lumbar vertel)ra^ with the normal number in the thoracic 
region. The number of coccygeal vertebrae may vary from sixteen to twenty-one. 



THE RIBS 

Thirteen pairs of ribs are normally present, 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 the breadth 
of the intercostal spaces is correspondingly diminished. 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 lower ends of the 
second to the tenth or eleventh inclusive form diarthrodial joints with the costal 



THE THORAX BONES OF THE SKULL BONES OF THE CRANIUM 115 

cartilages. The first costal cartilages are very short; they articulate by their 
internal surfaces with the sternum, but not with each other. 

Tlie 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. 

Tiie sternum consists of seven sternebne, 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 l)ase 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 l:)ehind 
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 
bortlers 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 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 to the middle of the lumbar region. 



Bones of the Skull 

Bones of the Cranium 

The occipital bone is situated in 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, to which the ligamentum nuchse is attached, and 
the surface on either side is depressed and rough for muscular attachment. 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. Two constant foramina are 
found in the condyloid fossa; the anterior one is the hypoglossal, the other (some- 
times double) conducts a vein from the condyloid canal. The latter passes upward 
from a foramen on the inner side of the condyle and opens into the parieto-temporal 
canal. The cranial surface of the supraoccipital presents a central depression, and 
above this is a variable but never very pronounced eminence, which corresponds 
to the tentorium osseum of the horse. On either sitle is a groove leading to the 
parieto-temporal canal. The basilar process is short and wide; its cranial surface 
is deeply concave, and the internal spheno-occipital crest is prominent. Two large 
tubercles below mark the junction with the sphenoid. 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 cranial surface of the body presents a deep 
sella turcica, in front of which it rises abruptly. The high anterior part bears a 
central ridge (Rostrum sphenoidale), 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, lacerum orbitale, and patheticum of the horse. The 
posterior one is the foramen ovale, which transmits the inferior maxillary nerve. 



116 



SKELETON OF THE OX 



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 
close to the sphenopalatine foramen, and contains a small sinus which communi- 
cates with an ethmoidal meatus. The temporal wing is small, but forms a promi- 
nent thick pterygoid crest. The pterygoid process is wide, and the pterygoid or 
alar foramen is absent. The sphenoidal sinus is absent in the calf and small in 




Fig. 89. — Skull and Atlas of Ox, Lateral View. 
9, Zygomatic arch; 11, eoronoid process; 13, supraorbital process; IS", paramastoid or styloid process; 
13"', occipital condyle; 14, parietal bone; 15, frontal bone; 16, squamous temporal bone; 17, external audi- 
tory meatus; 18, temporal condyle; 19, orbital surface of lacrimal bone; SO, malar bone; SI, facial surface of 
lacrimal bone; ^^, nasal bone; ^3, nasal process of premaxilla; 24', incisor teeth; 26, maxilla; ^7, facial tuber- 
osity; infraorbital foramen in front of ^7;' S8' , molar part of ramus of mandible; SO, broad vertical part of ramus; 
SO', angle of jaw; 31, condyle of mandible; 32, atlas; x, wing of atlas. (After EUenberger-Baum, Anat. fiir 
Kiinstler.) 



the adult; it communicates by one or two small openings with an ethmoidal meatus, 
and so with the nasal cavity. 

The ethmoid bone has an extensive perpendicular plate. The lateral mass 
consists of five endoturliinals and eighteen ectoturbinals (Paulli). The largest 
ethmoturbinal is so extensive as to be termed a third or middle turbinal loone; it 
projects forward between the upper and lower turbinals. The lamina papyracea 
appears to a small extent externally in the pterygo-palatine fossa, forming part 
of the upper margin of the sphenopalatine foramen. 

The interparietals are primitively paired, but unite before birth. As already 



BONES OF THE CRANIUM 



117 



mentioned, fusion occurs before or shortly after birth with the parietals and supra- 
occipital. No distinct tentorium osseum is present. 

The parietal bones do not enter into the formation of the roof of the cranium. 
They constitute the upper part of the posterior wall, and bentl sharply forward 




Fig. 90. — Skull of Ox, Basal View, Without Mandible. 
F , Pterygoid bone; G, horizontal and G' , perpendicular part of palate bone; H , occipital bone; J , malar 
bone; K, sphenoid bone; O, maxilla; P, vomer; Sch., squamous temporal; St., frontal bone; Z, premaxilla; 
1, for. magnum; 2, occipital condyle; 3, paramastoid (styloid) process of occipital; 4< hypoglossal and condy- 
loid foramina; 5, for. lacerum; 6, pharyngeal tubercles; 7, bulla ossea; 8, muscular process (left one is removed 
to expose for. ovale); 9, hyoid process; 10, ext. auditory meatus; 11, zygomatic process; 12, external opening of 
parieto-temporal canal; 13, postglenoid process; 14, temporal condyle; 15, for. ovale; 16, for. lac. orbitale 4- 
for. rotundum; 17, optic foramen; 18, ethmoidal foramen; 19, orbital opening of supraorbital canal; 20, ptery- 
goid crest; 21, hamulus of pterygoid bone; 22, lacrimal bulla; 23, temporal process of malar; 24, pterygoid 
process of inaxilla; 25, sphenopalatine foramen: 26, maxillary foramen; 27, posterior palatine foramen; 28,. 
anterior palatine foramen; 29, accessory palatine foramina; 30, palate process of maxilla; 31, interalveolar 
border; 32, palatine cleft; 33, palate process of prema.xilla; 34, fissura incisiva; 35, facial tuberosity; 36, pos- 
terior nares. (Ellenberger-Baum, Anat. d. Haustiere.) 



along the lateral wall, forming part of the wall of the temporal fossa. The line of 
inflection is marked by the prominent parietal crest, which is continuous with the 
temporal crest below. The parietals are excavated to form part of the frontal 
sinuses in the adult animal. 



118 



SKELETON OF THE OX 



The condition in the young suljject 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 ligamentum 
nucha?. From either side of this a line curves outward, and divides the surface into an upper 
smooth area and a lower area which is rough for muscular attachment. The upper border joins 
the frontal bone and concurs in the formation of the frontal eminence. The temporal parts 
(Plana temporalia) are much smaller and are concave externally; they join the frontal above and 
the squamous temporal below. 








15 





Fig. 91. — Skull, of Ox, Dors.-vl View (with Mandible). 
12, Supraorbital process; H, parietal bone; 15, frontal bone; 16, squamous temi)oral bone; 19, orbit; 20, 
malar bone; .27, lacrimal bone; 22,\xixs'3\. bone; 26, premaxilla; 26, maxilla; ^7, facial tuberosity; 2J,,'\VL(ii&0T 
teeth. (After Ellenberger-Baum, Anat. f. Kunstler.) 



The frontal bones are very extensive, forming about one-half of the entire 
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 jtmction of the posterior and the lateral borders 
are the processus cornu or "horn-cores," for the support of the horns. These 
processes 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 they are covered by the matrix of the horns. 
The base has a constriction, the neck. The interior is excavated to form a immber 



BONES OF THE CRANIUM 



119 



of irregular intercommunicating spaces, divided by bony septa, and communicat- 
ing with the frontal sinus. In the polled breeds these processes are absent, the 
skull is narrower in this region, and the frontal eminence more pronounced. The 
supraorbital process is situated about half-way between the anterior and posterior 
margins; it is short and joins the frontal process of the malar bone. The supra- 
orbital foramen (often double) is situated about an inch inward from the root of 
the process; it is the external orifice of the supraorbital canal (Canalis supraorbi- 



Wing 



Squamous tcinpora 

ZijyouKt 
Angle 
Malar bone 




External audilory 
meatus 



Maxilla- 
Facial tuberositij k 

Ratnus of mandible 



Premaxilla 



Fig. 92. — Skull and Atl.vs of Ux, Ventral View. 
13", paramastoid or styloid process; 13'", occipital condyle; ^4' , incisor teeth; 



28, 



13, Basi-occipital, i^ , t^^^^ — ^- — -- --.. . . ^,, , i, » * f „ 

body of mandible; ^2, condyle of mandible; 33, ventral tubercle of atlas. (After EUenberger-Baum, Anat. fur 

Kiinstler.) 

talis), which passes downward and forward into the orbit. The foramen is in the 
course of the supraorbital 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 orbital opening of the supraorbital canal, and below by the ethmoidal 
or internal orbital foramen. It does not articulate with the palatine, from which 
it is separated by the orbital wing of the sphenoid. The temporal part is also more 



120 SKELETON OF THE OX 

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 
external 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 auditory 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 parieto-temporal canal. 
The zygomatic process is much shorter and weaker than in the horse, and articu- 
lates with the malar only. The condyle is convex in both directions. The post- 
glenoid process is less prominent, and behind it is the chief external opening of the 
parieto-temporal canal. The internal surface is almost completely overlapped by 
the parietal and sphenoid. The petrous part proper is small, but the tympanic 
part is extensive. The external auditory meatus is smaller than in the horse and is 
directed outward. 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 laterally compressed. It is separated from the occipi- 
tal bone by a narrow opening which is equivalent to part of the foramen lacerum 
basis cranii of the horse. The parieto-temporal canal is formed entirely in the 
temporal bone. The facial canal, on the other hand, is bounded partly by the occi- 
pital bone. 

Bones of the Face 

The maxilla is shorter but broader and relatively higher than in the horse. 
Its external surface bears instead of the facial crest a rough facial tuberosity 
(Tuber malare), placed above the third cheek tooth; a rough curved line often 
extends from it to the upper part of the malar bone. The infraorbital foramen — 
often double — is situated above the first cheek tooth. The tuber maxillare is 
small, laterally compressed, and usually bears a small pointed process (Processus 
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, form- 
ing the palatine sinus. This communicates externally (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 separates the two palatine sinuses. The alveoli 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 inner side of the lacrimal bulla. The maxilla takes no part in the formation 
of the palatine canal. Sutural (or Wormian) bones may be found 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 externally, and is not 
closely attached 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 sur- 
face for the septal cartilage and the vomer. The palatine cleft is very wide. 

The palatine bone is very extensive. The horizontal part forms one-fourth or 
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. 



BONES OF THE FACE 



121 



Accessory palatine foramina 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 pos- 
terior part of the lateral wall of the nasal cavity and in part bounds the narrow pos- 
terior nares. Its internal surface is nearly flat, and is smooth and free, except 
behind, where it is overlapped by the pterygoid bone. The external surface is 
attached to a small extent to the pterygoid process l^ehind, and is free elsewhere. 
The spheno-palatine 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 sphenoid. 
The edge behind this foramen articulates with the orbital wing of the sphenoid, 
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 outer surface is almost entirely united 




Fir,. 93. — Median Section of Skull op Ox, Without the Mandible. 
The mucous membrane is retained. The septum nasi is removed, a, Superior meatus; b, middle meatus, 
with b' and b", its upper and lower divisions; c, inferior meatus; d, superior turbinal; e, superior turbinal fold; 
/, inferior turbinal; g, alar fold; h, inferior turbinal fold; i, lateral mass of ethmoid (ethmoturbinals); ;', large 
ethmoturbinal or middle turbinal; k, frontal sinus; /, sphenoidal sinus; m, cranial cavity; n, palatine sinus; 
o, nasal bone; o', parietal cartilage; p, palate process of maxilla; q, palate bone (horizontal part); 1, sphenoid 
bone; 2, 3, inner and outer plates of frontal bone; 4, 4', outer and inner plates of parietal bone; 5, 5' , occipital 
bone; 5", condyloid and hypoglossal foramina; 6, paramastoid or styloid process; 6' , occipital condyle; 7, 
petrous temporal bone; 7', internal auditory meatus; S, squamous temporal bone; 9, muscular process; 10, 
pterygoid bone (hamulus), (.\fter EUenberger, in Leisering's Atlas.) 



to the palate bone and the pterygoid process, Init 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 ])y several 
notches. The orl)ital part forms below 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 lacrimal 
fossa 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, and below this it is 
concave from above downward. The zygomatic process divides into two branches; 



122 



SKELETON OF THE OX 



of these, the frontal process turns upward and backward and joins the supraorbital 
process of the frontal bone; the temporal process continues backward, and is over- 
lapped by the zygomatic process of the temporal bone, completing the zygomatic 
arch. 

The superior turbinal bone is less cribriform and fragile than in the horse, and 
is thickest in its middle, small at either end. It is attached to the turbinal crest 
of the nasal bone, and curves downward, outward, and upward to be applied out- 
wardly to the frontal and lacrimal bones. It thus incloses a cavity which communi- 
cates 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 inferior turbinal bone is shorter l)ut much broader than in the horse. It 
is attached to the maxilla by a l^asal lamella about an inch (ca. 2 to 3 cm.) wide, 
which slopes downward and inward. At the inner edge of this it splits into two 
plates which are rolled in opposite directions, and inclose two separate cavities, 
subdivided by several septa. The upper one opens into the middle meatus, the 

lower one into the inferior 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 lower edge fits into the 
nasal crest of the maxilla; behind 
this it is free and separated by a 
considerable 'interval from the nasal 
floor. 

The two halves of the mandible 
do not fuse completely even in ad- 
vanced age. The symphyseal sur- 
faces are extremely rough and are 
marked by reciprocal projections and 
cavities. The body is shorter, wdder, 
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 constitutes a long narrow neck. 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 submaxillary space is wider 
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 
lower border is convex in its length. Its upper border bears 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 fora- 
men is al)out in the middle of its inner surface, and a groove for the lingual nerve 
curves downward and forward from it. The condyle projects inward 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 tul)erous lingual process. The middle cornua 
are almost as large as the small cornua. The great cornua are narrow, exce])t 
at the ends. The upper end divides into two branches, which correspond 




Fig. 94. — Hyoid Bone of Ox. 
a. Body; b, lingual proces.s; c, thyroid cornu and 
cartilage, c'; d, small cornu; e. middle cornu; /, great cornu; 
g, muscular angle of /. (EUgnberger-Baum, Anat. d 
Haustiere.) 



SKULL OF THE OX AS A WHOLE 123 

to the two angles of that of the horse. The thyroid cornua do not fuse with 
the body. 



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 sinus, 
and does not affect the cranial cavity, which is smaller than in the horse. 

The superior or frontal surface is formed by the frontals, nasals, and pre- 
maxillse. 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, 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 premaxillge 
do not bend do^vnward 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 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 above by a crest which extends from the postero-external 
angle of the frontal to the supraorl^ital process, and is analogous to the sagittal 
crest of the horse. Behind it is bounded by the temporal crest. It is clearly 
marked off from the orbit by the rounded posterior orbital ridge and the pterygoid 
crest. The zygomatic process 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 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 narrow forward extension (maxillary hiatus) between the vertical plate of 
the palate bone internally and the maxilla and lacrimal bulla externally; thus the 
sphenopalatine and maxillary foramina are deeply placed. The preorbital region 
is short but relatively high. A tuberosity and curved line take the place of the 
facial crest. The infraorbital foramen is situated al)ove the first cheek tooth and is 
often double. 

The basal surface is short and wide, especially in its cranial part. The occipi- 
tal condyles are limited in front by transverse ridges. The tubercles at the junc- 
tion of the occipital and sphenoid are large. The condyloid fossae 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 narroAV triangular plates, 
with one or two sharp points. The external auditory process is directed almost 
straight outward. A curved plate extends dowTiward from it and joins the bulla 
ossea internally, 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 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 liorder enters into the formation of the posterior nares; the 
lateral parts are notched and just above them are the posterior palatine foramina. 



124 



SKELETON OF THE OX 



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 posterior or nuchal surface is extensive and somewhat pentagonal in 
outline in the adult. About its center is the eminence for the attachment of the 
ligamentum nuchse. From this a median crest extends toward the foramen mag- 
num, and laterally two lines (Lineae nuchae 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 cranial roof by a 
thick border, which forms centrally the frontal eminence, and bears at its extremi- 




FiQ. 95. — Cross-section of Skull of Ox. Section Fig. 96. — Cross-section of Skull of Ox. Section 
Passes Through Fifth Cheek Tooth. Passes through Second Cheek Tooth. 

a, b, c, Superior, middle, inferior meatus; h' , communication between middle meatus and cavity of upper 
part of inferior turbinal; c', communication between inferior meatus and lower part of inferior turbinal; d, cavity 
of superior turbinal; e, /, outer and inner walls of d; g, h, upper and lower cavities of inferior turbinal bone; i, 
ba.sal lamella of inferior turbinal; ;', /", upper and lower divisions of inferior turbinal bone; k, floor of nasal cav- 
ity; m, lacrimal sinus; n, maxillary sinus; p, palatine sinus; q, septum between maxillary and palatine sinuses; 
r, infraorbital canal; s, septum between palatine sinuses; t, common meatus; !/, naso-lacrimal canal; v, floor of 
nasal cavity and roof of palatine sinus; 1, septum nasi; 2, posterior part of second cheek tooth; 3, posterior 
part of fifth cheek tooth; 4, hard palate. (After Ellenberger, in Leisering's Atlas.) 



ties the processus cornu — except in the polled breeds. The condyles are further 
apart, and the articular surfaces are more clearly divided into upper and lower parts 
than in the horse. 

The cranial cavity is shorter and its long axis is more oblique than in the horse, 
but it is relatively high and wide. The anterior fossa lies at a much higher level 
than the rest of the floor. The olfactory fossae are smaller, and the 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 sagittal crest is promi- 
nent anteriorly, but absent further back. A faintly marked elevation takes the 
place of the tentorium osseum. The small petrous temporal bone projects into 
the cavity laterally. The ridges and digital impressions are very pronounced. 
The parieto-temporal canal is formed entirely in the temporal bone, and opens at 



SKULL OF THE OX AS A WHOLE 



125 



the apex of the petrous, where it is joined by the condyloid canal. The foramen 
lacerum is divided into two parts (For. lacerum anterius et posterius). 

The nasal cavity is incompletely divided by the septum, which does not reach 
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 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 ethmoturbinal. The 
posterior nares are narrow and oblique. 




Fig. 97. — Skull of 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 (6); c, c', 
communications between frontal sinus and nasal cavity; d, supraorbital foramen; e, supraorbital canal; /, cavity 
of superior turbinal bone, and g, its opening into the nasal cavity; h, lacrimal sinus, i, its communication 
with the maxillary sinus; k, maxillary sinus; /, orbit; i, frontal bone; 1' , processus cornu; 2, nasal bone; 3, 
premaxilla (nasal process); 4, maxilla; .5, lacrimal bone; 6, malar bone; 7, dotted line indicating course of naso- 
lacrimal duct. (After Ellenberger, in Leisering's Atlas.) 



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 externally 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 tuberosity on the posterior surface 



126 



SKELETON OF THE OX 



the 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 he cut off from the main cavity (Baum). 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 superior turljinal and with the lacrimal part of the 
maxillary sinus which are seen in the macerated skull are closed in the fresh state 
by mucous mem])rane. 

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 upper limit is indicated 
approximately by a line drawn from the infraorbital foramen to the upper margin of 
the orbit. It is continued directly backward into the lacrimal bulla to a point 
nearly o]iposite to the ])ifurcation of the zygomatic process of the malar. It also 
extends upward and backward through a large opening into a cavity formed by the 




Fig. 98. — Skull op Ox, Lateral View without Mandible. 
The maxillary, lacrimal, and turbinal sinuses have been opened, and a portion of the orbit removed, a. 
Cavity of superior turbinal bone; b, 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, lacrimal bone; 1£, malar bone; 13, fissure between nasal bone and maxilla; 14, temporal 
bone (squamous); 15, external auditory meatus; 16, styloid or paramastoid process; 17, occipital condyle; 
IS, palate bone (peri)endicular part); 19, pterygoid bone (hamulus); 20, tympanic part of temporal; 20', mus- 
cular process of petrous temporal. (After EUenberger, in Leisering's Atlas.) 



lacrimal, frontal, ethmoid, and turbinal bones, at the inner 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 mueli 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 comnumication 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 
membrane in the fresh state. The palatine canal passes obliquely through the 
posterior part of the sinus. 

' This is termed the hicrimal sinus liy some authors. It is similar in location and in the posi- 
tion of its orifice to the turbinal part of the frontal sinus of the horse, with the important difference 
that it does not communicate with the frontal sinuses in the ox. 



BONES OF THE THORACIC LIMB 127 

The sphenoidal smus is ahnost entirely in the sphenoid bone and does not 
communicate witli thi^ jialatine and maxillary sinus. It has one or two openino;s 
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 lower 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. 
The spine is sinuous, bent backward in its middle, forward below. Its free border 
is somewhat thickened in its middle, but bears no distinct tubercle. Instead of 
subsiding l)elow as in the horse the spine becomes a little more prominent, and is 
prolonged 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. The coracoid process is short and rounded. The cartilage resembles 
that of the horse. 

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 lower third of the posterior surface. The external tuberosity is very large, 
and rises an inch or more (ca. 3 cm.) above the level of the head. Its anterior part 
curves inward over the bicipital groove, and below it externally there is a promi- 
nent circular rough area for the insertion of the tendon of the supraspinatus. The 
anterior part of the internal tuberosity has a small projection which 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 coronoid and 
olecranon fossae are deep and wide. The external 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 lower 
end being nearer the median plane than the upper. The curvature is more pro- 
nounced below than above. The shaft is prismatic in its middle part and has 
anterior, external, and posterior faces. There is a marked increase in width and 
thickness below. The proximal articular surface presents a synovial fossa which 
extends inward from the deep groove between the two glenoid cavities. The 
bicipital tuberosity is represented by a slightly elevated rough area. The posterior 
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 externally. The distal extremity is large, and is thickest internally. 
Its articular surface is oblique in two directions, i. e., from within upward and 
Ijackward. The grooves 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 



128 



SKELETON OF THE OX 



part of the limb in flexion. The facets for the radial and intermediate carpals are narrower than 
in the horse and run obliquely forward and outward. The surface for the ulnar carpal is extensive 
and saddle-shaped; its outer part is furnished by the ulna. 

The ulna is more fully developed than in the horse. The shaft is complete, 



Bicipital groove 




External tuberosity of humerus 



Deltoid tuberosity 

Musculo-spiral groove 
External condyloid crest 

■ =^ External tuberosity of radius 



Shaft of radius 



Radial carpal bone 
Fused second and third carpal bones 




Ulnar carpal bone 
Intermediate carpal bone 
Fourth carpal bone 
Metacarpal tuberosity 

Anterior groove of large metacarpal bone 



First phalanx 

Second phalanx 
Third ph(danx 



Fig. 99. — Skeleton of Left Fore Limb of Ox, from Shoulder Downward, Anterior View. (After Ellen- 

berger-Baum, Anat. fiir Kiinstler.) 

three-sided, and strongly curved. It is fused with the radius in the adult, except 
at the two interosseous spaces mentioned above. Its upper part contains a medul- 
lary canal which extends somewhat into the proximal end. The olecranon is 
large and bears a rounded tuberosity above. The distal end is fused with the 



BONES OF THE THORACIC LIMB 



129 



radius; it projects bolowtho level of the latter, formingthe styloid process (Processus 
styloitleus ulnse), which furnishes part of the facet for the ulnar carpal. The proxi- 
mal and distal ends unite with the shaft at three and one-half to four years. 

The carpus consists of six bones, four in the upper row, and two in the lower. 
The upper 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 



External condyle of humerns 
External tuberosity of radius 




Olecranon 



Proximal interosseous space 

'Shaft (f ulna 

Groove 



Distal end of radius 

Intermediate carpal hone 

Radial carped bone 

Fused second and third carpal bones 

Melacarpcd t uberosity 




Dit^I'd inferrosseous space 
Sly/did /)/-ncr.ss of ulna 
iccessory carpal bone 



Inar carpal bone 
Fourth carpal bone 
Small metacarped bone 



Large metacarpal bone 



Proximal sesamoid 
First phaleinx 

Second phalanx 
Distal s( so moid 
Third pJudanx 

Fig. 100. — Skeleton of Left Fore LiMn of Ox, i hom Ei.now Downward, External View. (After Ellen- 

berger-Bauin, Aiiat. fiir Ktinstler.) 

are less regular in shape, and their long axes are directed obliquely backward and 
inward. The radial is narrower than in the horse and curves upward behind. The 
intermediate is constricted in its middle, and wdder 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. Behind is a large oval facet for articulation 
with the accessory carpal. The accessory is short, thick, and rounded; it articu- 
9 



130 SKELETON OF THE OX 

lates with the uhiar 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 an external small meta- 
carpal 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 anterior 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 posterior surface is flat and presents a similar but much fainter 
groove. The borders are rough in the upper third. The proximal end bears two 
slightly concave facets for articulation with the bones of the lower row of the car- 
pus; the inner area is the larger, and they are separated by a ridge in front and a 
notch behind. The outer angle has a facet behind for the small metacarpal bone. 
The inner 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 canal is 
divided into two parts l)y a vertical septum which is usually incomplete in the adult. 

The small metacarpal l)one (Mc. 5) is a rounded rod about an inch and a 
half (ca. 3.5 to 4 cm.) in length, which lies against the upper part of the outer border 
of the large bone. Its upper end articulates wdth the latter, but not with the carpus. 
The lower end is pointed. 

Four cartilaginous metacarpals are present in the early foetal state, viz., the second, third, 
fourth, and fifth. The second commonly either disappears or unites with the third; sometimes 
it develops as a small rod of Ijone. The third and fourth graduallj^ unite, but can be cut apart 
at l)irth. Each has three centers of ossification; the proximal epiphysis fuses with the shaft 
before l^irth, 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 articulate with the rest of the skeleton. 

The first phalanges are shorter and narrower than in the horse and are three- 
sided. The interdigital surface is flattened and its posterior part bears a promi- 
nence 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 concave from before backward and is divided by a sagittal groove into 
two areas, of which the abaxial one is the larger and higher. Behind these are 
two facets for articulation wath the sesamoid bones. The posterior surface bears 
two tuberosities separated by a deep depression. The distal extremity is smaller 
than the proximal, especially in the antero-posterior 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 consists at birth of two pieces — the distal end and the fused 
shaft and upper extremity. Union occurs at one and one-half to two years. 

The second phalanges are about two-thirds of the length of the first and are 
distinctly three-sided. The proximal articular surface is divided by a sagittal 
ridge into two glenoid cavities, of which the al)axial one is much the larger. There 
is a central prominence in front and two lateral tubercles behind. The distal ex- 
tremity is smaller than the proximal. Its articular surface encroaches consider- 
ably on the anterior and posterior sin-faces, and is divided into two lateral parts by 
a 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 
with 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. 



BONES OF TFIE PELVIC LIMB 131 

Each has four surfaces. The dorsal or wall surface is marked in its lower part by a 
shallow 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. Below the groove the surface is prominent, rough, and porous. 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 degrees 
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 or sole surface is narrow and slightly concave, ancl presents 
two or three foramina of considerable size. It is separated from the wall 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 sole 
surface. The interdigital surface is smooth and grooved below, rough and porous 
above. At the upper angle it is perforated by a large foramen, which is equivalent 
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 wall surface, and by a sharp 
edge from the sole surface. The wdng or angle is very short and blunt, and there 
is no lateral 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 anterior surfaces, 
Vv^ith 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 external border; it joins the superior 
ischiatic spine. A rounded ridge separates the two parts of the ventral siu'face. 
The surface for articulation with the sacrum is triangular. The internal angle is 
truncated, does not extend as high as the vertebral spines, and is separated from 
the opposite angle by a wdder interval than in the horse. The external angle is 
relatively large and prominent; 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 wath 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 
superior ischiatic spine is high and thin, and bears a series of almost vertical rough 
lines externally. The tuber ischii is large and three-sided, bearing upper, lower, 
and external tuberosities. The ischial arch is narrow and deep. The symphj'sis 
bears a ventral ridge, which fades out near the ischial arch. 

The acetabular branch of the pubis is narrow, and is directed outward and a 
little forward. The anterior border is marked by a transverse groove which ends 
below the rough ilio-pectineal eminence. The longitudinal branch is wade and 
thin. 

The acetabulum is smaller than in the horse. The rim is rounded and is 
usually marked by two notches. One of these is postero-internal and is narrow 
and deep ; it leads to the deep acetabular fossa and is commonly almost converted 



132 



SKELETON OF THE OX 



into a foramen by a bar of bone. The other notch is antero-internal, small, and 
sometimes replaced by a foramen or absent. 

The obturator foramen is large and elliptical. Its inner border is thin and 
sharp. 



External condyle of femur 
External tuberosity of tibia 




External malleolus 
Fibular tarsal bone 



Internal malleolus 
Tibial tarsal bone 

Central + fourth tarsal bone 
Second tarsal bone 
First tarsal bone 
^ — Small metatarsal bone 




Proximal sesa)noid 
First phalanx 

Second phalanx 

Distal sesamoid 
Third phalanx 

Fig. 101. — Skeleton of Left Hind Limb of Ox, from Middle of Thigh Downward, Posterior View. 
SI, Tibia; 24, tuber calcis; 23, large metatarsal bone. (After P]llenberger-Baum, Aiiat. ftir Kiinstler.) 



The pelvic inlet is elliptical and is more oblique than in the horse. In a cow 
of medium size the conjugate diameter is about nine and a half inches (ca, 23 to 24 
cm.), and the transverse 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 



BONES OF THE PELVIC LIMB 



133 



sacral segments. The roof is concave in both directions. The floor is deeply con- 
cave, particularly in the transverse direction. The cavity is narrower and its axis 
isinchned strongly upward in the posterior part. The distance between theacetab- 
uhnn and the external angle of the ilium is only a little (oa. 3 to 4 cm.) more than 
the distance lictween the former and the tuber ischii. 

The femur has a relatively small shaft, which is cylindrical in its middle, pris- 
matic below. 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- 






ss*" 'sssr 



Fig. 102. — Front.^^l Section of Left Femur of Ox, Fig. 10.3. — Front,\l Section of Left Tihia of Ox, 

Front View. Anterior View. 

These figures show the internal architecture of these bone.s, and e.specially the great extent of the meduUary cav- 
ity as compared with those of the horse (Figs. 67 and 72). 



chanter major. The third trochanter is absent. The supracondyloid (plantar) 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. Instead of the notch there 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 external surface is 
very rough. The trochanteric fossa is deep, but does not extend so far downward as 
in the horse. The distal end presents no very striking differential features, but the 
lips of the trochlea are less oblique than in the horse, and converge very slightly 



134 SKELETON OF THE OX 

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. 
The shaft is distinctly curved, so that the inner 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 external groove is separated by a sharp ridge from an outer area which is for 
articulation with the external malleolus. The anterior part of the internal malle- 
olus is ])rolonged downward and has a pointed end. The groove l)ehind it is broad 
and well defined. Externally 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. 

The fibula usually consists of the two extremities only. The head is fused with 
the external condyle of the tibia and bears a small blunt-pointed prolongation 
below. The distal end remains separate and forms the external 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 inner articulates with the external ridge of the 
tibial tarsal bone. The outer surface is rough and irregular. 

The early cartilaginous fibula is complete, but later the shaft is reduced and is 
usually represented by a fibrous cord which connects the two ends. In some cases, 
however, the up]:)er part undergoes partial ossification, forming a slender rod which 
is usually united with the outer border of the tibia and is joined to the head by 
fibrous tissue. 

The patella is long, narrow, and very thick. The anterior surface is strongly 
convex 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 
inner side for the attachment of the accessory cartilage allows prompt determina- 
tion 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 outer ridge is the 
wider, and articulates with both tibia and fibula. The distal trochlea consists 
of two condyles divided by a groove, and articulates Avith the combined central 
and fourth tarsals. The posterior surface bears a large oval facet for articulation 
with the fi})ular tarsal; this occupies most of the surface, and is convex and grooved 
from above downward. The outer surface presents two facets for articulation with 
the fibular tarsal, and is excavated and rough elsewhere. The inner surface bears 
a tuberosity at its upper part, and is flattened below. 

The fibular tarsal bone is longer and more slender than in the horse. The 
distal part of the l)ody is compressed laterally, and Ijcars a projection in front which 
articulates with the external 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 upper surface is 
molded on the distal trochlea of the tibial tarsal, and its inner part rises high above 
the rest posteriorly. Externally there is a narrow undulating surface for articula- 
tion with the distal end of the fibular tarsal bone. The posterior surface bears two 



BONES OF THE PELVIC LIMB 



135 



tuberosities, of which the outer one is rounded, the inner more prominent and nar- 
rower. 

The first tarsal hone is quadrilateral and small. It articulates with the central 
above, the metatarsus b(>l()w, and the second tarsal in front. 

The second and third tarsals are fused to form a rhoml)oid piece. The proxi- 
mal surface is concavo-convex, and articulates with the central component. The 
distal surface is undulating and rests on the metatarsus. The external surface 
bears a small facet in front for the fourth tarsal component, and the posterior sur- 
face a very small onc^ 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 laterally and is distinctly 



Central 4- fourth tarsal bone 
First tarsal bone 



Proximal sesamoid 



Distal sesamoid 




i Tibial tnrsrd bone 



Second + third tarsal bone 



Fig. 104. — Skeleton of Dist.\l Part of Left Hind Li.mb of Ox, Internal View. 
54, Tuber ealcis; ;?.5, large metatarsal bone; 30, first phalanx; 37, second phalanx; 3;?, third phalanx, (.\fter 

EUenberger-Baum, Anat. fiir Kiinstler.) 



four-sided. The groove on the anterior surface is deep and wide. The posterior 
surface is marked by variable grooves. The upper 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 postero-internal 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 Avith the large 
metatarsal bone. 

The large metatarsal bone is usually regarded as consisting of the fused third and fourth 
metatarsal bones. The medullary cavity is subdivided like that of the large metacarpal bone 
borne anatomists, however, consider that the ridges at the upper end of each border represent the 
seconcl and htth metatarsals (Rosenberg and Retterer). On this basis the small bone would be 
the hrst metatarsal. 



136 



SKELETON OF THE PIG 



The phalanges and sesamoids reseml^Ie those of the thoracic limb so closely 
as to render separate description unnecessary. 



SKELETON OF THE PIG 
VERTEBRAL COLUMN 
The vertebral formula is C,T,,_,,LR-7S,CVon-o-,- 

7 1 1 1 o b 7 4 *' J U _' J 

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 
are slightly concave. A ventral crest is not present. The arches are wide from 
side to side, but the laminse are narrow, so that a considerable interval (Spatium 
interarcuale) separates adj acent arches dorsally. The pedicles are perforated by a 
foramen on either side in addition to the usual intervertebral foramina. The 




Fig. 105. — Skeleton of Pig, Later.^l View. 
a, Cranium; b, upper jaw; c, lower jaw; 1H.-7H ., cervical vertebra^; IR.w., first thoracic vertebra; 13^ 
R.W., thirteenth thoracic vertebra (next to last); IL., first lumbar vertebra; 6L., sixth lumbar vertebra (next 
to last usually); K., sacrum; S., coccygeal vertebra; IR., first rib; 14R-, last rib; R.kn., costal cartilages; St., 
sternum; d, supraspinous fossa of scapula; d' , infraspinous fossa; 1, spine of scapula; 2, neck of scapula; e, 
humerus; 3, head of humerus; 4, tuberosities of humerus; 5, deltoid tuberosity; 6, external epicondyle of 
humerus; /, radius; g, ulna; 7, olecranon; h, carpus; lS-25, carpal bones; i~i"" , metacarpus; k-k"" , proximal 
phalanges; l-l"", middle phalanges; jn—m"", distal phalanges; n, o, sesamoids; p, ilium; 8, external angle of 
ilium (tuber coxte); 9, internal angle of ilium (tuber sacrale); 10, superior ischiatic spine; q, ischium; 11, tuber 
ischii; r, pubis; 12, acetabulum; s, femur; IS, trochanter major; 14, trochanter minor; 15, external epicondyle; 
t, patella; u, tibia; 16, crest of tibia; 17, external condyle of tibia; v, fibula; w, tarsus; 26-31, tarsal bones; 
26', tuber calcis. (After Ellenberger, in Leisering's Atlas.) 



transverse processes divide into two branches, both of which increase in size from 
the third to the sixth. The upper branch projects outward and backward; it 
is short and is thickened at its free end. The lower branch is a quadrilateral plate 
directed ventrally; each overlaps the succeeding one to a small extent, and the 
series forms the lateral boundary of a deep and wide groove beneath the bodies. 
The spines increase in height from the third to the last; the anterior ones are in- 
clined backward, the posterior ones forward. 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 flatness of the body, which bears a pair of 



VERTEBRAL COLUMN 



137 



small facets on its posterior margin for the heads of the first ribs. It has foramina 
transversaria, and usually two foramina in either side of the arch. 

The dorsal arch of the atlas bears a large tuberosity'. The ventral tubercle is 
long, compressed laterally, and projects back under the axis. The wing is flattened 
and bears a posterior tuberosity. The foramen transversarium passes through the 
posterior border of the wing to the fossa under the latter, and is not visible dorsally; 
it is sometimes very small or absent. The sides of the vertebral foramen bear 
two lateral projections which partially divide it into a ventral narrow part, which 
receives the odontoid process, 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, wdiich is directed upw'ard and backward. 
The odontoid process is a thick cylindrical rod. The transverse process is verj^ 
small and the foramen transversarium is often incomplete. 

The thoracic vertebrae are often fifteen in number. Their bodies are relatively 
long, constricted in the middle, and without ventral crests. Their extremities are 




Fig. 106. — Atl.\s of Pig, Dors.\l View. 

«, Wing; b, ventral tubercle; c, foramen tran.sver- 
sarium; (/, alar foramen; e, intervertebral foramen; /, dor- 
sal tuberosity; g, articular surface corresponding to that of 
posterior articular process of typical vertebra; h, facet on 
ventral arch for odontoid process. (EUenberger-Baum, 
Anat. d. Haustiere.) 




Fig. 107. — Axis of Pig, Lf.ft L.\ter.\l View. 
a, Odontoid i)rocess (dens); b, .spinous process; 
c, anterior articular jsrocess; cl, posterior articular pro- 
cesses; c, transverse process; /, foramen transversar- 
ium; !j, bar of bone which bounds h. intervertebral 
foramen; i, vertebral foramen. (Ellenberger-Baum, 
Anat. d. Haustiere.) 



elliptical, depressed in the middle and prominent at the periphery. The arch is 
perforated by a foramen on either side, and in most of the series there is also a 
foramen in the posterior part of the root of the transverse process which communi- 
cates with the former or with the posterior intervertebral foramen. Sometimes 
there is a foramen in the anterior 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 transverse 
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 diminish 
very gradually in length to the tenth, beyond which they are about equal. The 
second 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. 



138 



SKELETON OF THE PIG 



The occurrence of fifteen thoracic vertebra? appears to b(> quite common, and some observers 
have recorded the existence of sixteen and even seventeen; a reduction to thirteen is rare. 

The lumbar vertebrae are six or seven in number. The iDodies 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- 
men in the posterior part. The spines 
are broad and incline forward, with the 
exception of the last, which is narrow 
and vertical. 

Lesbre states that six and seven lumbar 
vertebrae occur with almost equal frequency. 
The number may be reduced to five, and the 
munber 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 absent, excepting 
small rudiments on the last two seg- 
ments. 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 superior sacral fora- 
mina, and tubercles which indicate the 
fused articular processes. The wings re- 
semble 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 
and diminish very gradually. 

The numerical variation here is twenty to twenty-six according to the observation of several 
anatomists. Lesbre states that he has found twenty-three most frequently. 

Curves. — The cervical region is practically straight. The thoracic and lumliar 
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 pronounced as in the 
ox, and the sacral curve is flatter. 




Fig. 108. — Sacrum of Pig, Dorsal View. 
a. Wing; b, dorsal sacral foramina; c, arfieular 
process; I-4, segments or sacral vertebrae. (EUen- 
berger-Baum, Anat. d. Haustiere.) 



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 



THE STERNUM BONES OF THE SKULL CRANIUM 



139 



breeds, so that there is a fairly cUstinct angle, except toward the end of the series. 
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 tuberosity fuses 
with the head on the last five or six. The second to the fifth form diarthrodial 
joints with their cartilages, which are wide and plate-like. 



THE STERNUM 

The sternum consists of six segments and resembles that of the ox in general 
form. The first segment (Manubrium) is long, flattened laterally, 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, which are not com- 
pletely fused in the adult. The last segment has a long narrow part which bears 
the xiphoid cartilage. 

The thorax is long and is more Imrrel-shaped than in the horse or ox, since the 
ribs are more strongly curved and differ less in relative length. 



Occipital 
bnne 



Parietal 
bone 



Frontal 
bone 



Supraorbital 
process 

Ldcrimal 

foramina Lacrimal 
I bone 

/ N^nsal 

/ Maxilla bone 



Infraorbital 
foramen 



Premaxilla 




Fig. 109. — Skull of Pig, Lateral View without JL\xdible. 
/, Occipital condyle; 2, paramastoid or styloid process; 5, bulla ossea; 4, external auditory meatus, 
5, zygomatic process of temporal bone; 6, sphenoid bone; 7, orbital opening of supraorbital canal; 8, malar 
bone; S, pterygoid bone; iC, pterygoid process of sphenoid; i/, pterygoid process of palate bone; 77-3, incisor 
teeth; C, canine tooth; Pl-4, premolars; Ml-3, molars. 



BONES OF THE SKULL 
Cranium 
The occipital bone has an extensive squamous part or supraocci])ital, which 
forms a very broad and prominent 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 downward, and is continuous with the temporal crest. Two diver- 
gent ridges pass upward from the foramen magnum, and the surface between them 
IS concave and smooth. The greater part of the inner (or anterior) surface of the 
supraoccipital is united with the parietal bones, but a lower concave area faces 



140 



SKELETON OF THE PIG 



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 project almost straight downward. The hypo- 
glossal foramen is at the inner side of the root of the process. The basilar 
part is short and wide; its lower surface bears a thin median ridge and two 
lateral imprints or tubercles which converge at the junction with the sphenoid 
bone. 



Parietal hone 
Temporal fossa 



Squamous temporal 
bone 
External auditory 
meatus 



Zygomatic process 
of temporal bone 
Supraorbital pro- 
cess 
Frontal bone 

Supraorbital fora 

nien 
Zygomatic process 
of malar bone 
Lacrimal bone 



Maxilla 



Infraorbital foramen 

Nasal process of prcmaxiUa 

Nasal bone 

Canine tooth 

Palatine cleft 
Body of prvmaxilla 




Occipital crest 
Temporal crest 
Parietal crest 



Lacrimal foramen 
Preorbital fossa 



\ 

1 




i 




} 

k 


i 


\^v- 




M'.'' 



Fig. 110.— Skui, 



I )oRs.\i> View. 



The interparietal fuses before l)irth with the occipital. The tentorium osseum 
is absent. 

The parietal is overlapped by the occipital bone behind and concurs in the 
formation of the occipital crest. Its external surface is divided by the parietal 
crest into two parts. The inner part (Planum parietale) faces upward and forward, 
and is flattened and smooth. Its inner border is short and straight and unites early 
with the opposite l)one. Its anterior border is concave and joins the frontal bone. 
The outer part (Planum temporale) faces outward and is more extensive; it is 
concave, forms a large part of the temporal fossa, and is overlapped below by the 
squamous temporal. The parietal crest extends in a curve from the occipital crest 



CRANIUM 



141 



forward and outward to the supraorbital process. The internal surface is concave 
and is marked by digital impressions. The lower border projects into the cranial 
cavity and forms a crest which separates the cerebral and cerebellar compartments 
laterally. The interior forms part of the frontal sinus in the adult. There is no 
parieto-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 upper part of 
the inner wall of the latter. The supraorbital 
process is short and Ijlunt-pointed, and is not 
connected with the zygomatic arch. The gap 
in the orljital margin is closed by the orljital 
ligament in the fresh state. The orbital part 
is extensive and forms the greater part of the 
inner wall of the orbit. Its upper part is per- 
forated by the orbital orifice of the supraorbital 
canal, in front of which is the distinct fovea 
trochlearis. The ethmoidal or internal orbital 
foramen is situated in the lower part near the 
junction with the orbital wing of the sphenoid. 
The temporal part is very narrow and is se])ar- 
ated from the orbital plate by a ritlge which 
joins the 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 confined to the 
anterior part and the rest of the bone is thick. 

The temporal bone has a general resem- 
blance to that of the ox. The zygomatic pro- 
cess is short and stout and is bent at a right 
angle. The upper Ijorder of the process is thin ; 
traced from before backward it curves sharply 
upward and forms a high prominence in front 
of the external auditory meatus; beyond this 
it drops rather abruptly and is then continued 
upward to the occipital crest. The anterior 
part of the lower border joins the zygomatic 
process of the malar, which is deeply notched. 
The condyle is concave in the transverse direc- 
tion. The postglenoid process is absent, but 
the articular surface is bounded behind and in- 
ternally by a crest. There is no parieto-tem- 
poral canal. The external auditory canal is very 

long and is directed upward and outward. 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 
depression in front of the root of the paramastoid process, and the stylo-mastoid 
foramen is immediately external to it. The petrous part presents no important 
differential features. 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 




Fig. 111. — Basal Surface of Skull of 
Young Pig, without the Mandible. 
Sq.o., Supraoccipital; E.o., exoccipital; 
B.O., basioccipital; B.s., body of sphenoid; 
ti(j., squamous temporal bone; V, vomer; Mx., 
maxilla; Pa., horizontal part of palate bone; 
P.p., palate process of maxilla; Z., malar bone; 
J, premaxilla; D.c, canine tooth; Jl~3, in- 
cisor teeth; O, temijoral fossa; 1 , occipital crest; 
2, for. magnum; 3, occipital condyle; 4< para- 
ma.stoid (styloid) process; 6, bulla ossea; 6, 
for. lacerum basis cranii; 7, pterygoid process 
of sphenoid; 8, posterior nares; 9, anterior 
palatine foramen; 70, palatine cleft. (Struska, 
Anat. d. Ilaustiere.) 



142 SKELETON OF THE PIG 

is narrow. The pituitary fossa is very deep, and is limited behind In^ a prominent 
dorsum sellse; the dorsum bears lateral projections, the posterior clinoid processes. 
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 l)ones in the formation of the pterygoid fossa, which 
opens backward and is not present in the horse or ox. The sphenoidal sinus is 
very large and occupies the body, the temporal wings, and a great part of the ptery- 
goid processes in the adult; it is continued into the temporal bone 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 endoturl^inals and eighteen 
ectoturbinals (Paulli). The lamina papyracea concurs in the formation of the 
ptery go-palatine fossa. 

Face 

The maxilla is extensive. Its external 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 and 
is situated above the third or fourth cheek tooth. The alveolus for the canine 
tooth produces a ridge at the anterior end which is very pronounced in the boar. 
The facial crest extends forward from the root of the zygomatic process and fades 
out behind the infraorbital foramen; in some specimens it is prominent and thin- 
edged, in others it is rounded and projects little. The zygomatic process is short 
but stout and buttress-like; it is overlapped externally by the malar. The maxil- 
lary 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 trans- 
verse ridges 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 infraorbital 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 
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 upper border forms a very long suture with the nasal ])one, and the 
lower articulates to about the same extent with the maxilla. The palatine fissure 
is relatively wide. 

The horizontal part of the palate 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 externally by the maxilla and concurs in 
forming part of the palatine canal. Superiorly the two plates separate and inclose 



FACE 143 

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 (Lamina 
transversalis), which divides the posterior part of the nasal cavity into an upper 
olfactory part and a lower respiratory part. 

The pterygoid bone is nearly vertical in direction, and is narrow in its middle, 
wide at each end. The external surface is free below and forms the inner wall of 
the pterygoid fossa. The lower 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 i)ointed and reaches almost as far forward as the premaxilla. 
The facial surface is flattened from side to side. In jirofile it is nearly sti'aight in 
some subjects, variably concave in others. The external border is free to a small 
extent in front only; otherwise it is firmly connected with the premaxilla and 
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 orl^ital 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 
upper border articulates with the frontal only. The bone concurs in the formation 
of th<^ maxillary sinus. 

The malar bone is strongly compressed from side to side. Its facial surface 
is small and presents a fossa which is continuous 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 
external surface is convex and free, and bears a rough eminence in its middle. Its 
internal surface is concave; it is overlapped in front by the maxilla, and in the 
remainder of its extent is free and smooth. The upper 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 zygomatic process of the temporal. (It 
might be regarded as dividing into frontal and temporal branches.) The lower 
border is convex and becomes thinner behind. 

The turbinal bones resemble those of the ox. The superior turbinal is, however, 
relatively Icjnger, less fragile, and more firmly attached to the nasal bone. There 
is no middle turbinal. 

The vomer is very long. The anterior extremity reaches to the body of the pre- 
maxilla or very close to it. The lower border is received into a groove formed bj" 
the nasal crest of the maxillae and palate 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 upper surface is convex and is 
notched at each end. The lateral surfaces are concave, smooth, and converge 
below, forming a grooved lower 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 at the point of divergence of the rami. Above this promi- 
nence is a pair of foramina. The alveolar border presents six alveoli for the in- 
cisor 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 varial^le 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 outer 
surface is strongly convex from above downward. The inner surface is prominent 



144 



SKELETON OF THE PIG 



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 overhang noted above. 
There are seven alveoli for the lower cheek teeth, which increase 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 rela- 
tively wide above. The condyle is convex in both directions, 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 cartila- 
ginous in the young subject 
and does not ossify at either 
end. The great cornu is a 
very slender rod, slightly en- 
larged at either end ; the upper 
extremity is attached to the 
hyoid process of the temporal 
by a rather long and wdde bar 
of cartilage. 




Fig. 112. — Mandible of Pig. 
a, Body of mandible; b, horizontal part of ramus; /, vertical 
part of ramus; c, interalveolar border; c', interval between canine 
and corner incisor; c" , interval between first and second premolars; 
d, mental foramina; e, vascular impression; g, coronoid process; 
h, condyle; i, sigmoid notch; A-, mandibular foramen; 1-7, cheek 
teeth, S, canine tooth; 9, 10, 11, incisors. (Ellenberger-Baum, 
Anat d. Haustiere.) 



THE SKULL AS A WHOLE 

The length and the profile 
contour vary greatly in dif- 
ferent 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 semi-feral pigs, 
and exists also in the improved breeds during extreme youth. IVIost of the latter are 
decidedly brachyce])halic when fully developed; the face is "dished" in a pro- 
nounced fashion. The frontal region slopes sharply upward, and the nasal region 
is shortened, and in some specimens even distinctly concave in profile. The supra- 
orbital foramina are about midway between the orbital margin and the frontal 
suture. The supraorbital grooves extend forward from the foramina to the nasal 
region and turn outward and downward 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 occipital crest, behind by the temporal crest, in front by the parietal 
crest, and is marked off from the orbital cavity by the supraorl^ital 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 
above and bears a projection below. It curves sharply upward behind and forms 
a pointed recurved projection above and in front of the external auditory meatus. 



THE SKULL AS A WHOLE 145 

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 l:)ones, and is separated by a crest from the temporal fossa. The inner 
wall is perforated above by the orbital opening of the su]iraorbital canal, and l)elow 
by the optic and ethmoidal foramina; on its antero-inferior part is the fossa in 
which the inferior oblique muscle of the eye takes origin. Two lacrimal 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 large foramen 
in the sphenoid (like that of the ox) to the very large maxillary foramen. The pre- 
orbital region is tleeply grooved in its length and is clearly marked o& 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 foramen. There is a ridged 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 paramas- 
toid processes are extremely long, less flattened than in the horse and ox, and nearly 
vertical. At the inner side of the root of each is the hypoglossal 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 laterally, and bears a 
sharp, short, muscular process. The basioccipital is wide and flattened; it bears 
a median crest and two lateral tubercles. The posterior nares are small and are 
wider below than above. On either side of them is the tuberosity of the palate 
bone, and above this is the pterygoid fossa. The palate is remarkably long and is 
relatively narrow. It constitutes about two-thirds of the entire length of the skull. 
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 posterior or nuchal surface is remarkable for its height and the breadth 
of the occipital crest. The central part above the foramen magnum is smooth and 
concave from side to side, and is l)oundecl laterally by ridges, which converge below 
and end on two tubercles at the upper margin of the foramen magnum. The sur- 
face is separated from the temporal fossae by the temporal crests, which curve 
downward and outward and blend with the external auditory canals. The mastoid 
process has the form of a plate which overlaps the root of the paramastoiti 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 fossae are extensive and very oblicjue. 
The floor resembles that of the ox, but the foramen ovale is absent, the dorsum 
sellse is more developed, and the foramen lacerum basis cranii is like that of the 
horse. Two oblique lateral crests clearly mark the limit Ijctween the cerebral and 
cerebellar compartments. The tentorium osseum and the parieto-temporal canals 
are absent. 

The nasal cavity is very long. Its posterior part is divided by a horizontal 
plate into olfactory and respiratory parts. The olfactory part or fundus is above, 
and contains the ethmoturbinals and ethmoidal meatuses. The lower part is 
continuous with the inferior meatus and leads to the pharyngeal orifice; hence it is 
sometimes 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 
10 



146 SKELETON OF THE PIG 

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 subdivided 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 Ijone. 
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 infraorbital 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 by means of a consideral)le orifice. 

The sphenoidal sinus 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 palate bone which com- 
municates with an ethmoidal meatus. 



BONES OF THE THORACIC LIMB 

The scapula is very wide, the index being about 1 :0.7. The spine is tri- 
angular and is very wide in its middle, wdiich 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 an outer rough lip. The vertebral 
border is convex, and the cartilage is not so extensive as in the horse and ox. The 
cervical angle is thin and bent inward a little. The dorsal angle is thick and is 
about a right angle. The neck is wefl defined. The rim of the glenoid cavity is 
rounded and not notched. The tuberosity is just above the antero-internal part 
of the glenoid cavity and bears no distinct coracoid process. 

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 internal surface is extensive and flattened; it is separated from the 
anterior surface by a distinct l^order, and bears no teres tubercle. The musculo- 
spiral groove is shallow. The deltoid tuberosity is small, and there is a larger 
rounded eminence midway lietween it and the external tuberosity. The nutrient 
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 external tuber- 
osity is very large and extends upon the front of the extremity. It is divided into 
two high prominences by a wide deep groove. There is a third eminence below 
and externally for the attachment of the supras]iinatus muscle. The bicipital 
groove is at the front of the inner side ; it is undivided and is almost converted into 
a canal. The outer 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 some- 



BONES OF THE THORACIC LIMB 



147 



( 



times perforated. The proximal end unites with the shaft at three and a half 
5'ears, the distal at one year. 

The radius is short and narrow, but thick. The shaft 
increases in size from above downward. The greater part ^ 

of the posterior surface is in apposition with the ulna; this 
part is marked by a vascular furrow w^hich runs downward 
from the upper interosseous space, and has the nutrient 
foramen at its proximal i.'W'X. The l)icipital tuberosity is 
represented by a rough area. The distal end is relatively 
large. Its carpal surface 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 con- 
siderably heavier than the radius. The shaft is curved. 
The anterior surface is convex and most of it is rough 
and attached to the radius by the interosseous liga- 
ment. There is a smooth area on the upper third, 
which concurs with the radius in forming the upper 
interosseous space, and is marked in its upper part 
by the nutrient foramen. From this space a vascular 
furrow passes downward to the lower part of the shaft, 
where there is often a distal interosseous space for 
the passage of vessels. The internal surface is exten- 
sive, concave, and smooth. The external surface is 
slightly convex, and its upper part is marked by an 
oblique rough line or ridge. The proximal extremity is 
large and is bent inward somewhat; its length is more 
than one-third of that of the entire bone. The distal ex- 
tremity is relatively small; it articulates with the ulnar 
and accessory carpal bones, and is notched in front to 
accommodate the ridge on the radius. The bone contains 
a considerable medullary canal. The bone is consolidated 
at three to three and a half years. 

The carpus comprises eight bones, four in each row\ 
The bones of the proximal row resemble those of the ox, 
with the exception of the accessory, which is more like 
that of the horse, but has no external groove. The first 
carpal is small, elongated 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 below. The third carpal articu- 
lates 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 metacarpals below, and bears 
a tuberosity on its volar aspect. 

Four metacarpal bones are present. The first is 
absent, the third and fourth are large and carry the chief 
digits, while the second and fifth are much smaller and 
bear the accessory digits. Their proximal ends articulate 
Avith each other and with the carpus as indicated above, 
solidated at about two years of age. 



i- » .'/ 



/ -^ 



'h- 



(^ 



Fig. 113. — Skeleton of 

FOEEARM AND MaNUS 

OF Pig, Antero-ex- 

TERNAL View. 

a, Radiu.s; h, ulna; c, 
radial carpal; d, intermediate 
carpal; e, ulnar carpal; /, ac- 
cessory carpal; g, first carpal; 
h, second carpal; i, third car- 
pal; k, fourth carpal; l-o, 
second to fifth metacarpal 
bones; p-s, second to fifth dig- 
its; 1, olecranon; 2, beak of 
ulna (proc. anconeus); 3, semi- 
lunar notch; 4, styloid process 
of ulna; 5, styloid process of 
radius; 6, distal epiphyseal 
lines; 7, first phalan.x; 8, second 
Ijhalanx; 9, third phalanx. 
(Ellenberger-Baum, .\nat. d. 
Haustiere.) 



The bones are con- 



148 SKELETON OF THE PIG 

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 
lower 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 articulate 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. 



BONES OF THE PELVIC LIMB 

The OS coxae is long and narrow. The ilium and ischium are almost in line 
with each other and sagittal in direction. The wing of the ilium bends outward 
much less than in the horse or ox. The gluteal surface is divided into two fossse 
by a ridge, which is continuous with the superior ischiatic spine behind. The 
inner 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 or anterior border is convex, and is thick, rough, and prom- 
inent in'its middle, which forms the highest point of the bone. The internal angle 
is lower than the crest, is directed backward, and articulates internally with the 
sacrum. The external angle is lower still and is very little thickened. The 
ischia in the female are somewhat divergent and flattened behind. The tubera 
are everted and bear three prominences. 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 ridges on its outer 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 coxae are fused by the end of the first year, 
but the crest and the ischial tul^era are partially separate till the sixth or seventh 
year. The symphysis does not usually undergo complete anchylosis. Interischial 
bones are present. 

The inlet of the pelvis is elliptical and very oblique. In a sow of full size the 
conjugate diameter is about five to six inches (10 to 12 cm.) and the transverse 
about three and a half to four inches (ca. 8.75 to 10 cm.). In the female the floor 
is relatively wide and flattened, especially at the outlet, where the tubera are 
everted; it also has a decided downward inclination behind. The pelvic axis 
is therefore 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 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 third 
of the anterior surface. The posterior surface is wide, and is limited outwardly 
by a ridge which extends from the trochanter major to the large external supra- 
condyloid crest. There is no supracondyloid (plantar) fossa. The head is strongly 
curved, and is marked toward the inner side by a rather large depression for the 



BONES OF THE PELVIC LIMB 



149 



attachment of the round ligament. The neck is distinct. The trochanter major, 
although massive, does not extend up as high as the head. The trochanteric 
ridge and fossa resemble those of the ox. The external (third) trochanter is absent. 
The ridges of the trochlea are similar and almost sagittal. 

The shaft of the tibia is slightly curved, convex internally. The tuberosity 
is grooved in front, and a narrow sulcus separates it from the external condyle. 
The facet for the fibula is on the posterior border of the latter, and is bounded 
internally by an eminence. The upper 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 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 externally ; the lower part is narrower 
and thicker. The proximal end is flattened, grooved externally, and articulates 
internally with the external condyle of the tibia. The distal end forms the external 
malleolus. It is grooved 
externally, and articulates 
with the tibia and tibial 
tarsal internally, with the 
fibular tarsal bone dis- 
tally. 

The patella is very 
much compressed laterally 
and presents three sur- 
faces. 

The tarsus comprises 
seven bones. The tibial 
and the fil)ular tarsal re- 
semble in general those of 
the ox. The axis of the 
tibial is, however, slightly 
oblique downward and in- 
ward, and its distal end 
bears a double trochlea for 
articulation with the cen- 
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 posterior 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 
aljove, the third metatarsal below, the second tarsal internally, and the fourth tarsal 
externally. The fourth tarsal is large. Its external face is crossed by an oblique 
groove for the tendon of the peroneus longus. The internal 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 four metatarsal bones r(>soml)!e the corresponding bones of the fore limb, 
but are somewhat longer. The proximal ends of the third and fourth each have a 
considerable projection behind; the process on the third has a facet for articulation 




Fig. 114. — Cox.\l Bones of Pig, Left Posterior View. 
a. Wing, 6, shaft, c, external angle, d, anterior border, e, internal 
angle, /, gluteal line of ilium; g, great sciatic notch; /(, smooth, i, rough 
part of ventral surface of ilium; k, psoas tubercle; /, ilio-pectineal emi- 
nence; m, acetabular branch, n, symphyseal branch of pubis; o, obtur- 
ator foramen; p, p', ischium; q, q', tuber ischii; r, symphysis; s, ischial 
aich; t, t', superior ischiatic spine; n, acetabulum; r, epiphyseal line. 
(Ellenberger-Baum, Anat. d. Haustiere.) 



150 SKELETON OF THE DOG 

with a discoid sesamoid bone. The second and fifth are placed more on the pos- 
terior aspect of the large l)ones 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 CjTj3L7(g)S3Cy2Q_^3. 

The cervical vertebrae are relatively longer than in the ox and the pig. The 
bodies of the typical vertebra 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 upper 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 downward 
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 directed down- 
ward and outward and ridged on its inner 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 transverse 
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 upper surface of the dorsal arch is strongly 
convex and rough centrally. The wings are wide, flattened, and almost horizontal. 
The upper surface is rough. There is an alar notch (Incisura alaris) on the anterior 
border instead of the anterior foramen. The foramen transversarium is present. 

The l)ody of the axis is flattened dorso-ventrally, especially in front. The 
odontoid process 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 inferior surface is wide, and is divided 
by a median crest into two fossae. The transverse processes are single, pointed, 
directed backward and outward, and perforated by relatively large foramina 
transversaria. The spinous process is thin and of moderate height, but very long; 
it is prolonged forward so as to overhang the dorsal arch of the atlas, and is ter- 
minated l)ehind by a tuberosity which is connected by two crests with the posterior 
articular processes. The anterior notches are large and are never converted into 
foramina. 

The ])odies of the thoracic vertebrae are wide and compressed dorso-ventrally, 
especially at each end of the region. Their convex 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. The last three have acces- 
sory processes also. The first three or four spinous processes 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. 



VERTEBRAL COLUMN 



151 



The bodies of the 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 




Fig. 115.^ — Skeleton of Dog, Lateral View. 
a, Cranium; b, face; c, mandible; 1H-7H, cervical vertebrae; ISB, last thoracic vertebra; 1L-7L, lumbar 
vertebrae; K, sacrum; iS, coccygeal vertebrse; 1R-13R, ribs; R.kn., costal cartilages; St., .«ternum; d, scapula; d', 
supraspinous fossa; d", infraspinous fossa; i, spine of scapula; ;2, acromion; S, tuberosity of scapula; 3', articular 
end of scapula; e, humerus; -^, head of humerus; 5, external tuberosity of humerus; 5', deltoid ridge; 6, 6', epicon- 
dyles of humerus; 7, external condyloid crest; 7', coronoid fossa; /, radius; g, ulna; 8, olecranon; 9, "beak" of 
ulna; /i, carpus; /', metacarpus; A', proximal phalanges; Z, middle phalanges; »;, distal phalanges; n, sesamoid; p, 
ilium; 10, wing of ilium; 11, shaft of ilium; 12, crest of ilium; 13, external angle of ilium (tuber coxa;); 14, inter- 
nal angle of ilium (tuber sacrale); 75, superior ischiatic spine; q, pubis; r, ischium; 7&, tuber ischii; 77, acetabulum; 
S, femur; IS, head of femur; 19, trochanter major; 20, trochanter minor; 21, trochanter tertius; 22, 23, con- 
dyles; 24, 25, epicondyles; 26, trochlea; t, patella; u, tibia; ^, tuberosity of tibia; 28, 29, condyles of tibia; 
SO, internal malleolus; v, fibula; 31, external malleolus; 32, head of fibula; w, tarsus; x, metatarsus; ?/, phal- 
anges; S3, occipital bone; 34, paramastoid (styloid) process; SB, parietal bone; 36, frontal bone; .37, lacrimal 
bone; 38, malar bone; 39, squamous temporal; 40, maxilla; 40' , infraorbital foramen; 4'i , premaxilla; 42, 
nasal bone; 4^, external auditory meatus; 44. canine tooth; 45, masseteric fossa; 46, angular process of man- 
dible. (After Ellenberger, in Leisering's Atlas.) 



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 vertebriE. It is short, 
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 



152 



SKELETON OF THE DOG 



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 




Fig. 116. — Atlas of Dog, Viewed from Above and 
Behind. 
a. Wing; h, dorsal arch and tubercle; c, ventral 
tubercle; d, intervertebral foramen; e, foramen trans- 
versarium; /, articular surface for axis. (Ellenberger- 
Baum, Anat. d. Hundes.) 




Fig. 117. — Axis of Dog, Left Lateral View. 
a. Odontoid process; h, articular surface for atlas; 
<:, transverse process; d; foramen transversarium; rf', pos- 
terior opening of d; e, spine; /, posterior articular pro- 
cess. (EUenberger-Baum, Anat. d. Hundes.) 



facets which face upward and inward. 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 developed articular processes at 
each end. Behind this the posterior 
pair quickly disappears, and the an- 
terior ones become non-articular and 
gradually reduced in size. The trans- 
verse processes of the first five or six 





Fig. 118. — Sixth Cervical Vertebra of Dog, Left 
View. 
a, Ventral plate, 6, lateral part of transverse 
process; c, foramen transversarium; d, anterior artic- 
ular process; /, accessory process; g, spinous process; 
A, articular head of body. (Ellenberger-Baum, Anat. 
d. Hundes.) 



Fig. 119. — Fourth Thoracic Vertebra of Dog, Left 
View. 
a. Head; h, glenoid cavity; c, facet for head of 
rib; d, transverse process; e, facet for tubercle of rib; 
/, mammillary process; g, posterior articular process; 
h, spinous process. (Ellenlierger-Baum, .\nat. d. 
Hundes.) 



are relatively large; behind this they quickly disappear. Haemal arches (or 
chevron bones) in the form of a V or Y occur ventrally at the intercentral 
junctions of the third, fourth, and fifth usually. They transmit the middle 
coccygeal artery, which passes between pairs of ventral tubercles further back. 



THE RIBS — THE STERNUM — BONES OF THE SKULL 



153 



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-coccygcal region is somewhat S-shaped. 

Variations. — Numerical variations are not common except in the coccygeal 
region. The number of thoracic vertebrae may be twelve or fourteen, with or 
without compensatory change in the luml)ar region. Girard recorded a case with 
eight lumbar and the usual number of thoracic vertebrae. Six lumbar with fourteen 
thoracic vertebrae have been met with. The first coccygeal sometimes unites 
with the sacrum. 

THE RIBS 

Thirteen pairs of ril)s are present, of which nine are sternal anfl 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. The last rib is usually floating. 





Fic. 120. — Fourth Lumbar Vertebra of Dog, Left 
View. 
a, b, Articular surfaces of body; c, transverse 
process; cl, accessory process; e, anterior articular pro- 
cess; e', mauimillary process; /, posterior articular pro- 
cess; g, spinous process. (Ellenberger-Baum, Anat. d. 
Hundes.) 



Fig. 121. — Sacrum of Dog, Dorsal View. 

o. Dorsal sacral foramina; b, articular surface 
of body of first segment; c, d, anterior articular pro- 
cesses; e, wing; /, rudiments of articular processes; 
g, lateral part; h, spinous processes. (Ellenberger- 
Baum, Anat. d. Hundes.) 



The costal cartilages are long and curve forward; the length and curvature of 
the first pair is a striking special feature. 

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 

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. 



154 



SKELETON OF THE DOG 



Cranium 
The occipital bone is similar in position to that of the horse. The crest is 
prominent, anguhir, and directed baclvward. Just below the crest are two rough 




Fig. 122. — Base or Skull of Dog, without Mandible. 
/, Occipital; //, tymiianic part of temporal; 11a, squamous part of temporal; Ilh, mastoid part of tem- 
poral; ///, sphenoid; IV , pterygoid; T', palate bone; VI, vomer; VII. malar; ^'III, zjgomatic arch; IX, inner 
wall of orbit; A', palatine process of inaxilla; A'7, premaxilla; XII, orbital cavity; 1,1, tubercles above foramen 
magnum; 2, foramen magnum; 3, occipital condyle; 4. notch between occipital condyles; 5, condyloid fossa; 
6, hypoglossal foramen; 7, paramastoid (styloid, jugular) process; 8, for. lacerum and posterior opening of carotid 
canal; 9, petro-occipital synchondrosis; 10, petro-tympanic fissure; 11, tubercle; 12, bulla ossea; 13, muscular 
process of petrous; 14, carotid foramen; Id, osseous Eustachian tube; 16, postglenoid process; 17, glenoid 
cavity; 18, for. ovale; 19, posterior opening of alar canal; 20, external opening of parieto-temporal canal; 21, 
stylomastoid foramen; 22, external auditory meatus; 23, temporal crest; 24, zygomatic process of temporal 
bone; £5, body of postsphenoid; 26, body of presphenoid; 27, anterior opening of alar canal; 28, for. lacerum 
orbitale; 29, optic foramen; SO, hamulus of pterygoid; 31, horizontal part of palate bone; 32, perpendicular 
part of palate bone; 33, median palatine suture; 34, palato-maxillary suture; 35, posterior nasal spine; 36. 
anterior palatine foramen; 37, palatine groove; 3S, alveolar border of maxilla; 39, palatine process of maxilla; 
40, pterj'goid process of maxilla; 41, palatine fissure; 4^, body of premaxilla; 4'3. palatine process of premaxilla; 
.^^, alveolar border of premaxilla; .^5, supraorbital process of frontal bone. (Ellenberger-Baum, Anat. d. Hundes.) 



imprints or tubercles for muscular attachment. The surface below these is convex 
from side to side and concave from above downward. On either side, at the junction 



CRANIUM 



155 



with the squamous, there is a foramen which communicates with the parieto- 
temporal canal. The condyles are somewhat flattened and are widely separated 
above; at the inner side of each 
is a short condyloid canal, which 
opens into the parieto-temporal 
canal. The paramastoid processes 
are very short. The basilar part 
is wide and joins the bulla ossea on 
either side; its lower 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 liulla ossea, behind and 
internally by the occipital bone. 

The interparietal bone fuses 
with the occipital before birth. 
It forms the high posterior part of 
the sagittal crest, and is wedged in 
between the two parietal bones. 
The tentorium osseum is thin and 
curved, concave ventrally. Its base 
concurs with the occipital and parie- 
tal bones in the formation of a trans- 
verse canal which is continuous with 
the parieto-temporal canals. 

The parietal bone is rhoml^oid 
in outline and is strongly curved. It 
is extensive 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 sagittal 
crest which is continued upon the 
frontal bones. The lower border 
articulates with the temporal wing 
of the sphenoid by its anterior part 
and with the squamous temporal in 
the remainder of its extent. The 
external surface enters into the for- 
mation of the temporal fossa. The 
internal 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 sagittal crest to the 
supraorl)ital 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 orl)ital margin 
is incomplete as in the pig. The supraorbital foramen is absent. In front there 




Fig. 123. — Skui.l of Dog, Dorsal View. 
/, Occipital; //, parietal; ///, frontal; IV, lacrimal; 
V, malar; 1'/, squamous temporal; VII, nasal; VIII, max- 
illa; IX, premaxilla; 1, supraoccipital; 2, interparietal; S, 
parieto-occipital suture; 4, occipital crest; 6, sagittal crest; 
6, parieto-frontal suture; 7, squamous suture; S, parietal emi- 
nence; 9, antero-external angle of parietal bone; 10, frontal 
crest; 11, 14, orbital margin; 12, supraorbital process; 13, 
frontal fossa; lo, temporal part of frontal bone; 16, nasal 
process of frontal bone; 17, frontal suture; IS, lacrimal fora- 
men; 19, maxillary process of frontal bone; 20, lacrimo-maxil- 
lary suture; 21, frontal process of malar bone; 22, lacrimal 
process of malar; 23, zygomatic process of malar; 24, zygo- 
matic process of squamous temporal; 24', posterior end of 
nasal bone; 25, nasal suture; 26, anterior end of nasal bone; 
27, infraorbital foramen; 23, canine tooth; 29, cheek tooth; 
30, frontal process of maxilla; 31, body, 32, nasal process, 
33, palatine process of premaxilla; 34, palatine fissure; 35, 
incisor teeth. (EUenberger-Baum, Anat. d. Hundes.) 



156 



SKELETON OF THE DOG 




is a narroAv 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 below and articulates 
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 parieto-temporal canal. There is no condyle. The mastoid part 
is small, but bears a distinct mastoid process. The external auditory meatus is 
large and the canal very short, so that one can see into the tympanum in the dry 
skull. The bulla ossea is very large and is rounded and smooth; the inner side 
is united to the basioccipital. Above this junction and roofed in by the union 

of the petrous part and the basi- 
/ occipital is the petro-basilar 

canal (Canalis petrobasilaris) ; 
this transmits a vein from the 
floor of the cranium to the 
foramen lacerum posterius. 
The latter is in reality a de- 
pression and is situated behind 
the bulla ossea. In its pos- 
terior part is a foramen which 
transmits the ninth, tenth, and 
eleventh cranial nerves. The 
carotid canal branches off from 
the petrobasilar, passes forward 
external to it through the inner 
part of the bulla ossea, and 
opens in front at the carotid 
foramen; it transmits the in- 
ternal carotid artery. The Eu- 
stachian opening is immedi- 
ately external 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 inner sur- 
face presents a deep floccular 
fossa alcove the internal auditory 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 sella turcica 
is shallow, but the dorsum selUp is well developed and bears posterior clinoid 
processes. A pair of anterior clinoid processes project back from the roots of the 
orbital wings. The latter are relatively small and are crossed externally by a 
crest, which is continued forward upon the palate bone. The temporal wings are 
extensive and articulate above with the parietals. Perforating the roots of the 
wings are the following foramina, named from before backward: The optic passes 
through the orbital wing. The foramen lacerum 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 



Fig. 124. — Cranial Cavity of Dog. as Seen on Sagittal Sec- 
tion OF Skull. 
/, Roof of cranium; //, base of cranium; ///, posterior wall 
of cranium; IV, anterior wall of cranium; A, anterior cranial fossa; 
B, middle cranial fossa; C, posterior cranial fossa; a, body of pre- 
sphenoid; a', body of postsphenoid; c, palate bone; d, vomer; e, 
occipital; /, occipital condyle; g, sagittal crest; h, frontal sinus; 
h', cranial plate of frontal bone; i, cribriform plate of ethmoid bone; 
i', ethmoidal foramen; k, ethmoturbinals; I, parietal bone; l', I", 
squamous temporal bone; I'", temporal wing of sphenoid bone; 
m, sella turcica; m' , ilorsum sella; n, optic foramen; o, foramen 
lacerum orbitale; p, foramen rotundum; q, foramen ovale; r, ?•', 
carotid foramina; s, tentorium osseum; t, foramen lacerum; u, u' , 
orifices of parieto-temporal canal; i% condyloid canal; w, canal for 
trigeminal nerve; x, internal auditory meatus; y, y' , orifices of canal 
for inferior occipital sinus; z, floccular fossa. (After Ellenberger, 
in Leisering's Atlas.) 



FACE 157 

foramen ovale is near the posterior l)or(l(n- of the temporal wing. There is no 
sphenoidal sinus. 

The ethmoid bone is highly developed. The cribriform plate is extensive, 
and the olfactory fossse are very deep. The crista galli is little developed, and often 
incomplete. The perpendicular plate is long. The lateral masses are greatly 
developed and bulge upward into the frontal sinus. There are four large endo- 
turbinals and six ectoturbinals. The lamina papyracea is extensive and forms 
the inner wall of the maxillary sinus. Its lower border joins the palatine process 
of the maxilla and the horizontal part of the palate bone. A shelf-like plate extends 
inwartl from its lower part and concurs with the similarlj^ incurved part of the 
palate bone in forming the transverse lamina (Lamina transversalis), which divides 
the olfactory fundus of the nasal cavity from the naso-pharyngeal meatus. 

Face 

The maxilla is short, Init 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 
l)one, 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 
outwardly by the malar, and is perforated by a number of foramina (Foramina 
alveolaria). A maxillary tuberosity is not present in the adult, but there is a 
pointed projection, the pterygoid process, behind the last alveolus. The internal 
surface bears a short turbinal crest on its anterior part, behind which it is deeply 
concave and forms the outer wall of the maxillary sinus. The palatine process is 
short, wide behind, and moderately arched from side to side. The anterior palatine 
foramen is situated at or close to the transverse palatine suture about midway 
between the median suture and the alveolar border. The palatine groove is 
distinct. 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 
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 inner 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 
processes of the maxillae, and supports the end of the vomer. The palatine fissure 
is short but wide. 

The horizontal part of the palate bones is extensive, forming about one-third 
of the hard palate. It presents a variable number of lesser palatine foramina. 
There is usually a pointed posterior nasal spine 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 external surface is chiefly free and forms most of 
the inner wall of the large pterygo-palatine fossa. The maxillary 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 



158 



SKELETON OF THE DOG 



cavity. The posterior palatine and spheno-palatine foramina are situated further 
back and a Uttle lower; the former is immediately below the latter. A horizontal 
plate extends from the inner surface, meets that of the opposite bone and com- 
pletes 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 
of the lateral boundaries of the posterior nares. The lower and posterior JDorders 
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 external surface is variably concave in its length and is inclined toward the 
median suture so as to form a central groove. The inner 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 lacri- 
mal canal. 

The large zygomatic process con- 
stitutes the bulk of the malar bone. 
It is very long and is strongly curved. 
The upper 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 emi- 
nence, 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 
upward and fitting in l)etween the lacri- 
mal and maxilla, and a maxillary pro- 
cess directed downward. The facial 
surface is convex. 

The superior turbinal bone is in its 

anterior part a simple plate, attached 

by one edge to the nasal bone ; it curves downward and inward, and its free border 

is thickened and everted. The posterior part is wider and resembles the ethmo- 

turbinals, with which it is connected. 

The inferior turbinal 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 (Fig. 373). 

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 outw<ard and join 
the palate bones and assist in forming the lamina transversalis. 

The two halves of the mandible do not fuse completely even in old age. 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 down- 
ward and backward. There are usually two or more foramina on the mental 
surface. The rami diverge less than in the pig. The inferior border of the hori- 
zontal part is convex in its length and is thick and rounded. The alveolar border 
is slightly concave in its length and is a little everted, especially in its middle; 




Fig. 125. — Mandible of Dog, Right Anterior View. 
a, Right ramus; 6, left ramus; c, body; d, alveolar 
border; e, processus angularis; /, condyle; g, coronoid 
process; h, masseteric fossa; ;', k, crests which form the 
upper and lower boundaries of fossa; /, mandibular fora- 
men; m, mental foramina; n, masseteric line; o, sigmoid 
notch. (EUenberger-Baum, Anat. d. Hundes.) 



THE SKULL AS A WHOLE 159 

it presents seven alveoli for the lower che(>k 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 mental foramina on either side. The vertical part is 
relatively small. Its external surface presents a deep masseteric fossa which 
encroaches on the coronoid process and is limited by ridges in front and below. 
The internal surface is convex and is marked by the usual foramen. At about the 
same level as the latter is the rough angular process (Processus angularis), which 
projects 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 inner part of the articiilar surface is much the wider and extends 
over the posterior surface. Its long axis is a little oblique, the inner end being 
inclined somewhat downward and forward. The coronoid process is verj^ 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 
permanently 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 
compressed 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 l^reeds of dog 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., l)ull(log, small spaniels, pugs) have 
very l)road, short skulls and are termed brachycephalic. Intermediate forms 
(e. g., fox terrier, dachshund) are mesaticephalic. 

The length is usually measured from the occipital crest to the anterior end of the premaxil- 
lary suture, and the breadth between the summits of the zygomatic arches. The cephalic index 
is the relation of the breadth to the length, assuming the latter equal 100; the formula is: 

.^ n — — = cephalic index. The index of extreme dolichocephalic breeds is about 50 or 

length 
even less, as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in 
the bulldog and pugs. 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 from the occipital crest to the fronto-nasal suture 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 superior surface shows the wide outw^ard curve of the zygomatic arches, 
and the great extent of the temporal fosssD. The latter are separated by the sagittal 
crest, which in the larger breeds is very strong and prominent, and is continued by 
the diverging frontal ridges 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 
])rachycephalic l)reeds the differences are very striking. The cranium is strongly 
convex in both directions and is considerably longer than the face. The sagittal 
crest is more or less effaced and is formed by the interparietal only. The parieto- 
frontal crests are separated by an interval behind and diverge to the supraorbital 
processes, so that the temporal fossse 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 marked 



160 



SKELETON OF THE DOG 



depression at the fronto-nasal junction, producing what is termed Ijy fanciers 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 pro])er and the extensive pterygo-palatine fossa. The 
preorbital region is somewhat triangular, concave in its length, and convex from 
above downward. The infraorbital foramen is on its lower part above the third 
cheek tootli In extreme brachycephalic breeds the orbit is relatively very large 

and the preorl)ital region 
extremely short but high. 
In the Ijulldog the lower 
jaw protrudes beyond the 
upper — a condition known 
as prognathism. The op- 
posite condition, brachy- 
gnathism, is seen in the 
dachshund. 

Striking features on 
the basal surface of the 
cranium are the width and 
flatness of the basioccipi- 
tal, the small size of the 
paramastoid processes, the 
large size and rounded 
shape of the bulla ossea, 
and the grooved form of 
the articular surfaces for 
the mandible. The pos- 
terior nares are long and 
narrow and are not divided 
by the vomer. The hard 
palate is usually about half 
the length of the skull. It 
is commonly marked by 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 
degrees; it is smallest in the greyhound, largest in extreme brachycephalic tyi^es, 
e. g., bulldog, pug. 

The posterior or nuchal surface is somewhat triangular, with the base below. 
The summit is formed by the occipital crest, which projects very strongly backward 
in the large breeds. Below it there are two very distinct rough imprints for 
muscular attachment. In somp skulls there is a thin median crest, in others a 
rounded elevation. Laterally are the temporal crests and the mastoid processes. 




Fig. 126. — Skull of Brachycephalic Dog, Dorsal View without 
Mandible. 



THE SKULL AS A WHOLE 



161 



There is usually a foramen in the temporo-occipital suture above the root of the 
paramastoid process. The foramen magnum varies greatly in form; most often 
the transverse diameter is the greater, Ijut in some skulls it is equaled or exceeded 
by the vertical diameter. 

The cranial cavity (Fig. 124) corresponds in form and size with the cranium, 
specially 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 olfactory fossa? are very deep and the crista galli is little 
developed. The sella turcica is variable in depth, and tlie dorsum sella? is relatively 
liigh and bears clinoid i:)rocesses laterally. The cerel)ral and cerebellar compart- 
ments are well marked off laterally by the petrosal crests and al)ove by the ten- 
torium osseum. The base of the latter is traversed by a canal which connects 
the two parieto-temporal canals. The anterior angle of the petrous temporal is 
perforated by a canal for the fifth cranial nerve. 

The nasal cavity (Fig. 373) conforms to the shape of the face. Its anterior 




Fig. 127. — Ski'll of Brachyceph.\lic Dog, L.\ter.\i^ ^'IF.w withol't M.^ndible. 



aperture is large and nearly circular in most dogs. The complex inferior turlnnals 
occupy the anterior part of the cavity to a large extent, except near the aperture. 
Behind the inferior turbinals is the large opening of the maxillary sinus. Behind 
this the cavity is divided by a horizontal plate (Lamina transversalis) into a large 
upper olfactory region or fundus nasi and a lower naso-pharyngeal canal. The 
fundus is occupied largely ])y the ethmoturliinals. The posterior nares are undi- 
vided 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 superior ethmoidal meatus. 
The sinus is very small in extreme l^rachycephalic 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 
internally by the lamina papyracea of the ethmoid, and its outer wall is 
crossed obliquely by the lacrimal canal. The roots of the molar teeth do 
not project up into it. 
11 



162 



SKELETON OF THE DOG 



BONES OF THORACIC LIMB 

The clavicle is a small, thin, irregularly-triangular bony or cartilaginous plate. 
It is embedded in the mastoido-humeralis 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 external surface into two nearly 
equal fossse. 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. The rough area above it for the attachment of the serratus magnus 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 
cervical angle is rounded. The dorsal angle is thick and square. The neck is well 
defined and bears a rough eminence posteriorly. The glenoid cavity is continued 





Fig. 128. — Right Scapula of Dog, External View. 
a, Supraspinous fossa; 6, infraspinous fossa; 
c, spine; d, upper broad end of spine; e, aeroijiion; 
/, glenoid cavity; g, tuberosity; /(, vertebral border; 
i, posterior angle; k, scapular notch. (Ellenberger- 
Baum, Anat. d. Hundes.) 



Fig. 129. — Left Scapul.a of Dog, Costal Surface. 
a, Subscapular fossa; b, b, b, muscular lines; 
c, c, limiting line between subscapular fossa and serra- 
tus area; d, glenoid cavity; e, f, tuberosity; g, nutri- 
ent foramen. (Ellenberger-Baura, Anat. d. Hundes.) 



forward upon the lower face of the scapular tuberosity, which is blunt and bears 
no distinct coracoid process. There is a rough eminence on the posterior surface 
of the neck, from which the long head of the triceps arises. The cervical angle is 
opposite the first thoracic spine, the dorsal angle lies above the vertebral end of 
the fourth rib, and the articular angle at a point just in front of the sternal end 
of the first rib in the ordinary standing position. 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 upper 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 upward 
and backward and bears a tubercle on its upper part. Another line runs from it 
down the anterior aspect and forms the inner 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 inner surface represents 
the teres tubercle. The head is long and strongly curved from before backward. 



BONES OF THE THORACIC LIMB 



163 



The neck is better marked than in the horse. The undivided external tuberosity 
is placed well forward and extends little above the level of the head. The internal 
tuberosity is small. The Ijicipital groove is undivided and is displaced to the inner 
side by the extension forward of the external tuberosity. The distal end bears 
an oblique trochlear articular surface for articulation with the radius and ulna, 
the outer part of which is the more extensive and is faintly grooved. The epi- 
condyles are prominent. Tlu^ coronoid and olecranon fossae often communicate 
through a large supratrochlear foramen. 

The two bones of the forearm are relatively long and articulate with each 
other at either end in such a manner as to allow of slight movement. A narrow 
interosseous space separates their shafts. The radius is flattened from before 
backward and increases in size from above downward. The shaft forms two 
curves; one of these, an anterior convexity, involves the whole shaft; the other, 





Fig. 130. — Left Humerus of Dog, External View. 
a. Head; h, neck; c, cre.st; d, external tuber- 
osity; e, mark for in.sertion of infraspinatus tendon; 
/, external condyle; g, e.xternal condyloid cre!?t; h, 
coronoid fossa; i, olecranon fossa. (Ellenberger- 
Bavnn, Anat. d. Hundes.) 



Fig. 131. — Left Radiits and Uln.a. of Dog, Antero- 

EXTERNAL ViEW. 

A, Radius; B, ulna; a, groove for tendon of 
extensor carpi radialis; b, groove for common exten- 
sor tendon; c, proximal articular surface of radius; 
d, olecranon; e, beak (proc. anconeus) of ulna; /,. 
semilunar notch; g, coronoid process; /(, facet for 
radius; i, groove for lateral extensor tendon; k, 
groove for tendon of extensor carpi obliquus. (Ellen- 
berger-Baum, Anat. d. Hundes.) 



an inner convexity, affects the upper part. The anterior surface is convex in both 
directions and is marked by a groove for the oblique extensor of the carpus. The 
posterior surface presents the nutrient foramen in its upper third, and bears a 
rough line (Crista interossea) externally for the attachment of the interosseous 
ligament. The proximal end (Capitulum radii) is relatively small and is supported 
by a distinct neck (Collum rachi). It bears a concave surface (Fovea capituli) 
above for articulation with the humerus, and a convex marginal area (Circumfer- 
entia articularis) behind for the ulna. The bicipital tuberosity is small. There 
is a large external tuberosity and below this a rough eminence. The distal ex- 
tremity is much wider. It has an extensive concave carpal articular surface. 
Its inner border projects downward, forming the styloid process of the radius. 
Externally there is a concave facet (Incisura ulnaris radii) for the ulna. In front 
are three distinct grooves for the extensor tendons. The ulna is well developed, 



164 



SKELETON OF THE DOG 



but diminishes in size from above downward. It crosses the posterior surface of 
the radius from within outward. The shaft is large and three-sided in its upper 
two-thirds, smaller and more rounded below. Its anterior 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 internally, convex and rough ex- 
ternally. The olecranon is grooved and bears three prominences, of which the pos- 
terior 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 l)ack 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 is produced to a blunt point (Processus sty- 

loideus ulnae). It articulates with the ulnar carpal 
below, and has a convex facet on its antero-internal 
aspect for the radius. 

The carpus comprises seven bones, three in 
the proximal row" and four in the distal. The 
numerical reduction in the upper row is appar- 
ently clue to the fusion of the radial and inter- 
mediate, constituting a large bone which articu- 
lates with almost all of the distal surface of the 
radius and with the l)ones of the lower row. It 
projects prominently on the posterior surface of 
the carpus. The ulnar carpal is long; it articu- 
lates with the radius and ulna alcove and the acces- 
sory l)ehind; below it rests on the fourth carpal and 
is prolonged downw^ard to articulate with the fifth 
metacarpal also. The accessory is cylindrical, con- 
stricted in its middle and enlarged at each end; the 
anterior extremity articulates with the ulna and 
ulnar carpal bone. The first carpal is the smallest 
bone of the lower row; it articulates with the second 
carpal externally and the first metacarpal distally. 
The second carpal is wedge-shaped, the base being 
posterior; its upper surface is convex, and its lower 
is concave and rests on the second metacarpal. The 
third carpal is somewhat like the second; its lower 
surface is concave and articulates chiefly with the 
third metacarpal. The fourth carpal is the largest 
of the row; it articulates with the fourth and fifth 
metacarpals l)elow. Two small bones or cartilages 
may be found at the junction of the two rows 
behind, and a third small l)one articulates with the inner side of the radio- 
intermediate.^ 

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 below; 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 extremi- 
ties. The shaft is compressed from before backward. In the third and fourth it 

' This third bone was termed the phaooid in the cat by Strauss-Diirekeim, and is regarded by 
some authors as the vestige of an additional digit, the prepollex. 




■^«^ 



16 



Fig. 132. — Skeleton of Distal P.\rt 
OF Thoracic Limb of Doc:, 
External View. 
4, Radial + intermediate car- 
pal bone; .5, ulnar carpal; 6, accessory 
carpal; 7, second carpal; S, third car- 
pal; 9, fourth carpal; 10 -H, first to 
fifth metacarpals; 15, first jihalanx; 
16, .second phalanx; 17 , third phalanx. 
(After Leisering's Atlas.) 



BONES OF THE PELVIC LIMB 



165 



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 
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 behind, except the first, 
which is grooved. 

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 forward. The proximal end 
of each has a concave surface for articulation with the metacarpal bone and is 
deeply notched behind. The distal end has a trochlea for articulation with the 
second phalanx, and lateral depressions for ligamentous attachment. The 
second phalanges are aljout two-thirds of the length of the first phalanges. 
The proximal articular surface consists of two cavities separ- 
ated 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 articu- 
lar surface adapted to the second phalanx and is encircled 
by a collar of bone. The volar surface bears a wing or tuber- 
osity, and on either side of this is a foramen. The ungual 
part is a curved rod with a blunt-pointed free end. It is 
rough and jiorous. Its base forms with the collar previously 
mentioned a deep groove, into which the proximal border of 
the claw is received. The two phalanges of the first digit 
resemble in arrangement the first and third phalanges of the 
other digits. 

Nine volar sesamoids are usually present. Two are 
found at each metacarpo-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 exceptionally 
two are present. The distal volar sesamoids remain cartila- 
ginous. A nodular dorsal sesamoid occurs in the anterior 
part of the capsule of the metacarpo-phalangeal joints, 
and cartilaginous nodules are found in a similar position 
the joints between the first and second phalanges. 




Fig. 133. — Second and 
Third Phalanges 
OF Dog. 

a, Wing of third 
phalanx; b, coronary ridge; 
C foramen for digital ar- 
tery; d, ungual surface of 
third jjhalanx; e, .second 
phalanx; /, fir.st phalanx; 
g. ela.stic dorsal ligaments. 
(From Leisering's Atlas.) 



in connection with 



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 
IKac 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 anterior border or crest is strongly convex, 
thick, and rough. The internal angle is represented by a thickened part which 
bears two eminences, homologous with the posterior superior and posterior inferior 
iliac spines of man. The external angle also has two prominences, which are 
equivalent to the two anterior spines present in man. The shaft is almost sagittal 
and is compressed laterally. Above it is smooth and rounded, and below it bears a 
crest externally 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 



166 



SKELETON OF THE DOG 



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 




Fig. 1.34. — Oss.v Co.karum of Dog, Left Posterior View. 
a, Crest; 6, c, internal angle; d, great sciatic notch; e, /, external angle; g, posterior gluteal line; h, gluteal 
fossa of wing; i, shaft of ilium; k, anterior gluteal line; I, auricular surface; m, ilio-pectineal line; 7i, depression 
for origin of rectus femoris; o, acetabulum; p, acetabular, and q, symphyseal branch of pubis; r, psoas tubercle; 
s, obturator foramen; s', obturator notch; t, line for origin of coccygeus; u, superior ischiatic spine; v, external 
border of ischium; w, tuber ischii; x, ischial arch. (EUenberger-Baum, Anat. d. Hundes.) 



Fig. 135. — Left Femur of Dog, Anterior View. 
a, Head; b, neck; c, trochanter major; d, tro- 
chanter minor; e, rudimentary trochanter tertius; 
/, rough line; (j, trochlea; h, i, condyles; k, supra- 
patellar fossa. (Ellenberger-Baum, Anat. d. Hundes.) 



Fig. 136. — Left Tibia and Fibula of Dog, Antero- 
external View. 
A, Tibia; B, fibula; o, external condyle of 
tibia; h, spine; c, crest of tibia; d, muscular notch; 
e, internal malleolus; /, head of fibula; <7, interosseous 
space; h, external malleolus (distal end of fibula); i, 
groove for tendon. (Ellenberger-Baum, Anat. d. 
Hundes.) 



and has a prominent outer lip. There is no lesser sciatic notch, 
is relatively small and is semi-elliptical. 



The ischial arch 



BONES OF THE PELVIC LIMB 



167 



It is almost circular in the female, 



The symphysoal part of tlu^ pubis is thick and fuses late with the opposite bone. 
There is no subpubic groove. 

The acetabulum is about twice as far from the external angle of the ilium as 
from the tuber ischii. The fossa acetabuli is deep, and is bounded internally by a 
fiat plate of bone; its floor is so thin as to be translucent. There is a small notch 
behind. 

The obturator foramen resembles in ()utlin(> an ecjuilateral triangle with the 
angles rounded off. 

The inlet of the pelvis is very oblique, 
but in the male it is elliptical and the con- 
jugate diameter is the longer. The cavity is 
narrowest between the acetabula, and very 
wide behind. The floor is concave and rela- 
tively narrow in front, wide and flat behind. 

The femur is relatively much longer than 
in the horse or ox. The shaft is regularly 
cylindrical, except near the extremities, where 
it is wider and compressed from before l)ack- 
ward. It is strongly curved in its lower two- 
thirds, convex in front. The posterior surface 
is flattened transversely, narrow in the middle, 
and widens toward each end. It is Ijounded 
by two rough lines (Labium laterale, mediale) 
which diverge toward the extremities. The 
third trochanter and the plantar (supracondy- 
loid) fossa are absent. There are two supra- 
condyloid crests, the inner one being small. 
The nutrient foramen is in the upper third of 
the posterior surface. The head is a little more 
than a hemisphere and has a shallow depression 
behind and external to its center. The neck is 
well defined. The trochanter major does not 
extend as high as the head; a thick ridge runs 
from its anterior surface to the neck. The in- 
ternal trochanter has the form of a l>lunt tuber- 
osity. The trochanteric fossa is round and 
deep. The ridges of the trochlea are practi- 
cally sagittal in direction and are almost similar. 
The intercondyloid fossa is wide. Just alcove 
each condyle posteriorly there is a facet for 

articulation with the sesamoid (of Vesal), which is developed in the origin of the 
gastrocnemius muscle. 

The tibia is about the same length as the femur. The shaft forms a double 
curve ; the upper part is convex internally, the lower part externally. The proximal 
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 prominent. 
The nutrient foramen is usually in the upper third of the external border. The 
tuberosity is not grooved, l^ut bears a distinct mark where the ligamentum patellse 
is attached. There is a small facet for the fibula on the postero-external part of 
the external 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 
quadrangular and relatively small. The articular grooves and ridge are almost 
sagittal. There is a facet externally for articulation with the fibula. There is a 
vertical groove internally and a shallower one behind — both for tendons. 




Fig. 137. — Skeleton of Dist.\i, P.\rt of 
Pelvic Limb of Dog, External View. 
6, Tibial tarsal bone; 7, fibular tarsal; 
S, central tarsal; 9, second tarsal; 10, third 
tarsal; 11, fourtli tarsal; 12, metatarsal 
bones; IS, first phalanx. The first tarsal 
bone is not visible in the figure. (After 
Leisering's Atlas.) 



168 SKELETON OF THE DOG 

The fibula extends the entire length of the region. It is slender, somewhat 
twisted, and enlarged at either end. The upper part of the shaft is separated from 
the tibia by a considerable interosseous space, but the lower part is flattened and 
closely applied to the tibia. The proximal end is flattened and articulates with 
the external condyle of the tibia. The distal end is somewhat thicker and forms 
the external malleolus. It articulates internally with the tibia and the tibial tarsal 
bone. Externally it bears two tubercles. 

The patella is long and narrow. The anterior surface is convex in hoth direc- 
tions. The articular surface is convex from side to side and slightly concave from 
above downward. 

The tarsus comprises seven bones. The tibial tarsal consists of a body, neck, 
and head, like the bone in man. The body presents a trochlea above for articula- 
tion with the tibia and fibula. The posterior 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 inner process (sustentaculum) is short. The tuber calcis is grooved from 
before backward. 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 tubercles posteriorly. The first tarsal is flattened and ir- 
regularly quadrangular; it articulates above with the central and below with the 
first metatarsal. The second tarsal is the smallest and is w^edge-shaped ; it articu- 
lates below with the second metatarsal bone. The third tarsal is also wedge- 
shaped, the base being in front; it articulates with the third metatarsal below. 
The fourth tarsal is remarkably high, and resembles a quadrangular prism; it 
articulates with the fibular tarsal above, the fourth and fifth metatarsal below, and 
the central and third tarsal bones internally. A groove for the tendon of the pero- 
neus longus crosses its outer and posterior surface, and above it are one or two 
tubercles. 

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 
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 
posterior projections, which in the case of the third and fourth usually bear facets 
for articulation with two small rounded sesamoid l)ones. 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 the digit is double. The phalanges 
of the other digits resemble those of the fore limb. 



ARTHROLOGY 

THE ARTICULATIONS OR JOINTS 

An articulation or joint is formed l)y 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 media, and the form of the joint surfaces; (b) 
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 these surfaces is thereby effected. (2) Those in which the uniting 
medium has undergone interruption in its structural continuity, and in which a cavity of greater 
or less extent is thus formed in the interior of the joint. This distinction is of considerable im- 
portance clinically. 

Three chief subdivisions of joints are usually recognized — viz., S3marthroses, 
diarthroses, and amphiarthroses. 



SYNARTHROSES 

In this group the segments are united by fil^rous 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. Many 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. f/., the frontal suture. In others the edges are beveled and 
overia]!, forming the sutura squamosa, e. g., the parieto-temporal suture. If the 
edges are plane or slightly roughened, the term sutura harmonia is a]:)plietl to the 
joint, e. (J., the nasal suture. 

(2) Synchondrosis. — In these the two bones are united by cartilage, e. g., 
the joint between the basioccipital and the sphenoid bone, ^'ery few of these 
joints are permanent. 

(3) Symphysis. — This term is usually limited to a few median joints which 
connect symmetrical parts of the skeleton, e. g., symphysis pelvis, symphysis 
mandibulse. The uniting media are cartilage and fibrous tissue. In some cases 
a cleft-like rudimentary joint cavity occurs. 

(4) Gomphosis. — This term is applied to the implantation of the teeth in the 
alveoli. 

169 



170 



THE ARTICULATIONS OR JOINTS 



„. I Capsule 



DIARTHROSES 
These joints are characterized by the presence of a joint cavity and by their 
mobihty. They are often called movable or true joints. The structures which 
enter into their formation are: 

1. The joint surfaces (Facies articulares), which are usually more or less ex- 
panded. They arc in most cases smooth, and vary much in form. They are 
formed of specially dense bone, which differs histologically 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 thickness 
in different joints; they are thickest on the areas of the greatest pressure, and 
usually tend to accentuate the curvature of the bone, i. e., on a concave surface 
the peripheral part is the thickest, while on a convex 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 joint capsule (C'apsula articularis) is, in 
its simplest form, a sac, the margins of which are 
attached around the articulating surfaces. It con- 
sists of two layers — an external one, composed of 
fibrous tissue (Stratum fibrosum), and an internal 
one, the synovial layer or membrane (Stratum syno- 
viale). The fibrous layer, 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. 
Parts of the capsule may undergo thickening and so 
form ligaments, which are not separable, except 
artificially, from the rest of the capsule. The syno- 
vial layer lines the joint cavity except where this 
is bounded by the articular cartilages; it stops normall}" 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 commonly contain pads of 
fat which fill up interstices and vary in form and position in various phases of 
movement. The synovial membrane secretes a fluid, the synovia, which resembles 
white-of-egg and lubricates the joint.^ In many places the membrane forms extra- 
articular pouches, which facilitate the play of muscles and tendons. 

The joint cavity (Cavum articulare) is inclosed by the synovial meml)rane 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 sections. It is also 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 

' 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. 




Fig. 138. — Di.\gram of Section of 

DiARTHROSIS. 

f.l.. Fibrous layer, s.l., synovial 
layer of joint capsule. The articular 
cartilages are white, bones tlotted, and 
the joint cavity black in the figure. 



DI ARTHROSES 171 

■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. 

•1, Ligaments. — These are strong bands or membranes, usually composed 
of white, hbrous tissue, which bind the bones together. They are pHable, but 
practically inelastic. In a few cases, however, e. g., ligamenta flava, ligamentum 
nuchse, 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. Strictly speaking, intraarticular ligaments, though within the 
fibrous capsule, are not in the joint cavity; the synovial membrane is reflected 
over them. The term seems justifiable, however, on practical grounds. Liga- 
ments which connect directly opposed surfaces of bones are termed interosseous. 
The special names are based usually on their position, form, and attachments, e. g., 
lateral or collateral, cruciate, sacro-ihac, etc. In many places muscles, tendons, 
and thickenings of the fasciae function as ligaments and increase the security of the 
joint. Atmospheric pressure and cohesion play a considerable part in keeping the 
joint surfaces in apposition. 

5. Articular discs or menisci 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 certain surfaces congruent, 
e. g., femoro-tibial joint, allow greater range or variety of movement, and diminish 
concussion. 

6. A marginal cartilage (Lal^rum 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- 
atics. Nerve-fibers are especially numerous in and around the synovial membrane 
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 tiie 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 vertebrae. 

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 lower parts 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 should be applied 
to the corresponding movements of the spinal column. The meaning of the term 
lateral flexion is evident. These movements are all rotations around axes which 
are a])])roximately either transverse or vertical. Depression, elevation, and lateral 
movement of the lower jaw fall in this category. 

3. Circumduction. — This designates movements in which the distal part of 
the limb describes a circle or a segment of one. In man such movement is easily 



172 THE ARTICULATIONS OR JOINTS 

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 median 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- 
tw^een the articular processes of the cervical and thoracic vertebrae. 

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: occipito-atlantal 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 l^y 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, ex- 
tension, 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 vertebrae. There is usually no joint cavity, 
but in certain situations a rudimentary one exists. 



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 verteljrae; 
the foT-mer are termed intercentral, and the latter, interneural. Associated with 
these are ligaments uniting the arches and processes; some of these are special, 
i. e., confined to a single joint, while others are common, i. e., extend along the entire 

'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 seems desirable, but appears to 
be almost impossible on account of the great variety antl ii-regularity of form of the articular 
surfaces. 

-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-iliac joints. 



INTERCENTRAL ARTICULATIONS INTERNEURAL ARTICULATIONS 



173 



vertebral column or a consicleralole part of it. The joints between the atlas and 
axis and between the former and the skull require separate consideration. 



INTERCENTRAL ARTICULATIONS 

These are amphiarthroses, formed by the junction of the extremities of the 
bodies of adjacent vertebrie. The articular surfaces in the cervical region consist 
of a cavity on the posterior end of the body of the anterior vertebra, and a cor- 
responding 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 (Fibrocartilagines 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 lumbar regions, and thickest in 
the coccygeal region. Each consists of a dense fibrous peripheral part (Annulus 
fibrosus), and a soft pulpy 



Supraspi- 
710 us liga-^ 
merit 






ppo- 






Spf^iOSL 



, •^Ay.?*^^'*','?'' ■ -^ ;''®*?l^»5?>^ 







Fig. 139. — Sagittal Section of Last Two Thoracic and First 
Lumbar Vertebr.e, showing Ligaments and Spinal Cord 
(Medulla). (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



central part (Nucleus pul- 
posus). 

The fibrous ring consists 
of lamin.T of fil)rous tissue and 
fihro-cartilage, wliich pass ob- 
liquely between the two verte- 
bne and ahernate in direction, 
forming an X-shaped arrange- 
ment. The central part of the 
ring is largely cartilaginous, and 
gradually assumes the character 
of the ptilpy center. The latter 
is very elastic and is compressed, 
so that it bulges considerably 
from the surface of sections; it 
consists of white and elastic 
fibers, connective-tissue cells, 
and peculiar 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. In the latter the cavity is coextensive with the extremities of the bodies; in the former, 
it is usually not so extensive. 

2. The inferior common ligament (Ligamentum longitudinale ventrale) lies 
on the ventral surface of the l)odies of the vertebra and the intervertebral fibro- 
cartilages, to which it is firmly attached. It begins about the fourteenth or fifteenth 
thoracic vertebra, and is at first a narrow, thin band. Further back it becomes 
gradually thicker and wdder, and terminates on the pelvic surface of the sacrum 
by spreading out and blending with the periosteum. It is strongest in the lumlmr 
region, where the tendons of the crurp of the diaphragm fuse with it. 

3. The superior common ligament (Ligamentum longitudinale dorsale) lies on 
the floor of the vertebral canal from the dens or odontoid process to the sacrum. 
It is narrow over the middles of the vertebral Ijodies, and widens over the inter- 
vertebral 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 branch passes under the ligament. 



INTERNEURAL ARTICULATIONS 
Each typical vertebra i^-esents two pairs of articular processes, which form 
diarthroses with the two adjacent vertebra?. The articular surfaces are extensive, 



174 



THE ARTICULATIONS OF THE HORSE 



flat, and oval in the cervical region, small and flat in the thoracic region, 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. 

Associated with these joints are the ligamenta flava, which connect the arches 
of adjacent vertebrae. They are meml^ranous and consist largely of elastic tissue. 

The supraspinous ligament extends medially from the occipital bone to the 
sacrum. From the withers backward it consists of a strong cord of fibrous tissue, 
attached to the summits of the vertebral spines. In the neck and withers it is 



Atlas 

Funicular part 



Expansion at withers 




Last cervical 
vertebra 



First thoracic 
vertebra 



Fig. 140. — Ligamentum Nuch^ of Horse. 
./.Scapula; ^', cartilage of scapula; 4. lamellar part of ligamentum nuchsp; a-, wing of atlas. 

Baum, Anat. fur Kiinstler.) 



(After EUenberger- 



remarkably modified to form the ligamentum nucha?, which requires more extended 
notice. 

The ligamentum nuchae is a ]:)owerful elastic apjoaratus, the principal function 
of which is to assist the (^xtensor muscles of the head and neck. It extends from 
the ocei]5ital ])one to the withers, where it is directly continuous with the supra- 
spinous ligament. It consists of two parts — funicular and lamellar. The funic- 
ular part (Pars occipitalis) arises from the external occipital protuberance and the 
fossa ])elow it, and is inserted into the summits of the vertel^ral spines at the 
withers. Two bursae are usually found under it in the adult. The supra-atloid 
bursa lies between the ligament and the dorsal arch of the atlas. The supra- 



MOVEMENTS OF THE VERTEBRAL COLUMN 175 

spinous bursa occurs usually over the fourth thoracic spine, but may be over the 
third and may extend to the fifth.'' 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 expansion three to five inches (ca. 8 to 
12.5 cm.) in width, the lateral margins of which arc thin and overlie the trapezius 
and rhomboideus muscles. Behind the higher spines it becomes narrower and 
thinner, and is continued by the white fibrous lumbo-dorsal ligament.^ 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 "crest." The lamellar portion (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 portion, are directed downward and forward, 
and end on the spines of the cervical vertebra?, except the first and last. The digita- 
tion which is attached to the spine of the axis is very thick and strong. Behind 
this they diminish in size and strength ; that to the sixth cervical is quite thin and 
feeble, or may be absent. 

The interspinous ligaments (Ligamentainterspinalia) 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 forward. 

The intertransverse ligaments (Ligamenta intertransversaria) are membranes 
which connect adjacent transverse processes in the lumbar region. 



INTERTRANSVERSE ARTICULATIONS 

These joints (peculiar to eciuidae) are diarthroses formed by the transverse 
processes of the last two lumbar vertebrae 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- 
vaded by 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- 
cartilages, 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 extensive 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 very small, but the sum of the movements is considerable. The 

^ 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." 

^ No natural line of demarcation exists between the ligamentum nuch£e and the lumbo-dorsal 
continuation of the supraspinous ligament, since the change from the purely elastic to the white 
fibrous structure is gradual. 



176 



THE ARTICULATIONS OF THE HORSE 



movements are freest in the cervical and coccygeal regions, 
limited in the thoracic and lumbar regions. 



Rotation is extremely 



Fig. 



ATLANTO-AXIAL 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 usually 
confluent ventrally; (2) on the axis, reciprocal saddle- 
shaped surfaces which extend upon the odontoid pro- 
cess and are confluent on its ventral aspect. It will be 
observed that the joint surfaces are not at all accur- 
ately 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 superior atlanto-axial ligament (Ligamentum 
interarcuale) is meml:)ranous and reinforces the capsule 
dorsally. 

The interspinous ligament (Ligamentum inter- 
spinale) consists of two elastic bands which extend 
from the dorsal arch of the atlas to the spine of the 
axis. 

The inferior atlanto-axial ligament (Ligamentum 
dentis externum) arises from the ventral tubercle of the 
atlas and is attached by two branches on the ventral 
spine of the axis. 

The odontoid ligament (Ligamentum dentis in- 
ternum) is short, very strong, and somewhat fan- 
shaped. It extends from the rough concave dorsal 
surface of the dens or odontoid process, 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 odontoid process and body of the axis. 




141. — Atlanto -occipitai, 
AND Atlanto-axial Joints 
OF Horse, Dorsal ^'IE^v 
AFTER Removal of Dor- 
sal Arch of Atlas. 
a, Joint capsule of left part 
of atlanto-occipital joint; b, lat- 
eral ligament of same; c, c' , odon- 
toid ligament; d, atlanto-occijjital 
joint capsule; e, joint capsule of 
articulation between axis and 
third cervical vertebra; /, inter- 
spinous ligament; 1, occii^ital 
bone; 2, atlas; 3, axis; 4, third 
cervical vetrebra. (Ellenberger- 
Baum, Anat. d. Haustiere.) 



THE ATLANTO-OCCIPITAL ARTICULATION 

This joint may l)e 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 ])one. 



The joint surface.s are oblique, coming very close to the 
median line ventrally, but separated by a considerable interval 
dorsally. Posteriorly, a triangular rough area cuts into tlie middle of each articular suiface 
on the atlas. 

There are two roomy joint capsules, whicli sometimes communicate ventrally, 
especially in old subjects. 

The superior atlanto-occipital membrane extends from the dorsal arch of the 
atlas to the upper margin of the foramen magnum. It is lilcnded with the capsules 
and contains many elastic fibers. 

The inferior atlanto-occipital membrane extends from the ventral arch of the 



ARTICULATIONS OF THE THORAX COSTO-VERTEBRAL ARTICULATIONS 



177 



atlas to the lower margin of the foramen magnum. It is narrower and thinner than 
the superior membrane, and also fuses with the joint capsules. 

The lateral ligaments 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 outer surface of the paramastoid or styloid 
process of the occipital bone. 

Movements. — These are chiefly flexion and extension. A small amount of 
lateral oblique movement is also possible. 




Articular processes 

Transverse process 



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 tul:)ercle. They are termed respectively costo-central and costo- 
transverse joints. 

I. The costo-central articulations (Articulationes capitulorum) are trochoid 
or rotatory joints, formed l)y 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 separ- 
ated by a non-articular groove, 
and correspond to the two con- 
cave facets (Fovece costales) on 
the vertebral bodies. The cap- 
sules are rather tight, and are 
covered by the accessory liga- 
ments, which are as follows: 1. 
The radiate ligament (Ligamen- 
tum capituli costie radiatum) ex- 
tends ventrally from the neck of 
the rib to spread out on the 
vertebral bodies and the inter- 
vertebral fibro-cartilage. 2. The 
conjugal ligament (Ligamentum 
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 superior common ligament 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 attached to the intervertebral fibro- 
cartilage. The joint cavity is divided into two compartments by the conjugal 
ligament. 3. The ligament of the neck of the rib (Ligamentum colli costse) is 
a strong l)and 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 articulations. These occur between the facets on 
the tubercles of the ribs and those on the transverse processes of the vertebrae. 
They are gliding joints. The capsule is reinforced by the superior costo-trans- 
verse ligament (Ligamentum costo-transversarium dorsale), a distinct strong ])and 
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. 

12 



Capsule 

Radiate ligament 
Conjugal ligament 

Fig. 142. — Costo-vertebral Articulation, Anterior View. 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



178 THE ARTICULATIONS OF THE HORSE 

The cavity for the liead of the first rib is formed by concave facets on the bodies of the last 
cervical and first thoracic vertebra*. The conjuo;al ligament is absent, but the ligament of the 
neck is short and strong. The radiate ligament is very strong, and consists of two bands. 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 hmited 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. 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 mobility of the ventral ends of the asternal 
ribs and their elasticity, allows a great increase here in the range of movement, the effect of which 
is 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 cariniform cartilage 
(Manubrium sterni) ; the other seven are placed laterally at the jimction of the 
segments. The capsules are strong and tight; the first pair of joints has a common 
capsule, and the cartilages articulate with each other medially. The lower ends 
of the first pair of ribs are firmly attached to each other by dense fibrous tissue, 
which is prolonged forward along the upjjer margin of the cariniform cartilage and 
is continuous behind with the sternal ligament. Each of the other capsules is 
reinforced dorsally by the superior costo-sternal ligament (Ligamentum sterno- 
costale radiatum), composed of radiating fibers which blend with the sternal liga- 
ment. 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. 

STERNAL ARTICULATIONS 
In the new-born foal the sternum has seven bony segments (Sternel^rae), 
united by persisting cartilage. The last two segments coalesce within a few weeks 
after birth. In old subjects there is more or less ossification of the intersegmental 
cartilage, which may load to partial fusion of adjacent segments, especially pos- 
teriorly. Tli(> sternal ligament (Ligamentum sterni ])roprium internum) lies on the 
thoracic surface of the sternum. It arises on the first segment, and divides oppo- 
site the second chondro-sternal joint into three bands. The median band passes 
backward and spreads out on the last segment and the xiphoid cartilage. The 



THE SYNARTHROSES OF THE SKULL 179 

lateral branches — thicker and wider — lie along the lateral borders above the chon- 
dro-sternal joints, and end at the cartilage of the eighth ril); they are covered by 
the transversus thoracis muscle. 



The Articulations of the Skull 
temporo-mandibular articulation 

This joint (Articulatio numdibularis) is the only diarthrosis formed between 
bones of the skull. 

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 glenoid cavity, which is continued upon the post- 
glenoid process behind, and a condyle in front. The mandible presents a trans- 
versely elongated condyle. 

The articular disc is placed between the joint surfaces, which it renders con- 
gruent. Its upper and lower surfaces are molded upon the temporal and mandibular 
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 roomy. 

The joint capsule is strong and tight. It is reinforced by two ligaments. The 
external ligament (Ligamentum laterale) extends oblicjuely across the anterior 
part of the outer surface of the capsule, from which it is not distinctly separable. 
The posterior ligament (Ligamentum posterius) is an elastic band which is attached 
above to the ]wstglenoid 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 lies under the glenoid cavity. When the mandible is depressed, 
the condyle moves forward under the articular eminence of the temporal 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 lateral 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. 



THE 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 
various periods during development and growth. Their importance rests on 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, internasal, etc. Special names (borrowed from human 
anatomy) are sometimes used; thus the interparietal, the parieto-occipital, and 
the parieto-frontal sutures are often called the sagittal, lambdoid, and coronal re- 
spectively. 

Detailed description of the sutures has not sufficient chnical value to justify much addition 
to the statements'^made in the osteology in this connection. The obliteration or closure of the 
sutures is, however, worthy of brief merition. The cranial sutures 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 



180 THE ARTICULATIONS OF THE HORSE 

some be delayed for years or may not occur at all; the nasal suture, for example, often persists 
even in advanced age, so far as its anterior part is concerned. 

The principal synchondroses are: (1) That between the basioccipital and the 
body of the sphenoid (Synchondrosis sphenooccipitahs) ; (2) that between the 
presphenoid and postsphenoid (Synchondrosis intersphenoidahs) ; (3) those 
between the parts of the occipital bone (Synchondroses intraoccipitales). The first 
is usually ossified at four years, the second at three years, and the occipital bone is 
consolidated at two years. 

The symphysis of the lower jaw (Symphysis mandibulse) ossifies at one to six 
months. 

THE HYOIDEAN ARTICULATIONS 

The temporo-hyoid articulation is an amphiarthrosis, in which the dorsal angle 
of the proximal end of the great cornu (Stylo-hyal) is attached by a short bar of 
cartilage to the hyoid process of the petrous temporal bone. The cartilage (Arthro- 
hyal) is about half an inch (ca. 1 to 1.5 cm.) in length. The chief movement is hinge- 
like, the axis of motion passing transversely through both joints. 

The intercomual articulation is an amphiarthrosis formed by the junction of 
the distal extremity of the great cornu with the proximal end of the small cornu 
(kerato-hyal). 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 epihyal 
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 l^y the junction of each 
small cornu (kerato-hyal) with the body (basi-hyal). The small cornu has a con- 
cave facet which articulates with the convex facet on either end of the dorsal sur- 
face of the body. The capsule is ample enough to allow considerable movement, 
which is chiefly hinge-like. The movements of the hyoid bone are concerned 
chiefly in the acts of mastication and swallowing. In the latter the distal 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 x\rticulations of the Thoracic Limb 

In the absence of the clavicle the thoracic limb forms no articulation with the 
trunk, unless we regard as such the union by muscles. The movement of the 
shoulder on the chest-wall is chiefly rotation aroimd 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 surfaces are: (1) On the scapula, the glenoid cavity; 
(2) on the humerus, the head. Both surfaces are approximately spherical and 
similar in curvature, but the humeral surface is much more extensive than that of 
the scapula. 

The joint capsule is ample enough to allow the bones to be drawn apart about 
an inch (ca. 2 to 3 cm.) ; but this requires a very considerable amount of force unless 
air is admitted into the joint cavity. The fibrous layer (or capsular ligament) is 
not attached to the margin 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, 



THE ELBOW JOINT 



181 



which arise on the scapular tuberosity and end on the hps of the bicipital groove. 
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 seldom or never occurs. The large 
extent 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: ex- 
ternally, the supraspinatus, infraspinatus, and teres minor; internally, the subscapularis; in 
front, the biceps and supraspinatus; behind, the triceps. 

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 (Articu- 
latio cubiti), is a ginglymus formed be- 
tween the distal extremity of the humerus 
and the proximal ends of the bones of the 
forearm. 

The articular surfaces are: (1) A 
trochlear surface formed by the condyles 
of the humerus and the groove between 
them; (2) the corresponchng glenoid cavi- 
ties and ridge on the proximal extremity 
of the radius, together with the semilunar 
notch of the ulna. 



Olccrinwn 
fussa 



Extcrrud lahral 
ligavuut 



Transverse or 
arciform 
ligavient 




143. — Left Elbow Joint of Hor.se, Poste- 
rior View. The Capsule is Removed. 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



The articular surface of the condyles does 
not extend 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 groove there is a synovial 
fossa. The surface on the outer condyle is smaller 
than that of the inner one, and is subdivided 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 
fossa?. 

The joint capsule is extremely thin behind, where it forms a pouch in the ole- 
cranon fossa under the anconeus muscle and a pad of fat. In front it is strength- 
ened by oblique fibers (Ligamentum obhquum or anterior ligament) , and laterally 
it fuses with the lateral ligaments. Small pouches of the synovial membrane 
lubricate the origins of the flexors of the carpus and digit and the small radio-ulnar 
joints. There are two lateral ligaments. 

The internal lateral ligament (Ligamentum collaterale radiale) is attached 
above to an eminence on the internal epicondyle of the humerus, and divides into 
two parts: the long, superficial part ends on the inner border of the radius, just 
below the level of the interosseous space; the deep, short part is inserted into the 
internal tuberosity of the radius. (The superficial part represents the pronator teres 
muscle, which is only exceptionally present in the horse.) 



182 



THE ARTICULATIONS OF THE HORSE 



The external lateral ligament (Ligamentiim coUaterale ulnare) is short and 
strong. It is attached al)ove to a depression on the external epicondyle of the 
humerus, and below to the external 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 upper attachments 
of the lateral 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 lateral ligaments and the biceps 
muscle. (The axis of movement is slightly oblique, so that in flexion the forearm 
is carried somewhat outward.) 



External 

lateral ■ 

ligament 

Metacarpal ^-^■^'^ 
tuberosity ~'~^- J,i 




External dis- 
tal tuberosity 
of radius 

Accessory 
carpal bone 

Inferior liga- 
ments of ac- 
cessory car- 
pal 



External 

metacarpal 

bone 



Fig. 144. — Left Carpal Joints of Horse, Exter- Fig 
NAL View 
The capsule has been removed, q. Radius; 12, 
large metacarpal bone. (After Ellenberger-Baum, 



Internal dis- 
tal tuberosity 
of radius 



Internal 

lateral 

ligament 

Metacarpal 
tuberosity ~ 




.External dis- 
tal tuberosity 
of radius 

External 
hitirid 
ligament 



.External 
metacarpal 
bone 



145. — Left Carpal Joints of Horse, Anterior 
View. 

The capsule has been removed. The smaller liga- 
ments are shown. (After Ellenberger-Baum, Anat 



Anat. f, Kiinstler.) 



f. Kiinstler. 



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. 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 ligaments (Ligamentum transversum ulnare et radiale 
ulnse et radii) consist of fi))ers which pass above the interosseous space from either 
border of the shaft of the ulna to the posterior surface of the radius. The proximal 
radio-ulnar articulation, 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 consider- 
ation. The distal extremity of the ulna fuses early with the radius, and is, there- 
fore, regarded usually as a part of the latter. 

Movement. — This is inappreciable, the forearm being fixed in the position of 
pronation. 



THE CARPAL JOINTS 



183 



THE CARPAL JOINTS 

Those joints taken together constitute the composite articulatio carpi, or what 
is popuhu'h' termed the "knee-joint" in animals.' This consists of three chief 
joints, viz., (1) The radio-carpal joint, formed by the distal end of the radius and 
the proximal row of the carpus; (2) tlie intercarpal joint, formed between the two 
rows of the carpus; (3) tlie carpo-metacarpal joint, formed l^etween 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 addition there are 
arthrodial joints formed between adjacent bones of the same row (Articulationes 
interossese). All these constitute a very composite joint, with numerous ligaments. 
The articular surfaces have been described 
in the Osteology. 

The joint capsule may l)e regarded, 
so far as the fibrous ])art is concerned, as 
being common to all three joints. It is 
attached close to the margin of the articuT 
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 or anterior 
common ligament, is rather loose, and 
assists in forming the fibrous canals for 
the extensor tendons. Its posterior part, 
the volar or posterior common ligament, 
is very thick and dense, and is closel}^ 
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 flexor perforans about the middle of 
the metacarpus. 

The synovial membrane forms three 
sacs corresponding to the three joints. 
The radio-carpal sac is the most volum- 
inous; it includes the joints formed by the 
accessory carpal bone, and also those be- 
tween 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 communicates 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 lubricates also the lower parts of the joints between the 
distal carpal bones and the intermetacarpal joints. 

The external lateral ligament (Ligamentum carpi collaterale ulnare) is attached 
above to the external tuberosity of the distal end of the radius. Its long superficial 
part is attached below to the proximal end of the external small metacarpal chiefly, 

' The term is a very unfortunate one, since it is a distinct misapplication of the name as it ia 
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. 




Fig. 146. — Frontal Section of Carpal Joints of 
Horse (Right Side). 
/.);., External, l.r., internal, lateral ligament; 
Cr, radial carpal; Ci, intermediate carpal; Cu, ulnar 
carpal; C2, second carpal; CS, third carpal; C4, 
fourth carpal; Mc2, second (internal) metacarpal; 
Mc3, third (large) metacarpal; Mc4, fourth (exter- 
nal) metacarpal. 



184 



THE ARTICULATIONS OF THE HORSE 



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 internal lateral ligament (Ligamentum carpi collaterale radiale) resembles 
the preceding in general, but is stronger and wider distally. It is attached above 
to the internal tuberosity of the distal end of the radius and ends below on the 
proximal ends of the large and inner small metacarpal bones. Deep fasciculi are 
detached to the radial and second carpal bones. The first carpal bone, when pres- 
ent, is usually embedded in the posterior part of the distal end of the ligament. 
The posterior part of the ligament is fused with the posterior annular ligament 
(Ligamentum carpi transversum), and concurs in the formation of a canal for 

the tendon of the flexor carpi in- 

ternus. 



Internal lat- 
eral ligament 



Metacarpal 
V tuberosity 



A number of special short ligaments 
connect two or more adjacent l)ones; only 
the most distinct of these will be described 
here. 

The accessory carpal bone is con- 
nected with adjacent bones by three liga- 
ments (Fig. 444). The proximal one is a 
short band which extends from the acces- 
sory carpal in front of the groove on its 
outer 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 the 
ulnar carpal. The distal ligament consists 
of two strong bands which pass from the 
lower margin of the accessory to the fourth 
carpal and the proximal end of the outer 
metacarpal bone; these bands transmit 
the action of the muscles, which are in- 
serted into the accessory carpal l)one. 
The other bones of the proximal row are 
connected by two anterior or dorsal liga- 
ments, which are transverse in direction, 
and two interosseous ligaments. An ob- 
lique ligament passes from an eminence 
on the posterior siuface of the radial car- 
pal bone to a small depression on the 
radius internal to the facet for the acces- 
sory carpal bone. 

Two ligaments connect the proximal 
and distal rows posteriorly. The inner 
one joins the radial to the second and 
third carpal, and the outer one attaches 
the ulnar to the third and fourth carpals. 
The bones of the distal row are connected by two strong transverse anterior or dorsal liga- 
ments and two interosseous ligaments. 

There are four carpo-metacarpal ligaments. Two ol)lique anterior bands connect the third 
carpal with the large metacarpal. Two interosseous ligaments pass downward from the inter- 
osseous ligaments of the distal row to end in depressions in the interstices between the proximal 
ends of the metacarpal bones. 

Movements. — Taking the joint as a whole, the chief movements are flexion 
and extension. In the standing position the joint is extended. When the joint is 
flexed, slight lateral movement and rotation can be produced by manipulation. 
The anterior part of the capsule is, of course, tense during flexion, the posterior 
part in extension. 

The movement practically all occurs at the radio-carpal and intercarpal joints, the articular 
surfaces of which are widely separated in front during flexion, but remain in contact behind. The 
distal row remains in contact with the metacarpus. The intermediate and ulnar carpals move 
together as one piece, but the radial does not move so far as the intermediate, so that the anterior 
and interosseous ligaments connecting these bones become tense and oblique in direction. 




Internal distal 
tuberosity of 
radius 

Accessory car- 
pal boyie ' 



Inferior liga- __ 

ments of acces- - - ■ 

sory carpal 



Internal 
(second) meta- 
carpal bone 



Fig. 147. — Left Carpal Joixt.s of Horse, Inner View. 
g, Radius; 12, large (third) metacarpal bone. (After Ellen- 
berger-Baum, Anat. fiir Kiinstler.) 



THE FETLOCK JOINT 



185 



THE FETLOCK JOINT 
This, the metacarpo-phalangeal articulation (Articulatio nictacarpo-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 sort of socket formed by the first phalanx 

below and the two sesamoids together 
with the intersesamoid ligament be- 
hind. The latter is a mass of fibro- 
cartilage in which the sesamoid bones 
are largely embedded. It extends 
al)ove the level of the sesamoids, 
and is grooved to receive the ridge 
on the metacarpal bone; its posterior 
surface forms a smooth groove for the 
deep flexor tendon. 

The joint capsule is attached around 
the margin of the articular surfaces. It 



Branches of 
suspensory ligantent 








Fig. 14S. — Sagittal Section op Distal Part of Limb 
OF Horse. 
1, Large metacarpal bone; S, fetlock joint; 4, 
proximal sesamoitl bone; 5, fir.st phalanx; 8, pastern 
joint; 7, second jihalanx; S, coffin joint; 9, third phal- 
anx; 10, distal sesamoid (navicular bone); 1$, su.sj)en- 
sory ligament; 14. deep flexor tendon; 15, superficial 
flexor tendon; 16, posterior annular ligament of fetlock; 
£0, inferior sesamoidean ligaments; 21 , extensor tendon; 
^4, plantar cushion; 2o, periople; 2S, wall of hoof; 29, 
sole of hoof ; ^4, navicular bursa, proximal part. (After 
Ellenberger-Baum, Anat. fiir Kiinstler.) 



Fig. 149. — ARTifii \u Si m mi- of First Phalanx 
and Ses.^moius at Fetlock, with Interses.\- 
MoiD and Suspensory Ligaments. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



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. Pos- 
teriorly it forms a thin-walled pouch 
which extends upward lietween the 
metacarpal bone and the suspensory ligament about as high as the point of 
bifurcation of the latter. The capsule is reinforced by two lateral ligaments. 

The lateral ligaments, external and internal (Ligamentum 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 lateral area lielow the margin of the articular surface of the 
first phalanx; the deep layer, shorter and much stronger, arises in the lateral 
depression on the distal end of the metacarpal l^one, and passes obliquely downward 
and backward to be inserted into the outer surface of the sesamoid and the proxi- 
mal end of the first phalanx. 



186 



THE ARTICULATIONS OF THE HORSE 



The capsule is further strengthened by a layer of oljlique fibers which pass over the lateral 
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 upper attachments of the lateral ligaments. In the 
ordinary standing position the joint is in a state of partial dorsal flexion, the articu- 
lar 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- 



Extensor tendon 



Upper end of capsule of feiloch 
joint 

Biirsd 

Lateral ligament of fetlock joint 

Fascia 

Branch of suspensory liganunt 



Lateral volar ligament of paster n 
joint 





Superficial flexor tendon 
Deep flexor tendon 
rlcJd Air- 4\t — Suspensory ligament 

\Ml^ U(ff — -Lateral interrosseous tendon 

i ( iV * '"' f '^?Jper end of digital sheath. 

■/\ i^^.v-^' ^'^^S' o/ superficial flexor tendon 
n tersescnnoidean ligament 
Posterior annular ligament (cut) 



Lateral sesamoidean ligament 
Superficial inferior sesamwidean 

ligament 
Middle inferioi' sesamoidean 
ligeiment 
xittacJiments of proximal digital 
'annular ligament 



Suspetisory ligament of navicular 
bone 
Band from lateral cartilage to 
extensor tendon 
Lateral ligament of cofjin joint 



- Pouch of digital sheath 

Distal digital annular ligament 
Lateral cartilage 



Fig. 150. — Lig.\mexts .4^nd Tendons of Dist.\l Part of Limb of Horse. 

Mc. Ill, Large metacarpal bone; Ph. I, first phalanx; Ph. II, second phalanx; Ph. Ill, third phalanx; 1, deep flexor 

tendon; 2, band from first phalanx to plantar cushion, (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 

mally very limited on account of the resistance offered by the sesamoidean appara- 
tus, 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 lateral flexion is possible. 



THE SESAMOIDEAN LIGAMENTS 
Under this head will be described a number of important ligameivts which are 
connected with the sesamoid bones and form a sort of stay apparatus or brace. 



THE SESAMOIDEAN LIGAMENTS 



187 



The intersesamoidean ligament (Liganientum intersesamoideum) not only fills 
the space between and unites the sesamoid hones, but also extends above them, 
entering into the formation of the articular surface of the fetlock joint. Other 
facts in regard to it ha\'e l)een given al)0\'e. 

The lateral sesamoidean ligaments, outer and inner (Ligamenta sesamoidea 
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 



l>ifurcatLon of common (Ugitol (irlrri/ 
Inhrnal digital artery 



Oblique or middle inferior sesamoid 
ligament 
Straight or superficial inferior 
sesamoid ligament 



Distal annular ligament of digit {cut 
and reflected) 




Large metacarpal linne 

External small metacarpal bone 

Bifurcation of siispe7isory 

ligament 



Capsule of fetlock joint (upper 

pouch) 
Sesatnoid groove 

Posterior annular ligament of 
fetlock (cut and reflected) 

Latercd sesamoid ligament 

Stump of digital annular 

ligament 
Extensor branch of suspensory 

ligantent 
\'olar ligaments of pastern joint 

Insertion of superficial flexor 

tendon 
Fibrous plate 

Deep flexor tendon 

Lateral ligament of pastern joint 
Distal end of digital sheath 
Suspeiisory ligament of 

navicular bone 
Dorsal branch of digital artery 
Volar branch of digital artery 



Fig. 151. — Deep Dissection of Dist.\i. Part u. 1:...,,. J .,i,,, J.i.mji of Horse, Showing Joints and Lk^amknts, 

Posterior View. 
1, Lateral cartilage; 2, tendon surface of navicular bone; 3, inferior navicular or interosseous ligament; 
4, insertion of deej) flexor tendon. Small ^irrows jioint to ojienings made in cajjsules of pastern and coffin joints. 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



first phalanx. They are partly covered by the branches of the suspensory or 
superior sesamoidean ligament. 

The suspensory or superior sesamoidean ligament (Musculus interosseus 
medius) lies for the greater part in the metacarpal groove, where it has the form of 
a wide, thick l)and. It is attached above to the upper part of the posterior surface 
of the large metacarpal bone and to the distal row of carpal bones. At the lower 
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 



188 THE ARTICULATIONS OF THE HORSE 

part is attached. The remainder passes obUquely downward and forward to the 
anterior surface of the first phalanx, where it joins the extensor tendon. This 
ligament possesses considerable elasticity, and is the highly modified interosseous 
medius muscle. It consists mainly of tendinous tissue, but contains a variable 
amount of striped muscular tissue, especially in its deep part and in young subjects. 
Its principal function 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 extensor tendon limit volar flexion of the interphalangeal joints in 
certain phases of movement. 

The inferior sesamoidean ligaments are three in number — superficial, middle, 
and deep. The superficial or straight ligament (Ligamentum sesamoideum rec- 
tum) is a fiat band and is somewhat wider above than below. ^ It is attached above 
to the bases of the sesamoid bones and the intersesamoid ligament, below to the 
complementary fibro-cartilage of the proximal end of the second phalanx. The 
middle ligament is triangular, with thick, rounded margins (Ligamenta ol)liciua) and 
a thin central portion.- Its base is attached to the sesamoid bones and intersesa- 
moid ligament, and its deep face to the triangular rough area on the posterior 
surface of the first phalanx. The deep or cruciate ligament (Ligamenta sesamoidea 
cruciata) consists 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 short sesamoidean ligaments (Ligamenta sesamoidea brevia) are best 
seen 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 ])ase of the sesamoid bone outward to the posterior margin 
of the articular surface of the first phalanx. 

The inferior 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. 



THE PASTERN JOINT 

This, the proximal interphalangeal articulation (Articulatio phalangis se- 
cundse), 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 with 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 laterally, where it blends with the 
extensor tendon and the lateral ligaments respectively. Behind it pouches upward 
a little and is reinforced by the straight sesamoidean ligament and the branches of 
the superficial flexor tendon. 

There are two lateral and four volar ligaments. 

The lateral ligaments, internal and external (Ligamentum collaterale radiale, 
ulnare) are very short and strong bands which are attached alcove on the emi- 
nence and depression on each side of the distal end of the first phalanx, and below 
on the eminence on either 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 or posterior ligaments consist of central and lateral pairs of bands 
which are attached below to the i:)osterior margin of the proximal end of the second 

^This is often called the Y-shnped ligament — a rather undesirable name, since it is not 
bifurcate. 

^It is also called the V-shaped ligament. 



THE COFFIN JOINT 



189 



phalaiix and its complementary fibro-cartilage. The lateral pair is 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 chronic 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 ligament. 

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 flexion and rotation can be produced by 
manipulation. Dorsal flexion is prevented by the lateral, volar, and straight sesa- 
moidean ligaments. 



THE COFFIN JOINT 

This joint, technically termed the distal interphalangeal articulation (Articu- 
latio phalangis tertiae), is a ginglymus formed by the junction of the second and 
third phalanges and tlie third sesamoid bone. 

Articular Surfaces. — The surface on the distal end of the second phalanx is 
convex from before backward. 



Lateral cartilage 




Lateral ligaments of 
)asterii joint 
Susj)('ii-'<()rg liga- 
tnenls of iiavicu- 
lur bone 



Tendon surface 
of navicular 
bone 

Wings of third 
phalanx 

Volar foramina 



Fig. 152. — Lateral Lioaments of Pastern Joint and Suspen- 
sory LicAMENTS OF NAVICULAR BoNE. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



concave transversely. The 
articular surface of the third 
phalanx slopes sharply up- 
ward and forward; its cen- 
tral part is prominent, and is 
flanked by two glenoid cavi- 
ties. It is completed behind 
by the articular surface of 
the third sesmoid or navicular 
bone. 

Joint Capsule. — This is 
attached around the margins 
of the articular surfaces. In 
front and laterally it is tight, 
and is l^lended with the exten- 
sor tendon and the lateral liga- 
ments respectively. Posteriorly, it forms a considerable pouch w^hich extends 
upward to about the middle of the second phalanx, where it is separated by a 
fibrous membrane from the digital synovial sheath. Laterally small pouches pro- 
ject outward (especially during volar flexion) against the lateral cartilages, just 
behind the lateral ligaments.^ 

Ligaments. — The lateral ligaments, external and internal (Ligamentum colla- 
terale ulnare, radiale), are short strong bands which are attached above in the 
depressions on either side of the lower part of the second phalanx, under cover of 
the lateral cartilage. They widen below and end in the depressions on either side 
of the extensor j^rocess and on tlie anterior end of the lateral cartilages. 

The suspensory navicular ligaments, external and internal (Ligamentum sesa- 
moideum collaterale ulnare, radiale),- 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 either side of the distal end of the first 

1 This should be noted in regard to resection of the lateral cartilage or other operations in 
this vicinity. 

- These are termed the postero-lateral ligaments by IM'Fadyean. They may well be called, 
as by German authors, the suspensory ligaments of the navicular bone. 



190 THE ARTICULATIONS OF THE HORSE 

phalanx and are here partly blended with the lateral ligaments of the pastern joint. 
They are directed obliquely downward and backward, and end chiefly on the 
ends and proximal border of the third sesamoid, but detach a branch to the inner 
surface of each lateral cartilage and wing of the third phalanx. 

The inferior navicular ligament (Ligamentum phalangeo-sesamoideum) rein- 
forces the capsule inferiorly. It is a strong layer of fibers which extend from the 
distal border of the third sesamoid to the tendon surface of the third phalanx, 
near the posterior margin of the articular surface. 

Movements. — The chief movements are flexion and 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 l)e checked mainly by the deep flexor tendon, since in cases of rup- 
ture of the hitter the toe turns up. Tlie sUght mobihty of the posterior part of the socket for the 
second phahinx (formed by the third sesamoid) diminishes concussion when the weight comes 
on the foot. 

LIGAMENTS OF THE LATERAL CARTILAGES 

In addition to the bands mentioned al)ove, which attach the lateral 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 plantar 
cushion. 

A short strong l)and connects the anterior extremity of the cartilage with the 
rough eminence on the second phalanx in front of the attachment of the lateral liga- 
ment of the coffin joint. 

The lower l)order of the cartilage is covered externally by fibers which attach 
it to the wing of the third phalanx. 



The Articulations of the Pelvic Limb 
the sacro-iliac articulation 

This joint (Articulatio sacro-iliaca) is a diarthrosis formed between the auricu- 
lar surfaces of the sacrum and ilium. These surfaces are not smooth in the adult, 
l)ut are marked by eminences and depressions, and are covered by a thin layer of 
cartilage. The joint cavity is a mere cleft, and is often crossed by fibrous bands. 

The capsule is very close fitting, and is attached around the margins of the 
articular surfaces. It is reinforced by the ventral sacro-iliac ligament (Ligamentum 
sacro-iliacum ventrale), which surrounds the joint, and is exceedingly strong above. 

The movements ar(^ inappreciable in the adult — stability, not mobilitv^, 
being the chief desi(U>i'atum. 

The following ligaments may be regarded as accessory to the joint, although 
not directly connected with it. 

The dorsal sacro-iliac ligament (Ligamentum sacro-iliacum dorsale breve) is a 
strong l)and which is attached to the internal angle (Tuber sacrale) of the ilium and 
the summits of the sacral spines. 

The lateral sacro-iliac ligament (Ligamentum sacro-iliacum dorsale longum) 
is a triangular, thick sheet which is attached in front to the internal angle and 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 ligament, below with the 
sacro-sciatic ligament, and behind with the coccygeal fascia. 

The sacro-sciatic ligament (Ligamentum sacrospinosum et tuberosum) is a 



SYMPHYSIS PELVIS — OBTURATOR MEMBRANE 



191 



quadrilateral sheet which completes the lateral pelvic wall. Its upper border is 
attached to the border of the sacrum and the transverse processes of the first and 
second coccygeal vertebrae. Its lower border is attached to the superior ischiatic 
spine and tuber ischii. Between these it bridges over the ext(n-nal border of the 
ischium and completes the lesser sciatic foramen. The anterior border is concave, 
and completes the greater sciatic foramen. The posterior border is fused with the 
vertebral head of the semimembranosus muscle. 

The ilio-lumbar ligament (Ligamentum ilio-lumbale) is a triangular sheet which 
attaches the ends of the lumbar transverse ])rocesses to the ventral surface of the 
ilium below the attachment of the longissimus muscle (Fig. 184). 



enlral s(icro-ih(i( iK/dmcnt 




1 E.rtmuil angle 
of ilium 



Sdcro-iliac articidntion 



Ilio-peciineal 
eminence 



Depression for origin of inner tendon of 
hiccps femoris 

Posterior part of trochanter mojor 
Anterior part of trochanter 
maj(fr 
X 



Trochanter minor 



Fig. 153. — Left Os Cox.e and Adjacent Parts of Sacrum and Femur of Horse. (After Schmaltz, Atlas 

d. Aiiat. d. Pferdes.) 



SYMPHYSIS PELVIS 
The symphysis pelvis is formed l)y the junction of the two ossa coxarum at 
the ventral median line. In the young subject the l)ones are united by a layer of 
cartilage; in the adult the latter is gradually replaced by bone, the process beginning 
in the pubic portion and extending backward. The union is strengthened by white 
fibrous tissue above and below, and a transverse band also covers the anterior border 
of the pubis (pecten). No appreciable movement occurs even before synostosis 
takes place. 



OBTURATOR MEMBRANE 
This (Membrana ol^turatoria) is a thin Xslyqv of fibrous tissue which covers the 
obturator foramen, leaving, however, a passage (Canalis obturatorius) for the 
obturator vessels and nerve. 



192 



THE ARTICULATIONS OF THE HORSE 



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. Internally it is 
cut into by a deep notch for the attachment of the round and pubo-femoral liga- 
ments. The acetabulum is a typical cotyloid cavity. Its articular surface is 
somewhat crescentic, being deeply cut into internally by the acetabular notch and 




Fir.. 154. — Pelvic Ligaments and Hip Joint. 
1, Dorsal sacro-iliac ligament; 2, lateral sacro-iliac ligament; S, sacro-.sciatic ligament; 4, greater sciatic 
foramen; 6, lesser sciatic foramen; 6, line of attachment of intermuscular .septum between biceps femoris and semi- 
tendinosus; 7, capsule of hip joint; S, rectus parvus or capsularis muscle; 9, outer tendon of origin of biceps 
femoris; 10, internal, 11, external, angle of ilium; 12, shaft of ilium; IS, superior ischiatic spine; 14, pubis; i. 5, 
tuber ischii; /(?, trochanter major; /7, semimembranosus; /S, fifth lumbar spine; /9, ;20, first and second coccygeal 
vertebrse. 



fossa. It is increased and deepened by a ring of fibro-cartilage, the cotyloid 
ligament (Labrum glenoidale), which is attached to the bony margin; that part of 
the ligament which crosses the notch is called the transverse ligament (Fig. 456). 
The joint capsule is roomy. It is attached around the margin of the acetab- 
ulum and the neck of the femur. It is thickest externally. 

The attachment on the femur is about 1 cm. from the marsin of the articuhxr surface, except 
above, where 2 to 3 cm. of the neck is intracapsular. A thin oblique bantl corresponding in direc- 
tion with the rectus parvus muscle reinforces the antero-external 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 ilio-psoas, and is adherent to the muscle. Internally, its fibrous part is perforated 
by the pubo-femoral and round ligaments and the articular vessels. 



THE HIP JOINT 



193 



The round ligament (Ligamentum teres) is a strong band which is attached 
in the subpul)ic groove* close to the acetabular notch, passes outward, and ends 
in the notch on the head of the femur (Fig. 45G). 

The pubo-femoral ligament (Ligamentum accessoriuni) does not occur in the 
domestic animals other than the eciuidae. It is a strong band detached from the 
prepul)ic tendon of the abdominal muscles (Fig. 456). It is directed outward, 
backward, and upward, passes through the acetabular notch above 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 attachment to the greater part of the fibers of the muscle. 

The sjmovial membrane is reflected over the intracapsular parts of these 



External patellar ligament 
Middle patellar ligament 



Tuber ositii of tibia 




External lateral ligament 
External condyle of tibia 



Shaft of fibula 



Fig. 155. — Left Stifle Joint of Horse, External View, in Partial Flexion. 

The capsules have been removed. 18, Femur; 20, patella; '31, tibia: a", internal patellar ligament; h, external 

femoro-patellar ligament; d, external semilunar cartilage, (.\iter Ellenberger-Baum, Anat. fur Kiinstler.) 



ligaments and covers the fossa acetabuli. A pouch also extends from the acetabular 
notch for a variable distance along the subpubic groove above the pubo-femoral 
ligament. 

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 ligament, 
ligament is tensed most promptly by inward rotation of the thigh. 
13 



The pubo-femoral 



194 



THE ARTICULATIONS OF THE HORSE 



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 inner ridge is much the larger 
of the two, especially at its u]:)per part, which is wide and rounded. The outer 

Proximal part of femoro-patellar capsule 
\ 
\ 



Patella — 



Middle patellar ligament 

Distal part of femoro- 
patellar capsule 

Tendon of origin of long ex- .. 
tensor and peroneus teriius 



Pouch of femoro-tibial 

capsule 




Exiermd femoro-patellar 
ligament 



Femoro-tibial capsule 

3y _ External hdcrtd. ligament 
.^^ ~[ -. Se77iilu7iar cartilage 

External condyle of tibia 



Fig. 156. — Left Stifle Joint op Horse, IjAteral View. 
The capsules are distended and the external patellar ligament is removed. 



ridge is much narrower, and is more regularly curved; its upper part lies about 
an inch behind a frontal plane tangent to the inner ridge. The articular surface 
of the patella is much smaller than that of the trochlea. It is completed internally 
by a supplementary plate of fibro-cartilage (Fibrocartilago patellae), which curves 
over the internal surface of the inner lip of the trochlea. A narrow strip of cartilage 
is found along the outer border also. The articular cartilage on the trochlea 
completely covers both surfaces of the inner ridg(>, but only a narrow marginal area 
on the external 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 inner side 
it is an inch or more from the articular cartilage; on the outer side and above, 



THE STIFLE JOINT 



195 



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. 
Below the patella it is separated from the straight ligaments by a thick pad of 
fat, but inferiorly it is in contact with the femoro-patellar capsules. The joint 
cavity is the most extensive in the body. It usually communicates with the 
inner femoro-tibial joint cavity by a slit-like opening situated at the lowest part 
of the inner ridge of the trochlea. A similar, but smaller, communication with the 
outer femoro-patellar capsule is often found at the lowest part of the outer ridge. 

The inner communication appears to be constant in adult horses, liut is Hahle to V^e over- 
looked on account of the fact that it is covered by a valvular fokl of the synovial membrane. It 
is about half an inch wide, and lies under the narrow articular area which connects the trochlea 
and internal condyle. The outer communication occurs in 18 to 25 per cent, of cases, according 
to Baum. It is instructive to distend this capsule and thus obtain an idea of its potential capa- 
city and relations (Fig. 156). 



Accessoj'y cartilage of patella 
ridge of trocJdea of femur 
Middle patellar ligament \ 



Internal ridge of trochlea of femur — ^^~ 



Internal semilunar cartilage- 
Internal patellar ligament- 



Tuberosity of tibia __ 




External femoro-patellar ligament 

Externcd patellar ligament 

External femoro-tibial ligament 
External semilunar cartilage 

Extern(d condyle of tibia 



Fibula 



Fig. 1.57. — Left STiPiiE Joint of Horse, Front View, in Extension. 
The capsules are removed. i<S, Femur; ^0, patella; .^i, tibia. (After EUenberger-Baum, Anat. fvir Kfmstler.) 



Ligaments. — The lateral femoro-patellar ligaments, external and internal 
(Ligamentum femoro-patellare fibularc, tibiale), arc two thin bands which reinforce 
the capsule on either side. The external ligament is fairly distinct; it arises from 
the external epicondyle of the femur just above the lateral femoro-tibial ligament, 
and ends on the external border of the patella. The internal ligament is thinner 
and is not distinct from the capsule; it arises above the internal epicondyle, and 
ends on the patellar fibro-cartilage. 

The patellar ligaments (Ligamenta patellae), also called the straight ligaments 
of the patella, are three very strong bands which attach the patella to the tuberosity 
of the tibia. The external patellar ligament is attached above to the outer part 
of the anterior surface of the patella, and below to the outer part of the tuberosity. 
It receives a strong tendon from the biceps femoris muscle. The middle patellar 
ligament extends from the front of the apex of the patella to the lower part of 



196 



THE ARTICULATIONS OF THE HORSE 



the groove on the tuberosity of the tibia, a bursa Ijcing interposed between the 
Hgament and the upper part of the groove. The internal patellar ligament is 
attached above to the patellar fibro-cartilage, and ends on the tuberosity of the 
tibia, internally to the groove. It is joined by the common aponeurosis of the 
gracilis and sartorius. These so-called ligaments are, in reality, the tendons of 
insertion of the quadriceps femoris muscle, and transmit the action of the latter 

to the tibia; they also func- 
tion similarly for the other 
muscles attached to them as 
noted above. 




Posterior crucial 
ligamvnt 
Anterior cru- 
cial ligatnent 



Spine 
tibia 



^Anterior ligaments 
of semilunar car- 
tilages 



It will be noticed that the 
upper attachments are further apart 
than the lower ones, so that the liga- 
ments converge below. The inner 
ligament is especially ol:)lique. The 
middle ligament is more deeply 
placed than the others, and there- 
fore cannot usually be felt distinctly 
in the living animal. 



-Sj:MiLrxAR Cartil.^ges and C'ruci.al Ligaments of 
Right Stifle of Horse. 
F, Femoral ligament of external cartilage. (After Schmaltz, Atlas 
d. Anat. d. Pferdes.) 



Posterior crucial 
ligament 



Anterior crucial ligament 



Ligaments of ex- 
ternal cartilage 



Fig. 158 

The femoro-tibial articu- 
lation (Articulatio femoro- 
tibialis) is formed between the 
condyles of the femur, the 
proximal end of the tibia, and the interposed semilunar cartilages. 

Articular Surfaces. — The condyles of the femur are slightly oblique in direc- 
tion. The articular surface of the outer one is more strongly curved than that of 
the inner one; the latter is confluent below with the inner ridge of the trochlea, 
while the narrow ridge which connects the external 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 semilunar cartilages (Meniscus 
lateralis, medialis) are two C-shaped or 
crescentic discs of fibro-cartilage which 
produce congruence in the articular stir- 
faces. Each has an upper concave sur- 
face adapted to the condyle of the femur, 
and a lower surface which fits the cor- 
responding condyle of the tibia. The 
external cartilage does not cover the 
outer and posterior part of the condyle, 
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 comua are attached to the tibia 
in front of and behind the spine. The 

external cartilage has a third attachment by means of an obli(|ue hsa\(\ (Liga- 
mentum femorale menisci lateralis) which passes from the posterior cornu to the 
posterior part of the intercondyloid fossa of the femur. 

The cornua of the internal cartilage (Ligamenta tibia^ anterius ct posterius menisci medialis) 
are attached in front of and behind the inner eminence of the spine. The anterior cornu of the 
external cartilage (Ligamentum tibia^ anterius menisci lateralis) is attached in front of the outer 
eminence of the spine. The posterior cornu bifurcates; the lower branch (Ligamentum tibise 





Head of 
fibula 



Fig. 159. — Proximal End.s of Right Tibi.a and 
Fibula op Horse, with Semilunar Car- 
tilages and Crucial Ligaments, Exter- 
nal View. (After Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



THE STIFLE JOINT 



197 



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. 

T)ie joint capsule is attached to the margin of the til^al artictilar surface, 
but on the femur tlie line of attachment is for the greater part about half an inch 
from the articular margin. It is also attached to the convex borders of the semi- 
lunar cartilages and to the crucial ligaments. It is strong posteriorly, but in front 
it practically consists only of the synovial layer. 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 semilunar cartilage. The inner sac pouches upward about half an inch 
over the condyle of the femur. The external sac invests the tendon of origin of the 
popliteus muscle, and also pouches downward about three or four inches (ca. 8 
to 10 cm.) beneath the peroneus tertius and long extensor muscles (Fig. 156). 



r 



Internal Jcmoro-patcllar 
ligament 



Internal lateral (femoro- ■- 
tibial) ligament J^ 




A ccessory cartilage of patella 

Internal ridge of trochlea of 

femiir 
Internal patellar ligament 



Middle patellar ligament 



Tuberosity of tibia. 



Fig. 160. — Left Stifle Joint of Horse, Intern-.\Ij Vif.w ix Extreme Extension.' 
IS, Femur; i?0, patella (base); 21, tibia; d, internal semilunar cartilage. (After Ellenberger-Baum, Anat. fiir 

Kun.stler.) 



As stated above, the outer sac sometimes commimicates with the femoro-patellar 
joint cavity, and the inner sac usually, if not always, does so in the adult. 

Ligaments. — There are fotu" of these — two lateral and two crucial. 

The internal lateral ligament (Ligamentum collaterale tibiale) is attached 
above to the prominent internal epicondyle of the femur, and below to a rough 
area below the margin of the internal condyle of the tibia. 

The external lateral ligament (Ligamentum collaterale fil)ulare) is somewhat 
thicker; it arises from the upper depression on the external epicondyle, and ends 
on the head of the fibula. It covers the tendon of the origin of the popliteus 
muscle, and a bursa is interposed between the lower part of the ligament and the 
margin of the external condyle of the tibia. 

' In this figure the patella is pushed up above the trochlea — a position which it does not 
occupy normally. 



198 



THE ARTICULATIONS OF THE HORSE 



The crucial ligaments are two strong rounded bands situated mainly in the 
intercondyloid fossa of the femur, between the two synovial sacs. They cross 
each other somewhat in the form of an X, and are named according to their tibial 
attachments. The anterior crucial ligament (Ligamentum cruciatum anterius) 
arises in the central fossa on the tibial spine, extends upward and backward, 
and ends on the upper ]:)art of the inner surface of the external condyle of the femur. 
The posterior crucial ligament (Ligamentum cruciatum posterius) is internal to 
the preceding, and is somewhat larger. It is attached to an eminence at the 
popliteal notch of the tibia, is directed upward and forward, and ends in the an- 
terior part of the intercondyloid fossa of the femur. 



Semimembranosus 



Vastus inter medias 







Patella 



Femoro- 
patellar 

joint cavity 




Bran ('lies of 
jiiislt ri(n'fem~ 
oral artery 
~ Gastrocnemnis 
(internal head) 
Popliteal 
artery 



Middle ligament of 
patella 



Fig. 161. — Right Stifle Joint of Horse; S.\gittal Section Passing Through Outer Part op Inner Ridge 

OF Trochlea and Intercondyloid Fossa. 

1, Anterior crucial ligament; 3, posterior crucial ligament; S, po.sterior cornu of internal semilunar cartilage; 

4, femoral ligament of external semilunar cartilage; 5, articular artery; 6, part of vastus internus. 



It may be added that these ligaments do not He 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 w'hole are 
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 l^e brouglit into the same straight line. Rotation is limited, 
and is freest during semiflexion. The patella glides on the femoral trochlea up- 
ward in extension, downward in flexion. 

Extension is checked mainly by tension of the crucial and lateral 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 inner 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 



TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT 



199 



ridge. During flexion, whicli is accompanied by slight inward rotation of the leg, the condyles 
of the femur and the s(>milunar cartilages glide backward on the tibia; the movement of the ex- 
ternal condyle and cartilage is greater than that of the inner one. In extreme fi(>xion the patellar 
and posterior crucial ligaments are tense; the other ligaments are relax(>d. Tlie mo\'ement of tiu^ 
patella is gliding with coaptation, i. c, different parts of the opjiosing articular surfaces come into 
contact successively. Only a narrow transverse strip (ca. l.o to 2 cm. wide) of the patella is in 
contact with the trochlea at a time. 



TIBIO-FIBULAR ARTICULATION 

The head of the fibula articulates with a crescentic facet just below the outer 
margin of the external condyle of the tibia. The joint capsule is strong and close. 
The shaft of the fibula is attached to the external border of the tibia by the inter- 
osseous membrane of the leg (Membrana interossea cruris) ; this is perforated 
about an ineii 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 external malleolus. The latter is the 
distal end of the fibula which has fused with the tibia. No appreciable movement 
occtu's in this joint. 



Exterudl 

later (d 

(short) ,^-^ 

lignnwnt ,.-- 

Trochlea of 

tibial tarsal 

Dorsal liga 

mcnt 




Plantar 
liga mcnt 



Plantar 
ligament 



Small 


Small 


metatarsal 


meta- 


hone 


tarsal 




hone 




Internal 
lateral 
-:-:--■-. (short) 
ligament 
Trochlea of 
tibial tarsal 
Dorsal 
ligament 



Fig. 102. — Left Hock .Joint op Horse, Externai> Fk;. 16.3. — Left Hock Joint of Horse, Internal, 

View. View. 

^i, Tibia; ;?4, tuber calcis; ;2.5, large metatarsal bone; .4'', long external lateral ligament; oi, long internal lateral 
ligament. (After Ellenberger-Bauin, Anat. fur Kiinstler.) 



THE HOCK JOINT 

This is a composite joint made up of a number of articulations (Articulationes 
tarsi). These are: (1) The til)io-tarsal articulation; (2) the intertarsal articula- 
tions; (3) the tarso-metatarsal articulation. 

Tlu^ tibio-tarsal articulation (Articulatio talo-cruralis) is a typical ginglymus 
formed by the trochlea of the tibial tarsal bone (astragalus or talus) and the cor- 
responding surface of the distal end of the tibia. The ridges and grooves of these 
surfaces are directed ol)liquely forward and outward at an angle of al)Out 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 



200 



THE ARTICULATIONS OF THE HORSE 



arthrodia, which have joint surfaces and ligaments of such a nature as to allow 
only a minimal amount of gliding 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 free surface of the bones which it covers, and blends with the lateral 
ligaments. Its anterior part (anterior ligament) is rather thin; in distention of the 
capsule, as in ''bog-spavin," its antero-internal part, which is not bound down by 
the tendons passing over the joint, forms a fluctuating swelling over the inner ridge 
of the trochlea. The posterior part (posterior and tarso-metatarsal ligaments) is 
very thick, and is intimately attached to the tarsal bones. Its superficial face is 
in part cartilaginous, and forms a smooth surface for the perforans tendon. Su- 
periorly, it pouches upward behind the distal end of the tibia for a distance of about 




Short internnl Iater<il ligament - 
Long internal lateral ligament -■ 



Internal small metatarsal bone 




External lateral ligament 



External small metatarsal bone 



Fig. Ifi4. — Left Hock Joixt of Horse, Anterior View. 
21, Tibia; 22, trochlea of tibial tarsal bone; 25, large metatarsal bone; 50, dorsal or oblique ligament. 

EUenberger-Baum, Anat. fiir Kiinstler.) 



(After 



two inches (ca. 5 cm.). Inferiorly, it is continued downward, forming the sub- 
tarsal or check ligament, which unites with the perforans tendon about the middle 
of the metatarsus. 

There are four synovial sacs: 1. The tibio-tarsal sac lul)ricates the proximal 
joint, and is much the largest and most important. It is chiefly involved in the 
swelling produced by excess of fluid in the joint cavity, when the capsule bulges 
antero-internally and postero-superiorly. 2. The first intertarsal sac lines the joints 
formed by the tibial and fibular tarsal bones above, and the central and fourth 
tarsals below; it communicates in front with the proximal synovial capsule. 3. 
The second intertarsal sac lubricates the joints formed between the central tarsal 
and the bones below and on either side. 4. The tarso-metatarsal sac lubricates 
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. — Th(> external lateral ligament (Ligamentum collaterale 



THE HOCK JOINT 



201 



fibulare longum et breve) consists of two distinct bands which cross each other. 
The long (superficial) ligament arises on the posterior part of the external malleolus, 
is directed almost straight downward, and is attached to the fibular and fourth 
tarsal bones and the large and external small metatarsal bones. It forms a canal 
for the lateral extensor tendon. The short (deep) ligament arises on the anterior 
part of the external malleolus, is directed chiefly Imckward, and ends on the rough 
excavation on the external surface of the tibial tarsal and the adjacent surface of 
the fibular tarsal bone. 

The internal lateral ligament (Ligamentum collaterale tibiale longum et breve) 
also consists of two ])arts which cross each other. The long ligament arises on the 
posterior part of the internal malleolus, becomes wider below, and is attached on 
the lower tuberosity of the tibial tarsal, the large and outer small metatarsal bones, 
and the inner surface of the lower tarsal bones which it covers. The short ligament 
lies largely under cover of the long one. It extends from the anterior part of the 
internal malleolus runs backward and somewhat downward, and divides into two 



External lateral ligament 
Plantar ligament 



Small metatarsal bones .^rrr: 



Large metatarsal bone - 




Long internal lateral ligament 
Short internal lateral ligament 



Suspensory ligament 



Fig. 165. — Left Hock Joint of Horse, Posterior View. 
31, Tibia; 34, tuber caicis. (After Ellenberger-Baum, Anat. fur Kunstler.) 



branches; one of these ends on the upper tuberosity on the inner surface of the 
tibial tarsal bone, the other on the sustentaculum tali. 

The plantar or calcaneo-metatarsal Ugament (Ligamentum tarsi plantare) is a 
very strong fiat band which covers the outer part of the posterior surface of the 
tarsus. It is attached to the posterior surface of the fibular and fourth tarsal 
bones and the proximal end of the external metatarsal bone. 

The dorsal or oblique ligament (Ligamentum tarsi dorsale) is a triangular 
sheet which is attached above to the lower tuberosity on the inner 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 inner small metatarsal bones, to all of Avhich 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. 



202 



THE ARTICULATIONS OF THE HORSE 



(1) The tibial and fibular tarsal bones are united by four bands (astragalo-calcaneal liga- 
ments). The internal ligamentjextends from the sustentaculum tali to the adjacent part of the 
tibia tarsal, blending with the short lateral ligament. The external ligament extends from the 
anterior process of the fibular tarsal to the adjacent part of the external ridge of the trochlea. 
The superior 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 attached 
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 oblicjue anterior ligament (scaphoido-cunean ligaments). 
The central and fourth tarsal are united Ijy an interosseous and a trans^'erse external ligament 
(cuboido-scaphoid ligament). The third and fointh tarsals are similarly connected (cuboido- 
cunean ligaments). The third tarsal is joined by an interosseous (intercunean) ligament to the 



Superficial flexor tendon 

Gastrocnemius tendon 

Tarsal tendon of 
biceps femoris 

Calcanean bursa 

Gastrocnemius 
bursa 

Tuber calcis 

Upper pouch of 
joint capsule 

Tibial tarsal bone 



Interosseous ligament 

Plantar ligament 

Fourth tarsal bone 

Interosseous liga men t 
Large metatarsal bone 

S u spe nsory liga me n t 
Check ligament 



Deep flexor 
Tibia 




Tibialis anterior 
Peroneus tertius 



Tibio-tarsal joint carity 
Joint capsule 
Central tarsal bone 
Third tarsal bone 

Distal annular ligament 



Fig. 166. — Salittai. Section op Hock of Horse. 



(fused) first and second tarsals; the latter are connected with the fourth tarsal by a transverse 
posterior ligament. 

(3) The smaller bones are connected with the upper row as follows: The central is attached 
to the tibial tarsal by posterior 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 posterior (calcaneo-cuboid) ligaments. The (fused) first and second tarsals 
are connected with the fibular tarsal by a posterior (calcaneo-cunean) ligament. 

(4) The lower tarsal bones are connected with the metatarsus by tarso-metatarsal ligaments, 
which are not distinct from the common ligaments, 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) 
is about 150° to 160°. Complete extension is prevented by tension of the lateral 
ligaments. Flexion is checked only by contact of the metatarsus with the leg, 



JOINTS AND LIGAMENTS OF THE VERTEBRA 



203 



provided tho 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 movements of the hock joint must correspond witli those of tlie stifle on account of the 
tendinous hands in front and behind (peroneus tertius antl flexor perforatus), wliich extend from 
the lower part of the femur to the tarsus and metatarsus. 



limb 



The remaining joints differ in no material respect from those of the thoracic 



COMPARATIVE ARTHROLOGY' 

JOINTS AND LIGAMENTS OF THE VERTEBRA 

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 wider and flat. 
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 




Fir,. 167. — Ligamentum Nuch^ of Ox. 

a. Funicular part; h, wide portion; c. rf, lamellar part; e, interspinous ligaments; 1 , spinous process of first thoracic 

vertebra; .^, axis. (Ellenberger-Baum, Anat. d. Haustiere.) 



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. The 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 inferior common ligament is very strong in the lumbar region. 

The intervertebral fibro-cartilages are thicker than in the horse. 

The interspinous ligaments of the back and loins consist largely of elastic 
tissue. 

' This section consists necessarily only of a brief statement of the most important differences 
m the joints of the other animals. 



204 COMPARATIVE ARTHROLOGY 

There are no intertransverse joints in the lumbar region. 

Pig. — The hgamentum nuchse is represented by a fibrous raph^ 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 odontoid process. The two 
alar ligaments (Ligamenta alaria) arise on either side of the odontoid process, 
diverge, and end on either side of the foramen magnum. The transverse ligament 
of the atlas (Ligamentum transversum atlantis) stretches across the dorsal surface 
of the odontoid process and binds it down on the ventral arch of the atlas, a bursa 
being interposed. It is attached on either side to the lateral masses 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 externally. (They are synchondroses in the sheep.) 
The upper parts of the cartilages are attached to each other by distinct elastic 
ligaments (Ligamenta 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 a diarthrosis with the body. The 
anterior joint surface is concave, the posterior convex. The joint (Articulatio 
intersternalis) is surrounded by a close capsule, and the joint surfaces are attached 
to each by a small intra-articular ligament. Limited lateral movement is possible. 
(In the sheep the joint is a synchondrosis.) 

Both surfaces of the sternum are covered by a layer of fi])rous tissue. 

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 
lateral movement than in the horse. 

The condyle of the mandible is rehitively small and is concave transversely. The temporal 
articular surface is extensive antl is convex in both directions. The postglenoid process is small. 

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. Lateral movement is limited. The 
posterior ligament is absent. 

Dog. — The articular surfaces allow extremely little lateral or gliding movement. 
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 — THE CARPAL JOINTS 205 

Articulations of the Thoracic Limb 

SHOULDER joint 

Ox. — The articular angle is about 100°. 

Pig and Dog. — The joint capsule communicates freely with the bicipital bursa. 
There is a rudimentary marginal cartilage around the rim of the glenoid cavity. 
In the dog there is usually a strong band extending from the acromion to the outer 
part of the capsule; another band (Ligamentum coraco-acromiale) often stretches 
between the scapular tuberosity and the acromion. 



ELBOW JOINT 

Ox. — No important differences exist. The upper part of the interosseous 
radio-ulnar ligament is commonly ossified in the adult. 

Pig. — There are no important differences. The radius and ulna are so firmly 
united by the interosseous ligament as to prevent any apprecial)le movement 
between them. 

Dog. — The joint capsule is reinforced in front by an oblique ligament which 
arises on the front of the external condyle of the humerus above the joint surface, 
and joins the terminal part of the biceps and brachialis below. The external 
lateral ligament is thick and divides into two parts; the anterior part is attached 
to the radius and blends with the annular ligament; the posterior part widens 
below, forming a sort of cap, and is attached to the ulna. The internal lateral 
ligament also divides into two branches; the anterior branch ends on the inner 
surface of the neck of the radius; the posterior enters the interosseous space and 
is attached to both bones. An elastic band (Ligamentum olecrani) extends from 
the outer surface of the internal epicondyle to the anterior border of the ulna. 

There are two radio-ulnar joints. The proximal radio-ulnar joint is included 
in the capsule of the elbow, l)ut is provided with an annular ligament which extends 
from the lower part of the external ligament across the front of the proximal end 
of the radius to the ulna, blending with the biceps and brachialis tendons. The 
distal joint is formed by a concave facet on the radius and a convex one on the 
radius, and is surrounded by a tight capsule. The interosseous membrane unites 
the shafts of the two 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 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 articu- 
lar surfaces and certain ligamentous differences. The lateral ligaments are much 
weaker, the long external one being especially small in the ox. Two oblique, 
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 downward 
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 lateral ligaments are well defined, a ligament connects 

^ These movements are best seen in man, in whom the back of the hand may be turned for- 
ward (pronation) or backward (supination). 



206 



COMPARATIVE ARTHROLOGY 



the accessory carpal with the distal end of the ulna, and 'strong bands connect 

the distal bones with the 
metacarpus. 

The interosseous and in- 
terordinal ligaments vary with 
the number of carpal bones 
present in the different species. 



INTERMETACARPAL JOINTS 

In the ox the small (fifth) 
metacarpal bone articulates 
with the large metacarpal, l)ut 
not with the carpus. The joint 
cavity is connected with that 
of the carpo-metacarpal sac. 
The proximal end of the small 
metacarpal bone is attached 
by a ligament to the fourth 
carpal, and another band ex- 
tends from its distal part to 
the side of the large metacar- 
pal. There is also an inter- 
osseous ligament, which is per- 
manent and allows a small 
amount of movement. 

The chief metacarpal 
bones of the pig, and the second 
to the fifth of the dog, articu- 
late with each other at their 
proximal ends, and are connect- 
ed by interosseous ligaments, 
which do not, however, unite 
them closely, as in the horse. 



METACARPO-PHALANGEAL 
JOINTS 

Ox. — There are two 
joints, one for each digit. The 
two capsules communicate 
posteriorly. The two inter- 
digital lateral ligaments (Liga- 
menta collateralia interdigi- 
talia) result from the bifurca- 
tion of a band which arises in 
the furrow between the divi- 
sions of the distal end of the 
large metacarpal bone; they 
spread out and end on the 
proximal ends of the first 




F'lc. IGS. — Distal Part of Limb of Ox, Showing Ligaments 
AND Tendons. One Digit and 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 a; b, deep flexor 
tendon; h' , branch of b to digit removed; c, c, superficial flexor 
tendon; d, d' , intersesamoid ligament (cut); e, interdigital lateral 
ligament of fetlock joint; /, tendon of common extensor; g, proxi- 
mal interdigital ligament; h, digital annular ligament; i, posterior 
annular ligament of fetlock; A', lateral ligament of pastern joint; 
/, distal interdigital ligament; m, crucial interdigital ligament 
(cut); m' , vi" , attachments of m to second phalanx and distal 
sesamoid lione; n, suspensory ligament of distal sesamoid; o, an- 
terior elastic ligament; p, lateral volar ligament of pastern joint; 
1, metacarpus, sawn off at /'; 2, first phalanx; S, second phalanx; 
4, third phalanx. (Ellenherger-Baum, Anat. d. Haustiere.) 



phalanges. A strong superior 
interdigital ligament (Ligamentum interdigitale), consisting of short intercrossing 
fibers, unites the middles of the interdigital surfaces of the first phalanges. 



METACARPO-PHALANGEAL JOINTS 



207 



Crucial ligaments (Ligamenta phalango-sesamoideae) connect the 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 lateral sesamoidean ligaments end almost entirely on the first phalanges. 

The superficial inferior sesamoidean ligament is absent. The middle inferior 
sesamoidean ligaments of each digit are two short strong bands which extend from 
the distal margins of the sesamoids to the proximal ends of the first phalanges. 
The deep inferior sesamoidean ligaments are strong and distinctly crucial. 




Fig. 169. — Lig.^ments and Tendons op Digits op Pig, 
Volar View. 
a. Superficial fle.xor tendon; b, deep flexor tendon; 6', 
branches of 6 to acce.ssory 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; (j, abductor of accessory digit. (Ellen- 
berger-Baum, Anat. d. Haustiere.) 




Ill -V^* 



A'—i 



Fig. 170. — Ligaments and Tendons of Paw of 
Dog, Hind Limb, Volar View. 
a, a'. Superficial flexor tendon; b, tendon 
to large pad; c, lumbricales muscles; d, interossei 
muscles; e, /, annular ligaments at metatarso- 
phalangeal joints; ff, suspensory ligament of large 
pad; h, digital annular ligaments; (', deep flexor 
tendon; k, distal sesamoid; /, suspensory ligament 
of k; m, suspensory ligament of digital pad; n, 
digital pads. (EUenberger-Baum, Anat. d. Hau.s- 
tiere.) 



The suspensory or superior sesamoidean ligament is more distinctly muscular 
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 
branches or trifurcation of the middle branch. The four lateral bands end on the 
sesamoid bones and the distal end of the large metacarpal bone, and detach 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 



208 COMPARATIVE ARTHROLOGY 

which join the tendons of the proper extensors of the digits; it sends fibers also to 
the interdigital lateral 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 tendinous band descends from 
each accessory digit to the third phalanx and sesamoid l)one, blending with the 
tendon of the corresponding proper extensor. 

Pig. — There are four metacarpo-phalangeal joints, each of which has a capsule, 
lateral, intersesamoidean, and crucial sesamoidean ligaments. Since distinct inter- 
osseous muscles are present, there are, of course, no suspensory ligaments. 

Dog. — There are five metacarpo-phalangeal joints, each having its own capsule 
and indistinct lateral 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, lateral ligaments. Each joint has also two central and two lateral volar 
ligaments. The central ligaments are largely fused to form a strong band. The 
lateral ones extend from the borders of the first phalanx to the proximal end of the 
second phalanx. 

The distal interphalangeal joints have, in addition to the capsules and lateral 
ligaments, bands which reinforce them on either side. The central or 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 phal- 
anges at the margin of the articular surface. The lateral 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 crucial or inferior interdigital ligaments (Ligamenta cruciata interdigitalia) 
are two strong bands which limit the separation of the digits. They are attached 
above to the lateral (or abaxial) eminences on the proximal ends of the second 
phalanges (blending with the lateral ligaments), cross the deep flexor tendon 
obliquely, and reach the interdigital space, where they intercross and blend. Most 
of the fibers end on the third sesamoid of the opposite side, but some are attached 
to the interdigital aspect of the second phalanx and the third 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 third sesamoid 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 inferior interdigital ligament resembles, however, that of the sheep, 
and is intimately adherent to the skin. There is, besides, a remarkable arrange- 
ment of ligaments which connect the small digits with each other and with the 
chief digits. 

This apparatus is somewhat complex, but its chief features are as follows: A superior 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 ligaments) arise on the 
bases of the small digits, cross the flexor tendons ol)liquely downward and inward, pass through 
the superior interdigital ligament, and blend below with the inferior interdigital ligament. Two 
lateral bands (lateral longitudinal interdigital ligaments) are attached in common with the 



COMPARATIVE ARTHROLOGY 209 

superior interdigital ligaments to the third phalanges of the small digits, and blend below with 
the outer part of the inferior intenligital ligament. 

Dog. — Each joint has a capsule and two lateral ligaments. The distal joints 
have also two elastic dorsal ligaments (Ligamenta dorsalia), which extend from the 
proximal end of the second phalanx to the ridge at the base of the third phalanx 
(Fig. 133). 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. 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. 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. 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 pubo-femoral or 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 inner femoro-tibial joint cavities; this is situated as in the horse, but is wider. 
A small communication with the external femoro-tibial capsule sometimes occurs. 
The two femoro-tibial capsules usually communicate. The middle patellar liga- 
ment is not simken, as there is no groove on the tuberosity of the tibia where it is 
attached. The external patellar ligament fuses completely with the tendon of 
insertion of the biceps femoris, and a synovial bursa is interposed between them 
and the external condyle of the femur. 

In the other animals there is a single ligamentum patellae, and the synovial 
sacs communicate so freely as to constitute a common joint cavity. In the clog 
the semilunar cartilages are united anteriorly by a transverse ligament, and the 
posterior part of the capsule contains the two Vesalian sesamoids, w^iich articulate 
with the condyles of the femur. 

TIBIO-FIBULAR JOINTS 

Ox. — The proximal end of the fibula fuses with the external condyle of the 
tibia. The distal end remains separate, and forms an arthrosis with the distal end 
14 



210 COMPARATIVE ARTHROLOGY 

of the tibia; the movement here is imperceptible, as the two bones are closely 
united by strong peripheral fibers. 

Pig. — The superior 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 outer border 
of the tibia. 

The inferior joint is included in the capsule of the hock joint, and is strength- 
ened by oblique anterior and posterior ligaments. There is also an interosseus 
ligament. 

Dog. — The arrangement is essentially the same as in the pig, but there is no 
interosseous ligament in the inferior joint. 



HOCK JOINT 

Ox. — There is very considerable mobility at the first intertarsal joint, the 
capsule of which is correspondingly roomy. The short external lateral ligament 
is attached below on the til^ial tarsal only. A strong transverse ligament attaches 
the external malleolus (distal end of the fibula) to the back of the tibial tarsal bone. 
The dorsal or oblique ligament is narrow and thin. 

Pig. — The arrangement in general resembles that of the ox. 

Dog. — The long lateral ligaments are very small, and the short ones double. 
The plantar ligament is weak, and ends on the fourth metacarpal bone. No 
distinct dorsal (or oblique) ligament is present. Movement occurs almost ex- 
clusively at the tibio-tarsal joint. 

The remaining joints resemble those of the thoracic limb. 



THE MUSCULAR SYSTEM 

MYOLOGY 

The muscles (Musculi) are the active organs of motion. They are charac- 
terized by their ])roperty of contracting when stimulated. Muscular tissue is of 
three kinds: (a) Striated or striped; (5) non-striated, unstriped, or smooth; and 
(c) cardiac. Only the first of these varieties will be considered in this section. The 
striped muscles, being for the most part directly or indirectly connected with the 
skeleton, are often termed skeletal or somatic, while unstriped muscle may be spoken 
of as visceral or splanchnic. The former cover the greater part of the skeleton, 
and thus in a large measure determine the form of the animal. They are red in 
color, the shade varying in different muscles and under various conditions. 

Muscles vary greatly in form, and may be classified as — (o) Long; (6) short; 
(c) flat; (rf) ring-like or orbicular. Long muscles are found chiefly in the limbs, 
while the flat or l)road muscles occur principally in the trunk, where they assist in 
forming the walls of the body cavities. The ring-like or orbicular muscles circum- 
scribe orifices which they close, and are hence termed sphincters. 

Attachments. — The muscles are attached to bones, cartilages, Ugaments, 
fasciae, or the skin. In all cases the attachment is by means of fibrous tissue, the 
muscle-fibers not coming into direct relation with the bone or cartilage. The 
perimysium of the muscle may fuse directly with the periosteum or perichondrium 
(fleshy attachment), or the union may be by means of intermediary fibrous struc- 
tures called tendons or aponeuroses (tendinous attachment). Tendons may be 
funicular, riljbon-like, or in the form of membranous sheets; to the latter the term 
aponeurosis is commonly applied. 

In certain positions, especially where tendons play over joints or are subjected 
to great pressure, sesamoid bones develop in the original tendon tissue. Some 
of these are large and constant, as the patella and the great sesamoids of the fet- 
lock. 

The accessory structures connected with the muscles are the synovial mem- 
branes and the fasciae. 



_Mesotenclon 




J^ibrous sheatk. 

'Synovial sheath 






Fig. 171. — Dt.\(:R.\M.s of Cross-sections of Tendon She.^th (A) and BrRS.\ (B); T, Tendon. 

The synovial membranes are arranged in two principal forms: (a) Bursal; 
(6) vaginal. A bursa (Bursa mucosa) is a simple sac interposed between the tendon 
or muscle and some deeper seated structure— most commonly a bony prominence. 
A vagina tendinis or tendon sheath differs from a bursa in the fact that the synovial 
sac is folded around the tendon more or less completely, so that two layers can be 
distinguished; of these, the inner one adheres closely to the tendon, while the 
outer lines the groove or canal in which the tendon lies. The two layers are con- 

211 



212 THE MUSCULAR SYSTEM 

tinuous along a fold termed the mesotendon. The arrangement is shown in 
Fig. 171.^ The articular synovial membranes in some places form extra-articular 
pouches, which facilitate the play of tendons. 

The fasciae are sheets of connective tissue, mainly of the white fibrous variety, 
with a greater or less admixture of elastic fibers in certain cases. Two layers may 
usually be recognized. Of these, the superficial fascia (Fascia subcutanea) is com- 
posed of loose connective tissue which may contain more or less fat and is sub- 
cutaneous. The deep fascia is composed of one or more layers of dense fibrous 
tissue spread over the surface of the muscles chiefly. Its deep face may be very 
loosely attached to the underlying structures or may fuse with the epimysium, 
tendons, bones, or ligaments. In some parts, especially the limbs, septal plates 
pass between the muscles and are attached to the bones or ligaments; these are 
termed intermuscular septa. In this way many muscles are inclosed in fibrous 
sheaths which hold them in position. Not uncommonly special bands stretch 
across the grooves in which tendons play, converting these into canals. Such 
bands are termed vaginal or annular ligaments. The deep fascia is often so dis- 
tinctly tendinous in structure, furnishing attachment to special tensor muscles, 
as to render the distinction between fascia and a]wneurosis quite arl^itrary. Bursse 
occur in certain situations between the fascia and underlying structures (subfascial 
bursse), or between the fascia and the skin (subcutaneous bursie). 

It is convenient to divide the description of a muscle into seven heads, viz.: 
(1) Name, followed by important synonyms; (2) position and form; (3) attach- 
ments; (4) action; (5) structure; (6) relations; (7) blood and nerve supply. 

1. The name is determined by various factors, viz.: (a) The action, e. g., 
extensor, adductor, etc.; (6) the shape, e. g., quadratus, triangularis; (c) the chrec- 
tion, e. g., rectus, obliquus; (d) the position, e. g., the subscapularis, iliacus; (e) 
the division (into heads, etc.), e. g., biceps, triceps, etc.; (/) the size, e. g., major, 
minor, etc.; {g) the attachments, e. g., sterno-cephalicus, mastoido-humeralis; 
(/i) the structure, e. g., semitendinosus. In most cases two or more of these factors 
have combined to produce the name, e. g., adductor magnus, longus colli, obliquus 
externus abdominis. 

2. The shape is, in many cases, sufficiently definite to allow the use of such 
terms as triangular, quadrilateral, fan-shaped, long, flat, fusiform, ring-like, etc. 

3. The attachments are in most cases to bone, but many muscles are attached 
to cartilage, ligaments, fascia, the skin, etc. It is usual to apply the term origin 
to the attachment which always or more commonly remains fixed when the muscle 
contracts. The term insertion designates the movable attachment. Such a 
distinction cannot always be made, as the action may be reversible, or both at- 
tachments may be freely movable. 

4. The action l^elongs rather to physiological study, ])ut is briefly indicated 
in anatomical descriptions. 

5. The structure includes the direction of the muscle-fibers, the arrangement 
of the tendons, the synovial membranes, and any other accessory structures, e. g., 
annular ligaments and reinforcing sheaths and bands. The relation of the muscle- 
fibers to the tendon varies, and this fact has given rise to special terms. Thus a 
muscle in which the fibers converge to either side of the tendon is termed bipennate ; 
while one in which this arrangement exists only on one side of the tendon is called 
unipennate. The terms fleshy and tendinous are used to indicate the relative 
amounts of muscular and tendinous tissue. The muscular tissue is often spoken of 
as the belly (Venter) of the muscle. In the case of the long muscles, the origin is 

'The student will note in dissection that transition forms occur; also that the same sheath 
may l)elong to two or more tendons in common, c. (j., the sheath of the two flexors on the back of 
the carpus. In such cases the synovial membrane is reflected from one tendon to the other, and 
may form a secondary meso tenon. 



MUSCLES OF THE LIPS AND CHEEKS 213 

often termed the head (Caput). Muscles having two or more heads arc called 
biceps, triceps, etc. Digastric muscles are those which have two bellies joined by 
an intermechate tendon. Ring-like muscles which circumscribe openings are 
termed sphincters, on account of their action. 

6. The relations are, of course, important on surgical grounds. 

7. The nerve-supply is of clinical interest, and is important for the determina- 
tion of homologies. 



FASCIA AND MUSCLES OF THE HORSE 
PANNICULUS CARNOSUS 
The panniculus camosus (Musculus cutaneus) is a thin muscular layer de- 
veloped 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, thoracic, and abdominal 
portions, each of which will be described with the muscles of the corresponding 
region. 

The Fascia and Muscles of the Head 

The muscles of the head may be divided into three groups, viz. : (1) Superficial 
muscles, including the panniculus and those of the lips, cheeks, nostrils, eyelids, 
and external ear; (2) the orbital muscles; (3) the muscles of mastication. 

The superficial fascia forms an almost continuous layer, but is verj' 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 
covers the temporalis muscle, and is attached to the parietal and frontal crests 
internally, and to the zygomatic arch externally. The buccal fascia covers the 
buccinator muscle and the free part of the outer surface of the ramus of the jaw. 
Superiorly it is attached to the facial crest, and posteriorly it forms a band (Liga- 
mentum pterygomandi1)ulare) which stretches from the hamulus of the pterygoid 
bone to the mandible behind the last molar tooth. It is directly continuous with 
the pharyngeal fascia, which is attached to the great and thyroid cornua of the 
hyoid bone, covers the lateral walls of the pharynx, and blends dorsally with the 
median raphe of the constrictor muscles of the latter. 



SUPERFICIAL MUSCLES 
1. Panniculus camosus. — The facial panniculus (M. cutaneus faciei) consists 
of a thin and usually incomplete muscular stratum, which covers the submaxillary 
space and the masseter muscle. A branch from it passes forw^ard to the angle of 
the mouth and blends with the orbicularis oris; this part (M. cutaneus labiorum) 
retracts the angle of the mouth. (A number of the superficial muscles of the face 
may be considered modified parts of the panniculus, e. g., the corrugator supercilii, 
malaris, zygomaticus, etc.) 



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 



214 



FASCIA AND MUSCLES OF THE HORSE 



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-lal)ial, facial, and mental arteries. 

Nerve-supply. — Facial nerve. 

2. Levator nasolabialis (Levator labii superioris al^que nasi). — This thin 




Fig. 172. — Muscle.s op Head of Horse, L.\terai^ View. The Panniculus is Removed. 
a, Levator labii superioris proprius; b, levator nasolabialis; c, mastoido-humeralis; d, sterno-cephalicus; 
d', tendon of d; e, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; h, buccinator; /, depressor labii 
inferioris; A', orbicularis oris; /, dilatator naris superior; 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; t, splenius; v, stylo-maxillaris; y, mastoid tendon 
of mastoido-humeralis; 2, posterior, 3, anterior, border of external ear; 8, scutiform cartilage; 9, zj-gomatic 
arch; 10, depression behind supraorbital process; 18, temporo-mandibular articulation; 27, facial crest; SO', 
angle of jaw; 37, external maxillary vein; 38, jugular vein; 39, facial vein; 40, parotid duct; 41, transverse 
facial vein; 42, masseteric vein; 4^, facial nerve; 44, parotid gland; 45, chin; x, wing of atlas. (After Ellen- 
berger-Baum, Anat. ffir Kimstler.) 



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 outer wing of the nostril; (2) the com- 
missure of the lips. 

Action.- — (1) To elevate the upper lip and the commissure; (2) to dilate the 
nostril. 



MUSCLES OF THE LIPS AND CHEEKS 



215 



Structure. — The muscle arises by 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 u]:)per liji, blending with the 
lateral dilator; the ventral one is much 
smaller, and blends at the labial com- 
missure with the orbicularis and buc- 
cinator. 

Relations. — Superficially, the skin, 
fascia, and lateral dilator (in part); 
deeply, the levator labii superioris pro- 
prius, lateral dilator (in part), buccin- 
ator, branches of the facial vessels and 
nerve, and the infraorljital artery and 
nerve. 

Blood-supply. — Facial and palato- 
labial arteries. 

Nerve-supply. — Facial nerve. 

3. Levator labii superioris pro- 
prius. — 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. 

Insertion. — -The upper lip, by a 
common tendon, with its fellow. 

Action. — Acting with its fellow, to 
elevate the upper lip. This action, if 
carried to the fullest extent, results in 
eversion. In unilateral action the Hp 
is drawn upward and to the side of the 
muscle acting. 

Structure. — -The nmscle has a 
short, thin tendon of origin. The 
belly is at first flattened, but be- 
comes narrower and thicker, then 
tapers over the false nostril, to termin- 
ate in a tendon. The tendons of the 
two muscles unite over the alar car- 
tilages of the nostrils, forming an ex- 
pansion which spreads out in the sub- 
stance of the upper lip. 

i^etoions.— Superficially, the skin, 
the levator nasolabialis, and the angu- 
lar vessels of the eye; deeply, the 
superior and transverse dilators of 
the nostril 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. 




Fig. 173. — Muscles of Head op Horse, Dorsal View. 
The Panniculus is Removed. 
a, Levator labii superioris proprius; a', common 
tendon of a with opposite muscle; b, levator nasolabialis; 
/, dilatator naris lateralis; g, zj'gomatieus; /, dilatator 
naris superior; n, parotido-auricularis; o", scutulo-auricu- 
laris superficialis superior; p, interscutularis; p', fronto- 
scutularis, pars temporalis; r, cervico-auricularis superfici- 
alis; u, corrugator supercilii; x, transversus nasi; ^, poste- 
rior, 3, anterior, border of e.xternal ear; 8, scutiform carti- 
lage; 9, zygomatic arch; 10, supraorbital depression; 35, 
inner wing of nostril, containing lamina of alar cartilage; 
39, facial vein. (.\fter EIIenberger-Baum, Anat. fiir 
Kiinstler.) 



216 FASCIA AND MUSCLES OF THE HORSE 

Structure. — Fleshy, with a thin aponeurotic origin. 
Relations. — Superficially, the skin; deeply, the buccinator. 
Blood-supply . — Facial artery. 
Nerve-supply. — Facial nerve. 

5. Incisivus superior (Depressor labii superioris). — 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 arranged in the lower lip like the preceding 
muscle in the upper one. 

Origin. — The alveolar border of the mandible from the second incisor to a 
point near the first cheek tooth. 

Insertion. — The skin of the lower lip and the prominence of the chin. 
Action. — To raise the lower lip. 

7. Mentalis (Levator menti). — This is situated in tlie 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 outer 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 orbicylaris 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 external surface of the maxilla above the interdental space and 
the molar teeth; the alveolar border of the mandible at the interdental space and 
also posteriorly where it turns upward to the coronoid process ; the pterygo-mandib- 
ular ligament. 

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 may be recognized. The superficial layer (Pars buc- 
calis) extends from the angle of the mouth to the masseter. It is incompletely 
pennate, having a longitudinal raphe on which most of the muscle-fibers converge. 
The upper fibers are directed chiefly downward and l)ackward, 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 below 
with the depressor lal:)ii inferioris. 

Relations. — Superficially, the skin and fascia, the zygomaticus, levator naso- 
labialis, lateral dilator of the nostril, the superior buccal glands, the parotid duct, 



MUSCLES OF THE NOSTRILS 



217 



the facial vessels, and branches of the facial nerve ; deeply, the mucous membrane 
of the mouth and the inferior buccal glands. 

Blood-supph/. — P'acial and l)UCcinator arteries. 

Nerve-supply. — Facial nerve. 



MUSCLES OF THE NOSTRILS 

1. Levator nasolabialis. — This has been described (p. 214). 

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. 

Origin. — The maxilla, close to the anterior extremity of the facial crest. 
Insertion. — The outer wing of the nostril. 




Fig. 174. — Nasal and Superior Labial Muscles op Horse. 

a, a', Dilatator naris transversus; b, levator labii superioris proprius; b', tendon of b; b" , common tendon of 

two levatores labii superioris proprii; c, c', dilatator naris inferior; d, e, dilatator naris superior;/, orbicularis oris; 

g, levator nasolabialis, a portion of which is removed; /i, dilatator naris lateralis (cut); /, cornu of alar cartilage; 

A, nostril; it', false nostril; /, nasal diverticulum; ?/;, nasal bone. (After EUenberger-Baum, Top. Anat. d. Pferdes.) 



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 external 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. Dilatator naris transversus (M. transversus nasi). — This is an unpaired, 
quadrilateral muscle, which lies between the nostrils. It consists of two layers. 

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. 



218 FASCIA AND MUSCLES OF THE HORSE 

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. 

4. Dilatator naris superior (Pars dorsalis m. lateralis nasi) .^This very thin 
muscle occupies the angle between the nasal process of the premaxilla and the 
nasal bone. 

Origin. — The lateral border of the nasal bone. 

Insertion. — The inner wall of the false nostril and the parietal lamina of the 
septal cartilage. 

Action. — To dilate the vestibule of the nasal cavity. 

Struct ure. — Fleshy. 

Relations. — Superficially, the skin, fascia, and levator labii superioris proprius; 
deeply, the parietal cartilage and false nostril. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

5. Dilatator naris inferior (Pars ventralis m. lateralis nasi) .--This is a similar 
but thicker muscle, which lies on the nasal process of the premaxilla. 

Origin. — The maxilla and the nasal process of the premaxilla. 

Insertion. — The cartilaginous prolongations of the turbinal bones and the 
inner wall of the false nostril. 

Action. — To rotate the turbinal outward and dilate the nostril and the vestibule 
of the nasal cavity. 

Structure. — Fleshy. A division into two or more parts may be recognized. 
A small part posteriorly is inserted into the cartilage of the dorsal turbinal bone, 
while the bulk of the muscle is inserted into the cartilage of the ventral turbinal 
bone. A few fibers also pass between the cornu of the alar cartilage and the outer 
wing of the nostril. 

Relations. — Superficially, the levator labii superioris proprius, the levator 
nasolabialis, and the lateral nasal artery; deeply, the maxilla, the premaxilla, and 
the anterior nasal branch of the infraorbital nerve. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 



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 inner 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 ujiper eyelid, blending 
with the orbicularis. 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 orl)it 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. 



MUSCLES OF MASTICATION 219 

4. Levator palpebrae superioris. — This slender, flat muscle is almost entirely 
within the orbital cavity. It arises on the pterygoid crest, passes forward above the 
rectus oculi superior and below the lacrimal gland, and terminates in a thin tendon 
in the upper lid. 

Action. — To elevate the ujjper lid. 

Blood-sup ply. — Ophthalmic artery. 

Nerve-sup pi y. — Oculomotor nerve. 



MUSCLES OF MASTICATION 
The muscles of this group are six in number in the horse. They arise chiefly 
from the upper jaw and the base of the cranium, and are all inserted into the man- 
dible. 

1. Masseter. — This muscle extends from the zygomatic arch and facial crest 
over the l)road i)art of the mandi])ular ramus. It is semi-elliptical in outline. 

Origin. — By a strong tendon from the zygomatic arch and the facial crest. 

Insertion. — The outer surface of the broad part of the ramus of the mandible. 

Action. — ^Its action is to Ijring 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 ])y 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 somewdiat 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-maxillary joint, is not covered by the superficial layer. 
The two layers are se]:)arable only above and behind; elsewhere they are fused. 

Relations. — Superficially, the skin and panniculus, the parotid gland, the- 
transverse facial and masseteric vessels, and the facial nerve; deeplj^, the ramus of 
the mandible, the buccinator, depressor labii inferioris, and mylo-hyoideus muscles, 
the superior buccal glands, the buccinator nerve, and two large varicose veins which 
join 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 forward 
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 wdiich surround it. 

Insertion. — The coronoid process of the mandible, which it envelops. 

Action. — Chiefly to raise the lower jaw, acting with the masseter and internal 
pterygoid muscles. 

Structure. — The surface of the muscle is covered with a glistening ai)oneurosis, 
and strong tendinous intersections are found in its substance. The inner 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 somewhat with the 
masseter. 

Relations. — Superficially, the scutiform cartilage and anterior muscles of the 
external ear and the orljital fat; deeply, the temporal fossa and the deep temporal 
vessels and nerves. 

Blood-supply. — Superficial and deep temporal, and mastoid arteries. 

Nerve-supply. — Mandibular nerve. 

3. Pterygoideus intemus (s. medialis). — This muscle occupies a position on 
the inner surface of the ranms of the mandible similar to that of the masseter on the 
outside. 



220 



FASCIA AND MUSCLES OF THE HORSE 



Origin. — The crest formed by the pterygoid process of the sphenoid and the 
palate bone. 

Insertion. — The concave inner surface of the broad portion of the ramus of the 
mandible, and the inner lip of the lower 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 (internal), and its fibers are, for the most part, vertical in direc- 
tion. It contains much tendinous tissue (septa). The smaller portion is external 
to the foregoing, and its fibers are directed downward and backward. 

Relations. — Externally, the ramus of the mandil)le, the external pterygoid 
muscle, the inferior alveolar vessels and nerve, and the lingual and mylo-hyoid 
nerves; internally, the great cornu of the hyoid bone, the tensor palati, pterygo- 



Ethmo- 

tin-binals 

Superior meatus 

Superior turbinai 

Middle meatus 

Inferior turbinai 

Inferior meatus 



Septum of 
frontal sinuses 




My/0 hyoideuS 
7 




Stylo- 
maxil- 
laris 

Digastricus, 
posterior 
belly 



Digastriciis, 
anterior belly 



Iniermediate tendon 



Fig. 175. — Sagittal Section op Head of Horse, Showing Deep Pterygo-maxillary Region, and Nasal. 

AND Cranial Cavities. 
1, Cerebral compartment of cranial cavity; 2, cerebellar compartment of same; 3, tentorium osseum; 
4, tentorium cerebelli; 3, 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. 



pharyngeus, palato-pharyngeus, mylo-hyoideus, digastricus, and stylo-hyoideus 
muscles, the guttural pouch, the external maxillary vessels, the ninth and twelfth 
nerves, the submaxillary salivary gland, the submaxillary and parotid ducts, and 
the submaxillary and pharyngeal lymph-glands. 

Blood-supply. — Internal maxillary, masseteric, and inferior alveolar arteries. 

Nerve-supply. — Mandil)ular nerve. 

4. Pterygoideus extemus (s. lateralis). — This muscle is considerably smaller 
than the preceding one, and is situated external to its upper part. 

Origin. — The external surface of the pterygoid process of the sphenoid 
bone. 

Insertion. — The inner surface of the neck and the inner part of the anterior 
border of the condyle of the mandible. 

Action. — Acting together, to draw the lower jaw forward; acting singly, to 
move the jaw laterally, i. e., toward the side opposite to the muscle acting. The 



MUSCLES OF MASTICATION 



221 



latter action is due to the fact that tlie origin is nearer to the median plane than the 
insertion. 

Structure. — The muscle is almost entirely flesli>-, and the fibers are almost 




Fig. 176. — Submaxillary and Laryngeal Regions of Horse, after Removal of Skin and Panniculus. 
c, Mastoido-humeralis; d, sterno-cephalicus; e, omo-hyoideus and sterno-hyoideus; h, buccinator; i, 
depressor labii inferioris; m, masseter; v, stylo-maxillaris; w, mylo-hyoideus; 2, posterior, S, anterior, border 
of external ear; 30', angle of jaw; Sff, submaxillary lymi)h-glands: ^7, external maxillary vein; ,J9, facial continua- 
tion of 37; 40, parotid duct; 44, parotid gland; 4-5, prominence of chin; r, wing of atlas. (After Ellenberger- 
Baum, Anat. fiir Kiinstler.) 



longitudinal in direction. Some of them are inserted into the edge of the inter- 
articular meniscus. 

Relations.— ExternaWy, the temporo-maxillary articulation and the temporalis 
muscle; internally, the internal pterygoid and tensor palati muscles. The internal 



222 FASCIA AND MUSCLES OF THE HORSE 

maxillary artery crosses the lower face of the muscle and clips in between it and the 
tensor palati. The mandibular nerve lies on the ventral surface, and the buccinator 
nerve perforates the origin of the muscle. 

Blood-supply. — Internal maxillary and inferior alveolar arteries. 

Nerve-supply. — Mandibular nerve. 

5. Stylo-maxillaris (s.-mandibularis) (M. jugulomandibularis). — This is a short 
muscle extending from the paramastoid or styloid process of the occipital bone to 
the posterior border of the lower jaw; it is covered by the parotid gland. 

Origin. — The paramastoid or styloid 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. 

Structure. — -The muscle contains a good deal of tendinous tissue. It blends 
with the posterior belly of the digastricus. 

Relations. — Superficially, the parotid gland, the tendon of the sterno-cephalicus, 
and the fibrous expansion which connects it with the tendon of the mastoido- 
humeralis; deeply, the guttural pouch, the external carotid artery, the ninth and 
twelfth nerves, the pharynx, and the submaxillary gland. 

Blood-supply. — External carotid artery. 

Nerve-supply. — Facial nerve. 

6. Digastricus. — This muscle is composed of two fusiform, flattened ])ellies, 
united by a round tendon. 

Origin. — The paramastoid or styloid process of the occipital bone, in common 
with the preceding muscle. 

Insertion. — The inner surface of the lower border of the mandible behind the 
symphysis. 

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 inner surface of the stylo-maxillaris. It passes downward and forward, and is 
succeeded by a small rounded tendon. The latter perforates the tendon of in- 
sertion of the stylo-hyoideus, and is provided with a sjmovial sheath. The anterior 
belly is larger and terminates by thin tendinous bundles. 

Relations. — The posterior belly has practically the same relations as the stylo- 
maxillaris. The intermediate tendon is in contact externally with the internal 
pterygoid muscle, the submaxillary gland and duct, and the external maxillary 
artery. The anterior belly lies in the submaxillary space between the ramus of the 
jaw and the mylo-hyoideus muscle; the sublingual vessels run along its upper border. 

Blood-supply. — External carotid and sultlingual arteries. 

Nerve-supply. — Facial and mandibular nerves. 



THE HYOID MUSCLES 

This group consists of eight muscles, one of which, the hyoideus transversus, 
is unpaired. 

1. Mylo-hyoideus. — This muscle, together with its fellow, forms a sort of 
sling between the two rami of the lower jaw, in which the tongue is supported. 

Origin.— The inner 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 and body of the hyoid bone. 

Action. — It raises the floor of the mouth, the tongue, and the hyoid bone. 

Structiire. — Each muscle consists of a thin curved sheet, the fillers passing 
downward from their origin and then curving toward the median raphe. It is 



THE HYOID MUSCLES 223 

chiefly fleshy, and is thickest behind. The anterior superficial part of the muscle 
is termed the mylo-glossus. 

Relations.— On the superficial surface of the muscles are the ramus, the in- 
ternal pterygoid and digastricus muscles, and the submaxillary 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 submaxillary duct, and the lingual and hypo-glossal nerves. 

Blood-supply. — Sublingual artery. 

Nerve-s)i])])hi. — Mylo-hyoid l)ranch 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. 436). 

Origin. — The heel-like prominence on the proximal 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 
digastricus, and at this point there is a small synovial sheath. 

Relations. — Superficially, the internal 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). 

3. Occipito-hyoideus (M. jugulo-hyoideus ; occipito-styloideus).^ — 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 (styloid) process of the occipital bone. 

Insertion. — The proximal extremity and ventral edge of the great cornu of 
the hyoid bone. 

Action. — It carries the distal extremity of the great cornu backward and up- 
ward. Acting with the genio-hyoideus and digastricus, it raises the hyoid bone 
and the larynx. 

Structure. — The muscle is somewhat triangular, its fibers being longer as the 
ventral border is approached. It blends with the posterior l^ellj^ 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. 243). 

Origin. — The angle of union of the rami of the mandible. 

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. — Below, the mylo-hyoideus; above, the hyo-glossus, stylo-glossus, 
genio-glossus, the sublingual gland, submaxillary 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. 243). 

Origin. — The posterior edge of the small cornu and the adjacent part of the 
ventral Ijorder of the great cornu. 

Insertion. — The dorsal edge of the thyroid cornu. 
Action. — It raises the thyroid cornu and the larynx. 



224 FASCIA AND MUSCLES OF THE HORSE 

Relations. — The muscle is crossed outwardly by the lingual artery. 
Blood-supply. — Lingual artery. 
Nerve-supply. — Glosso-pharyngeal nerve. 

6. Hyoideus Transversus. — This is a thin, unpaired muscle, which extends 
transversely' between the two small cornua of the hyoid bone. 

Attachments. — The small cornua close to the junction with the great cornua. 
Action. — When relaxed, its upper 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 
surface of the neck. 



The Fascia and Muscles of the Neck 

It is convenient to divide the muscles of the neck into ventral and lateral 
groups, the two lateral groups being separated from each other by the ligamentum 
nuchse. 

THE FASCI.E OF THE NECK 

The superficial fascia is in part two-layered, and contains the cervical portion 
of the panniculus. The fasciae of the right and left sides are attached along the 
dorsal line of the neck to the ligamentum nuchse, while along the ventral line they 
meet in a fibrous raphe. A deep layer is detached which passes underneath the 
panniculus, bridges over the jugular furrow, and crosses over the deep face of the 
mastoido-humeralis and omo-hyoideus to join the superficial layer. It again sepa- 
rates 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 inclose the prescapular lymph- 
glands. 

The deep fascia also forms two layers. The superficial layer is attached to 
the wing of the atlas and the lower edge of the trachelo-mastoideus and scalenus. 
Passing downward, it incloses 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. An- 
teriorly 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 cornu 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 incloses 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, inclosing also the recurrent nerves. 



VENTRAL MUSCLES 

This group consists of eleven pairs of muscles which lie almost entirely 
ventral to the vertebrae. 

1 . Panniculus carnosus. — The cervical panniculus (platysma myoides of 
man) has a fleshy origin on the cariniform cartilage (manubrium) of the sternum. 



VENTRAL MUSCLES OF NECK 



225 



ft passes forward, outward, and upward, crossing over the sterno-ccphalicus and 
jugular furrow obliquely. On reaching the surface of the mastoido-humeralis 
it adheres closely to this muscle, and soon thins out, to be continued over the 
splenius and trapezius by an aponeurosis which is difficult to remove from the latter 
muscle. Scattered bundles may be traced on the ventral surface of the neck to 





Fig. 177. — Antero-laterai. Vikw of Musci.ks and Skeleton of Horse. 
a. Trapezius; c, mastoido-humeralis; d, .sterno-cephalicus; /, long head of triceps; /', external hea<l of 
■triceps; </, anterior superficial pectoral muscle; g' , posterior superficial pectoral; h' , anterior deep pectoral; r, 
cervical panniculus; z, supraspinatus; 29, omo-hyoideus; SO, sterno-thyro-hyoideus; 31, jugular vein; 32, 
cephalic vein; 1, scapula; 1' , cartilage of scapula; 2, spine of scapula; 4, shaft of humerus; 4', external epi- 
condyle; 5, external tuberosity of humerus; ff, deltoid tuberosity; /4, ventral border ("keel") of sternum; 14', 
cariniform cartilage; I.R., first rib. (After Ellenberger-Baum, Anat. fiir Kimstler.) 

the facial jiortion. The right and left muscles meet at a ventral median raphe in 
pennate fashion. 

2. Mastoido-humeralis. — This is described on p. 252. 

3. Sterno-cephalicus (Sterno-maxillaris s.-mandibularis)/ — This is a long, nar- 

^ This muscle is probably the homologue of the sternal portion 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. 
15 



226 FASCLE AND MUSCLES OF THE HORSE 

row muscle, extending 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. 

Origin. — The cariniform cartilage of the sternum. 

Insertion. — The posterior border of the lower jaw. 

Action. — Acting together, to flex the head and neck; acting singly, to incline 
the head and neck to the side of the muscle contracting. 

Structure. — The two muscles are fused at their origin, which is fleshy. Near 
the middle of the neck they separate, and, becoming thinner, each muscle passes 
under the parotid gland and terminates in a flat tendon. 

Relations. — Superficially, the cervical panniculus; deeply, the sterno-thyro- 
hyoideus and omo-hyoideus muscles. The upper edge of the muscle is related to 
the jugular vein, which lies in the jugular furrow. The carotid artery, the vagus, 
sympathetic, and recurrent nerves also lie along the upper edge at the root of the 
neck. The tendon passes under the submaxillary vein and the parotid gland, hav- 
ing the submaxillary gland and stylo-maxillaris muscle on its inner side. 

Blood-supply. — Carotid artery. 

Nerve-supply. — -Ventral branches of the s]:)inal accessory and first cervical 
nerves. 

4. Sterno-thyro-hyoideus (Sterno-thyroideus 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) The external surface of the thyroid cartilage of the larynx; 
(2) the body of the hyoid ])one. 

Action. — To depress and retract the hyoid bone, the base of the tongue, and 
the larynx, as in deglutition. It may also fix the hyoid bone wdien the depressors 
of the tongue are acting, as in suction. 

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 fleshy bands. The lateral 
bands diverge to reach their insertion into the thyroid cartilage; wdiile the inner 
bands, 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 has the sterno-cephalicus 
below, and the carotid arteries and recurrent nerves above. Further forward the 
trachea becomes the upper relation, and near the head the skin and fascia, the low^er 
one. 

Blood-supply .—Csirotid artery. 

Nerve-supply. — -Ventral branch of the first cervical nerve. 

5. Omo-hyoideus (Subscapulo-hyoideus). — This is a thin, ribbon-Hke muscle, 
almost entirely fleshy, which crosses the trachea very obliquely under cover of the 
mastoido-humeralis. 

Origin.^The subscapular fascia close to the shoulder joint. 

Insertion.— The body of the hyoid bone, in common with the hyoid branch of 
the preceding muscle. 

Action. — To depress the hyoid bone. 

Structure. — The muscle is composetl of parallel fleshy fibers, except at its origin, 
where it has a thin tendon. 

Relations. — In the first part of its course the muscle passes forward between 
the supraspinatus, anterior deep pectoral, mastoido-humeralis (outwardly), and 
the scalenus (inwardly). It is intimately adherent to the mastoido-humeralis. 
In the middle of the neck it is related superficially to the mastoido-humeralis, 
sterno-cephalicus, and the jugular vein; deeply, to the rectus capitis anterior major, 
the carotid artery, the vagus, sympathetic, and recurrent nerves, the trachea, and,. 



VENTRAL MUSCLES OF NECK 227 

on the loft side, the oesophagus. In its anterior ]:)art the musele blends with the 
hyoid part of the sterno-thyro-hyoideus, the two covering the thyroid portion of the 
latter muscle, the thyroid gland, and the ventral face of the larynx. 

Blood-supply. — Carotid and inferior cervical arteries. 

Nerve-supply. — Ventral branches of the cervical nerves. 

G. Scalenus (AI. scalenus primae 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 roots of the brachial plexus of nerves emerge. 

Origin.— The anterior border and outer surface of the first rib. 

Insertion. — (1) The dorsal (smaller) portion is attached to the transverse 
process of the seventh cervical vertebra; (2) the ventral portion is attached to the 
transverse processes of the sixth, fifth, and fourth cervical vertebra?. 

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 portion is composed of three or four fleshy bundles.* 
The ventral portion, which is much larger, is almost entirely fleshy, and not so 
divided. 

Relations. — Superficially, the anterior deep pectoral, mastoido-humeralis, and 
omo-hyoideus muscles, the phrenic nerve, and the other branches of the brachial 
plexus; deeply, the vertebrae, the longus colli and intertransversales muscles, the 
oesophagus (on the left side), the trachea (on the right side), the vertebral vessels, 
the vagus, sympathetic, and recurrent nerves. The roots of the ]:>rachial plexus 
form a flat anastomosis, which lies between the two portions 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. Rectus capitis anterior 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 vej- 
tebrae. 

Insertion. — The tubercles at the junction of the basilar process 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 l)y 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 mastoido-humeralis, omo-hyoideus, and rectus 
capitis anticus minor, the submaxillary gland, the carotid artery (which lies along 
the lower border), the occipital and internal carotid arteries, and the tenth, eleventh, 
and sympathetic nerves; deeply, the vertebrae, the longus colli, intertransversales, 
and the small straight muscle. 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. 

8. Rectus capitis anterior minor (M. rectus capitis ventralis). — This is a small 
muscle which lies under cover of the preceding one. 

Origin. — The ventral arch of the atlas. 

1 The upper part of this may be separated from the scalenus proper, and is then termed the 
cervicalis ascendens or iho-costalis cervicis — a continuation in the neck of the transversahs cos- 
tarum. 



228 FASCIA AND MUSCLES OF THE HORSE 

Insertion. — The basilar process, close to the preceding muscle. 

Action. — To flex the occipito-atlantal articulation. 

Str ud lire. — Fleshy . 

Relations. — Below, to the preceding muscle; above, to the atlas, occipito- 
atlantal articulation, and the basilar process; externally, to the rectus capitis 
lateralis and the guttural pouch. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Ventral branch of the first cervical nerve. 

9. Rectus capitis lateralis. — This is a still smaller, entirely fleshy muscle, 
which lies for the most part under the small oblique muscle. 

Origin. — The atlas, external to the preceding muscle. 
Insertion. — The paramastoid or styloid process of the occipital bone. 
Action. — -The same as the preceding muscle. 
Structure. — Fleshy. 

Relations. — Superficially, the small oblique muscle, 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. 

10. Longus colli. — This muscle covers the ventral surface of the vertebrse, 
from the sixth thoracic to the atlas, and is united with its fellow. It consists of 
two portions, thoracic and cervical. 

Origin. — (1) Thoracic portion, the bodies of the first six thoracic vertebrae; 
(2) cervical portion, the transverse processes of the cervical vertel^rae. 

Insertion. — (1) Thoracic portion, the bodies and transverse processes of the 
last two cervical vertebrae; (2) cervical portion, the bodies of the cervical vertebrse 
and the tubercle on the ventral surface 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 tendon 
and the spine at the first costo-vertebral articulation. The cervical portion con- 
sists of a number of smaller bundles, each of which passes from its origin on the 
transverse process of one vertebra forward and inward to its insertion into a vertebra 
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; clorsally, 
the vertebrse and the costo-vertebral joints; laterally, the dorsal, superior 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 
vertebrse and, in the middle third of the neck, the intertransversales muscles; 
laterally, the scalenus, the rectus capitis anticus major, and the intertransversales 
(in the anterior third). The terminal part of the muscle is separated from the 
trachea by the (jesophagus, which is here median in position. 

Blood-supply. — Subcostal and vertebral arteries. 

Nerve-supply. — Ventral branches of the spinal nerves. 

11. Intertransversales colli (Mm. intertransversarii cervicis). — These are six 
fasciculi which occujiy the spac(^s between the lateral aspects of the vertebrse 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 
ventral portion. 

Attachments. — The dorsal bundles pass from transverse process to articular 
process; the ventral bundles extend between adjacent transverse processes. 



LATERAL MUSCLES OF NECK 229 

Action. — To bend the neck laterally. 

Structure. — They contain strong tendinous intersections. 

Relations. — Superficially, the mastoido-hunieralis, rectus capitis anterior major, 
complexus, trachelo-niastoideus, splenius, scalenus, and longissinius muscles; 
deeply, the vertebraj, 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-sup phj. — The cervical nerves. 



LATERAL MUSCLES 
This group consists of twelve pairs of muscles arranged in layers. 

First Layer 

1. Trapezius cervicalis. — Described on p. 250. 

Second Layer 

2. Rhomboideus cervicalis. — Described on p. 25L 

3. Serratus magnus (AL serratus cervicis). — Described with the thoracic part 
on p. 254. 

Third Layer 

4. Splenius. — This is an extensive, flat, 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 portion of the ligamentum nuchse. 

Insertion. — The occipital crest, the mastoid process, the wing of the atlas, 
and the transverse processes of the third, fourth, and fifth cervical vertebra\ 

Action. — Acting together, to elevate the head and neck; acting singly, to 
incline 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, 
serratus anticus, 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 
splenius, trachelo-mastoideus, and mastoido-humeralis. The atlantal insertion 
is by a strong, flat tendon, also in common with these muscles. The remaining 
insertions are fleshy digitations. 

Relations. — Superficially, the skin and fascia, the trapezius rhomboideus, 
cervicalis, serratus magnus, and posterior auricular muscles; deeply, the com- 
plexus, trachelo-mastoideus, and longissimus muscles. 

Blood-supply. — Deep cervical and dorsal arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

Fourth Layer 

5. Trachelo-mastoideus (M. longissimus capitis et atlantis). — This muscle 
consists of two parallel, fusiform 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 cervical vertebrae. 

Insertion.— (1) The mastoid process; (2) the wing of the atlas. 



230 



FASCIiE AND MUSCLES OF THE HORSE 







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LATERAL MUSCLES OF NECK 231 

Action. — 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 vertebra is by 
aponeurotic slips which blend with the complexus. The suc- 
ceeding fleshy portion, in passing along the neck, receives 
fasciculi from each of the cervical vertebra except the first 
two. The dorsal division of the muscle is inserted into the 
mastoid process by a flat tendon which fuses with that of the 
splenius; the ventral division is inserted into the wing of the 
atlas by a ribbon-like tendon in common with the splenius and 
mastoido-humeralis. 

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 superior 

cervical vessels cross the deep face of the muscle obliquely at 

i -3 "3 ^- the level of the sixth and seventh cervical vertebrae. 

Blood-supply. — Vertebral and superior cervical arteries. 

Nerve-supply. — Dorsal branches of the last six cervical 



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6. Complexus (M. semispinahs capitis). — This is a 
s"^ large triangular muscle which lies chiefly on the hgamentum 

\o" nuchas, under cover of the splenius and trachelo-mastoideus 

vr muscles. 

i Origin. — (1) The second, third, and fourth thoracic spines, 

I in common with the splenius and serratus anticus; (2) the 

■3 transverse processes of the first six or seven thoracic vertebrae; 

■^ (3) the articular processes of the cervical vertebrae. 

"I Insertion. — ^The posterior surface of the occipital bone, 

: a external to the funicular portion of the ligamentum nuchae. 

i-.^ Action. — It is the chief extensor of the head and neck. Act- 

[ § ing singly, the muscle inclines the head to the same side. 

I »" * f- i i Structure. — The origin of the muscle at the withers is apo- 

^ ^-"^-ll^'^l neurotic. 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 upper 
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 magnus, 
is^-^ splenius, and trachelo-mastoideus muscles; deeply, the liga- 



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mentum nuchae, the multifidus cervicis, longissimus, and the 
oblique and posterior straight muscles of the head, the deep 
or superior cervical vessels, and the dorsal cutaneous branches 
of the cervical nerves. 
g|^|^-< Blood-supply. — Deep cervical, vertebral, and occipital 

^•3 g I .. . arteries. . 

S 1 I ill Nerve-supply. — Dorsal branches of the last six cervical 

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7. Multifidus cervicis (M. semispinalis colli; transverse 
spinous muscle of neck). — This muscle lies on the arches of the 
a^'S J «"-| last five cervical vertebrae. It consists of five or six segments. 

Origin. — The articular processes of the last five (or four) 
cervical and the first thoracic vertebrae. 

Insertion. — The spinous processes of the cervical vertebrae. 



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232 



FASCIA AND MUSCLES OF THE HORSE 




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LATERAL MUSCLES OF NECK 233 

Action. — Acting together, to extend the neck; acting singly, 
to flex and 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 dee]) bundles are shorter and 
run straight from an articular process to that of the preceding 
vertebra. 

Relations. — Superficially, the complexus, longissimus, tra- 
chelo-mastoideus, and great obliciue muscles; deeply, the 
spinalis muscle, the ligamentum nucha?, 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. 237. 

9. Obliquus capitis posterior (s. caudalis) (great oblique 
I'^S a| I muscle of the head). — This is a strong, quadrilateral muscle, 
Ji .^ t ^"11 which covers the dorso-lateral aspect of the atlas and axis. 

Origin. — The side of the spine and the posterior articular 
1 1 ^ I process of the axis. 

Insertion. — The dorsal surface of the wing of the atlas. 
K §■ 1 O i g -^ Action. — Chiefly to rotate the 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 
-? i i I II « parallel fleshy fibers directed obliquely forward and outward. 

Relations. — Superficially, the skin, the splenius, complexus, 

trachelo-mastoideus, and mastoido-humeralis muscles; deeply, 

the arch and spine of the axis, the wing of the atlas, the 

li^ifi^^ atlanto-axial joint, the multifidus cervicis, the posterior 

straight muscles, the occipital and vertebral vessels, and the 

|'3|»^_|'§~^ first and second cervical nerves. The terminal part of the 

.2 II ^^.11 vertebral artery joins the posterior branch of the occipital 

I " o g ^5 s "5 artery under cover of the muscle. 

II ^- S S«i"3 Blood-supply. — Occipital and vertebral arteries. 
•^ 1:3 1 1 1- 3 Nerve-supply. — Dorsal ])ranch of the second cervical nerve. 

III CO- S I I 10. Obliquus capitis anterior (s. cranialis) (small obhque 
muscle of the head). — A short, thick, quadrilateral muscle which 
lies on the side of the occipito-atlantal articulation. 

I 3 I ?, I 4 Origin. — ^The anterior edge of the wing of the atlas and the 

^ -g .2 '§ fossa atlantis. 
^|| l| Insertion. — The styloid process and 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. 
Relations. — Superficially, the posterior auricular muscles, 
artery, and nerve, the aponeurosis of the splenius, trachelo- 
mastoideus and mastoido-humeralis, and the parotid gland; 
deeply, the straight muscles, the complexus, the occipito- 
hyoideus, the occipito-atlantal articulation, branches of the 
occipital artery, and a branch of the occipital nerve. 



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FASCIA AND MUSCLES OF THE HORSE 



Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 

11. Rectus capitis posterior major (s. dorsalis major) (great posterior straight 
muscle of the head). — 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. 

Insertion. — The occipital bone, below and external to the complexus and 
ligamentum nuchse. 

Action. — To extend the head. 

Structure. — The muscle is fleshy and may be divided into two parallel portions, 




Fir,. ISO. — Deepest Layer of Muscles of Neck of Horse. 
a, Obliquus capiti.s anterior; b, obliquus capitis posterior; c, rectus capitis lateralis; d, rectus capitis anterior 
minor; e, rectus capitis anterior major; /, longus colli; g, <j' , scalenus; h, transversalis costarum; », longissimus 
dorsi; k, spinalis et semispinalis; /, multifidus dorsi; m, multifidus cervicis; n, intertransversales; o, o' , rectus 
capitis posterior major; p, rectus capitis posterior minor; q, tendon of insertion of complexus; 1, lamellar part, 
/'.funicular i>art of ligamentum nuchus ^, occipital crest; S, paramastoid process; 4. edge of wing of atlas; 5, 
transverse, and 6, articular, processes of cervical vertebras 7, nerves of brachial plexus (cut); 8, first rib. 
(EUenberger-Baum, Anat. d. Haustiere.) 



superficial and d(>ep. The former blends somewhat with the terminal part of the 
complexus. The deep portion may be termed the rectus capitis posterior medius. 

Relations. — Superficially, the anterior oblique, splenius, and complexus; 
internally, the ligamentum nucha?; deeply, the atlas, the occipito-atlantal articula- 
tion, and the rectus capitis jiosterior minor. The dorsal branch of the first cervical 
nerve appears between this muscle and the small ol)lique. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 

12. Rectus capitis posterior minor (s. dorsalis minor) (small posterior straight 
muscle of the head). — Tliis small muscle lies under cover of the preceding. 



THE FASCI.E AND MUSCLES OF THE BACK AND LOINS 235 

Origin. — The dorsal surface of the atlas. 

Insertion. — The occipital bone beneath the preceding muscle. 

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 small oblique; deeply, 
the atlas and the occipito-atlantal articulation. 

Blood-supph/. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 



The Fascia and Muscles of the Back and Loins 

The superficial fascia presents no special features. The lumbo-dorsal fascia 
(Fascia lumbo-dorsalis) closely invests the muscles, but is easily stripped ofT the 
longissimus. It is attached medially to the supraspinous ligament and the spinous 
processes of the vertebrce; laterally, it divides into two layers. The superficial 
layer is practically the aponeurosis of the latissimus dorsi. The deep layer gives 
origin to the serratus anticus and posticus, the lumbar part of the obliquus ex- 
ternus abdominis, the transversus abdominis, and the retractor costae. Its lateral 
edge curves under the longissimus and is attached to the ribs and lumbar transverse 
processes. Posteriorly, it is continuous with the gluteal fascia. At the withers it 
forms an important 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 dorsi, 
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 and are at- 
tached with it to the scapula. Three lamellae are detached from the deep face of 
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 lietween the longis- 
simus and transversalis costarum. The superficial one gives origin to the serratus 
anticus. A strong fascial layer, the ilio-lumbar ligament, extends from the last 
rib to the external angle of the ilium. 

There are nine pairs of muscles in this region, arranged in four layers. 



First Layer 



1. Trapezius thoracalis. 

2. Latissimus dorsi. 



Second Layer 

3. Rhomboideus thoracalis. 

The foregoing are descriloed with the other nuiscles which attach the thoracic 
limb to the trunk (p. 251). 

4. Serratus anticus (M. serratus dorsalisinspiratorius). — This is a thin quadri- 
lateral muscle, named from its toothed ventral border. It lies beneath the rhom- 
boideus, serratus magnus, and latissimus dorsi. 

Origin. — The lumbo-dorsal fascia and dorso-scapular ligament. 

Insertion. — The external surfaces of the fifth to the eleventh or twelfth ribs 
inclusive. 

Action. — To draw the ribs on which it is inserted forward and outward, thus 
assisting in ins]iiration. 

1 This seems due to pressure produced by pathological changes in the supra-atloid bursa, 
which are frequently extensive in dissecting-room subjects. 



236 FASCIA AND MUSCLES OF THE HORSE 

Structure. — The muscle arises by means of a thin aponeurosis which l:)Iencls 
with the lumbo-dorsal fascia and the aponeurosis of the latissimus dorsi. The 
muscle-fibers pass downward and backward to be attached to the ribs by seven or 
eight digitations below the outer edge of the transversalis costarum. 

Relations. — Superficially, the rhomboideus, serratus magnus, latissimus dorsi, 
and serratus posticus; deeply, the longissimus dorsi, transversalis costarum, ex- 
ternal intercostal muscles, and the ribs. 

Blood-supply. — Intercostal arteries. 

Nerve-supply. — Thoracic nerves. 

5. Serratus posticus (M. serratus dorsalis exspiratorius) . — This muscle re- 
sembles the preceding one, which it partly covers. 

Origin. — The lumbo-dorsal fascia. 

Insertion. — The outer 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 downward 
and forward and terminate in seven or eight digitations, one or two of which cover 
the posterior teeth of the anticus. The aponeurosis blends with that of the latissi- 
mus dorsi. 

Relations. — Superficially, the latissimus dorsi and external oblique; deeply, 
the longissimus dorsi, transversalis costarum, external intercostals, serratus anti- 
cus, and the ribs. 

Blood-sup ply. — Intercostal and lumbar arteries. 

Nerve-supply. — Thoracic nerves. 

Third Layer 

6. Transversalis costarum (M. ilio-costalis). — This long, segmental muscle 
extends, as its name indicates, across the series of ribs, in contact with the outer 
edge of the longissimus dorsi. 

Origin. — (1) The transverse processes of the second and third lumbar verte- 
bra and the deep layer of the lumbo-dorsal fascia. (2) The anterior borders and 
external surface of the last fifteen ribs.^ 

Insertion. — The posterior borders of the ribs and the transverse processes of 
the last two or three cervical vertebree. 

Action. — Chiefly to depress and retract the ribs and so help in expiration. 
Acting together, they may assist in extending this spine, acting singly in inclining 
it laterally. 

Structure. — This muscle j^resents a distinct segmental arrangement. It is 
composed of a series of bundles, the fibers of which are directed forward and a little 
downward and outward. From these are detached two sets of tendons. The 
superficial tendons spring from the outer 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 intercostal spaces to its origin on the anterior border or outer surface 
of a rib. Small bursje may l)e found between the ribs and tendons. 

Relations. — Superficially, the dorsal serrati and the complexus ; deeply, the ex- 
ternal intercostals and the ribs. The lumbar origin is covered by the longissimus. 
The superior (deep) cervical and dorsal vessels cross the surface of the muscle at 
the first and second intercostal spaces respectively, and branches of the intercostal 
vessels and nerves emerge between the transversalis and longissimus; here a fascial 
layer dips in between the two. 

1 Tho lumbar part of this muscle is subject to variation. It may, in quite exceptional cases, 
extend as far as the ilium. 



THE FASCIA AND MUSCLES OF THE BACK AND LOINS 



237 



Blood-supply. — Intercostal arteries. 

Nerve-supphj. — Dorsal Ijranches of the thoracic nerves. 

7. Longissimus/ — 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 transverse processes and the upper 
ends of the ribs below; consequently it has the form of a three-sided prism. 

Origin. — (1) The internal angle, crest, and adjacent part of the ventral surface 
of the ilium; (2) the first three sacral spines; (3) the lumbar 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 
cervical vertebrae; (4) the outer 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 de- 
veloped and constitutes the common mass 
of the loins. This is covered by a strong 
aponeurosis which blends with the supra- 
spinous and sacro-iliac ligaments, and is 
attached to the crest and inner (sacral) 
angle of the ilium and the first and second 
sacral spines; it furnishes origin to the lum- 
bar portion of the middle gluteus. In its 
course further forward the muscle receives 
fasciculi from the lumbar and thoracic 
spines, but diminishes somewhat in vol- 
ume. At the withers it divides into two 
parts. The dorsal division (spinalis et 
semispinalis), reinforced by bundles from 
the first four thoracic spines, passes for- 
ward under the complexus to be inserted 
into the spines of the last four cervical 
vertebrae. The ventral division passes 
forward and downward underneath the 
serratus magnus to be inserted 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 internal; (2) transverse, attached to the transverse 
and articular processes, which are internal and deep; (3) costal, w^hich are external. 

Relations. — Superficially, the middle gluteus, the lumbo-dorsal fascia, the 
latissimus dorsi, dorsal serrati, serratus magnus, 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, superior cervical, intercostal, and lumbar arteries. 

Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves. 

^The muscle as here described includes the spinalis and semispinalis components, as the 
separation of these is largely artificial in the horse. 




Fig. 181. — Right Poktion of Cross-section op 
Back of Horse. Section is Cut Through 
Seventh Thob.'VCic Vertebra. 
a, Ligamentum nuch»; b, trapezius mus- 
cle; c, cartilage of scapula; d, latissimus dorsi; e, 
panniculus carnosus; /, rhomboideus ilorsi; o, ser- 
ratus magnus; h, serratus anticus; h' , lumbo- 
dorsal fascia, which divides below into three 
layers; i, transversalis costarum; k, levator costa>; 
k' , internal intercostal muscle; I, longissimus dor- 
si; m, m' , seventh thoracic vertebra; «, head of 
eighth thoracic vertebra; o, head of eighth rib; 
p, seventh rib; r, intercostal artery and ner\'e; s, 
skin. The fascicp are indicated by dotted lines. 
(After Ellenberger, in Leisering's Atlas.) 



238 FASCIiE AND MUSCLES OF THE HORSE 

8. Multifidus dorsi (semispinalis of the back and loins). — This is a long 
segmental muscle which covers the sides of the spinous processes of the vertebrae 
from the sacrum to the neck. 

Origin. — (1) The lateral portion of the sacrum; (2) the articular processes of 
the lumbar vertebrae; (3) the transverse processes of the thoracic vertebrce. 

Insertion. — The spinous processes of the first two sacral, the lumbar, thoracic, 
and last cervical vertebrce. 

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 vertel^rae, 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; 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. 

Relations. — Superficially, the longissimus; deeply, the quadratus lumborum. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

The Fascia and Muscles of the Tail 

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, 
but 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 (Compressor coccygis; ischio-coccygeus). — This is a |flat, 
triangular muscle which lies chiefly between the sacro-sciatic ligament and the 
rectum. 

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 depress (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 outer layer is 
attached to the vertebrae, the inner to the fascia; included between the two lie 
the intertransversales. When the tail is raised, the ventral edges of the muscles 
produce a distinct ridge at either side of the anus. 

Relations. — Outwardly, the sacro-sciatic ligament and the semimembranosus; 
inwardly, the rectum and the sacro-coccygeus ventralis muscle. The internal 
pudic arter}' crosses the outer face of the origin of the muscle. 

2. Sacro-coccygeus superior (M. sacrococcygeus dorsalis medialis; erector 
s. extensor coccygis). — This muscle lies along the dorso-median aspect of the 
tail, in contact with its fellow. 

Origin. — The last three sacral spines and some of the coccygeal spines. 



THE FASCIA AND MUSCLES OF THE TAIL 



239 



Insertion. — The dorsal surface of the coccygeal vertebriB. 

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 inserted by means of 
short tendons which fuse with those of the next muscle. 

Relations. — Superficially, the coccygeal fascia; internally, its fellow; later- 
ally, the sacro-coccygeus lateralis; deeply, the vertebrae 

3. Sacro-coccygeus lateralis (M. sacro-coccygeus dorsalis lateralis; curvator 
coccygis). — This muscle lies im- 
mediately lateral to the preced- 
ing. 

Origin. — The sides of the 
sacral spines, with the multifi- 
dus, and the transverse processes 
of the sacral and coccygeal ver- 
tebrae. 

Insertion. — The lateral sur- 
face of the coccygeal vertebrae, 
except the first four. 

Action. — Acting with its fel- 
low, to assist the preceding mus- 
cle in elevating the tail; acting 
singly, to incline it to the same 
side. 

Structure. — This muscle ap- 
pears to be a direct continuation 
of the multifidus dorsi . The belly 



38 





Fig. 182. — Cross-section of Tail of Horse 
Close to Anus. 
34, Coccygeal vertebra; 35, sacro-coc- 
cygeus superior; 36, intertransversalis; 37, 
sacro-coccygeus inferior; 38, coccygeus; S9, 
recto-coccygeus; 40, coccygeal fascia. (After 
Ellenberger-Bauni, Anat. fiir Kiinstler.) 



Fig. 183. — Muscles of Perineum of Horse. 
«, Coccygeus; b, retractor ani; c, c', sphincter ani e.xter- 
nus; d, recto-coccygeus; e, sacro-coccygeus inferior lateralis; 
/, retractor penis; g, bulbo-cavernosus; h, ischio-caveriiosus; 
/, internal pudic artery; k, anus; I, penis. (After EUenberger- 
Baum, Top. Anat. d. Pferdes.) 



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 coccj'geal 
fascia; dorsally, the sacro-coccygeus superior; ventrally, the intertransversales; 
deeply, the vertebrae and a branch of the lateral coccygeal artery and accompanying 
vein and nerve. 

4. Intertransversales caudae (Mm. intertransversarii caudae). — These con- 
sist of muscular l)uii(lles which lie on the lateral aspect of the tail, between the 
preceding muscle and the sacro-coccygeus inferior. They begin on the lateral edge 



240 FASCIA AND MUSCLES OF THE HORSE 

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 inferior (Mm. sacro-coccygei ventrales; depressor 
coccygis). — This muscle lies on the ventral aspect of the sacrum and coccyx. 
It is composed of two portions, described by Bourgelat and the German anatomists 
as separate muscles. 

(a) The outer portion (M. coccygeus ventralis lateralis) is much the larger 
of the two. It arises from the outer part of the ventral surface of the sacrmn, about 
as far forward as the third foramen, and is inserted into the transverse processes 
and ventral surface of the coccygeal vertebrae. 

(b) The innsr portion (M. sacro-coccygeus ventralis meclialis) arises from 
the ventral surface of the sacrum internal to the preceding muscle and the first 
eight coccygeal vertebrae, and is inserted into the ventral surfaces of the coccj^geal 
vertebrae. 

Action. — Acting together, to depress (flex) the tail; acting singly, to incline 
it laterally also. 

Structure. — The outer portion has a somewhat compressed belly, and receives 
bundles from the transverse processes of the coccygeal vertebrae. The inner por- 
tion 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 iDctween the outer division of the muscle and the intertrans- 
versales. 

Blood-supply. — Middle and lateral coccygeal arteries. 

Nerve-supply .—Coccygesd nerves. 

The Muscles of the Thorax 

These consist of seven muscles or sets of muscles, which are attached to the 
thoracic vertebrae, to the ribs and their cartilages, and to the sternum. Func- 
tionally, they are muscles of respiration. 

1 . Levatores costarum. — These constitute a series of small muscles which occupy 
and overlie the upper ends of the intercostal spaces. 

Origin. — -The transverse processes of the thoracic vertebrae. 

Insertion. — The external surfaces of the upper ends of the ribs posterior to the 
vertebral 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 ril:) and are inserted 
on a succeeding one. At the first and last spaces the muscle cannot be distin- 
guished from the external intercostal, of which it is in reality onlj" a specially de- 
veloped part. 

Relations. — -Superficially, the longissimus dorsi; deeply, the ribs, internal 
intercostal muscles, and the intercostal vessels and nerves. 

Blood-supply. — Intercostal arteries. 

Nerve-supply. — Intercostal nerves. 

2. External intercostals (Mm. intercostales externi). — Each of these oc- 
cupies 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. 



THE MUSCLES OF THE THORAX 



241 



Insertion. — The anterior borders and external surfaces of the succeeding ribs. 

Action. — To draw the ribs forward in inspiration. 

Structure. — The fibers are directed downward and V)ackward. There is a 
considerable admixture of tendinous tissue. The thickness of the muscles grad- 
ually diminishes toward the lower ends of the spaces. 



Seventh cervical vertebra- " 



Section of scapald 



Intel trdiihursales 



Intercostal f 
nerve.'^ { 



Retractor 
IntertransverbC liqannittb <•'''( 
Ilio-lumbar ligament 




Levaiores costarum 



1 External 
\ intercostal 
\uscles 



•v^' 






7 ? (nisvcrsalis 
( o itarurn 



M 



■ Outer border of lo7i- 
gissimns dor si 

-- External angle 
of iliiitn 



Fig. 184.— Dorsal .\xr> Lfmbar Regions of Horse. Dorsal View. (After Schmaltz, Atlas <1. Anat. d. Pferdes.) 



72e?aiions.— Superficially, the serratus magnus, latissimus dorsi, serratus anticus 
and posticus, longissimus dorsi, transversalis costarum, rectus thoracis, deep 
pectorals, obliquus abdominis externus, and panniculus; 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. — Intercostal nerves. 
16 



242 FASCIA AND MUSCLES OF THE HORSE 

3. Internal intercostals (Mm. intercostales interni). — These occupy the 
entire length of the intercostal spaces, including their interchonclral 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 oblicpe downward and forward. 
There is a smaller amount of tendinous tissue than in the external set, and the 
thickness diminishes from below upward. In the upper part of the spaces fibers 
sometimes cross a rib in a fashion similar to the subcostals of man. A thin 
aponeurosis 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 al)dominis, and the internal thoracic and asternal 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 inner muscle. 

Blood-supply. — Intercostal and internal thoracic arteries. 

Nerve-supply. — Intercostal nerves. 

4. Retractor costae. — This is a small triangular nniscle which lies behind the 
last rib, chiefly under cover of the serratus posticus. 

Origin. — The transverse processes of the first three or four lumbar vertebrae 
by means of the lumbar fascia. 

Insertion. — The posterior l)order 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 posticus and external oblique; deeply, 
the transversus a!)dominis. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

5. Rectus thoracis (M. transversus costarum; lateralis sterni). — This is a 
thin nniscle which lies under cover of the deep pectoral muscles. It is directed 
obliquely backward and downward, and crosses the lower part of the first 
three intercostal spaces. 

Origin. — The outer surface of the first ril;), below the scalenus. 

Insertion. — The cartilage of the third or fourth rib. The aponeurosis usually 
joins the rectus alxlominis. It may reach the sternum. 

Action. — It may assist in inspiration or concur with the rectus abdominis. 

Relations. — Superficially, the deep pectoral muscles; deeply, the intercostal 
muscles and th(> ribs. 

6. Transversus thoracis (Triangularis sterni). — This is a flat muscle situated 
on the thoracic surface of the sternum and the cartilages of the sternal ribs. 

Origin. — The sternal ligament. 

Insertion. — The cartilages of the riljs, from the second to the eighth inclusive. 

Action. — It draws the costal cartilages inward and ])ackward, thus assisting 
in expiration. 

Structure. — Each muscle has the form of a scalene triangle, of which the base 
is the strongly serrated external l^order. The muscle contains a good deal of tend- 
inous tissue. The anterior bundles are directed forward and outward; the poste- 
rior backward and outward. 

^The function of the intercostal muscles is still a subject of much discussion. The statements 
made above seem to represent the view most commonly held in regard to their action. 



THE MUSCLES OF THE THORAX 243 

Relaiionfi. — Superiorly, the eiidotlioraoic fascia and pleura; inferiorly, the 
costal cartilages, the internal intercostal muscles, and the internal thoracic vessels. 

Blood-supply. — Internal thoracic artery. 

Nerve-.'iiipph/. — The intercostal nerves. 

7. Diaphragm. — This is a ])road, unpairtnl nuiscle 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 l)y the pleura. The abdominal surface is deeply concave, and is covered 
for the most part by the peritoneum. The muscle consists of a peripheral fleshy 
portion, two muscular crura, and a tendinous center. 

Attachments. — (1) Costal part: The cartilages of the ninth to the fifteenth 
ribs, and the last three ribs at an increasing distance from their sternal ends. 

(2) Sternal part: The upper surface of the xiphoid cartilage. 

(3) Lumbar part: (a) The right cms is attached to the inferior common 
ligament, and by this means to the first four or five lumbar vertebra?. (6) The left 
crus is attached in a similar fashion to the first and second lumbar vertebrse. 

Action.— It is the principal muscle of inspiration and increases the longi- 
tudinal 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 directly on the body walls, so that the bases of the lungs are in 
contact with the tendinous center and sternal portion only. In ordinary inspira- 
tion the fleshy rim recedes from the chest -wall, so that the bases of the lungs move 
backward to a line about parallel with the curve formed by the cartilages of the 
asternal ribs, and about four or five inches (ca. 10 to 12 cm.) therefrom. It is 
stated that the inspiratory movement affects the tendinous center much less than 
the fleshy part, since the posterior vena cava is firmly attached to the former. 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 inspiration at least. 

Structure. — The costal part (Pars costalis) consists of a series of digitations 
which meet, or are separated by a very narrow interval from, the transversus ab- 
dominis; between the two are the asternal vessels. From the tenth rib backward 
the attachments are to the ribs at an increasing distance above the costo-chondral 
junctions. Thus at the last rib the attachment is four to five inches (10 to 12 cm.) 
from the lower end. Anteriorly, the origin extends along the ninth costal cartilage 
to the xiphoid cartilage. From these points of origin the fibers curve inward and 
forward to join the tendinous center. The right crus (Crus dextrum) is about twice 
as thick as the left one and is also longer. It arises by a strong tendon from the 
lumbar vertebrse (by means of the inferior common ligament). The tendon is 
succeeded by a rounded belly which leaves the vertebral column, at the last thoracic 
vertebra. Passing downward and forward, its fibers spread out and join the tend- 
inous center. The left crus (Crus sinistrum) arises by a thin tendon from the 
inferior common ligament at the first and second lumbar vertebrae. This is suc- 
ceeded 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 attachment, forming the so-called lumbo- 
costal arch; 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 par- 

1 It should be noted, however, that in the embryo the diaphragm appears as a paired struc- 
ture, extending from the hiteral walls of the coelom to fuse with the septum transversum. 



244 



FASCIA AND MUSCLES OF THE HORSE 



tially divided into right and left halves by the descent of the crura into it. It is 
composed largely of radiating fibers, but many interlace in various directions; 
this is specially evident around the foramen venae cavae, which is encircled by fibers. 
A strong tendinous layer extends across below the hiatus a?sophageus. 



Longissinnis dorsi 

Lumbar trcmsrer&c 
process 




Costal arch 
A^ttrnul artery 

Transverszis 

abdominis {cut 

edge) 
Xiphoid cartilage 

{depressed) 



Fig. 185. — Diaphragm of Horse, Abdominal Surface. 
1, Inferior common ligament; 3, 2' , tendons of crura; 3, lumbar sympathetic trunks; 4. external siiermatic 
nerve; .5, 5, great splanchnic nerves; 6, cisterna chyli (opened); 7, 7, cesophageal continuations of vagus nerves; 
8, lynii)h-gland; 9, coronary ligament of liver (cut); 10, right lateral ligament of liver (cut); 11, left lateral liga- 
ment of liver (cut); 12, falciform ligatnent of liver (cut); A.I., lumbo-costal arch; N.i., intercostal nerve; C.d., 
right cms; C.s., left crus; A, aorta; fa, cociiac artery; Oe., cesophagus; I'.c, i)Osterior vena cava; V .p., phrenic 
veins. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an 
interval between the two crura and below the last thoracic verte])ra. It contains 
the posterior aorta, vena azygos, and cisterna chyli. (2) The hiatus oesophageus 
(or foramen sinistrum) perforates the right crus near its junction with the tendinous 



THE ABDOMINAL MUSCLES 245 

center. It is situated a little to the left of the median plane and two or three 
inches below the thirteenth thoracic vertebra (in expiration). It transmits the 
oesophagus, the vagus nerves, and the oesophageal branch of the gastric artery. 
(3) The foramen venae cavae (s. dextrum) pierces the tendinous center about an 
inch to the right of the median plane, and about six inches below the twelfth 
thoracic vertebra (in ex]iiration). The vena cava is firmly attached to the 
margin of the opening.' 

Relations. — The thoracic surface is related to the endothoracic fascia, pleura^, 
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, spleen, pancreas, kidneys and adrenals, and the anterior flexures of the colon. 
The sympathetic and splanchnic nerves pass between the crus and the psoas muscles 
on each side. The asternal vessels perforate the edge of the muscle at the ninth 
costo-chondral joint. 

Blood-supply. — Phrenic and asternal arteries. 

Nerve-supply. — Phrenic nerves (from the fifth, sixth, and seventh cervical 
nerves) . 



The Abdominal Muscles 

The superficial fascia covering the lateral and ventral walls of the abdomen is 
continuous dorsally with the lumbo-dorsal fascia, in front with the thoracic fascia, 
and behind with the gluteal fascia. 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 with the fascia of the thigh near the stifle joint. 
In this fold are the precrural lymph-glands. Medially it blends with the linea alba. 
It contains the abdominal portion of the panniculus carnosus. 

The abdominal panniculus (M. cutaneus maximus) covers a large part of 
the lateral surface of the abdomen and thorax. The general direction of its 
fibers is longitudinal. Its posterior extremity forms the basis of the fold of the 
flank. Its anterior extremity is inserted by a thin tendon into the internal tuber- 
osity of the humerus, with the posterior deep pectoral muscle. Its dorsal edge may 
be indicated by a line drawn from the upper end of the thirteenth rib to the fold of 
the flank. Its ventral limit corresponds to a line drawTi from the fold to a point 
about a hand-breadth external to the umbilicus, and from here to a point a little 
above the level of the elbow. Behind the shoulder the fibers become oblique and 
blend with the scapular portion. The aponeurosis extends ventrally to the linea 
alba, dorsally to the supraspinous ligament. The muscle is intimately adherent 
to the skin, so that special care is necessary in removing the latter. Its deep face, 
on the other hand, is loosely attached to the underlying structures by a quantity of 
areolar tissue which is more or less loaded with fat (panniculus adiposus) in animals 
in good condition. The large external thoracic (" spur ") vein is partially embedded 
in the lower part of the muscle. Its action is to twitch the skin. 

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 
obliciuus 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 intercostals and serratus magnus. 

^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 hitter should be examined while the alxlominal viscera 
remain in situ. 



246 FASCIA AND MUSCLES OF THE HORSE 

Traced forward, it passes as a thin layer beneath the posterior deep pectoral 
muscle. Posteriorly it is attached to the external angle of the ilium. In the in- 
guinal region it forms the deep fascia of the prepuce or of the mammary glands. 

The linea alba is a median fil^rous raphe which extends from the xiphoid 
cartilage to the symphysis pubis. It is formed chiefly by the junction of the apo- 
neuroses of the oblique and transverse muscles, but partly by longitudinal fibers. A 
little behind its middle is a cicatrix which indicates the position of the umbilical 
opening of the foetus. 

1. Obliquus abdominis extemus (great oblique; external ol^lique of the 
abdomen). — This is the most extensive of the al)dominal muscles. It is a broad 
sheet, irregularly triangular in shape, widest behind. Its fillers are directed chiefly 
downward and backward. 

Origin. — (1) The outer surfaces of the last fourteen ribs, and the fascia 
over the external intercostal muscles; (2) the lumbo-dorsal fascia. 

Insertion. — (1) The linea alba and the i^repubic tendon; (2) the external 
angle and shaft of the ilium ; (3) the internal 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. 

Structnre. — The muscle is composed of a fleshy portion and an aponeurosis. 
The muscular portion 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 
serratus magnus. The origin may l)e indicated by a slightly curved line (concave 
above) drawn from the lower part of the fifth rib to the external angle of the ilium. 
The fibers are directed downward and backward and terminate on the aponeurosis, 
except in the flank, where they are almost horizontal in direction. The line of 
junction is a curve (concave above) extending from the upper edge of the posterior 
deep pectoral muscle toward the external angle of the ilium. 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 upward and l)ackward and is inserted into 
the external angle of the ilium and the prepubic tendon. Between these points 
the aponeurosis is much strengthened and is called the inguinal (Poupart's) liga- 
ment (Ligamentum inguinale). This curves upward and somewhat forward, lie- 
comes 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 median plane the aponeurosis is pierced by a slit-like 
opening,^ the external inguinal ring (Annulus inguinalis subcutaneus). This is the 
external orifice of the inguinal canal. Its long axis is directed outward and forward, 
and is about four inches (ca. 10 cm.) in length. The inner angle is rounded and is 
well defined by the junction of the inguinal ligament with the prepubic tendon, but 
the outer angle is not so sharply defined. The borders or pillars are constituted by 
arciform fillers of the aponeurosis of the external oblique (Crus mediale, laterale). 
The femoral layer of the aponeurosis (Lamina femoralis) passes on to the inner sur- 
face of the thigh, where it blends with the femoral fascia. A thin iliac layer (Lamina 
iliaca) passes over the outer margin of the iliacus to the external border of the ilium. 

Relations. — Superficially, the skin, the panniculus carnosus, the abdominal 
tunic, and the posterior deep pectoral muscle; deeply, the ril)s and their cartilages, 
the intercostal muscles, the internal oblique, the contents of the inguinal canal, 
and the sartorius and gracilis. 

1 It is narrow and slit-liko in the natural condition, but may appear oval in the dissecting- 
room, especially if the hind limb is drawn back and abducted. 



THE ABDOMINAL MUSCLES 



247 



Blood-supply. — Intercostal and lumbar arteries. 
Nerve-supply. — Intercostal and lumbar nerves. 



i- '^ 




c a 



S fe p^ 



-: s 






- a 



1^ < 



2. Obliquus abdominis intemus (small oblique; internal oblique of the 
abdomen). — This muscle is situated under the preceding one. Its fibers are 
directed downward, forward, and inward. It forms a triangular curved sheet with 
the base behind. 



248 FASCIA AND MUSCLES OF THE HORSE 

Origin. — The external angle of the ilium and the adjacent }:)art of the inguinal 
(Poupart's) 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 fleshy portion is fan-shaped, and is situated chiefly in 
the flank. At its iliac origin it is covered by a glistening aponeurosis. Traced 
inward and downward along the abdominal surface of the inguinal ligament, 
the muscular origin is found to become much thinner, and also becomes loosely 
attached to the ligament. A])out four or five inches (ca. 10 to 12 cm.) from the 
linea all)a the muscle separates from the ligament and forms the antf^'ior wall 
of the inguinal canal. The abdominal orifice of the canal, the internal inguinal 
ring^ (Annulus inguinalis abdominalis), is found here. It is normally a narrow 
slit, liounded in front by the edge of the internal oblique, and behind by the in- 
guinal ligament. The aponeurosis is to a great extent blended with that of 
the external oblique, l^eing, indeed, considerably interwoven with it ventrally. 
Where it covers the rectus abdominis it is attached to the tendinous inscriptions 
of that muscle. 

Relations. — Superficially, the external ol)lique; deeply, the rectus abdominis, 
transversus abdominis, and the peritoneum. 

Blood-supply. — Circumflex iliac, 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 
abdominal wall; it extends from the lower part of the chest-wall to the pubis. 

Origin. — The cartilages of the fifth to the ninth ribs inclusive, and the adja- 
cent surface of the sternum. 

Insertion. — The pubis, by means of the prepubic tendon. 

Action. — Similar to that of the oblique muscles. It is specially adapted to 
flex the lumbo-sacral joints and the lumbar and thoracic parts of the spine. 

Structure. — The fibers of the muscle are directed longitudinally. Nine to 
eleven transverse bands of fibrous tissue extend in an irregular manner across 
the muscle. These are termed inscriptiones tendineae. They strengthen the 
muscle and serve to prevent separation of its fibers. The width of the muscle is 
greatest about its middle. 

Relations. — Superficially, the aponeuroses of the olilique muscles (which 
constitute the external rectus sheath), and the posterior deep pectoral; deeply, 
the transversus, intercostals, the cartilages of the ribs, and the sternum. The 
posterior abdominal artery runs along the outer 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 inner 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. 

1 It must 1)0 ailmitted that the term "ring" is ratlier misleading as applied to the abdomi- 
nal opening of the canal, sinec normally it is a more dilatable slit. _ The ring-like constriction 
which exists here in the male is constituted by the peritonomn, whicli descends into the canal 
to form the tunica vaginalis. This peritoneal ring is termed t lie vaginal ring (Annulus vaginalis), 
and must not be confused with the subperitoneal ring, i. c, the internal inguinal ring. 



THE ABDOMINAL MUSCLES 249 

Action. — Similar to that of the ol)hque muscles. 

Structure. — The muscular part is a sheet of parallel l)un(lles of fibers, directed 
downward and inward. It is thickest over the cartilages of the ribs, and from 
here it thins out ii;i''':^tl>' toward the aponeurosis and the lumbar region. The 
fibers of the aponeurosis directly continue those of the fleshy part. Posteriorly 
it becomes extremely thin and blends with the aponeuroses of the oblique muscles. 
It covers the deep face of the rectus, so forming the internal rectus sheath. 

Relations. — ^Superficially, the oblique and straight muscles, the retractor 
costse, the cartilages of the asternal ribs, and the internal intercostal muscles; 
deeply, the transversalis fascia and the peritoneum. The transversalis fascia is 
little developed 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 descends into the inguinal canal. The asternal 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 external surface of the muscle, to 
which they give branches. Branches of the first three lumbar nerves are simi- 
larly disposed further back. 

Blood-supply. — Intercostal, lumbar, and asternal arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

5. Cremaster extemus. — This small muscle may be regarded as a detached 
portion of the internal oblique, with which it blends at its origin (Figs. 272, 450). 

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 fiat muscular belly about one and a half to two inches (ca. 4 to5 cm.) in width.^ 
It passes down the inguinal canal on the postero-external surface of the tunica 
vaginalis, to which it is rather loosely attached. On reaching the point where 
the tunic is reflected on to the tail of the epididymis, the muscle is firmty attached 
to 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 
the internal ring it descends the inguinal canal on the postero-external surface of 
the tunica vaginalis communis. 

Blood-supply. — External spermatic or cremasteric 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 
internal inguinal or abdominal ring, and extends obliquely downward, inward, 
and somewhat forward, to end at the external inguinal or subcutaneous 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 (Poupart's) liga- 
ment. The average length of the canal, measured along the spermatic cord, 
is about four inches (ca. 10 cm.). The internal inguinal ring (Annulus inguinalis 
abdominalis) is bounded in front by the thin margin of the internal oblique muscle, 
and behind by the inguinal ligament. It is directed approximately from the edge 
of the prepubic tendon toward the external angle of the ilium. Its length is about 
four or five inches (ca. 10 to 12 cm.). The edge of the muscle is attached to the 

1 As might be expected, tlie cremaster usually undergoes more or less atrophy, and is paler 
in the castrated subject. In the mare the muscle is small, and ends in the connective tissue in 
the lower part of the inguinal canal. 

^ The term canal is somewhat misleading; it is rather a slit-like passage or space between 
the tw^o oblique muscles, since the inguinal ligament is that part of the aponeurosis of the exter- 
nal oblique muscle which stretches between the external angle of the ilium and the prepubic 
tendon. 



250 FASCIA AND MUSCLES OF THE HORSE 

surface of the ligament here by dehcate connective tissue, except where structures 
intervene between the walls of the canal. Consequently the limits of the ring 
are not very clearly defined. The external inguinal ring (Annulus inguinalis 
subcutaneus) is a well defined slit in the aponeurosis of the external oblique 
muscle, situated lateral to the prepubic tendon. Its long axis is directed from the 
edge of the prepubic tendon outward and forward, and its average length is about 
four inches (ca. 10 cm.). The canal contains in the male the spermatic cord, 
the tunica vaginalis, the external cremaster muscle, the external pudic artery 
and a small satellite vein, and the inguinal lymph-vessels and nerves. In the 
female it contains the mammarj^ vessels and nerves; in the bitch it also lodges 
the round ligament of the uterus, inclosed in a tubular process of peritoneum. 

The two rings do not correspond in direction, so tliat the length of the canal varies greatly 
wlien measured at chfferent points. The inner angle of the internal ring lies almost immediately 
above that of the external ring, Init the outer angle is situated five to six inches (ca. 12 to 1.5 cm.) 
from that of the external ring. The inner angles of the external rings are well defined and dis- 
tinctly palpable in the living subject; they are about three to four inches (ca. 8 to 10 cm.) apart. 

The Prepubic Tendon. — The prepubic tendon is essentially the tendon of 
insertion of the two recti abdominis, but aLs(j furnishes attachment to the obliciui, 
the gracilcs, and the ]7ectinei. It is attached to the anterior borders of the pul^ic 
bones, including the ilio-pectineal eminences. It has the form of a very strong 
thick band, with concave lateral borders which form the inner boundaries of the 
external 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 pubo- 
femoral or accessory ligament, which is inserted into the fossa of the head of the 
femiu' with the rouml ligament {vide hip joint). 



Muscles of the Thoracic Limb 

I. THE MUSCLES OF THE SHOULDER GIRDLE (Figs. 177, 178. 179. 186) 

This group consists of those muscles which connect the thoracic limb with 
the head, neck, and trunk. The group naturally falls into two divisions — dorsal 
and ventral.^ 

A. Dorsal Division 

This division consists of two layers which overlie the proper muscles of the 
neck and back. 

First Layer 

1. Trapezius. — This is a flat, triangular muscle, the base of the triangle 
corresponding with the spine. It is divided by an aponeurotic portion into two 
divisions: 

(a) Trapezius cervicalis, — Origin. — The funicidar portion of the ligamentum 
nuchas, from the second cervical to the third thoracic vertebra. 

Insertion. — The spine of the scapula and the fascia of tlie shoulder and arm. 

' The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical 
importance in regarfl to manipulation of the fretus in obstetrical cases. The slo])e varies in 
different subjects. In some cases the tendon forms about a right angle with the pubic bones. 

^ The terms dorsal and ventral are here used in the topographic and not in the morpho- 
logical sense. All the muscles of the group arc ventral in the latter sense. 



THE MUSCLES OF THE SHOULDER GIRDLE 251 

(b) Trapezius thoracalis s. dorsalis. — Origin. — The supraspinous ligament, 
from the third to the tenth thoracic vertebra. 

Insertion. — The tubercle of the spine of the sca]>ula. 

Action. — Acting as a whole, to elevate the shoulder; the cervical portion 
draws the scapula forward and upward and the thoracic portion draws it backward 
and upward. 

Structure. — The muscle arises by a short, thin aponeurosis, from which the 
fibers of the flat fleshy portion converge to the spine of the scapula and the apo- 
neurosis which separatees the two portions. The cervical fascia joins the ventral 
edge of the cervical portion to the mastoido-humeralis, or the two muscles may 
unite here. 

Relations. — Superficially, the skin and fascia; deeply, the rhomboideus, 
latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus magnus, 
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 the latissimus dorsi. 

2. Rhomboideus. — This consists of two portions: 

(a) Rhomboideus cervicalis s. cervicis. — Origin. — The funicular portion of 
the ligamentuni nuchie, from the second cervical to the second thoracic vertebra. 

Insertion. — The internal surface oi the cartilage of the scapula. 

(b) Rhomboideus thoracaUs s. dorsalis. — Origin. — The spinous processes 
of the second to the seventh thoracic verteljra by means of the dorso-scapular 
ligament. 

Insertion. — -The inner surface of the cartilage of the scapula. 

Action. — -To draw the scapula upward and forward. When the limb is 
fixed the cervical portion will elevate the neck. 

Structure. — The cervical portion is narrow, pointed at its anterior extremity, 
and lies along the funicular part of the ligamentum nuchae, to which it is attached 
by short tendon bundles. The fibers are directed for the most part longitudinally. 
The thoracic portion 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), the trape- 
zius, and the cartilage of the scapula; deeply, the dorso-scapular ligament, the 
splenius, complexus, longissimus dorsi, and serratus anticus. 

Blood-supply. — Dorsal and superior cervical arteries. 

Nervc-supph/. — Sixth cervical nerve. 

3. Latissimus Dorsi. — This is a wide muscle which has the form of a right- 
angled triangle. It lies for the most part under the skin and panniculus, 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 internal 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 posticus and with the lumbo-dorsal fascia. The muscular portion 
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 



252 FASCIA AND MUSCLES OF THE HORSE 

downward and forward. The thick belly formed by the convergence of these 
passes under the triceps to end on the fiat tendon of insertion, which is common 
to this muscle and the teres major. 

Blood-supply. — Subscapular, intercostal, and lumbar arteries. 

Nerve-supply. — Brachial plexus (eighth cervical and dorsal roots). 

B. Ventral Division 

1. Mastoido-humeralis (AI. brachiocephalicus; levator humeri). — 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 petrous temporal bone and the 
occipital crest ; (2) the wing of the atlas and the transverse processes of the second, 
third, and fourth cervical vertebrae. 

Insertion. — The deltoid tuberosity and the curved rough line which extends 
from this to the distal extremity of the humerus. 

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. 

Structure. — As already mentioned, the muscle is capable of incomplete 
division into two parts, the line of division being indicated by the emergence of 
superficial branches of the ventral divisions of the cervical nerves. The 
mastoid portion (M. cleido-mastoideus) partly overlaps the other portion (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 with that 
of the splenius and trachelo-mastoideus; it is also attached to the tendon of in- 
sertion of the sterno-cephalicus by aponeurosis. The dorsal portion is attached 
to the transverse processes by four fleshy digitations. The belly of the muscle 
is adherent superficially to the cervical fascia and the panniculus, and deeply 
to the subscapulo-hyoideus. In front of the shoulder its deep face is marked 
by a tendinous intersection of variable development.^ Here the muscle becomes 
wider, covers the shoulder joint, passes between the ])rachialis 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 pan- 
niculus, brachialis, and branches of the cervical nerves; deeply, the splenius, 
trachelo-mastoideus, rectus capitis anterior major, omo-hyoideus, serratus mag- 
nus, anterior deep pectoral and biceps muscles, the inferior cervical artery-, the 
prescapular lymph-glands, and branches of the cervical nerves. The ventral 
edge of the muscle forms the dorsal boundary of the jugular furrow. The dorsal 
border may be in contact with the cervical trapezius, or separated from it by a 
variable interval. 

Blood-supply. — Inferior cervical, carotid, and vertebral arteries. 

Nerve-supplj/. — Spinal accessory and cervical nerves. 

The pectoral fascia is a thin memlorane covering the surface of the pectoral 
muscles, to which it is, for the most part, pretty intimately attached. It de- 
taches 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 outer 
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 

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 of man. 



VENTRAL DIVISION 253 

between the ventral part of tlie ehest-wall and the shoulder and arm. They are 
clearly divisil)le into a superficial and a deep layer. The sui)erficial layer may be 
subdivided into two portions by careful dissection; the deep layer is clearly made 
up of two muscles. 

2. Superficial pectoral {'SI. pectoralis superficialis). 

(a) Anterior superficial pectoral (portio clavicularis s. descendens; pectoralis 
anticus). — This is a short, thick, somewhat rounded muscle, which extends between 
the anterior part of the sternum and the front of the arm. It forms a distinct pro- 
minence 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 mastoido-humeralis; 
(2) the fascia of the arm. 

Actio}i. — 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 pretty intimately attached to each other, and care 
must be exercised in making the separation. The tendon of insertion blends with 
that of the mastoido-humeralis and with the fascia of the arm. At the middle 
line of the breast a furrow occurs between the two muscles; laterally, another 
furrow, containing the cephalic vein, lies between the muscle and the mastoido- 
humeralis. 

Relations. — Superficially, the skin, fascia, and panniculus; deeply, the pos- 
terior division, the deep pectoral, and the biceps. The cephalic vein lies in the 
groove between this muscle and the mastoido-humeralis. 

(b) Posterior superficial pectoral (portio sternocostalis; pectoralis trans- 
versus). — This is a wide muscular sheet which extends from the ventral edge of 
the sternum to the fascia on the inner surface of the forearm. 

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 inner 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 posterior 
radial vessels, the median nerve, and the inner and middle flexors of the carpus. 

3. Deep pectoral (M. pectoralis profundus). — This muscle is much thicker 
and more extensive in the horse than the superficial pectoral. It consists of 
two distinct portions. 

(a) Anterior deep pectoral (portio prescapularis; pectoralis parvus). — 
This division is prismatic and extends from the anterior part of the lateral sur- 
face of the sternum to the cervical angle of the scapula. 

Origin. — The anterior half of the lateral surface of the sternum and the 
cartilages 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 inner side, and finally upward and backward along the anterior 



254 FASCIA AND MUSCLES OF THE HORSE 

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 panniculus, superficial pec- 
toral, trapezius, and mastoido-humeralis muscles, the cephalic vein, and the 
inferior cervical artery; deeply, the posterior deep pectoral, biceps, supraspi- 
natus, omo-hyoideus, and serratus magnus muscles, the brachial vessels, and the 
branches of the brachial plexus of nerves. 

(b) Posterior deep pectoral (portio humeralis s. ascendens; pectoralis 
magnus). — 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 internal tuberosity of the humerus; (2) the external lip 
of the bicipital groove; (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 also almost entirely fleshy. Its posterior part is 
wide 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 inner division of the supraspi- 
natus. 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 external lip of the bicipital 
groove, and a small part is attached to the tendon of origin of the coraco-brachialis. 

Relations. — Superficially, the skin, panniculus, 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 outer or upper border. 

Blood-supply. — Internal and external thoracic, inferior cervical, anterior 
circumflex, and intercostal arteries. 

Nerve-supphj. — Pectoral (or thoracic) nerves, from the brachial plexus. 

4. Serratus magnus (M. serratus ventralis). — 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 a 
cervical and a thoracic portion. 

(a) Cervical part (M. serratus cervicis; levator scapulae hominis). 
Origin. — The transverse processes of the last four or five cervical vertebrae. 
Insertion. — The anterior triangular area on the costal surface of the scapula 

and the adjacent part of the cartilage. 

(b) Thoracic part (M. serratus thoracis; serratus anterior hominis). 
Origin. — The external surfaces of the first eight or nine ribs. 

Insertion. — The posterior triangular area on the costal surface of the scapula 
and the adjacent part of the cartilage. 

Action. — The two muscles form a sort of sling in which the trunk is sus- 
pended. 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 contract separately and are antagonistic in their action 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 for- 
ward 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 



THE MUSCLES OF THE SHOULDER — EXTERNAL GROUP 255 

action, however, it seems desirable to distinguish the two portions. The cer- 
vical part is thick and almost entirely fleshy. The thoracic part 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 
alxlominis, and are covered by the abdominal tunic. The fourth, fifth, and sixth 
digitations extend nearly to the distal ends of the ribs. The last 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 lam- 
ellae derived from the dorso-scapular ligament. 

Relations. — Superficially, the mastoido-humeralis, trapezius, deep pectoral, 
subscapularis, teres major, latissimus dorsi, panniculus carnosus, the abdominal 
tunic, the brachial vessels, and the long thoracic nerve; deeply, the splenius, 
complexus, longissimus, transversalis costarum, the ribs and external intercostal 
muscles, and branches of the superior cervical and dorsal arteries. 

Blood-suppli/. — Superior cervical, dorsal, vertebral, and intercostal arteries. 

Nerve-supply. — Brachial plexus. 



II. THE MUSCLES OF THE SHOULDER 

Under this head will be described those muscles which arise on the scapula 
and end on the arm; they may be divided into two groups — one covering the 
dorsum, the other the venter of the scapula. 

The superficial fascia of the shoulder and arm contains the panniculus carno- 
sus of this region, and may be considered to be continued on the inner side of the 
limb by the subscapular fascia. 

The thoracic or scapulo-humeral portion of the panniculus (M. cutaneus 
scapulae et humeri) arises by a thin aponeurosis from the ligamentum nuchse at 
the withers. The fleshy portion begins over the upper part of the scapula and 
extends to the elbow. Its fibers have in general a dorso-ventral direction. It is 
continuous behind with the abdominal portion. 

The deep fascia of the shoulder and arm (Fascia omobrachialis) is much more 
developed and important. It is strong and tendinous, and is intimately adherent 
to the muscles on the outer 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 underly- 
ing muscles, for which it forms sheaths; it is attached to the humerus, especially 
to the lips of the bicipital groove and the deltoid tuberosity. It blends distally 
with the tendon of insertion of the biceps, and is continued by the antibrachial 
fascia. 

A. External Group iFigs. i78, t79) 

1. Deltoid (M. deltoideus; long abductor of the arm; scapular portion of 
the deltoid of man). — This lies partly on the triceps in the angle between the 
scapula 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 of the infraspinatus; the posterior part is 
attached to the scapula immediately in front of the origin of the long head of the 



256 FASCIA AND MUSCLES OF THE HORSE 

triceps. The belly of the muscle lies for the most part in a cavity formed in 
the triceps. It is widest about its middle. 

Relations. — Superficially, the skin, fascia, panniculus, and mastoido-humeralis; 
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. — Suprascapular and axillary nerves. 

2. Supraspinatus. — This muscle occupies the supraspinous fossa, which it 
fills, and beyond which it extends, thus coming in contact with the subscapularis. 

Origin. — The supraspinous fossa, the spine, and the lower part of the car- 
tilage of the scapula. 

Insertion. — The inner and outer lips of the l)icipital groove. 

Action. — To extend the shoulder joint. It also assists in preventing dis- 
location. 

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 below. At the neck of the 
scapula it divides into two branches, between which the tendon of origin of the 
biceps emerges. These branches, fleshy superficially, tendinous deeply, are 
inserted into the lips of the Ijicipital groove. They are united by a fibrous mem- 
brane already mentioned in connection with the deep pectoral muscle; some 
fibers are attached to this membrane and the capsule of the shoulder joint. 

Relations. — Superficially, the skin, fascia, panniculus, trapezius, and mas- 
toido-humeralis; deeply, the scapula and its cartilage, the sul)scapularis muscle, 
and the suprascapular vessels and nerve; in front, the anterior deep pectoral 
muscle; l^ehind, 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. 

Origin. — The infraspinous fossa and the scapular cartilage. 

Insertion. — (1) The outer tuberosity of the humerus, distal to the outer 
insertion of the supraspinatus; (2) the posterior eminence of the outer tuberosity. 

Action. — To abduct the arm and rotate it outward.' It also plays the part 
of 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 
insertion. This tendon, an inch or more (3 cm.) in width, passes over the posterior 
eminence of the external tuberosity of the humerus; it is bound down by a fibrous 
sheet, and a synovial bursa is interposed between the tendon and the bone. When 
the long insertion is cut and reflected, the short insertion, partly tendinous, partly 
fleshy, is exposed. 

Relations. — Superficially, the skin, fascia, panniculus, trapezius, and deltoid; 
deeply, the scapula and its cartilage, the shoulder joint and capsule, the long 
head of the triceps, the teres minor, and the nutrient artery of the scapula. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Suprascapular and axillary nerves. 

4. Teres minor. — This is a much smaller muscle than the foregoing. It 
lies chiefly on the triceps, under cover of the deltoid and infraspinatus. 

Origin. — (1) The rough lines on the distal and posterior part of the infra- 

' Giinther states that this muscle assists in extension or fie.xion according to the position 
of the head of the humerus relative to the glenoid cavity. 



INTERNAL GROUP 



257 



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 artery. 

Insertion. — The deltoid tuberosity and a small area just above it. 

Action. — To flex the 
shoulder joint and to ab- 'rfjfliitMii 

duct the arm ; also to assist ^Kwff^fcfc^-^- 

in outward rotation. 

Structure. — The muscle 
is not rounded in the horse 
and ox, but flat and triangu- 
lar. Its origin from the pos- 
terior border of the scapula 
is by means of an aponeu- 
rosis which also gives origin 
to fibers of the infraspinatus 
and 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. — Superfici- 
ally, the deltoid and infra- 
spinatus muscles ; deeply, 
the scapula, the shoulder 
joint, and the triceps mus- 
cle. 

Blood-supply. — Sub- 
scapular artery (circumflex 
branches) . 

Nerve-supply. — Axil- 
lary nerve. 



Coraco-bracfuali 
Biceps brae III I 

BuidtKilis 

Extensor (<n pi mil ml 




Tendon of extensor carpi 
obliquus 



Suspensory It 



Anterior extensor 



Branch of suspensory liga 




Tendon of tensor 
fascia; antibrachii 



Flexor carpi me- 
'dius 

..Flexor carpi in- 
ternus 



Deep flexor tendon 
Check ligament 



Superficial flexor 
tendon 



B. Internal Group 
1. Subscapularis. — 

This muscle occupies the 
sul)scapular fossa, beyond 
which, however, it extends 
both before and behind. 

Origin. — The subscap- 
ular fossa. 

Insertion. — The poste- 
rior eminence of the internal 
tuberosity of the humerus. 

Action. — To adduct the 
humerus. 

Structure. — The muscle 
is flat and triangular, with 

the base upward. The latter is thin and interdigitates with the scapular attach- 
ments of the serratus. Below this the belly thickens and becomes narrower. It 
is covered by an aponeurosis, and contains 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 capsule of the shoulder joint, and 
17 



Fig. 187. — Muscles of Thor.a.cic Limb of Horse, Internal View. 
3, 4, Rhomboideu.s; 5, latissimua dorsi; S, posterior deep pecto- 
ral; 9, anterior deep pectoral; 11, supraspinatu.s; 15, sub.scapularis; 16, 
teres major; 20, long head of triceps; i23a, 22b, tensor fasciae antibrachii; 
23, internal head of triceps. (After Ellenberger, in Leisering's Atlas.) 



258 FASCIA AND MUSCLES OF THE HORSE 

may be regarded as replacing the internal ligament of the latter. A small bursa 
may occur here. 

Relations. — Superficially, the scapula and shoulder joint, the supraspinatus, 
triceps, and teres major muscles; deeply, the serratus magnus 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. 

N erve-siipphj . — Su])scapular nerves (from the brachial plexus). 

2. Teres major (Teres internus; adductor of the arm). — This muscle is flat, 
widest about its middle, and lies chiefly on the deep face of the triceps. 

Origin. — The dorsal angle and the adjacent part of the posterior border of 
the scapula. 

Insertion. — The tubercle on the inner surface of the shaft 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 l^y a flat tendon which fuses with that of the latissimus dorsi. 

Relations. — Superficially, the triceps, infraspinatus, and deltoid muscles; 
deeply, the serratus magnus muscle. The subscapular vessels lie in a groove 
between the anterior edge of this muscle and the posterior border of the subscapu- 
laris; near the shoulder joint the posterior circumflex artery and the axillary 
nerve emerge between the two muscles. The deep face of the muscle is crossed 
by the thoracic branches of the brachial plexus, and by the branch of the subscap- 
ular artery which supplies the latissimus dorsi. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Axillary nerve. 

3. Coraco-brachialis (Coraco-humeralis). — This muscle lies on the inner sur- 
face of the shoulder joint and the arm. 

Origin. — The coracoid process of the scapula. 

Insertion. — (1) A small area above the internal 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 inner branch of the supraspinatus. It passes over the terminal part of 
the subscapularis and is provided with a synovial sheath. The muscular part 
spreads out and divides into two portions. The smaller and shorter portion is 
inserted into the proximal third of the shaft of the humerus, close to the origin 
of the lateral head of the triceps; the larger and longer portion is inserted into the 
middle third of the humerus, in front of the internal tubercle and the inner head 
of the triceps. 

Relations. — Externally, the subscapularis muscle and the humerus; inter- 
nally, the deep pectoral and brachialis muscles. The anterior circumflex artery 
and the nerve to the biceps usually emerge between the two insertions, and the 
brachial vessels lie along the posterior border of the muscle. 

Blood-supply. — Anterior circumflex artery. 

Nerve-supply. — Musculo-cutaneous nerve. 

4. Capsularis (Scapulo-humeralis posticus s. gracilis). — This is a ver}^ small 
muscle, which lies on the back of the capsule of the shoulder joint. 

On^m.— 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 may perhaps tense the capsule of the shoulder joint and prevent 
its being pinched during flexion. 



THE MUSCLES OF THE ARM 



259 



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. Its 
attachment to the joint capsule is slight. It passes through the brachialis muscle 
to reach its insertion. 

Relations. — Superficially, the teres minor and triceps muscles; deeply, the 
teres major and subscapularis muscles, and the capsule of the joint. 

Blood-sup ply. — Posterior circumflex artery. 

Nerve-supply. — Axillary nerve. 



III. THE MUSCLES OF THE ARM 
This group consists of five muscles 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. 



Spine of scapula'--- 



External tuberosity of humerus - 

Deltoid tuberosity - 
Biceps brachii ' 




Infraspinous fossa 



- - " Brachialis 

, - Musculo-spiral groove 



" Olecranon 



_, ^ . ,. ; «/ External lateral ligament of elbow joint 

Shaft of radius . ^ __ I 

■ - - Shaft of ulna 
Fig. 188. — Biceps .■vnd Br.\chialis Muscles of Horse. (.\fter Ellenberger-Baum, .\nat. fiir Kunstler.) 

1. Biceps brachii (Coraco-radialis; flexor brachii). — This is a strong, some- 
what rounded muscle, which lies on the anterior surface of the humerus. 

Origin. — The tuberosity of the scapula. 

Insertion. — (1) The bicipital tuberosity of the radius; (2) the internal lat- 
eral 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, and to tense the fascia of the forearm. 

Structure.— The muscle is inclosed in a double sheath of fascia, which is 
attached to the lips of the bicipital groove and the deltoid ridge of the humerus. 
The tendon of origin is moulded on the bicipital groove; it is very strong and dense 
and is partly cartilaginous. Its play over the groove is facilitated by the large 
bicipital bursa (Bursa intertubercularis). The synovial membrane covers not 
only the deep face of the tendon, but extends somewhat over the edges to the 
superficial face. A well-marked tendinous intersection runs through the belly 
of the muscle and divides distally into tw^o portions. Of these, the short, thick 
one is inserted into the bicipital tuberosity and detaches fibers to the internal 



2G0 FASCIiB AND MUSCLES OF THE HORSE 

lateral ligament. 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. 

Relations. — Externally, the mastoido-humeralis and brachialis muscles; in- 
ternally, the posterior deep pectoral and the superficial pectoral muscles; in front, 
the anterior deep pectoral muscle; behind, the humerus, the coraco-brachialis mus- 
cle, the anterior circumflex and anterior radial vessels, and the musculo-cutaneous 
nerve. 

Blood-supply. — Branches of the brachial and anterior radial arteries. 

Nervc-sjipply. — Musculo-cutaneous nerve. 

2. Brachialis (Humeralis obliquus s. externus; brachialis anticus). — This 
muscle occupies the musculo-spiral groove of the humerus. 

Origin. — The proximal third of the posterior surface of the humerus. 

Insertion. — The inner surface of the neck of the radius (under cover of the 
lateral ligament) and the arciform ligament. 

Action. — To flex the elbow joint. 

Structure. — The peculiar spiral course of this muscle gave rise to the name 
often applied to it — humeralis obliciuus. 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 inner side of the forearm by passing 
between the biceps and the extensor carpi. It is entirely fleshy, with the exception 
of its relatively slender tendon of insertion. 

Relations. — Externally the skin and fascia, the teres minor, deltoid, triceps 
(lateral head), liiceps, and mastoido-humeralis muscles. The anterior radial artery 
crosses the deep face of the muscle in its distal third, and the radial nerve accom- 
panies the muscle in the distal half of the musculo-spiral groove. 

Blood-supply. — Brachial artery. 

Nerve-supply. — Radial nerve. 

3. Tensor fasciae antibrachii (Fig. 187)^ (Scapulo-ulnaris; long extensor 
of the forearm; accessory anconeus of the latissimus dorsi). — This is a thin 
muscle which lies on the inner surface of the triceps. 

Origin. — The tendon of insertion of the latissimus dorsi and the posterior 
border of the scapula. 

Insertion. — (1) The fascia of the forearm; (2) a small eminence on the posterior 
border of 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. The muscular portion is 
quite 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, how- 
ever, a small but constant tendinous attachment to the olecranon. 

Relations. — Externally, the panniculus, trice]:)s (long and internal heads), 
the inner and middle flexors of the carpus, and the ulnar vessels and nerve; in- 
ternally, the latissimus dorsi, serratus magnus, and posterior pectoral muscles. 

Blood-supply. — Subsca])ular, ulnar, and deep brachial arteries. 

Nerir-suj)phi. — Radial nerve. 

4. Triceps brachii (Figs. 178, 179, 187) (Brachial triceps; triceps extensor 
cubiti). — This, together with the preceding muscle, constitutes the large muscular 

1 M'Fadyean and Vaughan term this muscle the .scapulo-uhiaris, while Arloing and Lesbre 
term it "Ancone accessoire du grand dorsal." The aboY(> name seems to agree best with the 
<'hief insertion and action, although it certainly arises largely from the tendon of insertion of 
the latissinnis dorsi. 



THE MUSCLES OF THE ARM 261 

mass which fills the angle botwoen the posterior border of the scapula and the 
humerus. It is clearly divisible into three heads, as described below. 

(a) Long head (Caput longum tricipitis; anconeus longus; caput magnum). 
— 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 outer 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. 

Relations. — Externally, the panniculus, deltoid, infraspinatus, teres minor, 
and the external head; internally, the tensor fasciae antibrachii, teres major, 
latissimus dorsi, and posterior deep pectoral muscles, and the subscapular vessels; 
in front, the brachialis, and the inner head, the deep brachial and posterior circum- 
flex vessels, and the axillary and radial nerves; behind, the skin and fascia. 

Blood-supply. — Subscapular and deep ]:)rachial arteries. 

Nerve-supply. — Radial nerve. 

(b) External head (Caput laterale tricipitis s. anconeus laterahs s. externus; 
caput medium). — This is a strong, ciuadrilateral muscle, which lies on the outer 
surface of the arm. Its proximal third is covered by the deltoid and teres minor 
muscles; the remainder only by the thin panniculus and the skin. 

Origin. — The deltoid tuberosity and the curved rough line which extends from 
it to the neck of the humerus. 

Insertion. — (1) A small prominent area on the outer 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. — Externally, the deltoid, teres minor, and panniculus muscles; 
internally, the long and inner 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 brachial artery and of the radial nerve. 

Blood-supply. — Posterior circumflex and deep brachial arteries. 

Nerve-supply. — Radial nerve. 

(c) Internal head (Fig. 193) (Caput mediale tricipitis; anconeus medialis s. 
internus; caput parvum). — This is much the smallest of the three heads. It is 
situated on the inner surface of the arm, and extends from the middle third of the 
humerus to the olecranon. 

Origin. — The middle third of the inner surface of the shaft of the humerus, 
behind and below the internal tubercle. 

Insertion.— The inner and fore part of the summit of the olecranon, between the 
insertion of the long head and the origin of the ulnar head of the flexor perforans. 

Action. — To extend the elbow joint. 

Structure. — The muscle is fleshy except at its insertion, where it has a flat 
tendon, under which a small bursa may be found. 

Relations. — Externally, the humerus, brachialis, anconeus, and the external 
head; internally, the posterior deep pectoral, coraco-brachialis, teres major, 



262 



FASCIA AND MUSCLES OF THE HORSE 



latissimus dorsi, and tensor fasciae 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 l^rachial and ulnar arteries. 
Nerve-supply. — Radial nerve. 

5. Anconeus (M. anconeus parvus s. subanconeus) . — This is a small fleshy 
muscle which covers the olecranon fossa and is covered by the triceps. It is some- 
what difficult to separate from the outer head. 

Origin. — The distal third of the posterior surface of the humerus. 

Insertion. — The outer 
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. 

Structure. — It is almost 
entirely fleshy, and is ad- 
herent by its deep face to 
the joint capsule. 

Relations. — Superfici- 
ally, the triceps muscle; 
deeply, the humerus and 
the elbow joint. 

Blood-supply. — Deep 
brachial artery. 

Nerve-supply. — Radial 
nerve. 




Deep flexor tendon 

■Distal end of small metacarpal bone 
Suspensory ligament 



Branch of stiperficial flexor tendon 
Distal digital annular ligament 
- Upper border of lateral cartilage 



Fin. 189. — Digit of Horse, Posterior View. 
14, Deep flexor tendon; 15, superficial flexor tendon; 16, posterior 
annular ligament of fetlock; 17 , proximal annular or vaginal ligament 
of digit; 11, lateral cartilage; 24, plantar cushion. (After EUenberger- 
Baum, Anat. fiir Kiin.stler.) 



IV. FASCIA AND MUSCLES 
OF THE FOREARM 

AND MANUS 

The forearm is covered 
on three sides by the mus- 
cles of this group, leaving 
the inner surface of the radi- 
us for the most part subcu- 
taneous. The extensors of 
the carpus and digit lie on the anterior (dorsal) and external part of the region, 
while the flexors occupy the posterior (volar) surface. 

The fascia of the forearm (Fascia antibrachii) forms a very strong and complete 
investment for all the muscles of the region. The superficial fascia is thin, and 
disappears at the carpus by fusing with the deep fascia. The deep fascia is very 
strong and tendinous in character. It furnishes insertion at its upper and inner 
part to the tensor fasciae antibrachii and posterior superficial pectoral muscles; 
at its upper anterior and outer part, to aponeuroses from the mastoido-humeralis 
and biceps. It is attached at the elbow by its deep face to the outer tuberosities of 
the humerus and radius, to the ulna, and to the lateral ligaments. On the inner 
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, Ijut is 
rather loosely attached to the flexors. From its deep face are detached inter- 
muscular septa, which form sheaths for the muscles and are attached to the untler- 
lying bones. The principal septa are: (a) One wdiich passes between the common 



FASCI.E AND MUSCLES OF THE FOREARM AND MANUS 263 

extensor (in front) and the lateral extensor and flexor carpi externus (behind) ; 
(6) one between the common extensor and the extensor carpi radialis; (c) one be- 
tween the inner 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 (pisiform) bone, and to the lateral ligaments. In front it forms the 
so-called anterior annular ligament (Ligamentum carpi dorsale), bridging over the 
grooves and binding down the extensor tendons and their synovial sheaths. Be- 
hind it is greatly thickened and forms the posterior annular or transverse liga- 
ment of the carpus (Ligamentum carpi transversum). This stretches across from 
the accessory carpal bone to the internal lateral ligament and the proximal 
extremity of the inner metacarpal bone. It thus completes the carpal canal, in 
which lie the flexor tendons, their synovial sheath, and the principal vessels and 
nerves of the region. 

The fascia of the metacarpus and digit (Fascia metacarpea et digitalis) is, in 
general, thinner than the preceding. It is attached to the tendons, ligaments, and 
the exposed bony prominences — especially to the small metacarpal bones. On the 
flexion surface of the fetlock joint it is much thickened by fibers passing transversely 
from one sesamoid bone to the other, forming an annular ligament which binds down 
the flexor tendons in the sesamoid groove or canal. Distal to this is a second thick 
quadrilateral sheet (Ligamentum vaginale) which covers and is adherent to the 
tendon of the flexor perforatus. It is attached on either side by two bands to the 
borders of the first phalanx, thus firmly binding down the flexor tendons. A little 
further down a crescentic fibre-elastic sheet 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. 

A. Extensor Division 

1. Extensor carpi radialis (M. extensor carpi radialis s. radialis dorsalis; ex- 
tensor metacarpi magnus; anterior extensor of the metacarpus). — This is the 
largest muscle of the extensor division, and lies on the anterior (dorsal) surface of 
the radius. 

Origin. — (1) The external condyloid crest of the humerus; (2) the coronoid 
fossa. 

Insertion. — The tuberosity on the anterior (dorsal) surface of the proximal 
extremity of the large (third) metacarpal bone. 

Action. — To extend and fix the carpal joint and to flex the elbow joint. 

Structure. — 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 anterior annular ligament and invested with a synovial 
sheath. The latter begins three to four inches (ca. 8 to 10 cm.) above the carpus 
and extends almost to the insertion of the tendon. In the lower 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; deepl}^ 
the capsule of the elbow joint, the biceps tendon, the radius, the carpal joint capsule, 
the anterior radial artery, and the radial nerve; externally, the anterior or com- 
mon extensor; internally, at the elbow, the brachialis and biceps. 

Blood-supply. — Anterior radial artery. 

Nerve-supply. — Radial nerve. 

2. Anterior or common digital extensor (M. extensor digitalis communis; 



264 



FASCIA AND MUSCLES OF THE HORSE 



anterior extensor of the phalanges; extensor pedis). — This muscle lies external to 
the foregoing, which it resembles in general form, although less bulky. 

Origin. — (1) The front of the distal extremity of the humerus, just external to 
the coronoid fossa; (2) the external tuberosity on the proximal extremity of the 
radius, the external lateral ligament of the elbow, and the external border of the 



Brachialis 



CcpliaUc vein 
Flexor carpi internui 



A nterior or common extensor of digit 



Extensor carpi obliquus 



Z 



Metacarpal tuberosity "^ 



Tendon of anterior extensor 
Tendon of lateral extensor 



Branch of suspensory ligament to extensor 
tendon 



Lateral cartilage 



Fig. 190. — Muscles of Left Thoracic Limb of Horse, from Elbow downward, Anterior View. 
a, Extensor carpi radialis; g' , superficial pectoral muscle. (After EIlenberger-Baum, Anat. fur Kiinstler.) 



radius at the junction of its proximal and middle thirds; (3) the external surface 
of the shaft of the ulna; (4) the fascia of the forearm. 

Insertion. — (1) The extensor (or pyramidal) process of the ^third phalanx; (2) 
the anterior surface 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,. 



EXTENSOR DIVISION 265 

togpther with vestiges of the proper extensors of the digits. Usually at least 
two heads maj' be distinguished. The principal or humeral head (Caput 
humerale) arises from the front of the extensor epicondyle of the humerus in 
common with the extensor carpi. Its ^belly is fusiform, and terminates in a 
jioint 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 inclines gradually 
inward, 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 liga- 
ment, and the tendon thus becomes much wider. Two synovial membranes 
facilitate the play of the tendon. The proximal one is a sheath which begins about 
three inches (ca. 7 to 8 cm.) above the carpus, and terminates at the proximal end 
of the metacarpus. At the fetlock a bursa occurs l^etween the tendon and the 
joint capsule, but otherwise the two are adherent. The smaller head, arising 
chiefly from the radius and ulna, is often divisil)le into two parts (Fig. 443). The 
larger of these (Caput radiale, muscle of Phillips)^ arises from the outer tuberosity 
and outer border of the radius, and from the lateral ligament of the ell)ow joint. 
The flat belly is succeeded by a delicate 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. Usually a slip is detached which is 
inserted on the proximal extremity of the first phalanx, or ends in the fascia here. 
The smaller and deeper division (Caput ulnare, muscle of Thiernesse)" 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 delicate tendon which 
may fuse with the principal tendon or may be inserted into the 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 internally, 
the extensor carpi radialis; behind, the lateral extensor and the interosseous vessels. 

Blood-supply. — Radial and interosseous arteries. 

Nerve-supply. — Radial nerve. 

3. Lateral digital extensor (M. extensor digitalis lateralis s. digiti quinti pro- 
prius; lateral extensor of the phalanges; extensor suffraginis). — This muscle is 
much smaller than the preceding, behind which it is situated. 

Origin. — The external tuberosity of the radius and the lateral ligament of the 
elbow joint, the shaft of the ulna, the outer 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. — The muscle is pennate, and is inclosed in a sheath formed by the 
deep fascia, from which many fibers arise. The belly is thin and fusiform and 
terminates at the lower third of the forearm. From here the tendon (at first 
small and round) passes downward through the groove on the outer tuberosit}^ 
of the distal end of the radius, then over the carpus, and, gradually inclining toward 
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 

1 This is considered to represent the part of the common extensor for the fourth and fifth 
digits. 

^ Martin considers that this muscle represents the extensor indicis proprius and the part 
of the common extensor for the second digit. 



266 



FASCIA AND MUSCLES OF THE HORSE 



with the tendon. A sheath envelops the tendon, Ijeginning about three inches 
(ca. 6 to 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 fiat and 



Extensor carpi ohliqiius 



Metacarpal tuberosity 



Tendon from anterior to lateral extensor \i 



External small metaearpal hone 



Branch of suspensory ligament to 
extensor tendon 




Olecranon 



Ulnar head of deep flexor 



Lateral extensor 
Deep flexor {h umeral head) 

Tendon of flexor carpi externus 
Accessory carpal bone 



Check ligament 

Susp( nsory ligament 
Flexor tendons 




Flexor tendons 
Latend cartilage 



Fig. 191. — Muscles of Left Thoracic Limb of Horse from Elbow Downward; External View. 
a. Extensor cariji radialis; o, brachialLs; g' , anterior superficial pectoral; c, anterior or common digital ex- 
tensor; e, flexor carpi externus. (After Ellenberger-Baum, Anat. fiir Ki'mstler.) 



much larger below the carpus, having received the tendon of the radial head of the 
anterior extensor and a strong band from the accessory carpal bone. 

Relations. — Superficially, the skin and fascia; deeply, the outer face of the 
radius and ulna; in front, the common extensor, the oblique extensor, and the 
interosseous artery; behind, the external flexor of the carpus and the deep flexor of 
the digit. 

Blood-supply. — Interosseous artery. 



FLEXOR DIVISION 



267 



Nerve-supplij. — Radial nerve. 

4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis 
brevis; oblique extensor of the metacarpus; extensor metacarpi obliquus). — This 
is a small muscle which curves ol)liquely over the distal half of the radius and the 
carpus. 

Origin. — The external border and adjacent part of the anterior surface of the 
radius (the attachment area beginning at a point above the middle of the bone and 
extending down to its lower fourth). 

Insertion.— The head of the inner (second) metacarpal bone. 

Action. — To extend the carpal joint. 

Structure. — The muscle is pennate and has a flat belly which curves downward, 
forward, and inward over the distal part of the radius. The tendon continues the 
direction of the muscle, crossing obliquely over the tendon of the extensor 
carpi radialis; it then occupies the oblique groove at the distal end of the radius, 
and crosses the inner face of the carpus. It is provided with a synovial sheath. 




Fig. 192. — Cross-sectiox of Middle of Rigitt Forearm of Horse 
a. Accessory cephalic vein; 6, cutaneous branch of median nerve; c, extensor carpi obliquus; d, posterior 
radial artery; e, satellite vein; /, median nerve; g, g' , ulnar vessels; h, ulnar nerve; i, cephalic vein; k, tendon of 
ulnar head of deep flexor; /, interosseous artery; m, extensor carpi radialis; n, anterior digital extensor; u, lateral 
digital extensor; p, flexor carjji externus; q, q, q, humeral heads of deep digital flexor; r, radial head of same; s, 
superficial digital flexor; /, flexor carpi medius; w, flexor carpi internus; v, radius; w, skin; x, anterior radial 
artery. (After Ellenberger, in Leisering's Atlas.) 

Relations. — Superficially, the skin and fascia, the lateral extensor, and the 
common extensor; deeply, the radius, the extensor carpi radialis, the carpal cap- 
sule, and the internal lateral ligament. 

Blood-supplij. — Interosseous and anterior radial arteries. 

Nerve-supply. — Radial nerve. 



B. Flexor Division 

1. Flexor carpi internus (AI. flexor carpi radialis s. radialis volaris; internal 
flexor of the metacarpus). — This muscle hes on the inner surface of the forearm, 
immediately behind the inner border of the radius. 

Origin. — The flexor (internal) epicondyle of the humerus, below and behind 
the lateral ligament. 

Insertion. — The proximal end of the internal (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. It is provided with a synovial sheath which begins two or 



268 



FASCI.E AND MUSCLES OF THE HORSE 



three inches (ca. 5 to 8 cm.) above the carpus and extends almost to the insertion 
of the tendon. 

Relations. — Superficially, 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 medius, the posterior radial 
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. — Posterior radial artery. 
Nerve-s upply. — Med i an nerve . 

On removing thedeop fascia on the inner surface of the elbow 
the student may notice a small muscle lying along the lateral liga- 
ment. 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 flexor epicondyle of the humerus, and is inserted into the in- 
ternal lateral ligament of the elbow. On account of its small size 
and the fact that the forearm is fixed in the position of pronation, 
the muscle can have no appreciable function. It is usually repre- 
sented by the long portion of the internal lateral hgament. 

2. Flexor carpi medius (M. flexor carpi ulnaris s. 
ulnaris medialis; oblique or middle flexor of the meta- 
carpus). — This muscle lies on the inner and posterior 
aspect of the forearm partly under, partly behind, the 
preceding muscle. It arises by two heads — humeral 
and ulnar. 

Origin. — (1) The flexor (internal) epicondyle of 
the humerus just behind the preceding muscle; 
(2) the inner surface and posterior border of the 
olecranon. 

Insertion. — The upper edge of the accessory carpal 
(pisiform) ])one. 

Action. — To flex the carpal joint, and to extend the 
elbow. 

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. The tendon of insertion is 
short and strong; it blends with the posterior annular 
ligament of the carpus. 

Relations. — Superficially, the tensor fascise anti- 
brachii, superficial pectoral, and flexor carpi internus, 
the skin and fascia, and cutaneous branches of the ulnar 
nerve; deeply, the superficial and deep flexors of the 
digit. In the distal half of the forearm the ulnar vessels 
and nerve lie between the outer edge of this muscle and 
the external flexor of the carpus. 

Blood-supply. — Ulnar and posterior radial arteries. 

Nerve-supply. — Ulnar and median nerves. 
3. Flexor carpi extemus (M. extensor carpi ulnaris^ s. ulnaris lateralis; 
external flexor of the metacarpus). — This muscle lies on the outer face of the 
forearm, behind the lateral extensor of the digit. 

1 In man the muscle is an extensor of the hand. 




Fig. 193. — Deeper Muscles of 
FoRE.\.RM OF Horse, In- 
TERN.\L View. 
23, Internal head of triceps; 
SO, flexor carpi mediu.s; 31, flexor 
carpi internus; 31', tendon of 31; 
32, superficial digital flexor; 32', 
radial check ligament; 32" , tendon 
of superficial flexor; 33a, 33b, 33c, 
humeral heads of deep flexor; 33' , 
deep flexor tendon; 33", subcarpal 
check ligament; 34, ulnar head of 
deep flexor; 35, radial head of deep 
flexor; 36, suspensory ligament. 
(After EUenberger, in Leisering's 
Atlas.) 



FLEXOR DIVISION 



269 



Origin. — The extensor (external) epicondyle of the humerus, behind and below 
the lateral ligament. 

Insertion. — (1) The outer surface and upper edge of the accessory carpal 
bone; (2) the proximal extremity of the outer (fourth) metacarpal bone. 

Action. — To fiex 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 tw^o 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 outer surface of the accessory carpal bone, enveloped by 
a synovial sheath, to reach its insertion on the outer metacarpal bone. A synovial 



For tendon of 
anterior extensor 



For tendon of ex- 
tensor carpi radialis 



Joint cavity 



For tendon of lateral 
extensor 

External lateral liga- 
ment 



For long tendon of 
flexor carpi externus 




Posterior annular 
ligament 



Infernal meta- 
carpal nerve in 
carpal canal 



For tendon of extensor 
carpi ohliquus 



Bursa 

Internal lateral liga- 
ment 



Posterior ligament of 
carpus 

For tendon of flexor carpi 

internus 

Large metacarpal artery 



Internal metacarpal vein 



Fig. 194.— Cross-section of Proximal Part of Left Carpus of Horse. 
The tendons have been removed to show the canals in which they lie. The joint cavity is black. 



By 



an over.sight the carpal canal for the two flexor tendons behind the jjosterior liganaent of the carpus is not marked. 
Cr, Radial, Ci, intermediate, Cu, ulnar, Ca, accessory carjjal bones. 



pouch lies under the origin of the muscle at the ell^ow joint, with the cavity of 
which it communicates. 

Relations. — Superficially, the skin, fascia, and cutaneous branches of the ulnar 
nerve; deeply, the ell)ow 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 or flexor perforatus (M. flexor digitalis sublimis; 
superficial flexor of the phalanges) . — This muscle is situated in the middle of the 
flexor group, chiefly under cover of the middle flexor of the carpus. 

Origin. — (1) The flexor epicondyle of the humerus, between the flexor carpi 
internus and the deep flexor of the digit; (2) a ridge on the posterior surface of the 
radius, below its middle and near the internal border. 

Insertion. — (1) The eminences on the proximal extremity of the second phalanx 



270 



FASCIA AND MUSCLES OF THE HORSE 



l)ehind the lateral ligaments; (2) the distal extremity of the first phalanx, also 
behind the lateral ligaments. 

Action. — To flex the digit and carpus, and to extend the elbow. 





Fig. 195. — Synovial Sheaths and Burs^ of Lower 
Part of Right Fore Limb of Horse, Lnter- 
NAL View. 

The synovial sheaths (colored yellow) and t 
a. Sheath of extensor carpi obliquus; b, sheath 
of flexor carpi internus; c, carpal sheath; d, d' , d" , d'" , 
digital sheath; e, bursa under anterior extensor ten- 
don; /, cajjsule of fetlock joint; 1, extensor carpi 
radiali.s; 2, tendon of extensor carpi obliquus; 3, 
flexor carpi internus; 4, flexor carpi medius; 5, superfi- 
cial flexor tendon; S, deep flexor tendon; 7, suspensory 
ligament; <S, small metacarpal bone; 9, large meta- 
carpal bone; 10. posterior annular ligament of fetlock; 
7/, proximal digital annular ligament; 12, radius; 13, 
radiocari)al joint; 14, fetlock joint; 15, lateral cartilage; 
16, band from first phalanx to lateral cartilage. (After 
EUenberger, in Leisering's Atlas.) 



Fig. 196. — Synovial Sheaths and Burs.13 of Lower 
Part of Right Fore Limb of Horse, Exter- 
nal View. 
he joint capsules (colored pink) are injected. 

a. Sheath of extensor carpi radialis; b, sheath 
of anterior extensor; c, sheath of lateral extensor; d, 
sheath of outer tendon of flexor carpi externus; e, e', 
carpal sheath; /,/',/", digital sheath; 3, bursa under 
anterior extensor tendon; h, bursa under lateral ex- 
tensor tendon; ;', capsule of fetlock joint; 1, extensor 
carpi radialis; 2, anterior digital extensor; 3, lateral 
digital extensor; 4, flexor carpi externus; 4', 4". 
tendons of 4>' 5, superficial flexor tendon; 6, deep 
flexor tendon; 7, suspensory ligament; 8, external 
metacarpal bone; 0, large metacarpal bone; 10, 
posterior annular ligament of fetlock; i^, digital annular 
ligament; 13. fetlock joint; 13, lateral cartilage; 14, 
band from first ijhalanx to lateral cartilage. (.\fter 
EUenberger, in Leisering's .\tlas.) 



Structure. — The fleshy portion of the muscle or humeral head takes origin 
from the humerus. The radial head (Caput tendineuin) consists of a strong fibrous 
band, usually termed the radial or superior check Ugament, which fuses with the 



FLEXOR DIVISION 



271 



tendon near the carpus. The ])elly of the muscle is intersected by tendinous strands, 
and fuses more or less with that of the deep flexor. Near the carpus it is succeeded 
by a strong, thick tendon which passes down through the carpal canal, formed by the 
posterior ligament of the carpus, the accessory carpal bone, and the posterior 
annular ligament (Ligamentum carpi transversum). Here it is enveloped by a 
synovial sheath, in common with the deep flexor. This carpal sheath (Vagina 
carpea) begins three or four inches (8 to 10 cm.) above the carpus, and extends down- 
ward nearly to the middle of the metacarpus. Below the carpus the tendon be- 
comes flattened and broader. Near the fetlock it forms a ring through which the 
tendon of the deep flexor passes (Fig. 150). Here the two tendons are bound 
down in the sesamoid groove by the posterior 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 diverge to reach their points 
of insertion, and between these branches the tendon of the deep flexor emerges 
(Fig. 189). A second synovial sheath, the digital or sesamoidean (Vagina 



Tendon of lateral extensor Tendon of anterior extensor 



Upper pouch of joint capsule 
Branch of suspensory ligament 




Inter sesamoid liga ment 
Digital vein 



Fig. 197. 



'^// ~~~ Digital artery 
'^ /^ ~^- Digital nerve 



Tendon of superficial flexor Tendon of deep flexor 
Cross-section of Distal Part of Left Metacarpus of Horse, Just Above Sesamoids. 



digitalis), begins at the distal third of the metacarpus, three to four inches (8 to 
10 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 medius, and, at its origin, to the ulnar vessels 
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. — Posterior radial artery. 

Nerve-supply. — Median nerve. 

5. Deep digital flexor or flexor perforans (M. flexor digitahs profundus; 
deep flexor of the phalanges). — The fleshy part of this muscle lies on the posterior 
surface of the radius, under cover of the preceding muscles. It is the largest 
muscle of the flexor group. 

Origin. — (1) The flexor (internal) epicondyle of the humerus; (2) the inner 
surface of the olecranon; (3) the middle of the posterior surface of the radius 
and a small adjacent area of the ulna. 

Insertion. — The semilunar crest of the third phalanx, and the adjacent surface 
of the lateral cartilage. 

Action. — To flex the digit and carpus, and to extend the elbow. 



272 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — This muscle consists of three principal heads. The humeral head 
(Caput humerale) constitutes the bulk of the muscle. It is marked ])y tendinous 
intersections, and is separable into three secondary heads. The ulnar head (Caput 
ulnare, ulnaris accessorius) is much smaller, and is at first superficially situated be- 
tween the outer and middle flexors of the carpus. The radial head (Caput radiale, 
radialis accessorius) 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 humeral 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 
to 10 cm.) above the carpus. It is soon 
joined by the small tendon of the ulnar 
head, which begins about the middle of the 
forearm. The tendon of the radial head 
fuses with the principal tendon close to 
the carpus. The conjoined tendon passes 
downward through the carpal canal, being 
included in the carpal synovial sheath 
with the superficial flexor tendon, as 
previously described. Continuing down- 
ward, it is joined about the middle of the 
metacarpus by a strong fibrous band, the 
so-called inferior or subcarpal check liga- 
ment (Caput tendineum) . This is a direct 
continuation of the posterior ligament of 
the carpus. Below this the tendon passes 
through the ring formed by the perfor- 
atus, then in succession over the sesamoid 
groove, the inferior sesamoidean liga- 
ments, and the tendon surface of the third 
sesamoid, to its insertion (Figs. 150 and 
151 ). Its terminal part is much widened. 
From the distal third of the metacarpus to 
the distal end of the second phalanx it is 
inclosed in the digital synovial sheath de- 
scribed in connection with the perforatus. 
The navicular bursa or bursa podotroch- 
learis is found between the tendon and 
the third sesamoid or navicular bone. 
The terminal part of the tendon is bound 
clown by the fibrous sheet descrilDed with 
the fascia. 

Relations. — The belly of the muscle is 
related posteriorly to the perforatus and 
the middle flexor of the carpus; internally, 
to the internal carpal flexor, the radial 
check ligament, and the posterior radial 
vessels and median nerve; externally, to the external flexor of the carpus; anteriorly, 
to the radius and ulna and branches of the posterior radial artery and median 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-external aspect of the 
proximal half of the forearm, and also on the outer aspect of the distal fourth. 
Blood-supply. — Posterior radial and ulnar arteries. 
Nerve-supply. — Median and ulnar nerves. 




Fig. 198. — Dioit of Horse, Lateral View. 
1, Large metacarpal bone; 2, distal end of small 
metacarpal bone; 3, fetlock joint; 6, first phalanx; 6, 
pastern joint; 7, second phalanx; 8, coffin joint; 9, 
third phalanx; 11, lateral cartilage; 11', upper (sub- 
cutaneous) border of cartilage; 12, suspensory liga- 
ment; 13, branch of 12 to extensor tendon; 14, deep 
flexor tendon; ^5, superficial flexor tendon; i5', branch 
of 15; 16, posterior annular ligament of fetlock; 17, 
proximal annular or vaginal ligament of digit; 18, 
distal annular ligament or reinforcing sheath of deep 
flexor tendon; 19, lateral ligament of coffin joint; 21 , 
tendon of common or anterior extensor; 22, tendon of 
lateral extensor; 23, digital vein. (After Ellenberger- 
Baum, Anat. fiir Ktinstler.) 



FASCIA AND MUSCLES OF THE PELVIC LIMB 273 

METACARPAL MUSCLES 

The five muscles of this group are either reduced to vestiges or modified greatly 
in structure. 

1, 2. Lumbricales (internus et externus). — These are two small muscles which 
lie on either side of the flexor tendons above the fetlock. They arise from the 
deep flexor tendon, and are lost in the fibrous tissue which lies under the nodule of 
horn or ergot at the fetlock (Fig. 447). Their action is inappreciable. The size 
of these muscles is subject to much variation. Often very little muscular tissue 
can be found, but the small tendon is constantly present. 

Blood-supply. — 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. Tw^o, the internus and externus, are very small 
muscles, each of which arises from the corresponding small metacarpal bone near 
its proximal extremit^^ and is provided with a delicate tendon which is usually lost 
in the fascia at the fetlock (Fig. 150). 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, 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. 



fasci.e and muscles of the pelvic limb 

The Fascia 

« 

The iliac fascia (Fascia iliaca) covers the ventral surface of the iliacus and psoas 
muscles, over which it is tightly stretched (Fig. 450). It is attached internally to 
the tendon of the psoas minor, externally to the inguinal (Poupart's) ligament 
and the external angle of the ilium. Its anterior part is thin. Posteriorly, it is 
in part attached to the ilium, in part becomes continuous with the pelvic fascia. 
It furnishes surfaces of origin for the sartorius, cremaster externus, and transversus 
abdominis muscles. 

The pelvic fascia (Fascia pelvis) lines the cavity (parietal layer) and is reflected 
on the viscera at the ])elvic outlet (visceral layer). LaminiE are detached from it 
to strengthen the various peritoneal folds. 

The superficial fascia of the gluteal region is continuous with the aponeurosis 
of the panniculus. It covers and partly blends with the deep fascia. The gluteal 
fascia (Fascia glutea) covers the superficial muscles of the region, and detaches 
intermuscular septa, which pass between the muscles. It is attached to the sacral 
spines, the dorsal sacro-iliac ligament, and the angles of the ilium, and is continuous 
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 ofT 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 semitendinosus, 
from which a lamella is detached which passes between the middle and posterior 
portions 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 fascia lata is continuous with the preceding, and covers the muscles on the 
18 



274 FASCIA AND MUSCLES OF THE HORSE 

outer surface and front of tlie thigh. It is tendinous and very strong, and for the 
most part easily separable from the underlying muscles. It furnishes insertion to 
the tensor fasciae 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 inner and outer straight 
ligaments. Internally it is continuous with the internal femoral fascia. It fur- 
nishes the following intermuscular septa: (1) One which passes between the vastus 
externus and biceps femoris to be attached to the external trochanter of the femur; 
(2) two which pass between the three branches of the biceps femoris; (3) a fourth 
between the biceps femoris and semitendinosus. 

The internal femoral fascia (Fascia femoralis medialis) covers the superficial 
muscles on the inner surface of the thigh. At its upper part it is joined by part of 
the aponeurosis of the external oblique muscle (Lamina femoralis) (Fig. 450). The 
posterior part is thin. It is continuous with the fascia lata in front and the crural 
fascia below. At the stifle it fuses with the tendons of the sartorius and gracilis. 

The crural fascia, or fascia of the leg (Fascia cruris), 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 the fascise of the thigh, while the 
second layer may l^e regarded chiefly as a continuation of the tendons of the super- 
ficial muscles of the hip and thigh (biceps femoris, semitendinosus, tensor fasciae latse, 
sartorius, and gracilis). The two layers frequently fuse, and are attached chiefly 
to the patellar ligaments and the crest and internal 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 downward in front of the tendons of the gastroc- 
nemius and superficial flexor, to be attached with the latter to the anterior and 
inner part of the tuber calcis. This may be regarded as an accessory or tarsal 
tendon of insertion of the biceps femoris and semitendinosus. The third layer 
forms sheaths for the muscles, furnishing origin in part to their fibers. Two im- 
portant intermuscular septa are detached, viz.: (1) One which passes between the 
anterior and lateral digital extensors to be attached to the fibula and the external 
border of the tibia; (2) one between the lateral extensor and the deep 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 an- 
terior extensor below the joint. Laterally, it is thin and fuses with the ligaments. 
Posteriorly, it is very thick and strong, forming an annular ligament which stretches 
from the internal lateral ligament to the filjular tarsal bone and the plantar liga- 
ment. 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 nerves. In 
front of the tarsus and above and below it there are three annular ligaments 
(Ligamenta transversa). The proximal one binds down the tendons of the anterior 
extensor, peroneus tertius, and tibialis anterior on the distal end of the tibia. The 
middle one stretches from the fibular tarsal lione to the outer tendon of the pero- 
neus tertius, forming a loop around the tendon of the anterior extensor. The distal 
band stretches across the proximal extremity of the large metatarsal bone and in- 
closes 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 limlj. 

The Muscles 

I. THE SUBLUMBAR MUSCLES (Figs. 450, 456) 
The muscles of this group are not confined to the sul)lumbar 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. 



THE SUBLUMBAR MUSCLES 275 

1. Psoas minor (s. parvus). — 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 be inserted at an acute angle on the tendon. The latter lies along 
the outer border of the fleshy portion and is flattened. It appears on the surface 
of the muscle 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 portion of the muscle is related 
to the pleura, crura of the diaphragm, and sympathetic nerve. 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 lumbar nerves. Near 
its insertion the tendon is crossed internally by the external iliac artery, and ex- 
ternally by the femoral nerve. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

2. Psoas major (s. magnus). — 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 vertebral ends of the last two ribs and 
the transverse processes of the lumbar vertebrae. 

Insertion. — The internal trochanter of the femur, by a common tendon with 
the iliacus. 

Ac//o^;,.^To flex the hip joint and to rotate the thigh outward. 

Structure. — The origin of the muscle is fleshy, the belly being in general 
flattened, thick in its middle, thin at its edges. The thoracic portion is small,, 
the abdominal part much thicker and wider, extending laterally beyond the ex- 
tremities 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), be- 
comes smaller and rounded, and passes downward and backward to terminate by a. 
strong tendon common to it and the iliacus.^ 

ReloMons. — 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, the 
kidneys, the spleen, the intestine (duodenum, caecum, etc.) and the circumflex 
iliac vessels. 

Blood-supply. — Lumbar and circumflex iliac arteries. 

Nerve-supply. — Lumbar and femoral nerves. 

3. Iliacus. — This muscle covers the ventral surface of the ilium external to 
the sacro-iliac articulation, and extends outward beyond the external border of the 
bone, underneath the middle gluteus. 

Origin. — The ventral surface of the ilium external to the ilio-pectineal line, 
the ventral sacro-iliac ligament, the wing of the sacrum, and the tendon of the 
psoas minor. 

Insertion. — The internal trochanter of the femur, by a common tendon with 
the psoas major. 

1 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. 



276 FASCIA AND MUSCLES OF THE HORSE 

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 outer and inner portions. 
When the psoas is removed, it is seen, however, that the two heads are not entirely 
separated. The outer, larger head arises from the wing of the ilium chiefly; the 
inner, smaller head arises chiefly from a small area on the shaft of the ilium, be- 
tween the psoas tubercle and the depression for the inner tendon of the rectus 
femoris, and from the tendon of the psoas minor. The two portions inclose 
the psoas major in front of the hip joint. 

Relations.— Dorssdly, 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 
hip joint the chief relations are: internally, the femoral vessels, the femoral nerve, 
and the sartorius muscle; externally, 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 outer part of the 
ventral 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 vertebra?; 
acting singly, to produce lateral flexion of the loins. 

Structure. — The muscle is pennate, and is curved with the convexity outward. 
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 intercostal and first three 
lumliar 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 (M. intertransversarii lumborum). — These 
are described with the other spinal muscles. (See p. 238.) 



II. THE EXTERNAL MUSCLES OF THE HIP AND THIGH 

Under this head will be described the muscles of the outer surface of the pelvis 
and thigh, and those which form the posterior contour of the latter. They are 
given in the order in w^iich they may be conveniently examined. 

1. Tensor fasciae latae (Fig. 178). — This is the most anterior muscle of the 
superficial layer. It is triangular in form, with its apex at the external angle of 
the ilium. 

Origin. — The external angle of the ilium. 

Insertion. — The fascia lata, and thus indirectly to the patella, the external 
straight ligament, and the crest of the tibia. 

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 external angle of the ilium. 
Below this the belly spreads out and terminates about midway between the point 
of the hip and the stifle in the aponeurosis. The belly fuses to a considerable ex- 
tent with the superficial gluteus. The aponeurosis fuses with the fascia lata, and 



THE EXTERNAL MUSCLES OF THE HIP AND THIGH 277 

detaches a lamina which passes with the tendon of insertion of the superficial gluteus 
to the external border of the femur. 

Relations — Externally, the skin and fascia; internally, the obliquus al)doniinis 
externus, the iliacus, superficial gluteus, rectus femoris, and vastus externus, 
branches of the circumflex iliac, ilio-lumbar, and iliaco-femoral arteries, and the 
anterior gluteal nerve; anteriorly, the precrural 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 (Figs. 178, 199) (Superficial gluteus; gluteus externus). — 
This muscle lies behind and partly underneath the tensor fascite latie. It is 
triangular and consists of an anterior and a posterior head united by the gluteal 
fascia. 

Origin. — (1) The external angle and the adjacent part of the external border 
of the ilium (anterior head); (2) the gluteal fascia (posterior head). 

Insertion. — The third (external) 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. The attachment to the border of 
the ilium is by means of an intermuscular septum, which passes beneath the thick 
outer border of the gluteus medius. 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, beneath the biceps femoris. 

Relations. — Superficially, the skin, fascia, and biceps femoris; deeply, the 
gluteus medius, iliacus, rectus femoris, and branches of the iliaco-femoral artery; 
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. 178, 179) (Middle gluteus; gluteus maximus). — 
This is a very large muscle which covers the dorsal 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. 

Origin. — (1) The aponeurosis of the longissimus, as far forward as the first 
lumbar vertebra; (2) the gluteal or dorsal surface and internal and external 
angles 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 outer 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 relatively 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- 
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 trochanteric ridge. The 
deep part (Gluteus accessorius) is smaller, and arises entirely from the ilium be- 
tween the gluteal line and the external angle (Fig. 455). It has a strong flat tendon 



278 FASCIA AND MUSCLES OF THE HORSE 

which passes over the convexit}" of the trochanter to be inserted into the crest 
below it. The convexity is covered with cartilage, and the trochanteric bursa 
(Bursa trochanterica) is interposed between the tendon and the cartilage/ 

Relations. — Superficially, the skin, lumbo-dorsal and gluteal fascise, the tensor 
fascise latae, 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 artery, 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 (Deep gluteus; gluteus internus; scansorius). — This 
much smaller, ciuadrilateral 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 great trochanter (Fig. 455). 

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 (Gluteo-biceps s. paramero-biceps). — This large muscle lies 
behind and in part upon the superficial and middle glutei. It extends in a curved 
direction from the sacral and coccygeal spines to the outer surface of the stifle 
and leg (Figs. 178, 199, 200, 201, 202). 

Origin. — (1) The dorsal sacro-iliac ligament, the gluteal and coccygeal fascise, 
and the intermuscular septum between this muscle and the semitendinosus; (2) 
the tuber ischii. 

Insertion. — (1) A tubercle on the posterior surface of the femur near the ex- 
ternal trochanter; (2) the anterior surface and external straight ligament of the 
patella; (3) the tibial crest; (4) the anterior and internal surface of the tuber 
calcis. 

Action. — -The action is somewhat complex, because the muscle is composed 
of three portions, 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 
the stifle and hip joints and abduct the limb. The middle part, being inserted 
chiefly on the tibial crest and the external straight ligament, would extend the 
hip, and, with the semitendinosus, flex the stifle. The posterior part, by virtue 
of its attachment to the tuber calcis, assists in extending the hock. 

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, 

* By some anatomists the portion inserted into the crest is termed the gkiteus accessorius, 
but Lesbre considers this the deep ghiteus, homologous with the ghiteus minimus of man. The 
portion inserted into the trochanteric ridge apparently represents the piriformis of man. 

'■* 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 EXTERNAL MUSCLES OF THE HIP AND THIGH 



279 



and the intermuscular septum. There is often a lar-e bursa l)etween this head and 
the trochanter major. The short or ischiatic head arises by a strong tendon irom 
the ventral spine on the tuber ischii. They unite, and a short tendon is detached 
from the deep face of the muscle, to be inserted into the posterior surface ot the 



Sacro-coccygcus superior 



> iliitfdl Jdscia 



External angle of ilium 



','-' Superficial gluteus 



Gastrocnemius tendon -jt" 



Superficial flexor tendon — -/ 



- Soleus 

■ Deep flexor 
—Lateral extensor 



Deep flexor tendon 
Superficial flexor tendon 



Suspensory ligament 



A*-' 



Pio 199 — MrscLES of Pelvic Limb of Horse, Postero-external View. 

17. Position of tuber ischii; o '. superficial gluteus; ., ,' . ," , biceps feiuons r^emite^dinosus ^ ^K^^^^ 

lateralis; ., semimembranosus; w, gracilis; /, gastrocnemius. (After Ellenberger-Baun., Anat. f, Kunstler.) 

femur near the third trochanter (Fig. 455), a bursa being interposed between the 
tendon and the l)one. The muscle then divides into three portions, which t^ermi- 
nate on a strong aponeurosis over the junction of the thigh and leg. The anterior 
branch is directed toward the patella, the middle toward the tibial crest, while the 



280 FASCIA AND MUSCLES OF THE HORSE 

posterior one assists in the formation of the posterior contour of the limb. The 
aponeurosis blends with the deep layer of the fascia cruris, as already descriljed. 
A synovial bursa occurs under the patellar insertion. 

Relations. — Superficially, the skin and fascia; deeply, the sacro-iliac and sacro- 
sciatic ligaments, the coccygeal fascia, the femur, the obturator, gemellus, quadratus 
femoris, adductor, semimembranosus, vastus externus, 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 super- 
ficial and middle glutei; behind and internally, the semitendinosus. 

Blood-supply. — Gluteal, obturator, and femoro-popliteal arteries. 

Nerve-supply. — Posterior gluteal and great sciatic nerves. 

6. Semitendinosus (Biceps rotator tibialis) . — This is a long muscle which 
extends from the first two coccygeal vertebrae to the proximal third of the inner 
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. 178, 179, 
199). 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 fa.scia and the tuber calcis. 

Action. — To flex the stifle and rotate the leg inward; also to extend the hip 
and hock joints, acting with the biceps and semimembranosus in propulsion of the 
trunk, rearing, etc. 

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 is joined by 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 inner 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. 
458). A bursa may occur under the long head where it passes over the tuber ischii. 

Relations. — Externally, the skin and fascia, the biceps, and the internal head 
of the gastrocnemius; internally, the coccygeal fascia, the sacro-sciatic ligament, 
the semimembranosus; anteriorly, the biceps femoris, jjranches of the femoral 
artery, and the great sciatic nerve. 

Blood-supply. — Posterior gluteal, obturator, and femoro-popliteal arteries 

Nerve-supply. — Posterior gluteal and great sciatic nerves. 

7. Semimembranosus^ (Figs. 179, 186, 199, 451). — This muscle lies on the inner 
surface of the preceding muscle and the gastrocnemius, and has two heads of origin. 

Origin. — (1) The posterior border of the sacro-sciatic ligament; (2) the ventral 
surface of the tuber ischii. 

Insertion. — The internal epicondyle of the femur, behind the lateral 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 much 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 assists in forming the lateral boun- 

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 INTERNAL MUSCLES OF THE THIGH 281 

dary of the pelvic outlet. It is related posteriorly and externally to the skin and 
fascia and the semitendinosus ; internally, to the anus and its muscles, the vulva 
in the female, and the internal pudic artery and nerve (Figs. 452, 453). Below 
the pelvis the chief relations are: externally, the semitendinosus, biceps, and 
gastrocnemius, branches of the obturator, femoral, and femoro-popliteal arteries, 
and the great sciatic nerve and its chief branches; internally, the crus penis 
and ischio-cavernosus muscle (in the male), and the gracilis; in front, the adduc- 
tor and the femoral vessels; behind, the skin and fascia. 

Blood-supply. — Obturator and femoral arteries. 

Nerve-supply. — Great sciatic nerve. 



IV. THE INTERNAL MUSCLES OF THE THIGH 
The muscles of this group are arranged in three layers. 

First Layer 

1. Sartorius (Figs. 186, 202, 203). — This long and rather narrow muscle is the 
most anterior one of the first layer. It extends from the sublumbar region to the 
lower and inner part of the stifle. 

Origin. — The iliac fascia and the tendon of the psoas minor. 

Insertion. — The internal straight ligament of the patella and the adjacent part 
of the tuberosity of the tibia. 

Action. — To flex the hip joint and adduct the limb. 

Structure. — The muscle is very thin at its origin, but becomes thicker and 
narrower as it passes downward and a little backward. It terminates near the 
stifle joint on an aponeurosis which blends with that of the gracilis and with the 
fascia of the leg. 

Relations. — Superficially, the inguinal (Poupart's) ligament, the abdominal 
muscles, the skin and fascia, and the saphenous vessels and nerve; deeply, the 
ilio-psoas, quadriceps femoris, and adductor. 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. 451). 

Blood-supply. — Femoral artery. 

Nerve-supply. — Femoral and saphenous nerves. 

2. Gracilis (Figs. 186, 199, 202, 203).— This is a wide, flat, quadrilateral 
muscle, situated behind the sartorius, which it exceeds greatly in extent. 

Origin. — The middle third of the pelvic symphysis, the prepubic tendon and 
pubo-femoral ligament, and the ventral surface of the pubis behind the prepubic 
tendon. 

Insertion. — The internal straight ligament of the patella, the internal surface 
of the tibia in front of the lateral ligament of the stifle joint, and the fascia of 
the leg. 

Action. — To adduct the limb. It may also rotate it inward. 

Structure. — The muscle arises by a strong tendon, chiefly in common with the 
opposite muscle. Its direct attachment to the ventral surface of the pelvis is not 
so extensive as a superficial inspection would suggest. The origin of the muscle 
presents anteriorly a round perforation for the passage of the external pudic vein. 
The belly is composed of parallel bundles, and is marked by a superficial furrow 
which, however, does not indicate a muscular division. It terminates on the inner 
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- 



282 FASCIA AND MUSCLES OF THE HORSE 

branosus and semitendinosus, and, at the middle of the femur, the femoral vessels; 
anteriorly, the sartorius. In the upper third of the thigh the sartorius and gracilis 
are separated by a triangular interval (femoral triangle), in which lie the deep 
inguinal lymph glands and the femoral vessels. 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Obturator and saphenous nerves. 

Second Layer 

1. Pectineus (Figs. 186, 451, 456). — This muscle is fusiform and extends from 
the anterior border of the pubis to the middle of the inner l^order of the femur. 

Origin.— The prepubic tendon, the pubo-femoral ligament, and the anterior 
border of the pubis. 

Insertion. — -The middle of the internal 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 filwous tissue. Its 
origin is perforated by the pubo-femoral ligament, and is thus divided into two 
unequal parts. The large upper part arises mainly from the prepubic tendon 
— only a very small part gaining direct attachment to the pubis. The small lower 
part does not reach the bone. The insertion is pointed and tendinous. 

Relations. — Superficially, the gracilis; deeply, the femur, the vastus internus, 
the terminal tendon of the psoas major and iliacus, and the deep femoral artery; 
anteriorly, the sartorius, the femoral vessels, the saphenous nerve, and the deep 
inguinal lymph glands; posteriorly, the adductor, obturator externus, and quadra- 
tus femoris, and the obturator nerve (anterior division). 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Femoral and obturator nerves. 

The femoral canal is exposed in the dissection of the preceding muscles (Figs. 200, 451). 
It is bounded anteriorly by the sartorius, posteriorly by the pectineus, and externally by the 
iliacus and vastus internus. Its internal wall is formed by the femoral fascia and the gracilis. 
Its upper or abdominal opening (Lacuna vasorum) lies behind and a little internal to the inter- 
nal inguinal ring and is bounded anteriorly by the inguinal ligament, posteriorly by the ante- 
rior border of the pubis, and externally 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. Adductor^ (Figs. 179, 186,451) (Great and small adductors of the thigh). — 
This fleshy, prismatic muscle lies behind the pectineus and vastus internus. It 
extends downward and forward from the ventral surface of the pelvis to the internal 
condyle of the femur. 

Origin. — The ventral surface of the pubis and ischium and the tendon of the 
gracilis. 

Insertion. — (1) The posterior surface of the femur from the level of the external 
trochanter to the groove for the femoral vessels; (2) the internal epicondyle of the 
femur and the internal lateral ligament of the stifle joint. 

Action. — To adduct the limb and assist in extending the hip joint. It may 
also rotate the femur outward. 

Structure. — It is almost entirely fleshy, and is composed of parallel bundles 
united rather loosely. It is usually possible to separate from the principal mass a 
small anterior short portion,- which is inserted into the femur behind the pectineus. 
The principal mass^ is perforated below its middle by the femoral vessels, and is 

1 It has been customary to describe two adductors — a parvus or brevis, and a longus or 
magnus. This division is largely artificial, and has been abandoned in the new nomenclature — • 
a return to the views of Bourgelat and Girard. 

2 This has been termed by various authors the adductor parvus or brevis. 
' Termed by various authors the adductor magnus or longus. 



THE INTERNAL MUSCLES OF THE THIGH 283 

thus divided into two brandies. The outer branch is inserted into the back of the 
femur witli the short portion, while the inner branch is attached to the internal 
epicondyle and lateral ligament. There is often a superficial slip which reaches 
the internal straight patellar ligament. Some fibers pass under the lateral ligament 
and end on the tendon of the semimembranosus. 

Relations. — Internally, the gracilis, and branches of the femoral artery and of 
the obturator nerve; externally, the femur, the obturator externus, quadratus 
femoris, biceps femoris, and gastrocnemius, and the femoral, deep femoral, and 
obturator arteries; anteriorly, the pectineus, vastus internus, 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. 280. 

Third Layer 

1. Quadratus femoris (Ischio-femoralis). — This is a narrow, flat muscle, 
which lies under cover of the upper part of the adductor (Figs. 455, 456). 

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 internal trochanter. 

Action. — To extend the hip joint, and to adduct the thigh and rotate it out- 
ward. 

Structure. — It is composed of parallel bundles of fibers directed downward, 
forward, and outward. 

Relations. — ^Internally, the adductor, semimembranosus, and the obturator 
vessels; externally, the obturator externus and biceps femoris, the deep femoral 
artery, and the great sciatic nerve. 

Blood-supply. — Deep femoral and obturator arteries. 

Nerve-supply .^-Greai sciatic nerve. 

2. Obturator Externus (Fig. 456) . — This is a pyramidal muscle which extends 
across the back of the hip joint from the ol^turator foramen to the trochanteric 
fossa. 

Origin. — The ventral surface of the j^ubis 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. — -Internally, the adductor and quadratus femoris and the deep 
femoral vessels; externally, 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. 451). — This arises by two heads within the pelvic 
cavity, 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. 



284 FASCIA AND MUSCLES OF THE HORSE 

Structure. — The ischio-pubic head Ues on the pelvic floor and covers the ob- 
turator foramen. It is thin and fan-shaped. The ihac 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. A synovial bursa facilitates the 
play of the tendon over the external border of the ischium.^ 

Relations. — The pelvic surface is covered by the pelvic fascia and the perito- 
neum. 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. 

Blood-supply. — Obturator and internal pudic arteries. 

Nerve-supply. — -Great sciatic nerve. 

4. Gemellus'' (Fig. 455). — This is a thin, triangular muscle, which extends 
from the external border of the .ischium to the trochanteric fossa. 

Origin. — The external border of the ischium near the ischiatic spine. 

Insertion. — The trochanteric fossa. 

Action. — To rotate the femur outward. 

Structure. — Fleshy, some fibers being inserted into the tendon of the obturator 
internus. 

Relations. — Dorsally, the tendon of the obturator internus and the gluteus 
profundus; ventrally, the obturator externus. 

Blood-supply. — Obturator artery. 

Nerve-supply. — Sciatic nerve. 



III. ANTERIOR MUSCLES OF THE THIGH 

This group consists of the sartorius, quadriceps femoris, and capsularis. 

1. Sartorius. — This is described on p. 281. 

2. Quadriceps femoris (Figs. 179, 186, 200) (Crural triceps). — This con- 
stitutes the large muscular 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 outer one 
is a bursa. The belly is rounded and rests in a groove formed by the other portions 
of the cjuadriceps. Its sides are covered by a strong tendinous layer which fur- 
nishes insertion to fibers of the vasti. The tendon of insertion is formed by the 
fusion 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. — Internally, the iliacus, sartorius, and vastus internus; externally, 
the tensor fasciae latse, glutei, and vastus externus; posteriorly, the hip joint and 
the vastus intermedins; anteriorly, the fascia lata and the skin. The anterior 

^ The iliac head is described by some authors as a separate muscle, and termed tlie pyri- 
formis. This does not seem desirable, especially since it is at least probable that the honio- 
logue of the pyriformis of man is that portion of the middle gluteus which is inserted into the 
back of the trochanteric ridge. 

2 The name is based on the arrangement in man, in whom the muscle consists of two 
fasciculi forming a groove between them for the tendon of the ol)turator internus. In the horse 
it is untlivided, and is grooved for the obturator tendon, so that at first sight it appears to be 
double. The gemellus may be regarded as the extrapelvic head of the obturator internus 
(Gegenbaur) . 



ANTERIOR MUSCLES OF THE THIGH 



285 



femoral artery and branches of the femoral nerve descend into the interspace be- 
tween the upper part of the rectus and the vastus internus; similarly, the iliaco- 
femoral artery dips in between the rectus femoris and vastus externus. 

Blood-supply. — Femoral and iliaco-femoral arteries. 

Nerve-supply. — Femoral nerve. 

(2) Vastus externus (s. lateralis). — This lies on the outer surface of the thigh, 
extending from the great trochanter to the patella. It is thick and wide in its 
upper part, and becomes much thinner and narrow below. 



Vast)is internus 

Sartorius 

SaphenouH vein 

Saphenous .lervc 

Femoral artery 

Gracilis 
Adductor 

Peroneal nerve 
Tibial nerve 



Semimem- 
branosus 

Semitendinosu 



Fold of flank 
Tensor fascia} latce 




Vastus externus 
Vastus intermedius 



Fig. 200. — CROSs-sicf ttox oi Miudi.e of Right Thigh of Horse. 



Origin. — The external border and surface of the femur, from the great tro- 
chanter to the supracontlyloid fossa. 

Insertion. — (1) The outer 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 
often found between the distal end and the patella. 



286 FASCIA AND MUSCLES OF THE HORSE 

Relations. — Externally, the fascia lata and skin, tensor fasciae latse, superficial 
gluteus, and biceps femoris; internally, the femur and femoro-patellar joint capsule, 
the rectus femoris, vastus intermedius, and the iliaco-femoral artery. 

Blood-supply. — Iliaco-femoral artery. 

Nerve-supply. — Femoral nerve. 

(3) Vastus intemus (s. medialis). — This is smaller than the preceding muscle, 
and lies in a similar position on the inner side of the thigh. 

Origin. — The internal surface of the femur, from the neck to the distal third. 

Insertion. — (1) The upper part of the inner border of the patella and its carti- 
lage; (2) the tendon of the rectus femoris. 

Action. — To extend the stifle joint. 

Structure. — This is very similar to that of the vastus externus. It is, how- 
ever, more difficult to separate from the intermedius, because many fibers of the 
latter arise on the tendinous sheet which covers the contact surface of the inner 
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 capsule. 

Relations. — Internally, the skin and fascia lata, the iliacus, sartorius, pectineus, 
and adductor, the femoral vessels and saphenous nerve; externally, the femur, 
femoro-patellar joint capsule, rectus femoris, and vastus intermedius, the anterior 
femoral artery, and branches of the femoral nerve. 

Blood-supply. — Femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

(4) Vastus intermedius (Crureus). — This muscle is deeply situated on the 
anterior face of the femur, and is entirely covered by the preceding heads. 

Origin. — (1) The anterior and external surfaces of the femur, from the proximal 
to the distal fourth ; (2) the aponeurosis of the vastus internus. 

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 
intefnus. The terminal part is intimately adherent to the femoro-patellar joint 
capsule, where the latter bulges upward above the level of the patella. 

Relations. — Internally, the vastus internus; externally, the vastus externus; 
anteriorly, the rectus; posteriorly, the femur and femoro-patellar capsule. 

Blood-supply. — Iliaco-femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

The straight ligaments of the patella 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. 154) (Rectus parvus). — This is a small muscle (scarcely as 
large as one's finger), which arises on the ilium immediately above the outer tendon 
of the rectus femoris, and passes down between the vastus internus and externus to 
be inserted into the anterior surface of the femur. It passes over the front of the 
hip joint, to the capsule of which some fibers are attached. Sometimes the nuiscle 
has two distinct 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. 

1 While it is true that the separation of the intermedius is prol)al)ly 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. 



THE MUSCLES OF THE LEG AND FOOT 



287 



IV. THE MUSCLES OF THE LEG AND FOOT 
The muscles of this region cover ahnost all of the tibia except its internal face, 
which is largely subcutaneous. As in the forearm, the nmscles fall into two groups, 



Patella 



Crest of tibia 

Anterior or long extensor 

Lateral extensor 



Proximal annular 
External 



Middle annular ligament 

Distal annular ligament 

Tendon of anterior extensor 

Tendon of lateral extensor — 



Branch of suspensori/ ligament to 
extensor tendon 




Gastrocnemius, external head 

Salens 

Tendon of gastrocnemius 
Tarsal tendon of biceps femoris 
Deep flexor 



~~~~ Superficial 
^'' flexor tendon 



Superficial flexor 
tendon 

Deep flexor tendon 



Suspensory 
~ ligament 



Fig. 201. — Muscles of Lower P.^rt ok Thigh, Leg, and Foot of Horse, External View. 
o', Fascia lata; q, q' , q", biceps femoris; r, semitendinosus; 21', external condyle of tibia. (After Ellenberger- 

Baum, Anat. fur Kiinstler.) 



an anterior or dorso-lateral, and a posterior or 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. 



288 FASCIA AND MUSCLES OF THE HORSE 

A. Anterior Group 

1. Anterior or long digital extensor (M. extensor digitalis longus; extensor 
pedis; anterior extensor of the phalanges). — This muscle is situated superficially 
on the antero-external aspect of the leg, and is provided with a long tendon which 
passes down over the front of the tarsus, metatarsus, and digit. 

Origin. — The small fossa (Fossa extensoria) between the external condyle and 
the trochlea of the femur. 

Insertion. — (1) The extensor process of the third phalanx; (2) the anterior 
surface 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. 

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 outer condyle and the tuberosity of the tibia, 
where a pouch from the femoro-tibial capsule descends four or five inches (ca. 
10 to 12 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 
fleshy part near the tarsus. It passes downward over the front of the hock, bound 
down by the three annular ligaments already described (see crural fascia), and 
enveloped by a synovial sheath which begins a little above the level of the external 
malleolus, and extends nearly to the junction with the lateral extensor tendon. 
This union occurs usually about a hand's l)readth 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 capsule, 
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. 460) . 

Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 

2. Lateral digital extensor (M. extensor digitalis lateralis; peroneus; lateral 
extensor of the phalanges). — This muscle lies on the outer surface of the leg, 
behind the preceding one. 

Origin. — The external lateral ligament of the stifle joint, the fibula, the ex- 
ternal border of the tibia, and the interosseus ligament. 

Insertion. — The tendon of the anterior extensor, about a third of the way down 
the metatarsus. 

Action. — To assist the anterior 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 lower fourth 
of the tibia. It passes downward through the groove on the external malleolus, 
bound down by an annular ligament, and, inclining forw^ard, blends (usually) with 
the tendon of the anterior extensor. It is ]:)rovided with a synovial sheath, which 
begins al^out one inch (ca. 2 to 3 cm.) above the external malleolus and ends about 
one and one-half inches (ca. 3 to 4 cm.) above the junction. Sometimes the fusion 
does not occur, and the tendon then passes down the metatarsus, alongside of that 
of the long extensor, to be inserted into the first phalanx like the corresponding 
muscle of the thoracic limb. 

Relations. — Externally, the skin and fascia and the superficial peroneal nerve; 
internally, the tibia and fibula; anteriorly, the intermuscular septum, the long 
extensor, and the tibialis anterior; posteriorly, the deep flexor and the soleus. 

Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 



THE MUSCLES OF THE LEG AND FOOT 



289 



3. Peroneus tertius (Tendinous part of the flexor metatarsi; tendo femoro- 
tarseus [Schmaltz]). — This consists in the horse of a strong tendon which lies be- 
tween the anterior extensor and the tibialis anterior. 



Snrtorius - 



Grdcilis 




y '. iff'- - Bice ps frmoris, anterior part 

i 

--- Biceps fctnoris, middle part 



External condyle of tibia 



Tubero.slti/ of tibia 



Tibialis anterior 



Lateral extensor 
Anterior or long extensor 



Internal nndleolus ■ 



■Peroneus tertius 
Proximal antiular ligament 
External malleolus 



Inner (cunean) tendon of tibirdis anterior 
Metatarsal tendon of tibialis anterior- 



■ Middle annular ligament 

Distal annular ligament 
Lateral extensor tendon 



Anterior or long extensor tendon 



Branch of suspensory ligame7it . 



Fig. 202. — Muscles of PEi.vir Limd of Horse, Anterior View. 
;/, Rectus femori^; 30, patella, (.\fter Ellenberger-Baum, .\nat. fiir Kiinstler.) 



Origin. — The fossa extensoria (between the external condyle and the trochlea 
of the femur), in common with the anterior extensor. 

^ It seems inadvisable to retain the old nomenclature, since it is inapplicable to other domes- 
ticated animals in which the muscle is well developed (e. g., ox, pig). 
19 



290 FASCIA AND MUSCLES OF THE HORSE 

Insertion. — (1) The proximal extremities of the large (third) and external small 
(fourth) metatarsal bones, 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.— This 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 anterior extensor. Fibers of the latter muscle and 
of the tibialis anterior arise on the tendon as it passes downward to the front of the 
hock. At the distal end of the tibia the tendon divides into two branches, between 
which the tendon of the tibialis anterior emerges. The anterior branch is attached 
to the third tarsal and third and fourth metatarsal bones, while the outer one curves 
outward, bifurcates, and is inserted into the fibular and fourth tarsal bones (Fig. 460). 

Relations. — Superficially, the anterior extensor; deeply, the tibialis anterior. 
The anterior tibial vessels cross the deep face of the outer l^ranch. 

4. Tibialis anterior (Aluscular portion of the flexor metatarsi). — This lies 
on the antero-external face of the tibia; it is wide and flattened al:)0ve, pointed 
below. 

Origin. — The external condyle and border of the tiliia and a small area on the 
external surface of the tuberosity. 

Insertion. — (1) The metatarsal tuberosity; (2) the first and second tarsal 
bones. 

Action. — To flex the hock joint. 

Structure. — The origin is fleshy, and is divided by the groove in which lie 
the common tendon of the long extensor and peroneus tertius and a synovial 
pouch. Passing downward on the tibia, the belly is united by tendinous and fleshy 
fibers with the peroneus tertius, and terminates close to the tarsus in a point on 
the tendon of insertion. The latter emerges between the branches of the peroneus 
tertius and bifurcates, the anterior branch being inserted into the metatarsal 
tuberosity, the inner one (cunean tendon) into the fused first and second tarsal 
bones (cuneiform parvum). The tendon is provided with a synovial sheath at 
its emergence, and a bursa (cunean bursa) is interposed between the inner branch 
and the internal lateral ligament. 

Relations. — Superficially, the anterior and lateral extensors, the peroneus 
tertius, and the deep peroneal nerve; deeply, the tibia, the deep flexor, and the 
anterior tibial vessels. 

Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 

B. Posterior Group 

1. Gastrocnemius (Figs. 179, 201, 203). — This muscle extends from the lower 
third of the femur to the point of the hock. It arises by two heads. 

Origin. — (1) Outer head, from the external rough margin of the supracondy- 
loid fossa (Fossa plantaris) ; (2) inner head, from the supracondyloid crest. 

Insertion. — The posterior part of the tuber calcis. 

Action. — To extend the hock. 

Structure. — The two bellies are thick, fusiform, and somewhat flattened. 
They are covered by a strong aponeurosis and contain tendinous intersections. 
They terminate toward the middle of the leg on a common tendon (Tendo calcaneus 
s. Achillis), 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 calcanei) lies in front of the insertion on the tuber 
calcis, and a large bursa is interposed between the two tendons from the twist 



THE MUSCLES OF THE LEG AND FOOT 



291 



downward. The superficial flexor lies between the two heads and is adherent to 
the outer one (Fig. 459). 

Relations. — Anteriorly, the stifle joint, the superficial flexor, popliteus, deep 
flexor, popliteal vessels, and tibial nerve; internally (above), the semitendinosus, 




Semite ndinos us 



Gaslrociiemtus 

Popliteus 

Long digital flexor 

Tibialis posterior 

Gastrocne m i us tendo n 

Deep digital flexor ■- 
Superficial flexor tendon -- 



Check ligament 
Superficial flexor tendo n 

Deep flexor tendon 

Suspensory ligament 



^^^ "'Patella 

Crest of tibia 

'^^--. •■ 

Anterior or long digital extensor 

Tibialis anterior 

?• Km 

Peroneus tcrtius 

J Proximal annular ligament 

jf^lg^^^^l niQlleolus 

..i-/ Janer {cunean) tendon of tibialis anterior 
DisUd annular ligament 
Anterior extensor tendon 




Branch of suspensory ligament 
to extensor tendon 




Fig. 203. — Muscles of Leg and Foot of Horse, Internal View. 
r', Tendon of semitendinosus; w, gracilis; x, sartorius; ?/, vastus internus. (After EUenberger-Baum, Anat. 

fiir Kiinstler.) 



semimembranosus, and adductor, (below) the fascia and skin; externally (above), 
the biceps femoris and peroneal (anterior tibial) nerve, (below) the fascia and skin. 

Blood-supply. — Popliteal artery. 

Nerve-supply. — Tibial nerve. 



292 



FASCIiE AND MUSCLES OF THE HORSE 




/ 



V- 



c.^ 



Poste- 



-T i b i a 1 



,Wf^^ 



\ 



/. 



'] 



\c 



2. Soleus (Fig. 201). — This muscle is very small in the horse. It lies immedi- 
ately under the deep fascia, on the proximal half of the outer surface of the leg, 
and is directed obliquely downward and backward. 
Origin. — The head of the filiula. 

Insertion. — The tendon of the gastrocnemius, about the middle of the leg. 
Action. — To assist the gastrocnemius. 

Structure. — It is a thin, fleshy band, aliout an inch (ca. 2 to 3 cm.) in width, 
terminating 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 
q flexor. 

: '^ '-^- Blood-supply. 

rior tibial artery. 

Nerve-supply.- 
nerve. 

3. Superficial digital 
flexor or flexor pedis per- 
foratus (Figs. 199, 201, 203) 
(M. flexor digitahs pedis sub- 
Hmis; superficial flexor of the 
phalanges). — The proximal 
part of this muscle lies be- 
tween and under cover of the 
two heads of the gastrocne- 
mius (Fig. 459). It con- 
sists almost entirely of a 
strong tendon, the belly be- 
ing very little developed. 

Origin. — The supracon- 
dyloid fossa (Fossa plantaris) 
of the femur. 

Insertion. — (1) The front 
and sides of the tuber calcis; 
(2) the eminences on the 
proximal extremity of the 
second phalanx, and the 
distal extremity of the first 
phalanx behind the lateral 
ligament. 
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, resulting 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. It is pretty 
intimately attached to the gastrocnemius, especially to the outer head. At the 
distal third of the tibia it winds around the inner surface of the gastrocnemius 
tendon, and then occupies a position behind the latter. At the point of the hock 
it widens out, forming a sort of cap over the tuber calcis, detaching on either side 
a strong band which is inserted into the tuber calcis with the tarsal tendon of the 
biceps and semitendinosus. It then passes downward over the plantar (Calcaneo- 
metatarsal) ligament, becomes narrower, and is arranged below^ as in the thoracic 
limb. A large synovial bursa lies under the tendon from the distal fourth of the 

'■ The soleus may, therefore, he iiicludctl with the two heads of the gastrocnemius under the 
name triceps surjE. 




y 



Fig. 204. — Cross-section of Left Leg of Horse; Section is Cut 
A Little Auovi-; Middle of R?:(;iox. 
a, Tiljia; b, filiula; c, tibialis anterior; d, peroneus tertius; 
e, anterior or long digital extensor; /, lateral extensor; g, deep 
head of deep flexor (flexor hallucis longus); /(, inner head of deep 
flexor (flexor accessorius s. digitorum longus) ; ;', superficial head of 
deep flexor (tibialis posterior); /.■, popliteus; /, superficial flexor 
tendon; 7n, gastrocnemius tendon; », soleus; o, skin; p, anterior 
tibial artery; q, superficial peroneal nerve; q' , deep peroneal nerve; 
r, branch of q; s, posterior tibial artery; t, cutaneous nerve; u, 
tibial nerve; v, recurrent tibial vein; w, saphenous artery; x, saphe- 
nous vein; ?/, branches of saphenous nerve. (After EUenberger, in 
Leisering's Atlas.) 



THE MUSCLES OF THE LEG AND FOOT 



29C 



tibia to the middle of the tarsus. A subcutaneous bursa is sometimes found on 
the wide part of the tendon at the point of tlie hock. (Either or })oth of these 
bursas may be involved in so-called "capped hock.") 

Relations. — Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the 
femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels; 
internally, the tibial nerve. 

Blood-supply. — Femoro-popliteal artery. 

Nerve-supply. — Tibial nerve. 

4. Deep digital flexor or flexor pedis perforans (M. flexor digitalis pedis pro- 





f 



Fig. 206. — Injected Synovial Sheaths and BtjrS/E 
OF Tarsal Region of Horse, External View. 
a. Synovial sheath of anterior or long digital 
extensor; h, synovial sheath of lateral digital exten- 
sor; c, c', bursa under superficial flexor tendon; d, 
capsule of hock joint; /, anterior or long extensor; 
2, lateral extensor; S, 3, 3, annular ligaments; 4, 
deep digital flexor; o, tendon of gastrocnemius; 6, 
superficial flexor tendon; 7, tibia; S, tar.sus; 9, tuber 
calcis; 10, metatarsus. (After EUenberger, in Leiser- 
ing'a Atlas.) 



Fig. 20.5. — Injected Synovi.\l Sheaths and Burs.b 

OF T.4.RSAL ReGIO.N OF HoRSE, InNER ViEW. 

a, Synovial sheath of peroneus tertius and 
tiliialis anterior; b, bur.sa under inner (cunean) tendon 
of tibialis anterior; c, synovial sheath of flexor longus 
s. accessorius; d, tarsal slieath of deep flexor; e, e', 
bursa under superficial flexor tendon; /, /', tibio-tarsal 
joint capsule; 1, anterior extensor; 2, tibialis anterior; 
2', inner (cunean) tendon of 2; 3, flexor longus; 4, 
deep digital flexor; 5, superficial flexor tendon; 6, 
gastrocnemius tendon; 7, tibia; S, tarsus; 9, tuber 
calcis; 10, large metatarsal bone; 11, inner small 
metatarsal bone; 12, 12', fascial bands, (.\fter EUen- 
berger, in Leisering's Atlas.) 

fundus; deep and oblique flexors of the phalanges). — The belly of this muscle lies 
on the posterior surface of the tibia, and is divisible into three parts or heads, 
which, however, finally unite on a common tendon of insertion. 

Origin. — (1) The posterior edge of the external condyle of the tibia; (2) the 
external border of the external condyle of the tibia, just behind the facet for the 
fibula; (3) the middle third of the posterior surface and the upper part of the ex- 
ternal border of the tibia, the posterior border of the fibula, and the interosseous 
ligament.^ 

^ The origins of these heads are given in the order in which they may be most conveniently 
dissected, not in order of size and importance. 



294 FASCIA AND MUSCLES OF THE HORSE 

Insertion.— The semilunar crest of the third phalanx and the adjacent surface 
of the lateral cartilaj2;e. 

Action. — To flex the digit and to extend the hock joint. 

Structure. — (1) The inner head (M. fiexor digitalis longus s. flexor accesso- 
rius) is easily isolated (Figs. 203, 459). It has a fusiform belly, which crosses the 
leg obliquely and lies in a groove formed by the other heads and the popliteus. 
This terminates near tlie lower third of the tibia on a round tendon which passes 
downward, partly embedded in the internal lateral ligament of the hock, and joins 
the common tendon about a third of the way down the metatarsus. In its course 
over the inner surface of the hock the tendon lies in a canal formed by the strong 
tarsal fascia, the tibia, and the lateral ligament, and is provided with a synovial 
sheath which extends from the distal fourth of the tibia to the junction with the 
principal tendon. (2) The superficial head (M. tibialis posterior) is only partially 
separable. It has a flattened belly, terminating near the lower third of the tibia 
on a flat tendon which soon fuses with the principal tendon. (3) The deep head 
(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 
tendinous tissue, and terminates behind the distal end of the tibia on a strong 
round tendon. The latter receives the tendon of the tibialis posterior, passes 
downward in the tarsal groove, bound down by the strong tarsal fascia (Ligamentum 
laciniatum) and enveloped in a synovial sheath, receives the tendon of the inner 
head below the hock, and, a little further down, the so-called check ligament (Caput 
tendineum [Schmaltz] ) . The tarsal sheath (Vagina tarsea) begins about two to three 
inches (ca. 5 to 7.5 cm.) above the level of the internal malleolus, and extends about 
one-fourth of the way down the metatarsus. (Distention of the sheath, as in 
"thoroughpin," affects chiefly its proximal end.) The check ligament resembles 
that of the fore limb, except that it is longer and very much weaker; it may be 
absent. The remainder of the tendon is arranged like that of the thoracic limb. 

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; externally, the fascia, skin, and the soleus; internally, 
the fascia and skin. 

Blood-supply. — Posterior tibial artery. 

Nerve-supply. — Tibial nerve. 

5. Popliteus (Fig. 203). — This thick and triangular muscle lies on the posterior 
surface of the femoro-tibial articulation and the posterior surface of the tibia above 
the popliteal line. 

Origin. — A small depression on the external epicondyle of the femur, close to 
the articular surface and under the lateral ligament. 

Insertion. — A triangular area on the posterior surface of the tibia, above and 
internal to the popliteal line; also the proximal half of the inner border and a 
narrow adjacent part of the internal 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 external condyle of the tibia and its 
semilunar cartilage, being invested by a reflection of the synovial capsule of the 
joint (Fig. 459). The tendon is succeeded by a thick triangular belly, the fibers 
of which are directed obliquely downward and inward. 

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 inner border 
of the muscle, separated from it, however, by the deep fascia. 

Blood-supply. — Popliteal and posterior tibial arteries. 

Nerve-suppiy.— Tibial nerve. 



THE MUSCLES OF THE OX — MUSCLES OF THE FACE 295 

MUSCLES OF THE METATARSUS AND DIGIT 

Extensor pedis brevis (M. extensor digitalis brevis). — This small muscle lies 
in the angle of union of the long and lateral extensors of the digit. (Shown in 
Fig. 201, but not marked.) 

Origin. — The outer tendon of the peroneus tertius, the middle annular liga- 
ment, and the outer lateral ligament of the hock. 

Insertion. — The tendon of the anterior or long extensor. 

Action. — To assist the anterior or 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 outer tendon of the peroneus 
tertius. The insertion is by a thin tendon. 

Relations. — Superficially, the skin and fascia and the tendons of the anterior 
and lateral extensors; deeply, the joint capsule, the great metatarsal artery, and 
the deep peroneal nerve. 

Blood-supply. — Great metatarsal artery. 

N^erve-supply. — Deep peroneal nerve. 

The interossei and lumbricales are arranged like those of the thoracic limb, 
the only noticeable dift'erence being the greater development of the lumbricales in 
the pelvic limb. 



THE MUSCLES OF THE OX 
Muscles of the Face 

The panniculus 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 com^plete ring, the defect being in the 
middle of the upper 11]). 

The levator nasolabialis is extensive, thin, and not very distinct from the 
frontalis; it divides into two layers, betw^een 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 jiremaxilla. 

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. 

The depressor labii superioris does not resemble the muscle of the same name 
in the horse. It 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 mandil^lo 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. 

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- 



296 



THE MUSCLES OF THE OX 



ward between the branches of the levator nasolabiahs, and terminates in the outer 
wing of the nostril. 

The dilatator naris transversus is replaced by the dilatator naris apicalis, 
which 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 premaxilla, the fibers passing 
obliquely upward and outward to the inner wing of the nostril. 

The dilatator naris superior arises from the alar cartilage of the nostril and 
ends in the inner wing of the nostril. 




Tig. 207. — Musci.es of Head of Ox, Lateral View. 
a. Levator labii superioris proprius; b, levator nasolabialis; c, trapezius; c' , mastoido-humeralis; d, d'. 
sterno-cephalicus; e, oino-hyoideus; /, dilatator naris lateralis; fj, zygomaticus; ;;', malaris; /;, buccinator; i, 
depressor labii inferioris; k, orbicularis oris; m, masseter; n, parotido-auricularis; o', zygoinatico-auricularis and 
scutulo-auricularis superficialis inferior; o", scutulo-auricularis superficialis superior; o'", scutulo-auricularis 
superficialis accessorius; p,p', scutularis; w, frontalis; w;, mylo-hyoideus; 7, concha; ^, 5, posterior and anterior 
borders of /; S, scutiform cartilage; 9, zygomatic arch; 2S' , rainvis of mandible; 37, external maxillary vein; 
S<S, jugular vein; 39, facial vein; 44. parotid gland; 50, 50', submaxillary gland; dotted line at 50 indicates posi- 
tion of large lymph gland, and another lies partly under parotid gland, just in front of 44! ^S, internal palpebral 
ligament; 59, laryngeal prominence, (.\fter Ellenberger-Baum, Anat. fiir Kiinstler.) 



Th(^ dilatator naris inferior consists of two layers which arise on the nasal pro- 
cess of the premaxilla and the lateral nasal cartilage and end in the outer wing 
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. 



MUSCLES OF MASTICATION — HYOID MUSCLES 



297 



MUSCLES OF MASTICATION " 

The masseter is not so large as in the horse; a considerable part of it arises 
on the facial tulxn-osity and is directed ol)li(]uely 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 pterygoidei are not quite clearly separated; their direction is more 
oblique, antl the origin of the pterygoideus internus is nearer the median plane 
than in the horse. 




Fio. 208. — Muscles of Head of Ox, Dorsal View. 
a, a', Levator labii superioris proprius; b, levator uasolabialis; /, dilatator naris lateralis; g', malaris; o, zygo- 
matieo-auricularis and scutulo-auricularis superficialis inferior; o", t-cutulo-auricularis superficialis superior; o'", 
scutulo-auricularis superficialis accessorius; p, scutularis; ;/, frontalis; z, orbicularis oculi; i , concave surface of 
concha; 3, 2, anterior and posterior borders of concha; 8, scutiform cartilage; ^4. parietal cartilage; S9, facial 
vein; J,9, muzzle; oS, internal paljjebral ligament. (After Ellenberger-Baum, Anat. fiir Kunstler.) 

The stylo-mandibularis is absent. 

The digastricus has a tendinous origin on the paramastoid or styloid process 
of the occipital bone; its bellies are short and thick. It does not perforate the 
stylo-hyoideus. The two digastrici are connected beneath the root of the tongue 
by a layer of transverse muscle-fibers (Transversus mandibulae). 



HYOID MUSCLES 
The mylo-hyoideus is thicker and more extensive than in the horse. 
The stylo-hyoideus has a long thin tendinous origin and is not perforated by 
the digastricus. 



298 



THE MUSCLES OF THE OX 



The genio-hyoideus is more developed. 

The kerato-hyoideus has an additional attachment on the middle cornu of the 
hyoid bone. 

The hyoideus transversus is l^ifid. 

The sterno-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 vertebra;. It blends here with the rectus capitis anterior major. 
The occipito-hyoideus is thick. 




Fig. 209. — Muscles of Head of Ox, Ventral View. 
d, d', Sterno-cephalicus; e, omo-hyoideus; o, zygomaticus; /;, buccinator; /, depressor labii inferioria; 
k, orbicularis oris; m, masseter; ?!, parotid o-auricularis; o', zygomatico-auricularis; w, mylo-hyoideus; 1, concha, 
convex surface; $, anterior border of concha; SO', angle of jaw; S9, facial vein; 44, parotid gland; 45, lower lip; 
48, angle of mouth; 50, 50', submaxillary gland; 59, larynx; x, wing of atlas. (After EUenberger-Baum, Anat. 
fiir Kiinstler.) 



Muscles of the Neck 
A. ventral group 

The sterno-cephalicus consists of two muscles. They arise from the manu- 
brium sterni and first rib. The superficial muscle (Sterno-mandibularis) is inserted 
on the anterior border of the masseter, the ramus of the mandible, and the buccal 
fascia. The deep muscle (Sterno-mastoideus) crosses under the preceding and ends 
on the mastoid process, the mandible, and, in common with the rectus capitis 
anterior major, on the basilar process of the occipital bone. 

There are two scaleni. The scalenus ventralis (s. primae costse) arises on the 
first rib and ends on the transverse processes of the third to the seventh cervical 



VENTRAL GROUP 



299 




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ti 


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3 'c — 
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300 THE MUSCLES OF THE OX 

vertebrjB. It is traversed by the roots of the brachial plexus, which partially 
divide it into a small dorsal and a large ventral part. The brachial vessels lie 
below the latter. The scalenus dorsalis (s. supracostalis) arises usually on the 
second, third, and fourth ribs, and ends on the transverse processes of the third 
to the sixth cervical vertebrae. 

The rectus capitis anterior major arises on the third to the sixth cervical 
transverse processes, and blends at its insertion with the sterno-mastoideus and 
the mastoid portion of the mastoido-humeralis. 

The rectus capitis anterior minor is larger than in the horse. 

The rectus capitis lateralis and longus colli reseml)le 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 mastoido-humeralis, 
trachelo-mastoideus, and omo-transversarius. The remaining muscles present no 
very marked differential features. 



Muscles of the Thorax 

The levatores costarum number ten or eleven pairs. 

The diaphragm presents several important differential features. Its slope is 
much steeper and its width is greater than in the horse. The costal attachment 
extends almost in a straight line from the upper fourth of the last rib to the junc- 
tion of the eighth rib with its cartilage, and along the latter to the sternum. The 
mid-line slopes from the twelfth thoracic vertebra obliquely as far as the vena 
cava, beyond which it is almost vertical. The right crus divides into two branches, 
which circumscribe the oesophageal opening, unite below, and then spread out in 
the tendinous center. The left crus is small. The oesophageal opening 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 venae cavae is a little more ventral 
and almost in the median plane. The other muscles resemble those of the horse. 



Muscles of the Back and Loins 

The serratus anticus is very thin. It is inserted on the fifth to the eighth ribs. 
It may be reduced to two or three digitations or may be absent. The serratus 
posticus is usually inserted on the last three or four ribs. 

The transversalis costarum (Iliocostalis) has a distinct lumbar portion which 
is attached to tlio lumbar transverse processes and the external angle of the ilium. 

The longissimus resembles that of the horse, but it is more fleshy anteriorly, 
and the spinalis dorsi is clearly distinguishable from the common mass. In the 
lumbar region the tendons meet across the summits of the s])ines. 

Intertransversales are present in the back, and interspinales in the back and 
loins. 

MUSCLES OF THE TAIL 

These resemble those of the horse; the coccygeus is, however, much more 
developed. 



ABDOMINAL MUSCLES 



301 



Abdominal Muscles 

The obliquus abdominis externus is somewhat tliinner and has a less extensive 
origin, whicli 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 external angle of the ilium, nor as high as the lumbar 
transverse processes. (In this region the abdominal tunic has a strong attachment 
to the point of the hip and the lumbo-dorsal fascia.) The aponeurosis is intimately 
united with the abdominal tunic, and does not detach a layer on the inner surface 
of the thigh. 

The obliquus abdominis internus is more developed and has an additional 




Fig. 211 — Deepeh Muscles op Neck, Shoulder, and Thorax of Ox. 
c', Cleido-occipitalis muscle; d, steruo-cephalicus; /, /', long and external heads of triceps; g, superficial 
pectoral muscle; h, h' , posterior and anterior deep pectoral muscles; /, i' , serratus magnus; A', latissimus dorsi; 
I, obliquus abdominis externus; r', biceps brachii; w, splenius; x, rhomboideus; y, trachelo-niastoideus; z, 
supra.spiiiatus; z', infraspinatus; 2", tendon of insertion of z' ; 1' , cartilage of scapula; 8, tuberosity of spine of 
scapula; 3, acromion; 5, external tuberosity of humerus; 6, deltoid tuberosity; S, olecranon; 26, transverse 
processes of cervical vertebrae; 27, posterior auricular muscles; X, wing of atlas, (.\fter EUenberger-Baum, 
Anat. fur Kiinstler.) 



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 
forward 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 
umbihcus is in a transverse plane through the third luml^ar vertebra.) There 
are five tendinous inscriptions, on the third of which is a foramen for the 
passage of the subcutaneous abdominal vein (milk vein). The prepubic 
tendon has, in addition to branches inserted into the ilio-pectineal eminences, 
a strong attachment to the median common tendon of the adductors of the 
thigh, so that the abdominal wall is strongly retracted and almost vertical at 
its junction with the pelvis. 



302 THE MUSCLES OF THE OX 

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 hgamentum nuchse and supraspinous hgament, from the atlas to 
the twelfth thoracic vertebra. 

The omo-transversarius is a muscle (not present in the horse) which arises 
on the wing of the atlas, and, inconstantly, the transverse process of the second 
cervical vertebra, and is inserted into the scapular spine and fascia. 

The rhomboideus is clearly divided into cervical and dorsal portions, 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, the fascia 
over the external intercostal and oblique abdominal muscles, and by a tendinous 
slip to the deep pectoral muscle. 

The mastoido-humeralis has two distinct parts. The dorsal division (M. 
cleido-occipitalis) arises on the occipital bone and the ligamentum nuchse. The 
ventral part (M. cleido-mastoideus) is smaller and arises by a round tendon on 
the mastoid process and the rectus capitis anterior major, and by a thin tendon on 
the mandible. At the shoulder a small muscle which arises on the first rib blends 
with the deep face of the mastoido-humeralis.^ 

The superficial pectoral muscle does not present any striking difference. 

The deep pectoral arises as far forward as the second rib and is undivided. 
However, the scapular portion may be considered to be represented by a small 
branch extending over the lower part of the supraspinatus. A tendon is detached 
from the dorsal edge, which blends with the latissimus dorsi and coraco-brachialis. 

The serratus magnus is clearly divided into cervical and thoracic portions. 
The former is large and extends from the third (or second) cervical vertebra to 
the fifth rib, being overlapped behind by the thoracic part. 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 into the 
inner face of the dorsal angle of the scapula. 



IL MUSCLES OF THE SHOULDER 

The deltoid is clearly divided into acromial and scapular portions. The former 
arises on the acromion, the latter 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 portions with a common tendon of inser- 
tion. 

The teres major and coraco-brachialis resemble those of the horse. 



III. MUSCLES OF THE ARM 
The biceps is smaller and less tendinous, and is situated more internally than 
in the horse. The tendon of origin is flat, and is bound down in the bicipital groove 

1 This is probably the homologue of the subclavius of man. 



MUSCLES OF THE ARM 



303 



by a fibrous band. (In the sheep the tendon is round antl passes through the 
shoulder joint.) 



\w 





Fig. 212. — Muscles of Antibra- 

CHIUM AND MaNUS OF Ox, 

Anterior View. 

a. Extensor carpi radialis; 
h, extensor digiti tertii; c, extensor 
digitalis communis; d, extensor 
digiti quarti (tendon) ; /, extensor 
carpi olaliquus; g, bracliialis; 12', 
metacarpal tuberosity. (After 
Ellenberger-Baum, Anat. fiir 
Kiinstler.) 



Fig. 21.3. — Muscles of Antihra- 

CHIUM AND MaNUS OF Ox, 

External View. 
a. Extensor carpi radialis; b, 
extensor digiti tertii; c, common or 
anterior digital extensor; d, exten- 
sor digiti qtiarti; e, flexor carpi ex- 
ternus; /, extensor carpi obliquus; 
/'.ulnar head of flexor carjii medi- 
us; g, bracliialis; /;, interosseus 
medius or suspensory ligament ; i, 
flexor tendons; i', branch of h, to 
superficial flexor tendon; 8, ole- 
canon; 11, accessory carpal bone; 
12', metacarpal tuberosity. (After 
Ellenberger-Baum, Anat. fUr 
Kunstler.) 




Fig. 214. — Muscles of Antibra- 

CHIUM AND MaNUS OF Ox, 

Internal View. 

a. Extensor carpi radialis; 
b, tendon of extensor digiti tertii; 
/, tendon of extensor carpi ob- 
liquus; (I, brachialis; /(, intero.sseus 
medius or suspensory ligament; i, 
flexor tendons; i' , branch of h; k, 
flexor carpi internus; /, flexor 
carpi medius; m, superficial digital 
flexor. (After Ellenberger-Baum, 
Anat. fiir Kiinstler.) 



The internal head of the triceps is more developed than in the horse. 
The tensor fasciae antibrachii is a slender muscle. 



304 



THE MUSCLES OF THE OX 



IV. MUSCLES OF THE FOREARM 
A. Extensor Division 
• The extensor carpi radialis is like that of the horse. There is sometimes a 
small muscle lying along its inner border, which may represent the extensores 
pollicis. 

There are three digital extensors : 1. The common or anterior digital extensor 
(M. extensor digitalis communis) arises by two heads from the extensor epicondyle 
and 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 





Fig. 21.5. — Right Carpus of Ox with Burs.e and Fig. 216. — Right Carpus of Ox with Burs.e and 
Synovial Sheaths Injected, External View. Synovial Sheaths Injected, Internal View. 

1, Extensor carpi radialis, with synovial sheath (!') and bursa (/"); S, 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, o, extensor digiti quarti proprius, with synovial sheath (5'); 6, 6' , flexor carpi externus, with 
bursa (6f"); 7, flexor carpi internus, with synovial sheath; S, deep digital flexor, with synovial sheath (8'); 9, 
flexor carpi medius; 10, superficial digital flexor, with synovial sheath 10'\ a, radius; b, carpus; c, metacarpus; 
d, cut edge of annular ligament, (.\fter Schmidtchen.) 



forward. At the fetlock joint it divides into two l)ranches, which are inserted 
into the third phalanges. 2. The internal digital extensor (M. extensor digiti 
tertii proprius) arises on the extensor epicondyle, and is inserted by two branches 
into the second and third phalanges of the inner digit. The tendon receives two 
reinforcing slips from the suspensory ligament. 3. The lateral digital extensor 
(M. extensor digitalis lateralis s. digiti quarti proprius) arises from the external 
lateral ligament of the elbow joint, the external tuberosity of the radius, and the 
ulna. The tendon terminates like that of the preceding nuiscle. 

The extensor carpi obliquus resembles that of the horse. 

The extensor tendons are bound down at the carpus by an annular ligament, 
and are furnished with synovial sheaths (Figs. 215, 216). 



METACARPAL MUSCLES 



305 



B. Flexor Division 

The three flexors of the carpus are hke those of the horse. 

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 
on tendons at the distal part of the forearm. The superficial tendon passes over 
the posterior annular ligament (Ligamentum 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 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. 

The deep digital flexor has the same heads as in the horse, the humeral head, 
as before mentioned, being connected with the deep portion of the superficial flexor. 
The tendon divides near the distal end of the metacarpus into 
two branches which arc inserted into the volar surfaces of the c s 

third phalanges. 

The synovial sheaths at the carpus present the follow- 
ing 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 extensor and the inner extensor. 

Bursse may occur under the tendons of the proper exten- 
sors 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 extend from the distal 
third of the metacarpus nearly to the distal sesamoids. 
Bursas occur l^etween the latter and the branches of the 
deep flexor tendon. 




Fig. 217. — Cross-section 
OF Distal Third 
OF Metacarpus of 
Ox. 

h. Tendon of exten- 
sor digiti tertii; c, tendon 
of common extensor; d, 
tendon of extensor digiti 
quarti; /t, interosseus medi- 
us or suspensory ligament; 
I, tendons of digital flexors; 
i' , branch of h; 12, meta- 
carpal bone. (After EUen- 
berger-Baum, Anat. fiir 
Kunstler.) 



METACARPAL MUSCLES 

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 lateral 
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. 

It is to be noted that the fascia on the posterior 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 

20 



306 



THE MUSCLES OF THE OX 



diverge to be inserted into the second and third phalanges, blending with the 
lateral ligaments. 



The Muscles of the Pelvic Limb 
i, the sublumbar muscles 

The psoas minor begins at the disc between the twelfth and thirteenth thoracic 
vertebr£E. 

The psoas major has a fleshy origin on the posterior border of the last rib, and 
a thin tendon attached to the twelfth rib. 

The iliacus liegins under the body of the sixth lumbar vertebra, and is more 

closely united with the psoas major than in the 
horse. 

The quadra tus lumborum extends as far 
forward as the body of the tenth or eleventh 
thoracic vertebra. 



11. EXTERNAL MUSCLES OF THE HIP AND 
THIGH 

The tensor fasciae latae is large, and the 
fleshy part extends further down than in the 
horse. 

The gluteus superficialis is not present as 
such; apparently its anterior part has fused 
with the tensor fascite latae and its posterior 
with the biceps femoris. 

The gluteus medius is small, the lumbar 
portion being insignificant and extending for- 
ward only to the fourth lumbar vertebra. Its 
deep portion (Gluteus accessorius) 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 
externus. 

The gluteus profundus is thin, but exten- 
sive, arising as far forward as the external 
angle of the ilium, and from the lower part of 
the sacro-sciatic ligament. The fibers converge 
on a tendon which passes under the upper part 
of the vastus externus, and is inserted into a 
tubercle a short distance below the great tro- 
chanter. 




Fig. 218. — Gluteal and Femoral Regions 
OF Ox, After Removal of Super- 
ficial Muscles. 

p. Gluteus medius; r.semitendinosus; 
V, coccygeus; 2S, vastus externus; 28' , rectus 
fenioris; 29, semimembranosus; SO, gastroc- 
nemius; 31, sacro-sciaticligament; 16, tuber 
coxae; 17, tuber ischii; 19, trochanter major; 
20, patella; 21', external condyle of tibia. 
(After Ellenberger-Bauiii. Anat. ftir Kiuist- 
ler.) 



The biceps femoris is very wide at its 
upper part, having apparently absorbed tlie posterior ]:)art of the superficial 
gluteus. It is divided in the thigh into two portions, which end on a wide 
aponeurosis. 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 external patellar ligament presents a fibro-cartilaginous thicken- 
ing, and an extensive bursa is interposed between it and the external condyle of 
the femur. 

The semitendinosus and semimembranosus arise on the ischium only. The 
latter has a branch attaclied to the internal contivle of the tibia. 



ANTERIOR MUSCLES OF THE THIGH 



307 



III. ANTERIOR MUSCLES OF THE THIGH 

The quadriceps femoris resembles that of the horse; th(> vastus intermedius is 
more clearly separable, and consists of two parts. Bursa? occur under the insertions 
of the internal and external vasti, and often under the end of the biceps in the adult. 




Fig. 219 — Muscles of Left Leo and Foot of Ox, 
Anterior View. 
a, Peroneus tertius; a', tibialis anterior; b, an- 
terior or long digital extensor; 6', extensor digiti tertii; 
c, peroneus longus; rf, extensor digiti quarti; ;',!, annular 
ligaments; k, external lateral ligament of hock joint; I, 
branch of suspensory ligament; 20, patella; 21' , external 
condyle of tibia; 2S, tuberosity of tibia. (After EUen- 
berger-Baum, Anat. fiir Kunstler.) 



Fig. 220. — Muscles of Leg and Foot of Ox, Ex- 
ternal View. 
a, Peroneus tertius; a' , tibialis anterior; 6, ante- 
rior or long digital extensor; b' , tendon of 6; c, peroneus 
longus; d, extensor digiti quarti; e, deep digital flexor; 
e', tendon of e; e" , branch of interosseus medius or sus- 
pensory ligament; /, gastrocnemius (the soleus lies just 
in front of /); /', tendon of /; g, tendon of superficial 
digital flexor; h, interosseus medius or suspensory liga- 
ment; i, I, annular ligaments; 20, patella; 21', external 
condyle of tibia; 28, crest of tibia. (After EUenberger- 
Baum, Anat. fur Kunstler.) 



The articularis genu or subcrureus is a small muscle which lies under the lower 
part of the vastus intermedius, and is inserted on the suprapatellar cul-de-sac of 
the synovial membrane. 

The capsularis is absent. 



308 



THE MUSCLES OF THE OX 



IV. INTERNAL 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 than in the horse. 
The pectineus is large, and arises by a single head from the pubic crest and 




Fig. 221. — Left Tarsu.s of Ox with Syno- 
vial Sheaths and Burs.b Injected, 
External View. 

1, Peroneus tertius; 1' , tendon of 1 and 
its sheath, 1" ; 2, extensor digiti tertii pro- 
prius; 2' , tendon of 2; 2" , common sheath of 
tendons of extensor digiti tertii and extensor 
digitalis longus (3, 3'); 4. peroneus longus and 
its sheath, 4' ! 5, extensor digiti quarti and its 
.sheath, 5'; 6, tendon of gastrocnemius; 7, 
superficial digital flexor and its sheath, 7'; 
8, tendon of tibialis anterior; a, tibia; b, proxi- 
mal annvilar ligament; c, tarsus; d, distal an- 
nular ligament; e, metatarsus; /, external 
lateral ligament. (After Schmidtchen.) 




Fig. 222. — Left Tarsus or Ox with Synovial Sheaths and 
BuRS.E Injected, Intern.-vl View. 
1, Peroneus tertius; 2, tendon of tibialis anterior with 
sheath, 2' , and bursa, 2" ; 3, long digital flexor and 3', its sheath; 
4, tibialis posterior; 5, deep digital flexor and its sheath, <5'; G, 
tendon of gastrocnemius and bursa, 6' ; 7 , superficial digital flexor 
and its sheath, 7'; S, subcutaneous bursa; a, tibia; b, proximal 
annular ligament; c, tarsus; d, metatarsus. (After Schmidtchen.) 



prepubic tendon. It divides into two branches, one of which is inserted as in the 
horse, while the other extends to the internal epicondyle of the femur. 

The adductor resembles that of the horse, but does not reach to the internal 
condyle. 

The quadratus femoris and obturator externus resemble those of the horse. 

The obturator internus arises from the ischium only, and its tendon passes 
through the ol)turator foramen. 

The gemellus is large. 



MUSCLES OF THE LEG AND FOOT 



309 



V. MUSCLES OF THE LEG AND FOOT 

There are four digital extensors, two of which are fused with each other and 
the peroneus tertius in tlic upper third of the leg. 

1. The anterior or long digital extensor (M. extensor digitahs longus) arises 
by the common tendon 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 termi- 



! / 




Fig. 223. — Muscles of Leg and Foot of Ox, Inner View. 
a, Peroneus tertius; 6', tendon of anterior or long extensor; e, deep digital flexor; e' , tendon of e; e", branch 
of h to superficial flexor tendon; /, gastrocnemius; .<;, tendon of superficial digital flexor; h, interosseus medius 
or suspensory ligament; i, annular ligaments; U branch of h; m, long digital flexor; o, popliteus; 20, patella; 28, 
tuberosity of tibia. (After Ellenberger-Baum, Anat. fur Kunstler.) 



nates on a tendon which passes down over the hock (l)ound down by two annular 
ligaments) and ends like that of the thoracic limb. 

2. The internal 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 cogenors and ends on the second phalanx of the inner digit. 

3. The lateral digital extensor (M. extensor digitalis lateralis s. digiti quarti 
proprius) arises on the external lateral ligament of the stifle joint and the external 
condyle of the tibia. Its tendon passes over the outer surface of the hock, and 
terminates on the anterior surface of the second phalanx of the external digit. 



310 



THE MUSCLES OF THE OX 



The reinforcing bands from the suspensory Hgament are arranged as in the 
fore Hmb. 

4. The extensor brevis resembles that of the horse, but is inserted on the ten- 
don of the anterior extensor only. 

The peroneus longus (not present in the horse) is situated in front of the lateral 
extensor. It arises on the external condyle of the tibia and the fibrous band which 
represents the shaft of the fibula. Its tendon passes doAvnward and backward 
over the outer surface of the hock, crosses over that of the lateral extensor and under 





Fig. 224. — Distal Part of Limb of Ox with Syno- 
vial Sheaths and Burs.e Injected, An- 
terior View. 

1, Tendon of extensor digiti tertii, with bursa 
(,!')', 2, tendon of anterior extensor; 2' , branch of 2, 
with synovial sheath (2")\ S, tendon of extensor digiti 
quarti, with bursa (■;}'); o, metatarsus; ?), first phalanx; 
c, .second phalanx. (After Schmidtchen.) 



Fig. 225. — Distal Part of Limb of Ox with Syno- 
vial Sheaths Injected, Posterior View. 
1, Superficial flexor tendon; 1' , 1', branches of 
;,• 1", 1'" , upper part of synovial sheaths oi 1' , 1' ; 2, 
deep flexor tendon; 2' , 2", branches of 2; 2", upper 
part of synovial sheath of 2'; 3, 3, lateral branches of 
interosseus medius or suspensory ligament; S', branch 
of same to superficial flexor tendon; a, fetlock joint; 
fe, pastern joint; c, coffin joint; rf, e, annular ligaments; 
/, crucial interdigital ligament, (.\fter Schmidtchen.) 



the lateral ligament, and ends on the first tarsal bone (Cuneiform parvum). It is 
enveloped by a synovial sheath. It would apparently 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 internal 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 
large metatarsal and second and third (fused) tarsal bones (Cuneiform magnum). 

The tibialis anterior is smaller, and arises by two heads. The larger head 



MUSCLES OF THE PIG MUSCLES OF HEAD 311 

springs from thv outer surface of the tuberosity of tlie tibia; the outer, smaller 
one (M. extensor liallucis longus) , from the upper part of the external border of the 
tibia and the fibrous l)and which replaces the shaft of the fibula. The tendon 
perforates that of the preceding nmscle and ends on the metatarsal and second antl 
third tarsal bones. 

B. Posterior Group 

The gastrocnemius and soleus resemble those of the horse. Tlu^ superficial 
flexor is more fleshy than in the horse. Its tendon terminates as in the fore limb. 

The deep flexor has in its upper part a close resemblance to that of the horse, 
but the superficial head (tibialis posterior) is larger and distinct. The tendon ends 
like that on the fore limb. 



MUSCLES OF THE PIG 
Muscles of Head 

The facial panniculus 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 penniform belly, which arises in the fossa on the lacrimal bone and 
maxilla. The tendon ends on the anterior part of the os rostri. A muscular slip 
connects it witli the premaxilla. 

The zygomaticus arises on tlie 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 devcloi^ed. It arises under the levator 
rostri and ends by a tendinous network around the nostril. 

The dilatator naris transversus 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 up and inward 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. 

MUSCLES OF MASTICATION 
The digastricus has only one belly. It ends on the inner and lower surface 
of the mandil)le, in front of the groove for the facial vessels. 
The other muscles have no important differential features. 
The same is true of the oral hyoid muscles. 



MUSCLES OF THE NECK 

The panniculus carnosus consists of two layers which cross each other ob- 
liquely. The fi]:)ers 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 mastoido-humeralis is described on p. 314. 



312 



MUSCLES OF THE PIG 



The stemo-cephalicus (Sterno-mastoicleus) arises on the sternum and is in- 
serted by a long round tendon on the mastoid process. 

The thyroid portion of the sterno-thyro-hyoideus has a pecuhar 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 
divides into two branches; one of these is inserted in the usual fashion, the other 
ends on the laryngeal prominence. The hyoid portion is well developed. 

The omo-hyoideus is thin. It arises as in the horse, but has no connection 
with the mastoido-humeralis nor with the opposite muscle. 

The omo-transversarius arises on the first or second cervical vertebra (under 
cover of the mastoido-humeralis) , and is inserted into the lower part of the scapular 
spine. 

There are two scaleni. The scalenus ventralis (s. primae costse) resembles 




Fig. 226. — Superficial Muscles of Pig, After Removal of Panniculus Carnosus. 
a. Levator nasolabialis; b, levator labii superioris proprius; b' , fleshy slip of b which comes from pre- 
maxilla; c, dilatator iiaris lateralis; d, depressor rostri; e, orbicularis oris; /, depressor labii inferioris; g, zygo- 
maticus; h, masseter; ?", i' , i", brachio-ceiihalicus (cleido-occipitalis, cleido-mastoideus, pars clavicularis) ; k, 
sterno-cephalicus; I, sterno-hyoideus; m, omo-transversarius; n, n' , trapezius; o, anterior deep pectoral; p, 
latissimus dorsi; q, lumbo-dorsal fascia; )•, obliquus abdominis externus; r', aponeurosis of r; s, serratus posticus; 
t, serratus magnus; u, posterior deej} jjectoral; v. supraspinatus; w, w' , deltoidetis; x, long head of triceps; y, 
external head of triceps; r, tensor fasciif antibrachii; 1, brachialis; 2, extensor carpi radialis; 3, extensor digiti 
quarti; 4, extensor digiti tjuinti; 5, extensor carpi ulnaris; 6, ulnar head of deep flexor; 7, gluteus medius; S, 
tensor fasciae latae; 9, 10, 10', biceps feraoris; 11, semitendinosus; 12, semimembranosus; 13, caudal muscles; 
14, panniculus adiposus in section. (After Ellenberger, in Leisering's Atlas.) 



that of the ox, is attached to the last four cervical vcrtelirffi, and is perforated l)y 
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 straight muscles of the head present no si:)ecial features. 

The longus colli is separated from the oi)i:)Osite muscle, so that part of the 
bodies of the cervical vertebrae is exposed as in man. 

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 trachelo-mastoideus is small, and its atlantal portion is blended with the 
longissimus. 

The complexus is large, and is clearly divided into two portions: the dorsal 



MUSCLES OF THE THORAX MUSCLES OF THE BACK AND LOINS 313 

portion (Biventer cervicis) is marked by several tendinous intersections; the 
ventral part is the complexiis proper. 

The obliquus capitis posterior is relatively thin. 

The recti capitis 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 anticus and 
posticus and the diiiitations 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 
abdominis. 

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 opening for the oesophagus, 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 externus 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 (Poupart's) ligament. 

The obliquus abdominis internus resemblessthat 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 intersections. 
Its tendon of insertion fuses largely with the common tendon of the gracilis, 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 externus is present in the female as well as in the male. 



Muscles of the Back and Loins 

The serratus anticus is inserted into the fifth to the eighth ribs inclusive, the 
serratus posticus into the last four or five ribs. There are usually no digitations 
attached to the ninth and tenth ribs. 

The transversalis costarum (Iliocostalis) extends to the wing of the atlas. 

The spinaUs 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 intertransver sales of the back 
and loins. 



314 MUSCLES OF THE PIG 

MUSCLES OF THE TAIL 
The superior 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 l)one 
to the tenth thoracic vertebra. There is no clear division ))etween its two parts, 
which are both inserted into the scapular spine. 

The omo-transversarius reseml)les that of the ox. 

The rhomboideus consists of three i:)ortions. The cervical portion (Rhom- 
boideus cervicalis) is greatly developed, its origin extending from the second cervi- 
cal to the sixth thoracic vertebra. The cephalic portion (Rhomboideus capitis) 
arises with the splenius on the occipital bone, and is inserted with the cervical part. 
The dorsal portion (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 internal lip of the bicipital groove. 

The mastoido-humeralis divides into two parts, the cleido-mastoideus and 
cleido-occipitalis, which arise on the mastoid process and occipital crest respectively, 
and unite at the fibrous vestige of the clavicle. 

The anterior superficial pectoral is thin. The posterior superficial pectoral 
is divided into parts, one of which ends on the humerus, the other on the fascia 
of the forearm. 

The deep pectoral is clearly divided into two parts. The scapular portion 
resembles that of the horse, l)ut its origin does not extend behind the first two 
chondro-sternal joints. The posterior deep pectoral is very long. 

The cervical portion of the serratus magnus is greatly developed, its origin 
extending from the wing of the atlas to the upper part of the fifth rib, and passing 
under the thoracic portion; 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 ends chiefly on the external tuberosity of the 
humerus. 

The infraspinatus is inserted into a depression below the posterior division of 
the external tuberosity. 

The teres minor is w(>ll developed; it ends on a tubercle l^etween the external 
and deltoid tul)erositios of the humerus. 

The subscapularis and teres major have no remarkable features. 

The coraco-brachialis is short and undivided. 

The capsularis is very small and frequently absent. 



MUSCLES OF THE ARM 
The biceps brachii is fusiform and not greatly developed. Its tendon of origin 
is roundetl and passes through the capsule of the shoulder joint. The tendon of 
insertion is bifid, entUng on the radius and ulna. 



MUSCLES OF THE FOREARM AND DIGITS 



315 



The brachialis is well developed, and also ends on the radius and ulna. 

The tensor fasciae antibrachii resembles that of the horse. 

The long head of the triceps is divided into two parts, except at its distal end, 
under which there i.s a synovial bursa. The external head is inserted into a crest 
on the outer surface of the olecranon by a thin tendon, under which there is a 
bursa. The internal head arises near the head of the 
humerus, beneath the coracobrachialis. 

There are two anconei. 



MUSCLES OF THE FOREARM AND DIGITS 

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 obliquus is well developed; it ends 
on the second metacarpal ])one. 

There are three (or four) digital extensors. 

1. The common or anterior digital extensor (M. ex- 
tensor digitalis communis) arises on the extensor epicon- 
dyle of the humerus and the lateral ligament of the elbow, 
and divides into three parts. The tendon of the inner 
part divides into two branches which end on the second 
and third digits ; the tendon to the second digit is small 
and often absent. The tendon of the middle part divides 
lower down into two branches for the third and fourth 
(chief ) digits ; above tiiis iDifurcation it detaches a small 
branch to the second digit, which usually unites with the 
tendon of the extensor indicis. The tendon of the deep 
head divides into two branches, the inner one joining the 
tendon of the middle head, while the outer one ends on 
the fifth digit. 

2. The extensor of the second digit (]M. extensor 
indicis proprius) is covered by the preceding muscle, 
with which it is partially fused. It arises on the ulna. 
Its delicate tendon usually unites Avith the tendon of the 
middle head of the common extensor which goes to the 
second digit. 

3. The lateral digital extensor (M. extensor digitalis 
lateralis) consists of two distinct parts: (1) The large 
dorsal (anterior) muscle (iM. extensor digiti quarti jiro- 
prius) has a long tendon which ends on the fourth digit, 
and often sends a slij:) to the fifth digit. (2) The small 
volar (posterior) muscle (M. extensor digiti quinti pro- 
prius) ends by a long tendon on the lateral aspect of the 
fifth digit. 

The supinator has been found by Arloing and Lesljre, 
but is usually absent in the pig. 

The pronator teres is a small muscle which lies on the 
internal lateral ligament of the elbow. It arises from the internal epicondyle of 
the humerus, and reaches about to the middle of the inner l^order of the radius. 

The flexor carpi internus is well developed. It arises on the flexor epicondyle 
of the humerus, and is inserted into the third metacarpal bone. 

The flexor carpi medius is narrow and has no ulnar head. 




Fig. 227. — Muscles of Anti- 

BRACHIUM AXD ilAXUS 

OF Pig, Axtero-Ex- 

TERNAL View. 

a, a', Extensor carpi 
radialis; b, extensor carpi 
obliquus (s. ahiluctor poUicis 
longus); c, d, e, common or 
anterior digital extensor; c', 
c", tendons of insertion of c; 
d' , d" , tendons of d; e', e", 
tendons of e; /, tendon of 
extensor indicis; (i, extensor 
digiti quarti; li, extensor 
digiti quinti; //, tendon of 
h; i, tendinous, and k, fleshy 
part of flexor carjji externus; 
A', tendon of k; I, ulnar head of 
deep fligital flexor; in, superfi- 
cial digital flexor; n , brachialis. 
(After F211enberger, in Leis- 
ering's Atlas.) 



316 MUSCLES OF THE PIG 

The flexor carpi externus (M. extensor carpi ulnaris) is covered by a thick, 
tendinous band, which extends from the extensor epicondyle to the accessory carpal 
bone and outer aspect of the carpus. The tendon of the muscle 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 has two bellies. The tendon of the superficial 
head passes down behind the posterior 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 l^ranches on the second phalanx of the fourth 
digit. The tendon of the deep head, after detaching a slip 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 
common tendon divides into four branches, the larger central pair ending on 
the third phalanges of the principal digits, the smaller pair on the accessory 
digits. The latter are bound down by a peculiar spiral band. There is no check 
ligament. 

The lumbricales are represented by bundles which extend from the tleep 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 forward as far as 
the twelfth rib. 

MUSCLES OF THE HIP AND THIGH 

The tensor fasciae latae is broad, and its fleshy part reaches almost to the pa- 
tella. 

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 external angle of the 
ilium. 

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 resembles that of the horse. 

The semimembranosus has two insertions as in the ox. 

The sartorius has two heads of origin, between Avhich the external iliac vessels 
are situated. The inner arises from the tendon of the psoas minor, the outer 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 l^ackward. 

The adductor shows no division and is partially fused with the gracilis. It 
ends on the femur just above the origin of the gastrocnemius. 



MUSCLES OF THE LEG AND FOOT 



317 



The quadratus femoris is large. 

The obturator externus resembles that of the horse. 

The obturator internus is extensive and strong; its tendon emerges through 
the obturator foramen. 

The gemellus is fused in part with the obturator internus. 

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. 



MUSCLES OF THE LEG AND FOOT 

The peroneus tertius resembles that of the ox, but its 
tendon is not perforated by that of the tibialis anterior, 
and ends on the inner (second) large metatarsal bone, de- 
taching a strong branch to the first and second tarsal 
bones. 

The tibialis anterior arises on the tibial crest. Its 
tendon passes over the hock along the inner border of the 
tendon of the peroneus tertius (both being bound down 
by an annular ligament), and is inserted into the inner 
(second) metatarsal and first tarsal bones. 

The peroneus longus lies partly on the outer surface 
of the peroneus tertius. Its tendon crosses those of the 
lateral extensor, passes along a groove on the plantar 
surface of the fourth tarsal bone, and ends on the first 
tarsal and second metatarsal bones. 

The anterior or long digital extensor arises with the 
peroneus tertius and is largely covered by it and the per- 
oneus longus. It divides into three parts. The tendon 
of the inner division (M. extensor digiti tertii) ends on 
the inner chief (third) digit ; that of the middle division 
by two branches on the principal digits; and that of the 
outer division by three branches on the second, fourth, 
and fifth digits. 

The lateral digital extensor divides into proper ex- 
tensors of the fourth and fifth digits (Extensores digiti 
quarti et quinti). 

The extensor hallucis longus arises on the fibula and 
ends on the inner small (second) digit. 

The extensor digitalis brevis is well developed and 
consists of three parts. The inner and outer tendons end 
on the first phalanges of the chief digits, the middle 
one joins the common extensor tendon of the same. 

The gastrocnemius presents nothing special. 

The soleus is wide, and is partly blended with the 
external head of the gastrocnemius. 

The superficial digital flexor has a large belly. Its 
tendon ends on the two chief digits, and is also connected 
with the ligaments of the accessory digits. 

The inner head of the deep digital flexor (flexor digitalis longus) is relatively 
small. The common tendon ends as in the thoracic limb. 

The popliteus ]iresents no special features. 

The plantar muscles resemble their homologues of the fore limb, except that 
the adductors of the accessory digits and the lumbricales are absent. 




Fig. 228. — Muscles of Leg 
AND Foot of Pig, An- 

TERO-EXTERNAL ViEW. 

a, Tibialis anterior; a', 
tendon of preceding; b, pero- 
neus tertius; b' , tendon of b; 
c, anterior or long digital ex- 
tensor; d, e, f, /', /", tendons 
of c; g, peroneus longus; g', 
tendon of g; h- extensor digiti 
quarti; h' , tendon of 'i. which 
receives h" , from the inter- 
osseus inedius; i. extensor 
digiti quinti; k. deep digital 
flexor; I, soleus; m. gastroc- 
nemius; n, extensor brevis. 
(After EUenberger, in Leiser- 
ing's Atlas.) 



318 



THE MUSCLES OF THE DOG 



THE MUSCLES OF THE DOG 
Muscles of the Face 

The panniculus carnosus is well developed and presents two distinct bands, 
one of which is inserted into the lower lip, the other into the scutiform cartilage of 
the ear. 

The orbicularis oris is poorly developed. In the upper lip it is divided cen- 
trally, and in the lower it is distinct only near the angles of the mouth. 

The levator nasolabialis is wide and undivided, and ends in 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 
around the nostril, some blending with those of the opposite side. 

The zygomaticus, long and narrow, arises on the scutiform cartilage, and 
ends at the angle of the mouth. 




Fig. 229. — Muscles of Head of Dog 
a, Scutularis; b, c, anterior auricular muscles; d, helicis; e, antitragicus; /, /, zygomaticus, out of which 
a portion is cut; g, slip of panniculus; /(, parotiJo-auricularis; i, masseter; k, malaris; I, levator nasolabialis; 
m, levator labii superioris proprius; n, dilatator naris lateralis; o, p, buccinator (buccalis, molaris); q, retractor 
anguli oris; r, digastricus; s, mylo-hyoideus; 7, base of concha; ^, parotid gland; ;2', parotid duct; 5, submaxil- 
lary gland; 4< submaxillary lymph glands; 5, buccal glands; 6, zygomatic arch; 7, maxilla; S, dorsum nasi; 
9, parotid lymph gland. (EUenberger-Baum, Anat. d. Hundes.) 

The depressor labii inferioris is absent, unless we recognize as such a thin 
stratum arising on the body of the mandible and spreading out in the orbicularis. 

There are no special nasal muscles, the homologue of the lateral dilator ending 
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. 



MUSCLES OF MASTICATION 

The masseter is large. It arises from the zygomatic arch, and extends beyond 
the branch of the jaw below and behind. Three 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. 



HYOID MUSCLES — MUSCLES OF THE THORACIC LIMB 



319 



The digastricus is usually not digastric, but is a strong, round, fleshy muscle, 
which arises on the paramastoid or styloid process and is inserted into the border 
and inner surface of the ramus at the level of the last molar teeth. 

The stjdo-mandibularis is absent. 



HYOID MUSCLES 
The mylo-hyoideus is well developed. 

The stylo-hyoideus is very slender, and is inserted into the body of the hyoid 
bone: it is not perforated by the digastricus. 




Fig. 230. — Superficial Muscles of Dog, After Removal of Panniculus Carnosus. 
1, Levator nasolabialis; 2, levator labii superioris proprius; 3, dilatator naris lateralis; 4, 4', buccinator; 
5, retractor anguli oris s. risorius; 6, zygomaticus; 7, malaris; 8, masseter; 9, digastricus; 10, scutularis; 11, 
other auricular muscles; 12, parotido-auricularis; 13, mylo-hyoideus; 14, sterno-hyoideus; 15, sterno-thyroideus; 
16, splenius; 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 superior; 23, sacro- 
coccygeus inferior; ^4. great trochanter; ^-5, jugular vein; a, 6, c, brachio-cephalicus; rf, clavicle; e, /, trapezius; 
g, serratus cervicis; h, omo-transversarius; ;', latissimus dorsi; k, posterior deep pectoral; /, supraspinatus; 
TO, m' , deltoid; n, infraspinatus; o, triceps, long head; o', triceps, external head; p, brachialis; </, extensor carpi 
radialis; r, gluteus medius; s, gluteus superficialis; i, V , tensor fascia^ latse; w, sartorius; r, biceps femoris; r', 
fascia lata; w, semitendinosus; x, semimembranosus; y, sartorius; z, gracilis; 26, pronator teres; 27 , flexor carpi 
radialis; 28, flexor carpi ulnaris; 29, tibialis anterior; 30, popliteus; 31, 31', deep digital flexor; 32, superficial 
digital flexor; S3, gastrocnemius; 34, spine of scapula; a, parotid gland, with a', its duct; /3, submaxillary gland; S, 
submaxillary lymph glands; ij, parotid lymph gland; C,, inferior buccal glands. (After Ellenberger, m Leisering's 
Atlas.) 

The hyoideus transversus and omo-hyoideus are absent. 
The sterno-thyro-hyoideus is large and arises chiefly on the first costal carti- 
lage. 

Muscles of the Thoracic Limb 

The trapezius is thin, and is not clearly divided into cervical and thoracic 
portions. Its line of origin extends from about the middle of the neck to the 
ninth or tenth thoracic spine, the right and left muscles meeting on a median 
fibrous raphe. 

The omo-transversarius arises by a tendon on the lower part of the spine of 
the scapula (often partially blended with the trapezius), and is inserted into the 
wing of the atlas. 



320 



THE MUSCLES OF THE DOG 



The rhomboideus consists of three parts. The dorsal portion (Rhomboideus 
thoracahs) is small; it arises from the fourth to the sixth or seventh thoracic 
spine, and is inserted into the inner surface (chiefly) of the dorsal angle of the scap- 
ula. The cervical portion (Rhomboideus cervicalis) arises from the ligamentum 
nuchse as far forward as the second or third cervical vertebra, and is inserted into 
the inner surface of the cervical angle of the scapula. The cephalic portion (Rhom- 
boideus capitis) is a continuation of 
the preceding which is inserted into 
the occipital crest. 

The latissimus dorsi is extensive, 
and has a fleshy attachment to the 
last two ribs. Its lower edge blends 
near the shoulder with the panni- 
culus. 

The mastoido-humeralis con- 
tains in front of the shoulder a 
fibrous mass in which the clavicle is 
embedded. Anterior to this it sepa- 
rates into two diverging portions. 
The dorsal portion (M. cleido-cervi- 
calis) is attached to the median raphe 
of the neck and to the occipital bone. 
The ventral portion (M. cleido-mas- 
toideus) is attached to the mastoid 
process. The common mass posterior 
to the clavicle and the fibrous inter- 
section, which is attached to the 
humerus, is homologous with the 
clavicular portion of the deltoid of 
man. 

The superficial pectoral muscle 
is small. It arises on the sternum 
from the first to the third costal 
cartilage, and is inserted into the 
anterior siu'face of the humerus. A 
superficial slip detached from it is 
inserted into the fascia of the fore- 
arm. The deep pectoral has no pre- 
scapular portion. It arises on the 
sternum and costal cartilages from 
the second costal to the xiphoid car- 
tilage. It is inserted chiefly into the 
internal tuberosity of the humerus, 
but also by small slips into the ex- 
ternal tuberosity and the fascia of 
the arm. 

The serratus magnus shows no 
clear division into cervical and thor- 
acic portions. It arises from the last five cervical vertebrse and the first seven 
or 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 former 
arising on the spine, the latter on the acromion of the scapula. Both end on the 
deltoid tuberosity. 




Fig. 231. — Ventral Muscles of Head, Neck, and 
Thorax of Doi:. 
a, Mylo-hyoideus; b, digastricus; c, sterno-hyoiileus; 
c', sterno-thyrokleus; d, sterno-eephalicu.s; e, brachio- 
cephalicus; /, subscapularis; g, superficial pectoral; li, 
deep ])ectoial; i, rectus abdominis; k, obliciuus abdoniinis 
externus; /, long head of triceps; m, internal head of 
triceps; n, biceps brachii; o, braehialis; 1, 1' , 1" , sub- 
maxillary lymph glands; 2, thyroid gland; 3, external 
jugular vein. (Ellenberger-Baum, Anat. d. Hundes.) 



MUSCLES OF THE THORACIC LIMB 



321 




The supraspinatus ends chiefly on the external tu})erosity of the humerus, but 
has a small attachment to the internal tuberosity also. 

Th(> infraspinatus is inserted into the outer surface of the external tuberosity 
of the humerus. 



Siihscapularis 

Teres major - ^ V\ 

I 4 Suprusjnruilus 

La(issi)nus dorsi .„~" ""■ \ 'ft Pn 

\ ' /'^i" Coraco-lmicliialis 
Long licdil of triceps I 7" / ' i , i i- , ■ 

■1-^-4 / y /■ -r -- - Accessory head of triceps 

Tensor fascia' a)i.tibracJtii 

/ ', - Biceps hracldi 

, / 

'/ Mf 
Internal Jtcad of triceps —£i»..l, , ,,. 

r f y ii/,, ^ 

Humerus 

m 

Flexor carpi medius .l|[|'i \ i \^ |1| -^ -- Extensor carpi radialii 

Flexor carpi intern us »^\l.\T"~"'- — Pronator teres 

Superficial digital flexor --*.„_\ \ v i 

Deep digital flexor ^ .ll\. _vA i U ~^' Radius 

.% V~.u. , Radial head of deep 

digital flexor 

%f 

f 




Ftg. 2.'?2.— Muscles of Thoracic Limb of Dog, Intfrnai. Vii:w. (Ellenberger-Baum, Anat. des Himdes.) 



The teres minor arises on a tubercle on the posterior border of the scapula, 
just above the olenoid cavity, and is inserted into the deltoid ridge. 

The subscapularis is wide and is somewhat multipennate in structure, being 
intersected by fil)rous septa which are attached to the rough lines on the costal 
surface of the scapula. 
21 



322 



THE MUSCLES OF THE DOG 



The teres major is thick. It arises on the upper part of the posterior bordei 
of the scapula and on the subscapularis. 

The coraco-brachialis is short and undivided, and is inserted into the upper 
part of the postero-internal surface of the humerus. 

The capsularis is absent. 

The biceps brachii lies almost entirely on the inner 
surface of the humerus. It is long and fusiform. The 
tendon of origin is round, and passes through the cap- 
sule of the shoulder joint. The tendon of insertion is 
bifid, one branch being attached to the ulnar, the other 
to the radial tuberosity. 

The brachialis is very little curved, and is inserted 
chiefly into the tuberosity and inner border of the ulna. 

The tensor fasciae antibrachii is thin and narrow. 
It arises on the outer 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 brachio-radialis is a long, narrow, delicate 
muscle, situated superficially on the anterior surface of 
the forearm. It arises with the extensor carpi on the 
crest above the extensor epicondyle of the humerus, 
and is inserted into the distal part of the inner border 
of the radius. It is often much reduced, and is some- 
times absent. It rotates the forearm and paw out- 
ward. 

The extensor carpi divides into two parts. The 
larger outer part, the extensor carpi radialis brevis, ends 
on the proximal end of the third metacarpal })one. 
The inner and more superficial part, the extensor 
carpi radialis longus, ends on the second metacarpal 
bone. (A tendon to the fourth metacarpal may occur.) 

The extensor carpi obliquus or abductor pollicis 
longus arises from the outer border and anterior 
surface of the ulna, the interosseous ligament, and 
the outer border of the radius. It is inserted into 
the first metacarpal bone by a tendon which contains 
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 extensor epicondyle of 
the humerus and the lateral ligament of the elbow 
joint. It has four bellies, each terminating in a tendon. 
These are inserted into the third phalanges of the 
second, third, fourth, and fifth digits. 

2. The extensor of the first and second digits 
M. extensor ])ollicis longus et extensor indicis j)ro- 
prius) is small, and is covered by the common and 

lateral extensors. It arises on the proximal part of the ulna. Its tendon passes 
down with that of the common extensor and divides into two branches. The 
delicate inner branch ends on the first digit, while the other lilends with the tendon 
of the common extensor for the second digit. 

3. The lateral digital extensor (M. extensor digitalis lateralis) consists of two 




Fig. 233. — Muscles of Antibra- 

CHIUM AND MaNUS OF DoG, 

External View. 

a. Triceps brachii; b, brachi- 
alis; c, extensor carpi radiaUs; </, 
common or anterior digital e.xten- 
sor; d', d" , d'", d"" , tendons of 
preceding; e, lateral digital exten- 
sor; e', /, tendons of preceding; g, 
extensor carpi ulnaris; h, h' , flexor 
carpi ulnaris; i, extensor carpi ob- 
liquus (s. abductor pollicis longus) ; 
k, interossei; /, branches from pre- 
ceding to extensor tendons; 1 , ole- 
cranon; 3, radius; 3, extensor epi- 
condyle of humerus. (After Ellen- 
berger, in Leisering's Atlas.) 



MUSCLES OF THE THORACIC LIMB 



323 



muscles which are not rarely fused. They arise on the extensor epicondyle of the 
humerus and the lateral ligament of the elbow joint. The larger, superficial belly 
(M. extensor digiti tertii et quarti) terminates on a tendon which 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 com- 
mon extensor. The posterior belly (M. extensor digiti quinti) terminates by a 
tendon which fuses with that of the common extensor for the fifth digit. 

The ulnaris lateralis or extensor carpi ulnaris corresponds to the flexor carpi 
externus of the horse, but is an extensor of the carpus. It is a large flat muscle 
which lies on the outer surface of the ulna. It arises on the ex- 
tensor epicondyle of the humerus, and is inserted into the proxi- 
mal end of the fifth metacari:)al and the accessory carpal bone. 

The ulnaris medialis or flexor carpi medius (s. ulnaris) 
consists of two quite distinct heads. The larger, humeral 
head arises on the flexor epicondyle, while the smaller, super- 
ficial ulnar head arises on the posterior l)order of the ulna. 
The tendons of the two entl together on the accessory 
carpal bone. 

The radialis volaris or flexor carpi internus (s. radialis) 
arises on the flexor epicondyle of the humerus and is inserted 
l)y a bifid tendon into the second and third metacarpal bones. 

The tendons of the foregoing muscles are provided with 
synovial sheaths at the carpus. 

The pronator teres is a round muscle, which is situated 
superficially on the inner border of the proximal part of the ra- 
dius. It arises on the flexor epicondyle of the humerus, and is 
inserted into the internal border of the radius. Its action is to 
flex the elbow and rotate the forearm inward. 

The superficial digital flexor is situated superficially on the 
posterior and inner surfaces of the forearm. It arises on the 
flexor epicondyle of the humerus and terminates near the 
carpus on a tendon which passes downward 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 inner side of the carpus. Below this 
it divides 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 latter arising from the inner 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 accessorius (?) is a small muscle which arises from the 
deep 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, wide muscle which arises on the humerus beneath the 
external lateral ligament, crosses the anterior surface of the radius, and is inserted 
into the inner border of the radius. (A pouch of the capsule of the elbow joint 
lies under the tendon of origin.) Its action is to rotate the forearm outward 
(supination). 




Fig. 234.— Volar Mus- 
cles OF Fore 
Paw OB' Dog. 
a, -Abductor pol- 
licis brevis et opponens 
pollicis; h, flexor polli- 
cis brevis; c, adductor 
pollicis; d, adductor 
digiti secundi; e, ad- 
ductor digiti quinti; /, 
flexor digiti quinti 
brevis; g, abductor 
digiti quinti; h, in- 
terossei; 1, accessory 
carpal bone; 2, first 
digit; S-6, sesamoids 
of metacarpo-phalan- 
geal joints. (Ellen- 
berger-Baum, .\nat. d. 
Hundes.) 



324 THE MUSCLES OF THE DOG 

The pronator quadra tus consists of fibers which cross the inner surface of the 
interosseous hganient of the forearm, except at the two extremities of the latter. 
It is attached to the inner l^order of the uhia and the anterior surface of the radius. 
It rotates the forearm inward (pronation). 

The palmaris brevis (?) is a very small muscle, which arises on the tendon 
of the superficial digital flexor for the fifth digit, and is inserted at the fifth meta- 
carpo-phalangeal joint into the sheath and annular ligament of the deep flexor. 

The lumbricales are three very delicate muscles, which arise on the tendons 
of the deep flexor, and are inserted into the first phalanges of the third, fourth, 
and fifth digits. 

The abductor pollicis brevis et opponens poUicis, a 'very small pale muscle, 
arises on the fibrous band which connects the superficial flexor tendon with the 
inner carpal sesamoid, and ends on the cUstal end of the first metacarpal bone and 
the first phalanx of the first digit. It abducts the first digit.^ 

The flexor pollicis brevis arises on the posterior carpal ligament over the second 
metacarpal bone, and ends on the volar sesamoid of the first digit. 

The adductor pollicis, situated externally to the preceding, is the largest of 
the thumb muscles. It arises between the preceding and the second interosseous 
muscle, and is inserted into the first phalanx of the first digit. 

The adductor digit! secundi is situated between the second interosseous 
muscle and the adductor cUgiti quinti. It arises on the carpal ligament, and ends 
on the first phalanx of the second digit. 

The adductor digiti quinti arises close to the preceding muscle, and passes 
outward to end on the first phalanx of the fifth digit. 

The flexor digiti quinti arises on the ligament connecting the accessory carpal 
to the third and fourth metacarpal bones, crosses the corresponding interosseous 
muscle, and ends on the fifth digit with the next muscle. 

The abductor digiti quinti is larger than the two preceding muscles; it arises 
on the accessory carpal bone, and ends on the outer sesamoid of the fifth digit and 
on the lateral ligament. 

There are four interossei which lie on the volar (posterior) surface of the meta- 
carpus. They are well developed and fleshy. They arise on the distal row of the 
carpus and on the proximal ends of the metacarpals. Each divides distally into 
two branches, which are inserted by small tendons on the corresponding sesamoid 
bones, and detach slips to the extensor tendons. 



Muscles of the Neck 

The sterno-cephalicus is well developed. It arises on the manubrium sterni 
and ends on the mastoid process, blending with the cleido-cervicalis. 

The scalenus ventralis (s. primse costse) arises on the last four cervical trans- 
verse processes, and is inserted into the first rib. 

The scalenus dorsalis (s. supracostalis) is large. Anteriorly it blends with the 
preceding muscle, while posteriorly it divides into two parts. The upper part is 
inserted on the third and fourth ribs, the lower part by a long, thin tendon on the 
eighth rib. 

The longus colli resembles that of the horse. 

The rectus capitis anterior major arises on the transverse processes of the second 
to the sixth cervical vortel)np and ends as in the horse. The rectus minor and 
lateralis resoml^le those of the horse. 

The intertransversales resemble those of the ox. 

The splenius is strong and extensive. It arises on the first four or five thoracic 

1 Movements of individual digits are specified with regard to the axis of the manus (hand, 
paw), and not to the median plane of the body. 



MUSCLES OF THE THORAX — MUSCLES OF THE TAIL 325 

spines and the median rajihe of the neck, and is inserted into the occipital crest and 
mastoid process. 

The complexus is composed of two parts — the biventer cervicis and the com- 
plexus major proper. The biventer cervicis arises from the transverse processes 
of the fifth and sixth, and the spines of the second to tlie fifth (or sixth) thoracic 
vertebrae, from the ligament um nuchas, and the median raphe. It has four ten- 
dinous intersections. The complexus major arises on the transverse processes of 
the first three or four thoracic vertebra; and the articular processes of the last five 
cervical. Both end on a strong common tendon which is inserted into the occipital 
crest and the depression below it. 

The trachelo-mastoideus consists of two unequal portions. The large dorsal 
part (M. longissimus capitis) arises on the transverse processes of the first four thor- 
acic and the articular process of the last three or four cervical vertel)ra;, and ends 
with the splenius on the mastoid process of the temporal bone. The small ventral 
part (M. longissimus atlantis) arises on the articular processes of the third, fourth, 
and fifth cervical vertebrae, and ends on the wing of the atlas. 

The other muscles present no striking differential features,but it may be noted 
that distinct interspinales are present. 



Muscles of the Thorax 

There are twelve pairs of levatores costarum. 

The external intercostals do not occuj^y the spaces between the costal carti- 
lages. 

The diaphragm has a small tendinous center. The oesophageal opening is 
between the pillars. The fleshy rim is attached at the costo-chondral junctions 
from the eighth backward, and along the thirteenth rib nearly its entire length. 



MUSCLES OF THE BACK AND LOINS 

The serratus anticus arises from the median raphe of the neck and the first 
six or seven thoracic spines, and is inserted into the second to the ninth ribs. 
It is well developed. The serratus posticus — much weaker — arises on the lumbo- 
dorsal fascia, and is inserted into the last three or four ribs. Thus one or two ribs 
intervene betw^een the two. 

The transversalis costarum (Ilio-costalis) is well developed, and extends from 
the ilium to the sixth, fifth, or fourth cervical vertebra. 

The longissimus resembles that of the other animals, but the spinalis et 
semispinalis separates clearly at the sixth or seventh thoracic vertebra. It is 
inserted into the articular and spinous processes of the last six cervical vertebrae. 
It has no depression in the lumbar region for the gluteus medius. 

The intertransversales are fleshy, as in the ox. 

The interspinales are distinct, especially in the lumbar region. 



Muscles of the Tail 

These present the same general arrangement as in the horse. The sacro- 
coccygei, however, arise on the luml)ar vertel)rie also, and the coccygeus on the 
ischiatic spine. There is found a sacro-coccygeus accessorius, which arises on the 
internal border of the ilium, the edge of the sacrum, and the transverse processes 
of the first coccygeal vertebrae, and is inserted between the superior and lateral 
sacro-coccygei. It is homologous with the intertransversales. 



326 



THE MUSCLES OF THE DOG 



MUSCLES OF THE ABDOMEN 
The abdominal tunic is practically absent. 

The obliquus abdominis externus has an extensive fleshy portion. It arises 
from the last eight or nine ribs and the lumbo-dorsal fascia. 

The obliquus abdominis internus arises from the external angle of the ilium 
and the lumbo-dorsal fascia. The fibers have an almost vertical direction, and 
there is a fleshy attachment to the last rib. 

The rectus abdominis is attached by a long tendon on the first five or six costal 
cartilages, and l)y fleshy fibers on the xiphoid cartilage. It has three to six indis- 
tinct tendinous inscriptions. 

The transversus abdominis presents no special features except that the poste- 
rior part of its aponeurosis 
3 splits into two layers which 

6 h ^ _—]-—■ include the rectus between 

them. 



muscles of the pelvic 
Limb 
The psoas minor arises 
on the last thoracic and first 
four or five lumbar vertebrae, 
and is inserted into the ilio- 
pectineal line. 

The psoas major is 
short, arising from the last 
four lumbar vertebra?. 

The outer head of the 
iliacus is small, while the 
inner head is large and fuses 
with the psoas major. 

The quadratus lumbor- 
um is well developed, and 
extends laterally beyond the 
outer edge of the ilio-psoas. 
It arises from the last four 
ribs and the lumbar transverse processes, and ends on the pelvic surface of the 
wing of the ilium. 

The tensor fasciae latae consists of two parts. The anterior part is long and 
rounded; the posterior is shorter and fan-like. 

The gluteus superficialis is small. It arises on the sacrum, first coccygeal 
vertebra), and sacro-sciatic ligament. It is inserted below and behintl the tro- 
chanter major of the femur, on the outer branch of the linea aspera. 

The gluteus medius has no lumlxir portion. It is inserted into the trochanter 
major l)y a strong tendon. 

The gluteus profundus is broad and fan-shaped. It arises on the superior 
ischiatic spine and on the ilium as far forward as the gluteal line, and is inserted 
into the trochanter major below the medius. 

The pyriformis is not ])lended with the gluteus medius. It arises from the 
border of the sacrum and from the sacro-sciatic ligament, and ends on the tro- 
chanter major. 

The biceps femoris has two heads of origin which soon fuse. The larger head 
arises from the sacro-sciatic ligament and tuber ischii, the smaller one from the tuber 




Fig. 235. — Muscles of Tail, Anus, and Genital Organs of Dog. 
1, Ilium; 2, femur; 3, tuber ischii; 4, sacro-sciatic lig.; 5, sacral 
region; 6, tail; 7, penis; 8, anus; 9, rectum; a, sacro-coccygeus supe- 
rior; b, sacro-coccygeus accessorius; c, coccygeus; d, sacro-coccygeus 
inferior; e, retractor ani; /, /', sphincter ani externus; g, retractor 
penis; h, bulbo-cavernosus; (', transversus perinei (?); k, m, ischio- 
urethrales; /, ischio-cavernosus; n, tendon of obturator internus; o, 
gemellus; p, urethral muscle, (.\fter Ellenberger, in Leisering's Atlas.) 



MUSCLES OF THE PELVIC LIMB 



327 



ischii. The aponeurosis of insertion ends on the patella, the patellar ligament, 
and the tibial crest. There is also a tendinous band, which comes from the deep 
face of the muscle and terminates at the tarsus, as in the horse. 

The abductor cruris posterior may be regarded as an accessory head of the 
biceps femoris. It is a thin, muscular band which arises on the sacro-sciatic 
ligament, passes downward between the biceps and semimembranosus, and ends by 
blending with the former. 

The semitendinosus arises from the tuber ischii only. It ends as in the horse. 



Muscles of 



Pelvic 
View. 




Limb of Dog, Internal 



a, Tlio-psoas; b, tendon of psoas minor; c, sacro-coccy- 
geus ventralis lateralis; d, coccygeus; e, pyrifonnis; /, obtur- 
;itor internus; g, origin of retractor ani; h, h', sartorius; i, rec- 
tus femoris; k, vastus internus; /, pectineus; m, adductor; 
11. gracilis; o, semitendinosus; p, semimembranosus; q, gas- 
trocnemius, inner heail; i/, tendon of gastrocnemius; r, super- 
lioial digital flexor; r', tendon of r; s, tarsal tendon of biceps 
femoris; t, popliteus; u. deep digital flexor, outer head tflexor 
hallucis longus); u', long digital flexor; u'\ common tendon of 
u and u'; v, tendon of tibialis posterior; w, tibialis anterior; 
X, tension of anterior or long digital extensor; I, pelvic sur- 
face of ilium; 2, section of symphysis pelvis; S, tuber ischii; 
4, internal condyle of femur; 5, ligamentum patella; 6. 7, in- 
ternal surface of tibia; S, tarsus; S' , fibular tarsal bone; 9, 
metatarsus. (EUenberger-Baum, Anat. d. Hundes.) 



The semimembranosus is large and arises from the ischium only. It divides 
into two portions: the anterior portion ends on the tendon of the pectineus, on the 
femur above the internal condyle, and on the inner (Vesalian) sesamoid bone; 
the posterior portion ends on the internal condyle of the tibia, the tendon passing 
under the internal lateral ligament of the stifle joint. 

The rectus femoris has only one tendon of origin. The single patellar ligament 
acts as the tendon of insertion of the ciuadriceps. 



328 THE MUSCLES OF THE DOG 

The capsularis is usually present, but is small and pale. 

The sartorius consists of two portions. It arises from the external angle 
and border of the ilium. The anterior portion ends on the patella, the 
posterior on the internal surface of the tibia, its tendon blending with that 
of the gracilis. 

The graciles are not so much fused at their origin as in the other ammals. 

The pectineus is long and slender. It arises from the ilio-pectineal eminence 
and ends on the internal branch of the linea aspera above the distal end of the 
femur. 

There are two distinct adductors. The small anterior one ends on the proximal 
third of the femur, the posterior one on the distal part of the femur and on the 
inner face of the stifle joint. 

The quadratus femoris is short and strong. The other external rotators of 
the thigh present no special features. 

The peroneus tertius is represented by a tendinous Ijand which arises on the 
internal surface of the tibia below the crest. It passes downward on the inner 
surface of the tibialis anterior, blends with the annular ligament above the tarsus, 
and is attached to the joint capsule and the proximal end of the third metatarsal 
bone. 

Arloing and Lesbre say: "The third peroneus is a proper extensor of the fifth digit; it 
is a very feeble, fleshy band, situated ]>ehind the peroneus brevis, which it partially covers. 
It is attached to the upper part of the fibula, and is continued by a long, delicate tendon which 
passes in the same malleolar groove with the muscle mentioned; it then crosses behind the 
tendon of the peroneus longus and extends to the phalanges of the outer digit, where it joins 
one of the branches of the common extensor." 

The tibialis anterior is large and superficial. It arises on the external condyle 
and crest of the tibia, and is inserted into the first metatarsal bone, or into the first 
tarsal and second metatarsal. 

There are four extensors of the digits. 

1. The anterior or long digital extensor (M. extensor digitalis longus) is fusi- 
form, and lies largely under the preceding muscle. It arises from the extensor fossa 
of the femur. The tendon is bound down by two annular ligaments, and divides 
below the tarsus into four branches, which end on the distal phalanges of the digits 
(second to fifth). 

2. The lateral digital extensor (M. extensor digitalis lateralis) is feeble and semi- 
pennate. It arises on the filnila below the head. The tendon passes under the 
lateral ligament of the tarsus and joins the branch of the tendon of the long extensor 
for the fifth digit. 

3. The extensor hallucis longus is a very thin muscle which arises from the 
fibula under the long extensor. Its delicate tendon accompanies that of the tibialis 
anterior to the first metatarsal bone, or l^ecomes lost in the fascia. 

4. The extensor digitalis brevis has three divisions. It arises on the fibular 
tarsal bone ami the adjacent ligaments. The three tendons are inserted into 
the second, third, and fourth digits, blending with the interossei. (Sometimes 
there is fountl a tendon to the rudimentary first digit, which may represent the 
extensor hallucis brevis. There may be a fourth belly for the tendon to the second 
digit.) 

The peroneus longus arises on the external condyle of the tibia, the 
head of the fibula, and the lateral ligament. The long tendon passes down 
the leg parallel to the fibula, crosses the plantar (posterior) surface of the 
tarsus transversely, and ends on the first metatarsal bone. A short l^ranch is 
detached to the ext(>rnal metatarsal bone. 

The peroneus brevis is semipennate and arises from the distal half or more 
of the outer face of the tibia and the fibula. Its tendon accompanies that of 



MUSCLES OF THE PELVIC LIMB 



329 



the lateral extensor over the external malleolus of the tibia, and ends on the 
proximal end of the fifth metatarsal bone. 

The soleus is al)sent. (It is present and large in the cat.) 

The gastrocnemius arises on the rough lines al)Ove the condyles of the femur. 
The heads of origin each contain a bone about the 
size of a pea — the sesamoid of Vesal — which articu- 
lates with the corresponding condyle of the femur. 
The tendon comports itself as in the horse. 

The superficial digital flexor has a large round j^, ' ^^^ 

bell3^ It arises in connnon with the outer head of ^^ 'jt 

the gastrocnemius from the external rough line and 
Vesalian sesamoid bone, and from the aponeurosis K/^ 

of the vastus externus. The tendon winds around m.: if 

that of the gastrocnemius, passes over the tuber p' ■:id, "' 

calcis (where it is arranged as in the horse), and 
divides below the tarsus into two branches. Each 
of these divides into two ])ranches which end as in c- 

the fore limb. The outer and inner branches detach 
slips to the suspensory ligaments of the large digital // 

pad. Muscle-fibers often occur in the tendon in the ,j 7/ 

metatarsal region. ,. 

The deep digital flexor has two heads. The 
large outer head, the flexor hallucis longus, arises 
from the tibia anil fibula, filling the interosseous *^ '^^ 

space. The small inner head, flexor digitalis pedis 9. 
longus, also arises from the tibia and fibula, its tendon V^i^wV '^ 

joining that of the large head below the tarsus. The q..--\t\W»l....J- 

common tendon detaches a branch to the large digital 
pad and terminates as in the fore limb. /- 

The tibialis posterior is a small but distinct ^,^ %\;'U\ 

muscle, which arises on the proximal part of the »'nv\\ h' 

fibula. The thin tendon accompanies that of the lliTOv^ i^' 

flexor longus and ends on the internal lateral liga- W'sk^VHi-^ 

ment of the tarsus. 

The tendon of the popliteus contains a small Cf^} -^ 

sesamoid bone. ^tj^^^^ 

The adductors of the second and fifth digits, the ^^ 

lumbricales, and the interossei are arranged as in the ^^°- 237.— muscles of leg and 

,, . ,. , Foot of Dog, External 

thoracic hmb. View. 

The quadratus plantae arises on the outer surface a. Quadriceps femoris; 6, gas- 

of the distal end of the fibular tarsal bone and on the trocnemius, external head; c, super- 

1,1, ii- , 1 II* 1 ficial digital flexor; d, deep digital 

lateral tarsal ligament, passes downward and inward, ^^^^^. ^ ^^^^^^^^^^ ^^^^^^. ^ ^^^_ 
and terminates on a thin tendon which fuses with don of lateral extensor; 3, peroneus 

that of the deep flexor. brevis; h, long or anterior digital 

rr-ii 1 t ^ 1- •!• • i« • 11 1 extensor; /(', /t", ^"', tendons of pre- 

The abductor dlgltl qUintl is a very small muscle ceding; ,, tibialis anterior; a, exten- 

which consists of two parts. One of these is a ten- .sorbrevis; /.slips from interossei (m); 

dinOUS slip which extends from the posterior surface ^.external condyle of femur; ^, pa- 

. , f ^ r•^ ^ i i tella; 5, tibia: 4, tuber calcis; 5, ff, an- 

Ot the proximal part of the fibular tarsal bone to the nnlar ligaments. (After Ellenberger, 

head of the fifth metatarsal bone; the other part in Leisering-s Atias.) 

arises from the inner surface of the fibular tarsal 

bone (or from the tendinous part) and ends on the first phalanx of the fifth digit. 

In case the skeleton of the first digit is well developed, there are found three 
muscles homologous with those of the same digit in the fore limb. These are the 
abductor hallucis, adductor hallucis, and flexor hallucis brevis. 




THE DIGESTIVE SYSTEM 

This system consists of the organs directly concerned in the reception and 
digestion of the food, its passage through the ))ody, and the expulsion of the un- 
absorbed portion. These organs are conveniently grouped under two heads, 
viz.: (1) the alimentary canal; (2) the accessory organs. 

The alimentary canal (Tractus alimentarius) is a tube, about 100 feet (ca. 
30 m.) in length in the horse, and extends from the lips to the anus. It has a com- 
plete lining of mucous membrane, external to which is an almost continuous muscu- 
lar coat. The abdominal portion of the tube is largely covered with a serous 
membrane — the visceral peritoneum. The canal consists of the following consecu- 
tive segments: 

1. Mouth. 4. Stomach. 

2. Pharynx. 5. Small intestine. 

3. (Esophagus. 6. Large intestine. 

The accessory organs are the teeth, tongue, salivary glands, liver, and pancreas. 



DIGESTIVE SYSTEM OF THE HORSE 

THE MOUTH 
The mouth^ (Cavum oris) is the first part of the alimentary canal. In the 
horse it is a long cylindrical cavity, and when closed, it is almost entirely filled up 
by the contained structures. The entrance to it (Rima oris) is closed by the lips. 
Laterally it is bounded l^y the cheeks; above, by the hard palate; below, by the 
body of the mandible and the mylo-hyoid muscles; behind, by the soft palate. 

The cavity of the mouth is subdivided into tw^o parts by the teeth and alveolar 
processes. The space external to these and inclosed externally by the lips and 
cheeks is termed the vestibule of the mouth (Vestibulum oris). In the resting 
state of the parts the walls of this cavity are in contact, and the space is practically 
obliterated. Its existence becomes very evident in facial paralysis, when the food 
tends to collect in it laterally, pouching out the cheeks. The space within the 
teeth and alveolar processes is termed the mouth cavity proper (Cavum oris pro- 
prium). When the teeth are in contact, it communicates with the vestibule only 
i)y the interdental spaces and the intervals behind the last molar teeth. Poste- 
riorly it communicates with the pharynx through the isthmus of the fauces. 

The mucous membrane lining the mouth (Tunica mucosa oris) is continuous 
at the margin of the lips with the common integument, and behind with the mucous 
hning of the pharynx. During hfe it is chiefly of a pink color. 

The lips (Labia oris) are two musculo-membranous folds which surround the 
orifice of the mouth. Their angles of union (Anguli oris s. commissurse labiorum) 
are situated near the first cheek tooth and are rounded. Each lip presents two 
surfaces and two borders. The outer surface is covered by the skin, which pre- 
sents long tactile hairs in addition to the ordinary fine hair. The upper lip shows 

1 The term "mouth" is conmionly used to signify either the oral cavity (Cavum oris) or the 
entrance to it (Rima oris). 

330 



THE MOUTH 



331 



a shallow median furrow (Philtrum), the lower a rounded prominence, the chin 
(Mentum). The inner or oral surface is covered with mucous membrane which is 




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commonly more or less pigmented. The small papillse on this surface show 
on their summits the openings of the ducts of the labial glands. Small folds of 
mucous membrane which pass from the lip to the gum represent the frsenula labii 



332 DIGESTIVE SYSTEM OF THE HORSE 

(superioris, inferioris). The free border of the Hp is dense and presents short, 
very stiff hairs. The attached border is continuous with the surrounding struc- 
tures, and is adherent to the alveolar borders of the bones of the jaws. 

Structure. — The lips are covered externally Ijy the skin, and are lined by 
mucous membrane; between these are muscular tissue and glands. The skin 
lies directly on the muscles, many fibers of which are inserted into the former. The 
muscles have been described (page 214). The labial glands (Glandulse labiales) 
form a compact mass near the angles; they are numerous in the upper lip, fewer 
in the lower. The mucous membrane is often pigmented, and is reflected upon 
the bones of the jaws to form the gums. 

Blood-vessels and Nerves. — The arteries are derived from the superior and 
inferior labial and palato-labial arteries. The sensory nerves come from the 
trigeminus, and the motor from the facial nerve. 

The cheeks (Buccce) form the sides of the mouth, and are continuous in front 
with the lips. They are attached above and below to the alveolar ])orders of the 
bones of the jaws. 

Structure. — This comprises: (1) The skin; (2) the muscular and glandular 
layer; (3) the mucous membrane. The skin offers nothing in particular to notice. 
The muscular tissue is formed mainly by the buccinator, but also by parts of the 
panniculus, zygomaticus, dilatator naris lateralis, levator nasolabialis, and depressor 
labii inferioris. The buccal glands (Glandulse buccales) are arranged in two rows. 
The upper row (superior buccal or molar glands) is found on the outer surface of 
the buccinator muscle, near its upper border. The anterior part of the row con- 
sists of scattered lobules; the posterior part, which lies under cover of the masseter 
muscle, is more developed and compact. The lower row (inferior buccal or molar 
glands) , less voluminous than the upper, is situated in the submucous tissue at the 
lower border of the buccinator muscle. The mucous membrane is reflected above 
and below upon the gums, and is continuous behind with that of the soft palate. 
It is reddish in color and frequently shows pigmented areas. Opposite the third 
upper cheek tooth is the opening of the parotid (Stenson's) duct, surrounded by a 
circular fold of the mucous membrane. A linear series of small papillse above 
and below indicates the orifices of the small ducts from the buccal glands. 

Blood-vessels and Nerves. — The blood-supply is derived from the facial and 
buccinator arteries. The sensory nerves come from the trigeminus and the motor 
from the facial nerve. 

The gums (Gingivae) are composed of a dense fibrous tissue intimately united 
with the periosteum of the alveolar processes, and blending at the edges of the alveoli 
with the alveolar periosteum, which fixes the teeth in their cavities. They are 
covered by a smooth mucous membrane, destitute of glands, and of a low degree 
of sensibility. 

The hard palate (Palatum durum) is bounded in front and on the sides by 
the alveolar arches; behind it is continuous with the soft palate. Its osseous basis 
is formed by the premaxilla, maxilla, and palate bones. The mucous membrane 
is smooth, and is attached to the bones by a submucosa which contains in its 
anterior part an exceedingly rich venous plexus, constituting an erectile tissue. 
A central raphe (Raphe palati) divides the surface into two equal portions. Each 
of these presents about eighteen transverse curved ridges (Rugse palatini) which 
have their concavity and their free edges directed backward. They are further 
apart and more prominent anteriorly. There are no glands in the submucosa. 

Vessels and Nerves. — Tlie bloo(l-sup]:)ly is derived chiefly from the palatine 
arteries and the nerves from the trigeminus. 

The soft palate (Palatum molle) is a musculo-membranous curtain which 
separates the cavity of the mouth from that of the pharynx. It slojies downward 
and backward from its junction with the hard palate. The oral surface faces 



THE MOUTH 



333 



downward and forward, and is covered with a mucous membrane continuous with 
that of the hard palate. It is corrugated and presents numerous small orifices 
(of gland-ducts) and two sagittal ridges. On each side a short, thick fold passes 
to join the base of the tongue; this is the anterior pillar of the soft palate (Arcus 
glossopalatinus). The pharyngeal surface looks upward and backward and is 
covered by a mucous meml)rane continuous with that of the nasal cavity. The 
free border (Arcus palatinus) is concave and thin; it is in contact (except during 
deglutition) with the epiglottis. It is continuous with a fold of the mucous mem- 
brane, which passes on each side along the lateral 
wall of the pharynx and unites with its fellow 
over the beginning of the a'sophagus; this fold 
is termed the posterior pillar of the soft palate 
(Arcus pharyngopalatinus). The space between 
the diverging anterior and posterior pillars (Sinus 
tonsillaris) is occupied by the faucial tonsil. In 
the horse, however, there is not a compact tonsil, 
as in man, dog, etc., but a somewhat extended 
group of mucous glands and masses of lymphoid 
tissue. These cause elevations of the surface, on 
which are seen numerous depressions (crypts) in 
which the gland-ducts open. The soft palate is 
greatly developed in equidse, its length being five 
to six inches (12 to 15 cm.). Its length and con- 
tact with the epiglottis account for the fact that 
in these animals mouth-breathing does not occur 
under normal conditions, and that in vomiting the 
ejected matter escapes usually tlirough the nasal 
cavity.^ 

Structure. — The soft palate consists of: (1) 
The oral mucous membrane, continuous with that 
of the hard palate; (2) the palatine glands (Glan- 
dulse palatinae), which form a layer al)out half an 
inch in thickness; (3) the aponeurotic and mus- 
cular layer; (4) the pharyngeal mucous mem- 
brane, continuous with that of the nasal cavity. 

The muscles ]:)roper to the soft palate are the 
azygos uvulie, the levator palati, and the tensor 
palati. 

The azygos uvulae (M. palatinus) consists of 
two small muscular bundles which lie together 
at the median line. It is attached through the 
medium of the palatine aponeurosis to the pala- 
tine arch, and terminates near the free edge of 
the soft palate. Its action is to shorten and 
raise the soft palate. 

The levator palati (M. levator veli palatini) arises from the muscular process 
of the petrous temporal bone and from the Eustachian tube, and passes forward 
and downward externally to the latter, to spread out on the pharjmgeal surface 
of the soft palate. It raises the soft palate, thus closing the posterior nares 
during deglutition. 

The tensor palati (M. tensor veli palatini) is larger than the levator, and is 
fusiform and flattened. It arises from the muscular process of the petrous tem- 
poral bone and the Eustachian tube, and passes forward external to the levator. 
^ The epiglottis may be either in front of or behind tlie soft palate; most often it is prevelar. 




Fig. 239. — Hard Palate and Part of 
Soft Palate of Horse. 
/, Raphe palati; ;?,'ridges of palate; 
S, anterior end of soft palate, showing ori- 
fices of ducts of palatine glands. 



334 



DIGESTIVE SYSTEM OF THE HORSE 



Its tendon is then reflected around the hamulus of the pterygoid bone, being held 
in position by a fibrous band and lubricated by a bursa. It turns inward and ex- 
pands in the aponeurosis of the soft palate. It tenses the soft palate. 

Vessels and Nerves. — The blood-supply of the soft palate is derived from the 
internal and external maxillary arteries. The nerves come from the trigeminus, 
vagus, and glosso-pharyngeal nerves. 

The floor of the mouth in its anterior part is free and is formed by the body of 
the mandible, covered by mucous membrane. The remainder is concealed by the 
attached portion of the tongue, with the exception of a narrow space on each side 



Septutn nasi Superior Diaitits 



N aso-lacrimal duct 



Infraorbital nerve 
and vessels 

Levator labii superi- 
oris proprius 



Superior buccal 
nerve 
Facial artery 

Superior buccal 
glands 

Parotid duct 



Labial veins 
Lnferior labial artery 
Mylo-hyoideus 




Superior turbinal 
Common meatus 

Middle meatus 

Inferior turbinal 
Inferior meatus 



'Maxillary sinus 
{anterior end) 

f^ P (dative artery 
Facial artery 

Buccal mucous 
membrane 

Buccinator 



Hypoglossal 
nerve 
Lingual artery 



Inferior buccal nerve 
Branches of lingual nerve 

Submaxillary duct 
Sublingual gland 



Digastricus Suhlingual artery 



Fig. 240. — Cross-skction of Head of Horse just in Front of Faci.\l Crest. 

cavity of inferior turbinal; 3, cavuni oris; 4. 4. genio-glossi; 5, 5, genio-hyoidei; 
', lower fourth cheek tooth. Line to facial artery cros.ses zygomaticus. 



1, Cavity of superior turbinal; 2 
6, hyo-glossus; 7, upper, 



of the latter. About ojiposite the canine tooth on each side is a papilla, the 
caruncula sublingualis, through which the duct of the submaxillary gland opens. 
Just behind these papilla? is a median fold of mucous membrane which passes to the 
under surface of the tongue, constituting the frenum linguae. On either side are 
the sublingual crests, which extend from the frenum to the level of the fourth 
cheek tooth. The crest presents numerous small papilla^, through which open the 
ducts from the subjacent sublingual gland. ^ Behind the last tooth a vertical fold 

' In the undisturbed state of the parts there is no space between the tongue and the rami 
of the lower jaw; consequently the tongue must be drawn aside to see the sublingual crest. 



THE TONGUE 



335 



of the mucous membrane passes from upper to lower jaw. This is termed the pHca 
pterygomandibularis: it contains a ligament of like name. 

The isthmus faucium is the orifice of communication between the mouth and 
the pharynx. It is bounded above by the soft palate, below by the root of the 
tongue, and laterally by the anterior pillars of the soft palate. It is long, relatively 
small, and not very dilatable in the horse, and is closed by the soft palate under 
normal conditions, except dur- 

Trachea 



ing deglutition. 



Thyroid gland' 



Foliate papilla 



Vallate papillce 




Crico-arytenoid- 
eus posterior 

Arytenoideus 

Arytenoid carti- 
lages 

Vocal cord 



Adilus laryngis 
Epiglottis 

Tonsil 

Adenoid tissue of 
root of tongue 

Anterior pillar of 
soft palate (cut) 



Dorsum linguoe 



THE TONGUE 

The tongue (Lingua) is 
situated on the floor of the 
mouth, between the rami of 
the mandible, and is sup- 
ported mainly in a sort of 
sling formed by the mylo- 
hyoid muscles. Its posterior 
portion, the root (Radix 
linguae), is attached to the 
hyoid bone, soft palate, and 
pharynx. Only the upper 
surface of this part is free, 
and slopes downward and 
backward. The middle por- 
tion, the body (Corpus linguae), 
has three free surfaces. The 
upper surface or dorsum (Dor- 
sum linguae) is rounded. The 
lateral surfaces are nearly flat 
for the most part, liut an- 
teriorly become rounded and 
narrower. The lower surface 
is attached to the mandible. 
The apex or tip (Apex linguae) 
is free, spatula-shaped, and 
presents superior and inferior 
surfaces and a rounded border. 

Structure. — The tongue 
consists of: (1) The mucous 
membrane; (2) the glands; 
(3) the muscles. 

The mucous membrane 
(Tunica mucosa linguae) ad- 
heres intimately to the subjacent tissue, except on the lower part of the 
lateral surfaces of the body and the under surface of the tip. It varies 
considerably in thickness. On the dorsum it is very thick and dense. 
Underneath this portion there is a dense fibrous cord, which extends medially 
a distance of five or six inches forward from the vallate papillae. On 
the sides and under surface of the tongue the membrane is much thinner and 
smooth, and can more readily be dissected off the muscular tissue. From 
the under surface of the free part of the tongue a fold of the mucous membrane 
passes to the floor of the mouth, forming the frenum linguae. This contains the 
anterior edges of the genio-glossi muscles. Posteriorly a fold passes on each side 



Apex linguce. 



Fig. 241. — Tongue of Horse, Dorsal Aspect. 



336 



DIGESTIVE SYSTEM OF THE HORSE 



from the edge of the dorsum to join the soft palate, forming the anterior pillars of 
the latter. A central glosso-epiglottic fold (Plica glossoepiglottica) passes from 
the root to the base of the epiglottis. The mucous membrane presents numerous 
papillae, which are of four kinds — filiform, fungiform, vallate, and foliate. The 
filiform papillae (PapilliB filiformes) are fine, pointed ])rojections. They cover the 
upper surface of the l)ody and tip, to which they give a distinct pile. The fungi- 
form papillae (Papilla? fungiformes) are rounded at the free end, which is supported 
by a neck. They occur principally on the lateral part of the tongue, but are also 
found scattered over the dorsum and upper surface of the free portion. The 
vallate papillae (Papillae vallatse) are usually two or three in number. The two 
constant ones have a diameter of about 7 mm., and are found on the posterior part 
of the dorsum, one on each side of the median plane, about an inch (ca. 3 cm.) apart. 




Depressor iabii 
inferioris 



Kcrato-h yoideus 

II yo-pharyngeus 



Thyroid gland 



Trachea 



Fig. 242. — Muscles of Tongue, Hyoid Bone, Pharynx, etc., of Horse. 
T. p.. Tensor palati; L. p., levator palati; Pt. p., pterygo-pharyngeus; P. p., palato-pharyngeus; S. p., 
stylo-pharyngeus; Th. p., thyro-pharyngeus; C. p., crico-pharyngeus; Th. h., thyro-hyoideu.s; Hyo. gl., hyo-glossus; 
G. p. .guttural pouch; F. p., foliate papilla; A. v., facial artery and vein. The concealed parts of the hyoid bone are 
indicated by dotted line. 



The third, when present, is behind these, is centrally situated, and is always smaller. 
Rarely a fourth may be seen. They are rounded, broader at their exposed than 
at their attached surfaces, and are situated in a cup-shaped cavity. The foliate 
papillae (Papilla? foliatce) are situated just in front of the anterior pillars of the soft 
palate, where they form a rounded eminence about an inch (ca. 2 to 3 cm.) in length, 
marked by transverse fissures. The last three varieties are covered with micro- 
scopic secondary papillae and are furnished with taste-buds. The mucous mem- 
brane of the root of the tongue presents numerous folds and depressions. Into 
the latter open the ducts from the lingual glands (Glanduhr linguales), which 
constitute a thick layer in the loose submucous tissue. Mucous glands are found 
also on the dorsum and sides of the tongue. In the submucosa of the root is 
found also a large quantity of lymph follicles (Folliculi tonsillares) and diffuse 
lymphoid tissue. 



THE TONGUE 



337 



The muscular tissue may be divided into intrinsic and extrinsic. The in- 
trinsic musculature consists, not of distinct muscles, but rather of systems of fibers 
which run longitudinally, vertically, and transversely, blending with the extrinsic 
muscles, wliich are now to be described. 

1. Stylo-glossus. — This is a long, thin nuiscle, which lies on the lateral part 




M i< M 



s,:S 



S ^ 'So 



2 a|=< 

. p 03 



« 5 E-, fc, 

z -Q 2 o 



f^ ;S 



o — . 



<0 . — 

2 h 'f . -2 

> ^ '"" ° 

0) o £ ~ 

-..2 o >. 

. •- « J 
a. o _ 

^ =' I - 

•H o ^' .2 

g s u — 

C ~ ■- -c 

03 cj i 0; 

ry s ° 



of the tongue. It arises by a thin tendon from the outer surface of the great 
cornu of the hyoid bone, near the articulation with the small cornu. It terminates 
near the tip of the tongue by blending with its fellow of the opposite side and with 
the intrinsic musculature. The action is to retract the tongue. Unilateral con- 
traction would also draw the tongue toward the side of the muscle acting. 
22 



338 DIGESTIVE SYSTEM OF THE HORSE 

2. Hyo-glossus. — This is a wide, flat muscle, somewhat thicker than the pre- 
ceding. It hes on the lateral part of the root and body of the tongue, partly under 
cover of the preceding muscle. Its deep face is related to the genio-glossus. It 
arises from the lateral aspect of the hyoid bone, from the lingual process to the oral 
extremity of the great cornu, and from the thyroid cornu. The fibers pass oliliquely 
forward and upward, and for the most part turn toward tlie median plane of the 
dorsum of the tongue. Its action is to retract and depress the tongue. 

(It is usually possible to recognize in this muscle three portions, which would 
correspond to the l)aseo-, kerato-, and chondro-glossus of human anatomy.) 

3. Genio-glossus. — This is a fan-shaped muscle, which lies parallel to the me- 
dian plane of the tongue. It is separated from the muscle of the opposite side by a 
quantity of fat and connective tissue. It arises from the inner surface of the ramus 
of the mandible near the symphysis. From the tendon the fibers pass in a radiating 
manner, some toward the tip, others toward the dorsum, and others toward the 
root of the tongue; some fil)ers pass from the posterior end of the tendon to the 
body and small cornu of the hyoid bone. The muscle as a whole is a depressor of 
the tongue, and especially of its middle portion; when both muscles act, a median 
groove is formed on the dorsum. The posterior fibers protrude the tongue, the 
middle fibers depress the tongue, and the anterior fillers retract the tip of the 
tongue. 

Vessels and Nerves. — The arteries of the tongue are the lingual and sub- 
lingual branches of the external maxillary artery. The sensory nerves are the 
lingual and glosso-pharyngeal, and the muscles are innervated by the hypoglossal 
nerve. 

THE TEETH 
The teeth are hard white or yellowish-white structures, implanted in the alveoli 
of the bones of the jaws — premaxilla, maxilla, and mandible. Morphologically 
they are large calcified papillae. Functionally they are organs of prehension 
and mastication, and may serve as weapons of offense and defense. They are 
classified according to form and position as follows: 

1. The incisor teeth (Dentes incisivi) are situated in front and are implanted 
in the premaxilla and mandible. 

2. The canine teeth (Dentes canini) are situated a little further back, at or 
near the premaxillary suture in the upper jaw; in the lower jaw they are nearer 
the incisors. 

3. Thecheekteeth (Dentes premolares et molares), the remaining teeth, occupy 
the sides of the dental arch. The space between the incisors and cheek teeth is 
termed the interdental or interalveolar space. It is customary to divide the cheek 
teeth into an anterior series, termed premolars, which appear as temporary, 
deciduous, or milk teeth, and are replaced l)y permanent successors, and a posterior 
series, the molars, which aj^pear only as permanent teeth without deciduous pre- 
decessors. 

As the teeth of the two sides of the jaws are alike in numljer and character 
(in normal cases), the complete dentition may be briefly indicated V)y a dental 
formula such as the following: 



/ 2 1 2 :3\ 
2 I I - C - P - M - I = 32. 
V 2 1 2 3/ 



In this formula the letters indicate the kinds of teeth, and the figures above and 
below the lines give the number of teeth of one side in the upi^er and lower jaw 
respectively in man. 

The individual teeth of each group are designated numerically, the starting- 
point being the middle line; thus the incisor on either side of the middle line is the 



THE TEETH 339 

first incisor, and may be conveniently indicated by the notation V. The tem- 
l->orary or deciduous teeth may be designated in a similar manner, prefixing D 
(for deciduous) to the letter indicating the kind of tooth. In addition to the alcove 
systematic method of notation other terms have received the sanction of popular 
usage. Thus the first incisors are commonly called "pinchers," or "nippers"; 
the second, intermediate; and the third, corner teeth. The canines, when highly 
developed, may be termed tusks or fangs. The vestigial and inconstant first 
premolar of the horse is popularly termed the "wolf tooth." 

Each tooth presents for description a portion coated with enamel, termed the 
crown (Corona dentis), and a portion covered with cement, termed the root (Radix 
dentis). The line of union of these parts is the neck (Collum dentis).^ In many 
teeth the neck is distinct and is embraced by the gum, e. g., the teeth of the dog 
and the temporary incisors of the horse. In other teeth no constriction is seen, as 
in the permanent incisors of the horse. Between these extremes may be noted 
the molars of the horse, in which the neck is seen only in advanced age. 

The surface of a tooth directed toward the lips is termed labial ; toward the 
cheek, buccal; and toward the tongue, lingual (Facies labialis, buccalis, lingualis). 
The surface opposed to a neighboring tooth of the same dental arch is termed the 
contact surface (Facies contactus). The grinding or masticatory or "table" 
surface (Facies masticatoria) is that which comes in contact with a tooth or teeth 
of the opposite jaw. 

Structure. — Teeth are comjiosed of four tissues, which are considered here 
from within outward. The pulp (Pulpa dentis) is a soft gelatinous tissue, which 
occupies a space in the central part of the tooth termed the pulp cavity (Cavum 
dentis). The pulp is well supplied with blood-vessels and nerves. It occupies 
a relatively large space in young growing teeth, but later the dentine deposited 
on its surface gradually encroaches on it until, in advanced age, the cavity is 
obliterated or much reduced. The dentine (Substantia eburnea) forms the bulk 
of most teeth, covering the surface of the pulp. It is very hard, and is yellowish- 
white in color. The enamel (Substantia adamantina) constitutes a layer of varying 
thickness covering the dentine of the crown of the tooth. It is easily distinguished 
by its clear bluish-white appearance and its extreme density. The cement 
(Substantia ossea) is always the outermost tooth substance. In simple teeth it 
forms usually a thin layer on the surface of the dentine of the root only, but in com- 
plex teeth it exists in considerable quantity, tending to fill in the spaces between the 
enamel folds of the crown also. Its structure is practically the same as that of 
bone without Haversian canals, and even these occur where the cement forms a 
very thick layer. The embedded part of the tooth is attached to the alveolus by 
a vascular layer of connective tissue, the alveolar periosteum (Periosteum alveolare), 
which constitutes the periosteum at once of tooth and alveolus. 

The blood-supply to the pulp is derived from the alveolar or dental branches 
of the internal artery; the nerve-supply comes from branches of the trigeminus. 

1 It will be noted that this definition of crown and root does not agree exactly with the 
popular view that the crown is the free portion and the root the eml)odded portion. The objec- 
tion to the latter statement lies in the fact that it is not capable of general appHcation. Thus 
the morphological crown of the permanent molars in the horse is extremely long, and is, for the 
most part, embedded in tlie l)one in the young animal. The root proper begins to form at four 
or five years of age, and continues its growth for al)out eight years. As the exposed part of the 
crown wears down, the embedded part pushes out of the alveolus, thus preventing deficiency of 
length. On tlie old basis we should liave to say that successive portions of the root become 
crown, while in point of fact it is only in very extreme age that the true root comes into wear. 



340 



DIGESTIVE SYSTEM OF THE HORSE 



The Teeth of the Horse 

The Permanent Teeth 
The formula of the permanent teeth of the horse is: 



(3 1 3or4 3\ 
I - C - P M - ] 
3 13 3/ 



40 or 42 





Fig. 244. — Upper Teeth of Horse, About Four and One-half Fig. 245. — Lower Teeth of Horse, 

Years Old. Four Years of Age. 

/', /-, P, Incisors; C, canine; P', P-, P^, P^, premolars; il/i, .1/^ AP, /', I-, First and second permanent 

molars. incisors; Dfl, third deciduous incisor. The 

cheek teeth are numbered according to 
popular usage. 

In the mare the canines usually are very small and do not erupt, reducing the num- 
ber to 36 or 38.^ 

1 Ellen})erger found, as the result of extensive observations (8000 subjects), that about 
2 to 3 per cent, of mares have erupted canines in l)oth jaws; that 6 to 7 per cent, have them in 
the upper jaw; while 20 to 30 per cent, have them in the lower jaw. 



THE TEETH OF THE HORSE 



341 



Incisor Teeth. — These are twelve in number. The six in each jaw are placed 
close together, so that their labial edges form almost a semicircle. They have the 
peculiarity (not found in existing mammals other than the equidse) of presenting, 
instead of the simple cap of enamel on the crown, a deep invagination, the infundi- 
bulum, which becomes partly filled up with cement. Hence as the tooth wears 
the table surface has a central ring of enamel surrounding this cavity in addition 
to the peripheral enamel. The cavity becomes darkened by deposits from the 
food, and is commonly termed the "cup" or "mark." Each tooth is curved so 
that the labial surface is convex and the roots converge. The average length of 
the incisors at five or six years of age is about two and a half to three inches (ca. 7 
cm.). They taper regularly from crown to root, without any constriction, and 
in such a manner that in young horses the exposed crown is broad transversely ; 
toward the middle, the two diameters of a cross-section are about equal ; near the 
root the antero-posterior diameter is considerably greater than the transverse. 

This fact is of value in the determination of age ])y the teeth, since the table 
surface at different ages represents a series of such cross-sections. As the exposed 





Fig. 246. — Lower Incisor and Canine Teeth of Fig. 247. — Upper Incisor and Canine Teeth of 

Horse, Five Years Old. Horse, Five Years Old. 

/', /', /s. Incisors; (', canine. 



crown wears down the embedded part (reserve crown) pushes up out of the alveolus,, 
so that the tables of the first and second lower incisors are at first oval, with the 
long diameter transverse ; later — at about fourteen years usually for the first lower 
incisors — the tables are triangular, with the base at the labial edge. At the same 
time the infundibulum or cup becomes smaller, approaches the lingual border, and 
finally disappears; it remains longer on the upper incisors, as it is deeper in them. 
Another marked feature in old age is the progressive approach to a horizontal direc- 
tion as seen in profile; at the same time the teeth become parallel and finally con- 
vergent. 

Canine Teeth. — These are four in number in the male; in the mare they are 
usually absent or rudimentary.' They interrupt the interdental space, dividing 
it into two unequal parts. The upper canine is situated at the junction of the pre- 
maxilla and the maxilla; the loWer canine is placed nearer the corner incisor. 
The canines are simple teeth, smaller than the incisors, and are curved with the 
concavity directed backward. The crown is compressetl, convex, and smooth 

1 It is interesting to notice that vestigial canines arc not at all uncommon in mares, espe- 
cially in the lower jaw. They are very small, and do not usually erupt; their presence is indi- 
cated in the latter case by a prominence of the gum. This is in conformity with the fact that 
they were present in both sexes in Eocene and IVIiocene ancestors of existing equidae. 



342 



DIGESTIVE SYSTEM OF THE HORSE 



Infumiibulum 



Cemcn 
Peripheral eti<ui 

Dentine 

Central enamel 

Cement 

Lingual surface 



Cement 



■ Labial surface 



externally; concave with a median ridge internally; its edges are sharp, and the 
apex is jjointed in the unworn tooth. The root is round and the pul]) cavity is 
large, persisting to advanced age. 

Cheek Teeth (Premolars and Molars).'— The constant number of these is 

twenty-four - twelve in each jaw. 
Quite commonly, however, the 
number is increased l)y the pres- 
ence in the upper jaw of the so- 
called wolf-tooth. This tooth is 
usually situated just in front of 
the first well-developed tooth; it 
is a much-reduced vestige, not 
often more than one-half or three- 
fourths of an inch (ca. 1 to 2 cm.) 
in length. (It is interesting as 
being the remnant of a tooth 
which was well developed in the 
Eocene ancestors of the horse.) 
It may erupt during the first six 
months, and is often shed about 
the same time as the milk-tooth 
behind it, but may remain in- 
definitely. The occurrence of a 
similar tooth in the lower jaw — 
which rarely erupts — increases 
the dental formula to 44, which 
is considered the typical number 
for mammals. They may be 
regarded as belonging to the permanent set, having no predecessors. The cheek 
teeth are very large, prismatic in form, and quadrilateral in cross-section, except 
the first and last of the series, which are triangular. The crown is remarkably 
long, most of it being embedded in the bone or situated in the maxillary sinus in 



Pulp-cavity 




Fig. 



248. — Longitudinal Section of Permanent Incisor 
Tooth of Horse, About Natural Size. 



Central 

enamel I nfundihulum 




Canine tooth 




Fig. 249. — Intisor Tooth of Horse, Lingual Aspect. 
(After Ellenberger-Baum, Anat. fiir Kunstler.) 



Fig. 2.50. — Canine and Incisor Teeth of Horse. 

The bone has been removed to show the embed- 
ded iiarts of the teeth. (After Ellenberger-Baum, Anat. 
fiir Ktin.stler.) 



the young horse. As the exposed part wears down the emliedded part pushes up 
to replace it, so that a functional crown of about four-fifths of an inch (ca. 2 cul) 

1 It is common in veterinary works to call all the cheek teeth molars, since, in the horse 
particularly, the premolars are molariform, i. c, do not differ materially from the true molars 
in size or form. The term cheek teeth conveniently includes the premolars and molars. 



THE TEETH OF THE HORSE 



343 



is maintained. The root ])eoins to j>ro\v at four or five years of age, and is com- 
plete at twelve to fourteen, altiiough the deposition of cement may continue 
indefinitely. 

The upper or maxillary teeth are embedded in the alveolar processes of the 




X t 



maxilla. The exposed parts of the crowns are normally in close contact, forming a 
continuous row which is slightly curved, with the convexity toward the cheek. 
The embedded parts diverge in the manner shown in the annexed figures (Figs. 
251, 253). Thus the long axis of the first is directed upward and a little forward, 



344 



DIGESTIVE SYSTEM OF THE HORSE 



that of the second is ahnost vertical, while in the remainder it is curved backward 
in an increasing degree. The average length at six years of age is about three to 
three and a half inches (ca. 7 to 9 cm.). The buccal (or outer) surface presents a 
central ridge running lengthwise, antl se]:)arating two grooves; the first tooth has, in 
addition, a less prominent ridge in front of the primary one. The lingual (or 
inner) surface is marked by a wide, rounded ridge, the accessory pillar or column, 
which separates two very shallow grooves. The masticatory or table surface 
presents two infundibula, an anterior and a posterior. It slopes obliquely down- 
ward and outward, so that the outer edge is prominent and sharp. The first and 
last teeth have three roots, the remainder four or three. 

The position of the embedded crowns and roots of the last four varies at 
different ages and in different subjects. Two factors in this variation may be 
noted. All these teeth are developed in the maxillary sinus close to the orbital 
fossa. As growth proceeds the teeth move forward, so that commonly only the 
last three, but sometimes also the third, remain (except as to their free crowns) 
in the sinus. The second cause of variation is the fact that the anterior limit of 
the maxillary sinus may be at the extremity of the facial ridge, or more than an 
inch beyond it. In the latter case the third tooth projects into the sinus.^ 




A B 

Fig. 252. — Cross-sections of Cheek Teeth of Horse. 
Buccal (outer) surfaces face to left. A, Upper tooth, B, lower tooth; /, anterior, /', posterior infundibulum, both 

almost filled up with cement. 



The structure is quite complex. Two infundibula run vertically through the 
entire lengtli of the crown; these become filled with cement. There are five main 
divisions of the pulp-cavity and five enamel folds, four of which are arranged 
symmetrically, while the fifth is an outgrowth from the inner side of the antero- 
internal fold. On the exposed crown of the unworn tooth the enamel folds form 
rounded ridges covered with a thin layer of cement. After the tooth comes into 
wear the enamel on the masticatory surface stands out in the form of sharp 
prominent ridges. Progressive cementation of the periphery of the tooth takes 
place, thus leveling up the irregularities of surface to a considerable extent. 

The lower or mandibular cheek teeth are implanted in the rami of the mandi- 
ble, forming two straight rows which diverge behind. The space ])etween the rows 
is considerably less than that separating the upper teeth, especially in the middle 
of the series. The length of the lower teeth is about the same as that of the upper 
set. Their direction is also similar, but the embedded portions diverge even more, 
with the exception of the first and second. The long axis of the first is vertical; 
the remainder project downward and backward in a gradually increasing obliquity. 
The buccal (outer) surface has a longitudinal furrow; the last molar has a secon- 

1 The student is advised to amplify these very general statements by the examination of 
heads of subjects of varying ages. It may also be noted that the position of the septum betweert 
the two divisions of the sinus varies much. 



THE TEETH OF THE HORSE 



345 



dary, shallower furrow in addition. The lingual (inner) surface is uneven, but the 
grooves are not regular ; there are usually three on the first and last tooth. The 
masticatory or table surface is oblique, sloping upward and inward in corra- 




ls pi 2 



■^ s 



£3 



a S ^ 



P .^ -©» 



g C5 



^ s 

3 ^ 



S o S- 



^■^ ~ 



spondence with the opposing tooth ; thus the inner edge is prominent. The first 
five have two roots, while the sixth commonly has three. The width of the lower 
molars is a little more than half that of the upper. There are two infundibula, 
which are open along the inner face of the tooth until closed by cement. The 



346 DIGESTIVE SYSTEM OF THE HORSE 

pulp-cavity has two principal divisions, and four or three secondary diverticula. 
The enamel folds correspond, forming a pattern even more complicated than on 
the upper teeth. 

The Temporary Teeth 
The deciduous, temporary, or "milk" teeth (Dentes decidui) are smaller and 
fewer than those of the permanent set. The formula is: 



(3 3\ 
Di - Dc - Dp - J 
3 3/ 



Di - Dc - Dp - J = 24. 
3 3/ 

The deciduous incisors are much smaller than the permanent ones. They 
have a distinct neck at the junction of the crown and root. The crown is short, 
white in color, and its labial surface is smooth. The infundibulum is shallow. 
The root is flattened; it undergoes absorption as the permanent tooth develops 
behind it. 

The deciduous canines are quite vestigial. They occur in both sexes as slender 
spicuhe about a quarter of an inch in length, but do not erupt. The lower one 
develops close to the corner incisor. They are not usually included in the formula, 
as they are never functional. 

The deciduous cheek teeth differ from the permanent set chiefly in that they 
have much shorter crowns than the latter. The roots form early, so that a distinct 
neck occurs. 

The subjoined table indicates the average periods of the eruption of the teeth: 

Teeth Eruption 

A. Deciduous: 

1st incisor (Di 1) Birth or first week. 

2nd " (Di 2) 4-6 weeks. 

3rd " (Di 3) 6-9 months. 

Canine (Dc ) 

1st premolar !Sp S 1 Birth or first 

1"? " :::::::::::::::::::::::::::::(B^4i| '-"-^s. 

B. Permanent: 

1st incisor (I 1) 2J2 vears. 

2nd " (I 2) 33^ years. 

3rd " (I 3) 4y2 years. 

Canine (C ) 4-,5 years. 

1st premolar (or wolf-tooth) (P 1) .5-6 months. 

2nd " (P 2) 214 years. 

3rd " (P 3) 3 years. 

4th " (P 4) 4 years. 

1st molar (M 1) 10-12 months. 

2nd " (M 2) 2 years. 

3rd " (IM 3) 3J2-4 years. 

(The periods given for P 3 and 4 refer to the upper teeth; the lower ones may erupt about six 
months earlier.) 

THE SALIVARY GLANDS 

This term is usually restricted to the three pairs of large glands situated on the 
sides of the face and the adjacent part of the neck^ — the parotid, submaxillary, and 
sublingual. Their ducts open into the mouth. 

The parotid gland (Glandula parotis) (Fig. 172)— ^so named from its proximity 
to the ear — is the largest of the salivary glands in the horse. It is situated chiefly 
in the space between the ramus of the mandible and the wing of the atlas. It is 
somewhat triangular in shape, the apex partially emliracing the base of the external 
ear. Its length is about eight to ten inches (ca. 20 to 25 cm.), and its average thick- 
ness nearly an inch (ca. 2 cm.). Its average weight is about seven ounces (ca. 
200 to 225 g.). 



THE SALIVARY GLANDS 347 

It j^rescnts for description two surfaces, two borders, a base, and an apex. 
The external (or superficial) surface is covered by the parotid fascia, the panniculus, 
and the parotido-auricularis muscle. It is crossed obliquely by the jugular vein, 
which is embedded in the gland tissue to a varying extent. It is also related to 
the great auricular vein, the cervical branch of the facial nerve, and branches of the 
second cervical nerve. The internal (or deep) surface is very uneven, and has nu- 
merous important relations. Some of these are: the guttural pouch, and the great 
cornu of the hyoid bone; the masseter, stylo-maxillaris, tligastricus, and occipito- 
hyoideus muscles; the tendons of the mastoido-humeralis and sterno-cephalicus 
(which se})arate the parotitl from the underlying submaxillary gland) ; the external 
carotid artery and some of its branches; the facial nerve; the pharyngeal 
lymph glands. The anterior (or facial) border is closely attached to the ramus of 
the mandible and the masseter muscle; it overlaps the latter to a varying extent. 
(In some cases there is a well-marked triangular facial process, which covers the 
temporo-mandibular joint, the facial nerve, and the transverse facial vessels.) 
The posterior (or cervical) border is somewhat concave, and is loosely attached to 
the underlying muscles. The base or ventral border is related to the external 
maxillary vein. The apex is attached to the base of the external ear, which it 
partially emliraces. 

The gland has a yellowash-gray color and is distinctly lobulated. It is in- 
closed in a capsule formed by the parotid fascia. The parotid duct (Ductus paro- 
tideus Stenonis) is formed at the lower part of the gland, near the facial edge, by 
the union of three or four radicles. It leaves the gland about an inch (ca. 2 to 3 
cm.) above the external maxillary vein, crosses the tendon of the sterno-cephalicus, 
and gains the inner face of the pterygoideus internus. It then runs forward in the 
submaxillary space below the external maxillary vein and winds around the lower 
border of the mandible behind the vein, passes upward between the vein and the 
masseter muscle for about two inches (ca. 5 cm.), turns forward underneath the 
facial vessels, and perforates the cheek obliquely opposite the third upper cheek 
tooth. Before piercing the cheek it is somewhat dilated, but its termination is 
small, and is surrounded by a circular mucous fold (Papilla salivalis). 

Blood-supply. — Branches of the carotid and maxillary arteries. 

Nerve-supply. — Trigeminal, facial, and sympathetic nerves. 

The submaxillary gland (Glandula submaxillaris) is much smaller than the 
parotid. It is long, narrow, and curved, the dorsal edge being concave. It 
extends from the fossa below the wing of the atlas to the body of the hyoid bone, 
so that it is covered partly by the jiarotid gland, partly by the lower jaw. Its 
length is about eight to ten inches (ca. 20 to 25 cm.), its width an inch to an inch 
and a half (ca. 2.5 to 3 cm.), and its thickness about half an inch (ca. 1 cm.). It 
weighs about one and a half to two ounces (ca. 45 to 60 g.). It is often divisible 
into two parts. 

It presents for description two surfaces, two borders, and two extremities. 
The external surface is covered by the parotid gland, the stylo-maxillaris, digas- 
tricus, and pterygoideus internus muscles. The tendon of the sterno-cephalicus 
crosses this surface, and is a useful guide in separating the parotid gland from it. 
The internal surface is related chiefly to the flexor muscles of the head; the gut- 
tural pouch; the larynx; the division of the carotid artery; and the tenth, eleventh, 
and sympathetic nerves. The superior border is concave and thin. It is related 
to the guttural pouch and the duct of the gland. The inferior border is convex 
and thicker. It is related to the thyroid gland and the external maxillary vein. 
The posterior extremity is loosely attached in the fossa atlantis. The anterior 
extremity lies at the side of the root of the tongue, and is crossed externalh' by 
the external maxillary artery. 



348 DIGESTIVE SYSTEM OF THE HORSE 

The submaxillary duct (Ductus su])niaxillaris Whartoni) is formed by the union 
of small ratlic'les which emerge along the concave edge. It runs forward along this 
border, and, after leaving the anterior extremity, crosses the intermediate tendon 
of the digastricus, passes between the hyo-glossus and mylo-hyoideus, and 
gains the inner surface of the sublingual gland. Its terminal part lies on 
the body of the mandible, under the mucous membrane, which it pierces 
opposite the canine tooth. The orifice is at the end of a flattened papilla 
(Caruncula sublingualis) . 

Blood-supply. — Occipital, external carotid, and external maxillary arteries. 

Nerve-supply. — Chorda tympani and sympathetic nerves. 

The sublingual gland (Glandula sublingualis) is situated beneath the mucous 
membrane of the mouth, between the body of the tongue and the ramus of the 
mandible. It extends from the symphysis to the third or fourth lower cheek tooth. 
Its length is about five or six inches (ca. 12 to 15 cm.) and its weight about half an 
ounce (ca. 15 to 16 g.). 

It is flattened laterally, and has a thin upper border which causes an elevation 
of the mucous membrane of the floor of the mouth, termed the sublingual crest 
(Plica sublingualis). The external surface is related to the mylo-hyoideus muscle, 
and the internal surface to the genio-glossus and stylo-glossus, the submaxillary 
duct, and branches of the lingual nerve. The inferior border is related to the genio- 
hyoid muscle. 

The sublingual ducts (Ductus sublinguales minores), alwut thirty in number, 
are small, short, and twisted; they open on small papillae on the suljlingual crest. 

Blood-supply. — Sublingual artery. 

Nerve-supply. — Trigeminal and sympathetic nerves. 



THE PHARYNX 

The pharynx is a musculo-membranous sac which l^elongs to the digestive and 
respiratory tracts in common. It is funnel-shaped, the base joining the mouth 
and nasal cavity, while the apex is continued Ijy the oeso]:)hagus. Its long axis 
is directed obliquely downward and backward, and has a length of about six inches 
(ca. 15 cm.). 

The pharynx is attached by its muscles to the palate, pterygoid, and hyoid 
bones, and to the cricoid and thyroid cartilages of the larynx. 

Its principal relations are: dorsally, the hsise of the cranium and the guttural 
pouches; ventrally, the larynx; laterally, the internal pterygoid muscle, the great 
cornu of the hyoid bone, the internal and external maxillary arteries, the glosso- 
pharyngeal, superior laryngeal, and hypoglossal nerves, the submaxillary salivary 
gland, and the pharyngeal lymph glands. 

It presents seven openings. The posterior nares (Choanae) communicate 
dorsally with the nasal chaml^ers. The pharyngeal orifices (Ostia pharyngea) of 
the two Eustachian tubes are situated on the lateral wall behind the nares and a little 
below the level of the inferior nasal meatus. They are slit-like openings, slightly 
oblique downward and backward, and are a little more than an inch (ca. 3 cm.) in 
length. They are bounded internally by a valvular flap formed by the expanded 
extremity of the cartilaginous Eustachian tul^e. The isthmus faucium is situated 
below and in front. It is closed by the soft palate except during swallowing. The 
laryngeal orifice (Aditus laryngis) occupies the greatcM- part of the ventral wall or 
floor of the ])harynx. Behind this is the oesophageal opening. 

The wall of the pharynx comprises from without inward: the muscles, the 
pharyngeal aponeurosis, and the mucous membrane. 

The muscles (Figs. 243, 244) are covered by the pharyngeal fascia, which is. 



THE PHARYNX 



349 



attached to the base of the skull, the great cornu of the hyoid bone, and the 
thyroid cartilage of the larynx. They are as follows: 

1. The stylo-pharyngeus arises from the inner surface of the dorsal third of the 
great cornu of the hyoid bone, passes downward and inward, and enters the wall of 
the pharynx by passing between the pterygo-pharyngcnis and palato-pharyngeus. 
Its fibers radiate, many passing forward, others inward beneath the hyo-pharyngeus. 
It raises and dilates the pharynx to receive the bolus in swallowing. 




;^3 






.-:.\^°- 



Septum 
nasi 







jMcerebellum 

31 30^ 



/^ons Medulla *' 







Fig. 254 — Posterior Part of a Sagittal Section of Hf.ad of Horse, Cut about 1 cm. to the Left of the 

Median Plank. 
/, Posterior nares; 2, pharyngeal orifice of Eustachian tube; 3, aditus laryngis; 4, entrance to cesophagus; 
5, posterior pillar of soft palate; 5', junction of -5 with its fellow over entrance to oesophagus; 6, epiglottis; ~, body 
of thyroid cartilage; (?, arytenoid cartilage; 9, 5, cricoid cartilage; 10, true vocal cord; 11, false vocal cord; 12, 
lateral ventricle of larynx; i5, crico-arytenoideus post. s. dorsalis; 74, oesophagus; /a, external carotid artery; 16, 
hypoglossal nerve; 17, glosso-pharyngeal nerve; 18, great cornu of hyoid bone; 19, Eustachian tube; 20, body of 
hyoid bone; 21, hyoideus transversus; 22, ridges of hard palate; 22', soft palate; 23, septum between frontal 
sinuses; 24, olfactory mucous membrane; 25, sphenoidal sinus; 26, basilar part of occipital bone; 26' . supra- 
occipital; ;27', body of si)henoid hone; .?i', pituitary body; ^S, chiasma opticum; ^0, corpora quadrigemiiia; 31, 
thalamus; 3.2, arachnoid; 33, odontoid ligament; 34, posterior auricular muscles. 



2. The palato-pharyngeus arises by means of the aponeurosis of the soft 
palate from the palate and pt(>rygoid bones. Its fibers pass backward on the lateral 
wall of the pharynx, and are inserted in part into the upper edge of the thyroid 
cartilage, in part turn inward to end at the median fibrous raphe. Its action is to 
shorten the pharynx, and to draw the larynx and oesophagus toward the root of the 
tongue in swallowing. 

3. The pterygo-pharyngeus is flat and triangular. It lies on the anterior part 
of the lateral wall of the pharynx. It arises from the pterygoid bone above the 



350 DIGESTIVE SYSTEM OF THE HORSE 

preceding muscle — from which it is not distinctly separated — crosses the levator 
palati, and is inserted into the median raphe. Its action is similar to the preceding. 

4. The hyo-pharyngeus may consist of two portions: 

(a) The kerato-pharyngeus is a small and inconstant muscle which arises 
from the inner surface of the great cornu of the hyoid bone near its lower end. 
It passes upward and backward, turns inward toward the raphe, and spreads out 
under the next muscle. 

(6) The chondro-pharyngeus, broad and fleshy, arises from the thyroid cornu 
of the hyoid ])one and by a thin fasciculus from the wing of the thyroid cartilage and 
ends at the median raphe. 

5. The thyro-pharyngeus arises from the lateral surface of the wing of the 
thyroid cartilage. Its fibers pass forward and inward to the median raphe. 

6. The crico-pharyngeus arises from the cricoid cartilage and ends at the 
raphe. The fibers are directed upward, forward, and inward; they blend behind 
with the longitudinal fibers of the oesophagus. 

The last three muscles are constrictors of the pharynx. 

The pharyngeal aponeurosis is attached to the base of the cranium. It is 
well develoi)ed on the inner face of the palato-pharyngeus muscle and forms a 
median raphe (Raphe pharyngis) dorsally, which is wide in its posterior part. 

The mucous membrane of the pharynx is continuous with that of the several 
cavities which open into it. It is thin and closely adherent to the base of the skull 
in the vicinity of the posterior nares, where the muscular wall is absent. Behind 
the Eustachian openings is a median cul-de-sac, the pharyngeal recess. The recess 
is somewhat variable, but is usually about an inch in depth and will admit the end 
of the finger. In the ass and mule it is much deeper. Here also the muscular 
wall is absent and the mucous membrane lies against the guttural pouches. From 
the Eustachian opening a fold of the mucous membrane (Plica salpingo-pharyngea) 
passes toward but does not reach the laryngeal opening. Below, a horizontal fold, 
the posterior pillar of the soft palate (Arcus pharyngo-palatinus), passes along the 
lateral wall and unites with its fellow over the entrance to the oesophagus. The 
upper part of the cavity (the naso-pharynx) is lined with a ciliated epithelium, 
while the lower part (oro-pharynx) has a stratified squamous epithelium. The 
communication between the two is oval and is l)Ounded liy the free edge of the soft 
palate and its posterior pillars; it is termed the pharyngeal isthmus. On either side 
of the laryngeal opening is a narrow deep depression, the pyriform sinus (Recessus 
piriformis) . 

The sul)mucous tissue contains numerous mucous glands (Glanduhp pharyn- 
gese). In the young subject the lymph follicles are numerous and form a collection 
dorsally and between the Eustachian openings, known as the pharyngeal tonsil. 

Blood-supply. — External carotid, external maxillary, and thyro-laryngeal 
arteries. 

Nerve-supply. — Glosso-pharyngeal, vagus, and sympathetic nerves. 



THE (ESOPHAGUS 
The oesophagus is a musculo-memliranous tube, a])Out 50 to 60 inches (ca. 
125 to 150 cm.) in length, which extends from the pharynx to the stomach. It 
begins in the median plane above the cricoid cartilage of the larynx. In its course 
it shows several changes of direction. At the level of the fourth cervical vertebra 
it inclines to the left side of the trachea, and continues this relation to the level of 
the third thoracic vertebra. Here it again gains the dorsal surface of the trachea, 
and passing backward, crosses the left bronchus, being here almost in the median 
plane. It continues in the mediastinum between the lungs backward, upward, 
and a little to the left, to reach the hiatus ocsophagcus of the diaphragm. Passing 



THE CESOPHAGUS 



351 



through this it terminates at once at the cardiac orifice of the stomach, at the level 
of the fourteenth thoracic vertel)ra, a little to the left of the median plane, and 
about four or five inches (ca. 10 to 12 cm.) ventral to the vertebral colunni. 

Viewed with reference to the frontal plane, its course^ is downward and back 
ward till it enters the thorax and passes upward to gain the dorsal face of the trachea. 
For a short distance (i. e., to the root of the lung) its direction is almost horizontal; 



Tetu jHirtd wii-sclc 



Nerves III, 
IV, VI, and 

opJiUiulmic 

Itdcrnnl tnaxil- 

larij artery 

Transverse 
facial nerve 
Buccinator 
nerve 
Inferior maxil- 
lary nerve 
Inferior al- 
veolar artery 

Great cornu of 
hyoid hone 

Lingual branch 
of IX nerve 

External max- 
illary artery 

Hypoglossal 

nerve 

Masseteric 

vessels 



Thyroid cornu of 
hyoid bone 




Parotid duct 



Lytnj>h gland. 



Coronoid process 



Transverse fa- 
cial vessels 
Transverse fa- 
cial nerve 
External ptery- 
goid muscle 

Internal max- 
illary vein 
Internal ptery- 
goid muscle 
Ratnus of 
mandibh' 
Hyo-pharyn- 
geus muscle 
Istltmus fau- 
cium 
Tonsil 
Digast7-icus 
{intermed. ten- 
don) 

Anterior end of 
submaxillary 
gland 

Lingual vein 

External max- 
illary vein 



Fig. 255. — Cross-section of Head of Horse. 
The .section passes through the temporo-mandibular articulation, but is slightly obliciue. 1, Corpu.s cal- 
losum; ^, lateral ventricle of brain; oJ, caudate nucleus; >^, internal capsule; 5, lenticular nucleus; 6, optic ehiasnia; 
7, middle cerebral artery; 8, .sphenoidal sinuses; 9, cavernous sinus; 10, Eustachian tube, inner lamina; //, 11, 
guttural pouches; 12, soft palate; 13, epiglottis; 14, hyo-epiglottic muscle; lo, thyro-hyoid muscle. 



behind this it passes somewhat upward to its termination. The cervical part of 
the tube is about four to six inches (10 to 15 cm.) longer than the thoracic part, 
while the so-called abdominal part is about an inch (2 to 3 cm.) long.^ 

^ Careful observations (especially on frozen sulijects and those in which the ors;ans have been 
hardened in situ) show that there is no abdominal part of the a'sophagiis in the strict sense of the 
term. The stomach here lies directly on the diaphragm, so that the last inch or so of the oesopha- 
gus is placed obliquely in the hiatus cesophageus, and is partly covered by the pleura, l)Ut not by 
peritoneum. In soft subjects the weight of the stomach, or traction on it, draws part of the 
oesophagus into the abdomen, inclosed in a collar of peritoneum. 



352 DIGESTIVE SYSTEM OF THE HORSE 

The principal relations of the oesophagus at its origin are: to the cricoid 
cartilage below; to the guttural pouches and the ventral straight muscles above; 
and to the carotid arteries laterally. In the middle of the neck the relations are: 
to the leftlongus colli muscle above; to the trachea internally; to the left carotid 
artery, vagus, sympathetic, and recurrent nerves externally. At its entrance 
into the thorax it has the trachea on its inner side; the first rib, the roots of the 
brachial plexus of nerves and the inferior cervical ganglion externally. After 
gaining the upper surface of the trachea, it has the aorta on its left and the vena 
azygos and right vagus nerve on its right side. In its course through the posterior 
mediastinum the oesophageal trunks of the vagus nerves lie above and below it, 
and the oesophageal artery is dorsal to it. 

Structure. — The wall is composed of four coats: (1) A fibrous sheath; (2) the 
muscular coat; (3) a submucous layer; (4) the mucous membrane. The muscular 
coat is of the striped variety as far as the l)ase of the heart, where it rapidly changes 
to the unstriped type. In addition to this change, the muscular coat becomes 
much thicker and firmer, while the lumen is diminished.^ The outer fibers are 
arranged longitudinally, beginning in two bundles attached in the interval be- 
tween the arytenoid and cricoid cartilages. The inner fibers run in two spiral 
strata to the terminal part of the tube, where the arrangement is an outer longi- 
tudinal and an inner circular layer.^ The mucous membrane is pale, and is covered 
with squamous stratified epithelium. It is loosely attached to the muscular coat 
by an abundant sul)mucosa, and lies in longitudinal folds which oliliterate the lumen 
except during deglutition. 

Blood-supply. — Carotid, broncho-oesophageal, and gastric arteries. 

Nerve-supply. — Vagus, glosso-pharyngeal, and sympathetic nerves. 



THE ABDOMINAL CAVITY 

The abdominal cavity (Cavum abdominis) is the largest of the body cavities. 
It is separated from the thoracic cavity by the diaphragm and is continuous behind 
with the pelvic cavity. 

It is ovoid in form but somewhat compressed laterally. Its long axis extends 
obliquely from the center of the pelvic inlet to the sternal part of the diaphragm. 
Its dorso-ventral diameter is greatest at the first lumbar vertebra, while its greatest 
transverse diameter is a little nearer the pelvis. 

The dorsal wall or roof is formed l^y the lumbar vertebrae, the luml)ar muscles, 
and the lumbar part of the diaphragm. 

The lateral walls are formed by the oblique and transverse abdominal muscles, 
the abdominal tunic, the anterior parts of the ilia, the cartilages of the asternal 
ribs, and the parts of the posterior ribs which are below the attachment of the dia- 
phragm. 

The ventral wall or floor consists of the two recti, the aponeuroses of the oblique 
and transverse muscles, the abdominal tunic, and the xiphoid cartilage. 

The anterior wall is formed by the diaphragm, which is very deeply concave, 
thus greatly increasing the size of the abdomen at the expense of the thorax. 

It should be noted that tlie cHaphragm also concurs practically in the formation of a con- 
siderable part of the lateral walls, since its costal portion even during ordinary- inspiration lies 
directly on the ribs over a width of four or five inches (ca. 10 to 12 cm.); in expiration this area 

' The potential lumen is difficult to determine at all accurately. When distended, its diam- 
eter (according to Rubeli) i^aries from 5.7 cm. at its origin to 4 cm. at its cardiac end. The 
thickness of the wall varies (inversely as the lumen) from 4 mm. to 1.2 cm. or more. 

- At the origin of the tube muscular l)undles arise on the raphe pharyngis and blend with the 
crico-pharyngeus. \'(>ntrally fil)ers come from the depression between the cricoid and arytenoid 
cartilages. Bundles of striped fibers may be continued in the superficial part of the muscular 
coat as far as the cardia. 



THE PERITONEUM 353 

of contact would be about twice as wide, including about all of the fleshy rim. This fact is of 
clinical importance, with reference to auscultation and percussion, and penetrating wounds. 
The cupola of the diaphragm extends as far forward as a plane through the sixth intercostal 
space to the right of the heart. 

There is no wall between the abdominal and pelvic cavities. The line of de- 
marcation here is the terminal line (Linea terminalis) or brim of the pelvis; it is 
formed by the base of the sacriiin, the ilio-pectineal lines, and the anterior borders 
of the pubic bones. 

The muscular walls are lined by a layer of fascia, tlistinguished in different 
parts as: (1) the diaphragmatic fascia; (2) the transversalis fascia; (3) the iliac 
fascia; (4) the deep layer of the hmibo-dorsal fascia. 

The subperitoneal or extraperitoneal connective tissue (Tela subserosa) unites 
the fascia and peritoneum. It is composed of areolar tissue, more or less loaded 
with fat according to the condition of the subject, except over the diaphragm. It 
sends laminae into the various peritoneal folds. 

The peritoneum, the serous membrane which lines the cavity, will be described 
later. 

The abdominal walls are pierced in the adult by five apertures. These are: 
the three openings in the diaphragm which transmit the aorta, posterior vena cava, 
and the oesophagus; the inguinal canals, w^hich contain the spermatic cord or the 
round ligament (in female carnivora). In the fa'tus there is the umbilical opening 
also. 

The cavity contains the greater part of the digestive and urinary organs, part 
of the internal generative organs, numerous nerves, blood-vessels, lymph vessels and 
glands, ductless glands (spleen and adrenal bodies), and certain foetal remains. 

For topographic purposes the abdomen is divided into nine regions by imagin- 
ary planes.^ Two of these planes are sagittal, and two are transverse. The 
sagittal planes cut the middles of the inguinal (Poupart's) ligaments; the transverse 
planes pass through the last thoracic and fifth lumbar vertebrae, or the lower end 
of the fifteenth rib and the external angle of the ilium respectively. The transverse 
j)lanes divide the abdomen into three zones, one behind the other, viz., epigastric, 
mesogastric, and hypogastric: these are subdivided by the sagittal planes as in- 
dicated in the subjoined table. 

Left parachondriac Xiphoid Right parachondriac 

Left lumbar Umbilical Right luml)ar 

Left iliac Prepubic Right iliac. 

Other useful regional terms are: sublumbar, diaphragmatic, inguinal. The 
first two require no explanation. The inguinal regions (right and left) lie in front 
of the inguinal (Poupart's) ligament. The flank is that part of the lateral wall 
which is formed only of soft structures. The depression on its upper part is termed 
the paralumbar fossa. 

THE PERITONEUM" 

The peritoneum is the thin serous membrane which lines the abdominal and 
(in part) the pelvic cavity, and covers to a greater or less extent the viscera con- 
tained therein. In the male it is a completely closed sac, but in the female there 
are two small openings in it ; these are the abdominal orifices of the Fallopian tubes, 
which at their other ends communicate with the uterus, and so indirectly with the 
exterior. The peritoneal cavity is only a potential one, since its opposing walls 

' This method of division, although long in use, is of very little value for accurate descrip- 
tion. It is mentioned here chiefly because agreement on a more useful topographic method has 
not been arrived at. 

" Only a general account of the arrangement of the peritoneum is given in this section, since 
a detailed description cannot be understood wthout a knowledge of the viscera concerned. 
23 



354 DIGESTIVE SYSTEM OF THE HORSE 

are normally separated only l^y the thin film of serous fluid (secreted by the mem- 
brane) which acts as a lubricant. 

The free surface of the membrane has a glistening appearance and is very 
smooth. This is due to the fact that this surface is formed by a layer of flat en- 
dothelial cells, and is moistened by the peritoneal fluid. Friction is thus reduced 
to a minimum during the movements of the viscera. The outer surface of the peri- 
toneum is related to the subperitoneal tissue, which attaches it to the abdominal 
wall or the viscera. 

In order to understand the general disposition of the peritoneum, we may 
imagine the abdominal cavity to be empty and lined by a simple layer of perito- 
neum, termed the parietal layer (Lamina parietalis). We may regard the organs as 
beginning to develoj) in the subperitoneal tissue, enlarging, and migrating into the 
cavity to a varying extent. In doing so they carry the peritoneum before them, 
producing introversion of the simple sac, and forming folds which connect them 
with the wall or with each other. The viscera thus receive a more or less complete 
covering of peritoneum, termed the visceral layer (Lamina visceralis). The con- 
necting folds are termed omenta, mesenteries, ligaments, etc. They contain a 
varying quantity of connective tissue, fat and lymph glands, and furnish a path for 
the vessels and nerves of the viscera. Some contain unstriped muscular tissue. An 
omentum is a fold which passes from the stomach to other viscera. There are three 
of these, namely: (1) the small or gastro-hepatic omentum (Omentum minus), which 
passes from the lesser curvature of the stomach to the liver; (2) the gastro-splenic 
omentum (Ligamentum gastrolienale), which extends from the greater curvature 
of the stomach to the spleen; (3) the great omentum (Omentum majus), which 
passes from the greater curvature of the stomach and from the spleen to the terminal 
part of the great colon and the origin of the small colon. It does not pass directly 
from one organ to the other, ])ut forms an extensive loose sac (Figs. 278, 279). 
A mesentery (Mesenterium) is a fold which attaches the intestine to the dorsal 
wall of the abdomen. There are two mesenteries, namely: (1) the great mesentery 
which connects the greater part of the small intestine with the dorsal abdominal 
wall; (2) the colic mesentery, which attaches the small colon to the dorsal abdom- 
inal wall. Ligaments are folds which pass between viscera other than parts of the 
digestive tube, or connect them with the abdominal wall. The term is also applied 
to folds which attach parts of the digestive tract to the abdominal wall, but do not 
contain their blood-vessels and nerves. In some cases (e. g., the lateral and cor- 
onary ligaments of the liver) they are strengthened by fibrous tissue; in other cases 
(e. g., the broad ligaments of the uterus) they contain also unstriped muscular tissue. 

THE PELVIC CAVITY 

The pelvis is the posterior part of the trunk. It incloses the pelvic cavity 
(Cavum pelvis), which communicates in front with the abdominal cavity, the line 
of demarcation being the pelvic brim or terminal line. 

The dorsal wall or roof is formed by the sacrum and first three coccygeal 
vertebrae. The lateral walls are formed l)y the parts of the ilia behind the ilio- 
pectineal lines and the sacro-sciatic ligaments. The ventral wall or floor is formed 
by the pubic and ischial bones. The boundary of the outlet is formed by the third 
coccygeal vertebra dorsally, the ischial arch ventrally, and the posterior edges of 
the sacro-sciatic ligaments and the semimembranosus muscles laterally. The out- 
let is closed by the perineal fascia; this consists of superficial and deep layers, 
which are attached around the margin of the outlet and centrally to the organs at 
the outlet — the anus and its muscles, the vulva (in the female), and the root of the 
penis (in the male). 

The cavity contains the rectum, parts of the internal generative and urinary 



THE PELVIC CAVITY 



355 



organs, some foetal remnants, muscles, vessels, and nerves 
the fascia pelvis, and in part by the peri- 
toneum. 

The pelvic peritoneum is continuous in 
front with that of the abdomen. It lines 
the cavity as far back as the third or fourth 
sacral vertebra in the horse, where it is re- 
flected on to the viscera, and from one organ 
to another. We may therefore distinguish 
an anterior, peritoneal, and a posterior, re- 
troperitoneal part of the cavity. Along the 
mid-dorsal line it forms a continuation of 
the colic mesentery, the mesorectum, which 
attaches the first or peritoneal part of the 
rectum to the roof. In animals in fair con- 
dition a considerable quantity of subperi- 
toneal and retroperitoneal fat is found on 
the walls and in the various interstices. 

In the male the genei'al disposition of 
the peritoneum here is as follows. If 
traced along the dorsal wall, it is re- 
flected at the third or fourth sacral verte- 
bra on to the rectum, forming the visceral 
peritoneum for the first part of that tube. 
Laterally it is reflected in a similar fashion. 



It is lined by 




Fig. 250. — Diagram of Sagittal Section of 
Male Pelvis to show Disposition op 
Peritoneum. 

a. Pouch between rectum and roof of cavity, 
continuous laterally with b, recto-genital jjouch; 
c, vesico-genital pouch; d, pouch below bladder 
and its lateral ligaments. The lateral line of re- 
flection of the peritoneum is doited. The area 
of rectum covered by peritoneum varies widely. 
When the rectum is empty, the reflection dorsally 
may be at the posterior end of the sacrum; when 
the rectum is very full, the reflection may occur a 
short distance behind the promontory. 



If the rectum be raised, it will be seen 





Fig. 257. — Schematic Cross-sections to show Arr.angement of Pelvic Peritoneum of Horse: A, in Male; 

B, in Female. 
A: a, b, Recto-genital pouch; c, c, vesico-genital pouch; d, d, pouch below bladder and its lateral ligaments; 
1, mesorectum; 2, 2, urogenital fold; 3, 3, lateral, Jt, median ligaments of bladder; v. d., vas deferens; u m., uterus 
masculinus. B: a, b, recto-genital pouch; c, c, vesico-genital pouch; d, d, pouch below bladder and its lateral 
ligaments; 1, mesorectum; 2, 2, broad ligaments of uterus; 3, 3, lateral, 4. median ligaments of bladder. 



that the peritoneinn passes from its ventral surface and forms a transverse fold 
which lies on the dorsal surface of the bladder (Fig. 272). This is the urogenital 



356 



DIGESTIVE SYSTEM OF THE HORSE 



fold (Plica urogenitalis). Its concave free edge passes on either side into the in- 
guinal canal. The ventral layer of this fold is reflected on to the dorsal surface 
of the bladder near its neck. Thus there is formed a pouch between the rectum 
and bladder — the recto-vesical pouch (Excavatio recto-vesicalis), which is partially 
subdivided by the urogenital fokl into recto-genital and vesico-genital cavities. 
The fold contains the vasa deferentia, part of the vesiculae seminales, and the 
uterus masculinus (a fcetal remnant). The space on either side of the rectum is 
occupied by coils of the small colon and the pelvic flexure of the great colon usually. 
If the bladder is now raised, it is seen that the peritoneum passes from its ventral 
surface on to the pelvic floor, forming a median fold, the so-called middle ligament 
(Plica umbilicalis media). It also forms on each side a lateral fold, the lateral 

Saccus areas {left rrh-nnilif) 



O 



Area of attachment to dia- 
phragm (non-peritoneal) 



Bile-duct 




^\ 



:3\ 






<h 



Fin. 2.58. — Stomach op Horse, P.\rietal Surface, with First Part of Duodenum. 
Fixed in situ when full but not distended. The larger branches of the anterior gastric artery with two satellite 

veins are shown. 



ligament (Plica umbilicalis lateralis), which contains in its edge the so-called round 
ligament (Ligamentum teres) — the partially occluded umbilical artery, which is a 
large vessel in the foetus. 

In the female the arrangement is modified by the presence of the uterus; 
the urogenital fold is very large, so as to inclose the uterus and a small part of the 
vagina. It forms two extensive folds, the broad ligaments of the uterus (Liga- 
menta lata uteri), which attach that organ to the sides of the pelvic cavity and the 
lumbar part of the abdominal wall (Fig. 271). It thus divides the recto-vesical 
pouch completely into dorsal and ventral compartments — the recto-genital pouch 
(Excavatio recto-uterina), and the vesico-genital pouch (Excavatio vesico-uterina). 

Further details will be given in the description of the pelvic viscera. 



THE STOMACH 



357 



THE STOMACH 

The stomach (Ventricuhis) is the large dilatation of the alimentary canal be- 
tween the oesophagus and the small intestine. It is a sharply curved, U-shaped 
sac, the right branch being, however, much shorter than the left one. The con- 
vexity is directed ventrally. When moderately distended, there is often a slight 
constriction which indicates the division into right and left sacs. It is relatively 
small, and is situated in the dorsal part of the abdominal cavity behind the dia- 
phragm and liver, mainly to the left of the median plane. 



Saccus ccECus 
{left extremity) 



Area of attachment to dia- 
phragm {non-peritoneal) 



Lesser curvature 
I^ylorus 




Fig. 259. — Stomach of Horse, Visceral, Surface, with First Part of Duodenum. 
Fixed in situ when full but not distended. The posterior gastric artery and its larger branches with two satellite 

veins are sliown. 



It presents for description two surfaces, two curvatures, and two extremities. 
The parietal surface (Facies parietalis) is convex and is directed forw^ard, upward, 
and toward the left ; it lies against the diaphragm and liver. The visceral surface 
(Facies visceralis), also convex, faces in the opposite direction; it is related to the 
terminal part of the large colon, the pancreas, the small colon, and the small in- 
testine. The lesser curvature (Curvatura minor) is very short, extending from the 
termination of the oesophagus to the junction with the small intestine. When 
the stomach is in sitv, its walls are here in contact, and the cardia and pylorus 
close together. The greater curvature (Curvatura major) is very extensive. From 
the cardia it is first tlirected upward and curves over the left extremity; it then 
descends, passes to the right, crosses the median plane, and curves upward to end 
at the pylorus. Its left portion is related to the spleen, while its ventral portion 
rests on the left divisions of the great colon. The left extremity or saccus caecus 
is a rounded cul-de-sac which lies under the upper ends oi the fourteenth, fifteenth, 



358 



DIGESTIVE SYSTEM OF THE HORSE 



and sixteenth ribs and -the diaphragm/ It is related to the pancreas behind and 
the base of the spleen externally. The right or pyloric extremity is much smaller 
and is continuous with the duodenum, the junction being indicated by a marked 
constriction. It hes on the liver, a little to the right of the median plane, and a 
little lower than the cardiac opening. About two or three inches (ca. 5 to 8 cm.) 
from the pylorus there is a constriction which marks off the antrum pylori from the 
rest of the right sac. The oesophageal orifice or cardia is situated at the left ex- 
tremity of the lesser curvature, but about eight to ten inches (ca. 20 t