■■■J: 1 '•f'-'* J 1 |f:£?'r tel^-ii''-^^ M-C. /3 THE HORSE By J. H. WALSH, F.R.C.S. AND HAROLD LEENEY, M.R.C.V.S., Etc. I u en < ^ THE HORSE IN THE STABLE AND THE FIELD HIS VARIETIES MANAGEMENT IN HEALTH AND DISEASE ANATOMY, PHYSIOLOGY, Etc. By J. H. WALSH, F.R.C.S. (Stonehenge) EDITOR OF ' THE FIELD ' AUTHOR OF 'BRITISH RURAL SPORTS,' ETC. REVISED BY HAROLD LEENEY, M.R.C.V.S., Etc. WITH TWO HUNDRED AND THIRTEEN ILLUSTRATIONS u r HARRISON WEIR, ZWECKER, AND OTHERS SIXTEENTH EDITION, IN TWO VOLUMES WITH FOUR COLOURED PLATES VOL.11 LONDON GEORGE ROUTLEDGE AND SONS, Limited NEW YORK : E. P. DUTTON AND CO. 1907 PRINTED BY COWAN & CO., LTD. PERTH CONTENTS THE ANATOMY OF THE HORSE CHAPTER XVII CLASSIFICATION OF THE VARIOUS ORGANS, AND PHYSIOLOGY OF THE SKELETON Classification of the various organs — Of the structure of bone — Of the skeleton in general — The artificial skeleton — Number of bones composing the skeleton — General anatomy of the spinal column — Of the head and face and of the hyoid arch — Of the thoracic arch and anterior extremities — Of the pelvic arch and hind extremities — The tail — The fore and hind extremities considered as organs of locomotion ............. 344 CHArTER XVIII DESCRIPTIVE ANATOMY OF THE SEVERAL BONES The head — Bones of the cranium — Bones of the face — The lower jaw — The teeth — Os hyoides — Characters of Vertebra in general — General characters of the cervical vertebra — Peculiarities of certain cervical vertebrae— General characters of the dorsal vertebrre — Peculiarities of the dorsal vertebras— General characters of the lumbar vertebra — Peculiarities of the lumbar vertebrae — The sacrum — The i coccygeal vertebrte — The ribs and their cartilages — The sternum, or breast-bone — Scapula, blade-bone or shoulder-blade — Humerus, the upper arm-bone — The , bones of the fore-arm (os brachii) — The carpus (knee) and metacarpus (cannon) — The phalangeal bones (pasterns and foot)— The pelvis — The fejour (round-bone) and patella — Bones of the leg— Metatarsal and posterior phalangeal bones . . 354 CHAPTER XIX OF THE JOINTS, AND THE TISSUES ENTERING INTO THEIR COMPOSITION General remarks — Cartilage — Fibrous tissue — Fibro- cartilage — Synovial membranes — Classification of the joints — Movements of the joints — Articulations of the vertebral column — The ligamentum nucha?, or great cervical ligament, and other peculiarities in the ligaments of the neck— Movements of the vertebra in general, and of certain of their joints in particular — Thoracic articulations — Peculiarities in the articulations of the lumbar vertebras — The lumbo-sacral articulation and sacral ligaments — The coccygeal joints — The temporo-maxillary articulation — The sacro-iliac articulation — Ischio-pubic sj'mphysis— The shoulder joint — The elbow joint — Tlie knee joint (carpus, or wrist) — Inter-metacarpal articulations — Fetlock joint — The pastern joint — The coffin joint — The hip joint — Stifle joint or coxo-femoral articulation — Tibio-fibular articulation — The hock joint — Tarso- metatarsal articulation— Terminal articulation of the posterior limbs . . . 391 xii CONTENTS CHAPTER XX THE MUSCULAR SYSTEM PAOB Physiology of muscle— Cutaneous muscles — Muscles of the head — Anterior maxillary region — Muscles whose office it is to move the lower jaw — Muscles of the external ear — External muscles of the eyelids— Ocular region — Muscles of the tongue — Muscles of the pharynx — Larj-ngeal region — Palatine region — Superficial muscles of the neck and trunk — Lateral cervical region — Inferior cervical region— Superior cervico-occipital region — Inferior cervico-occipital region— Muscles connecting the scapula with the head, neck, and chest — Muscles of the thorax— Dorsal region — Muscles of the abdomen — Superficial abdominal region — Deep abdominal region — Pelvic region — Muscles of the fore extremity — External scapular region — Antero-inferior scapular region — The internal scapular region — Postero-external scapular region — The antero-external humeral region — The postero-internal humeral region — ISIuscles of the arm and fore-leg — Muscles of the haunch — Gluteal region — External ilio-femoral region — Anterior ilio-femoral region — Internal ilio-femoral region — The deep muscles of the ilio-femoral region — Anterior femoro-crural region — Posterior femoro-crural region .... 429 CHAPTER XXI THE THORACIC ORGANS AND THEIR APPENDAGES Contents of the thorax — The blood — General plan of the circulation — The heart and arteries — The veins — Physiology of respiration — Mechanism of the pulmonary apparatus — The nasal orifices and cavities — The larynx — The trachea and bronchi — The lungs — Pulmonai-y glands, etc 456 CHAPTER XXII THE ABDOMEN AND PELVIC VISCERA The abdomen and its contents — Physiology of digestion — Structure of glands and physiology of secretion — Depuration, and its office in the animal economy — Anatomy of the salivary glands, pharynx, cesophagus, and stomach — The intestines — The liver — The spleen — The pancreas — The kidneys — The pelvis — The bladder — The organs of generation, male and female ..... 474 CHAPTER XXIII THE NERVOUS SYSTEM Physiology of the nervous system — Chief divisions of the nervous system — The spinal cord— The medulla oblongata — The encephalon — The sympathetic system 490 CHAPTER XXIV SPECIAL ORGANS The organ of smell — The eye— The ear — The organ of touch — The foot . . . 496 THE DISEASES OF THE HOESE CHAPTER XXV THE DISEASES AND INJURIES OF BONE General remarks— Splints— Ringbone and sidebone— Bone spavin— Exostosis of the humerus and scapula — Fistula — Poll evil — Caries of the jaw — Osteo sarcoma — Fractures — Split pasterns CONTENTS xiii CHAPTER XXVI INJURY AND DISEASES OF THE JOINTS, MUSCLES, AND TENDONS t>AOE Diseases of muscle, tendon, and ligament — Inflamed tendinous sheaths — Inflamed bursaj mucosce — Strains — ^Those of the back and loins— Of the shoulder — Of the knee — Of the fetlock — Of the coffin joint — Of the suspensory ligaments — Of the back sinews — Breaking down — Strains of the hip 'Joint, stifle, and hock — Curb — Dislocation — Wounds of joints .......... 523 CHAPTER XXVII DISEASES OP THE THORACIC ORGANS AND THEIR APPENDAGES General remarks — Catarrh or cold — Influenza — Bronchitis— ^Chronic cough — Laryn- gitis, roaring, whistling, etc.— Pneumonia and congestion of the lungs — Pleurisy — Broken wind — Thick wind— Sj^asm of the diaphragm — Diseases of the heart — Diseases of the blood-vessels of th;< chest and nose ...... 537 CHAPTER XXVIII DISEASES OF THE ABDOMINAL VISCERA AND THEIR APPENDAGES General remarks — Diseases of the mouth and throat — Dyspepsia— Gastritis — Stomach staggers — Grass staggers — Rupture of the stomach — Colic : Gripes or fret — Flatulent colic — Inflammation of the bowels — Twisted gut — Peritonitis — Constipation — Diarrhoea — Calculi in the bowels — Diseases cf the liver — Diseases of the kidneys — Diabetes — Inflammation of the bladder — Diseases of the gener- ative organs — Cancer of the penis 553 CHAPTER XXIX DISEASES OF THE NERVOUS SYSTEM Paralysis of the lips — Epilepsy and convulsions — Megrims — Mad staggers— Sun- stroke— Rabies, or madness — Tetanus, Lock jaw — Apoplexy and paralysi? — String halt ' . , 571 CHAPTER XXX DISEASES AND INJURIES OF CERTAIN SPECIAL ORGANS Diseases of the ear— Diseases of the eye — Torn eyelids — Inflammation of the eyes — Periodic or constitutional ophthalmia — Cataract — Amaurosis — Buck eye . . 578 CHAPTER XXXI SKIN DISEASES Mange — Lice— Poultry lousiness— Ringworm— Eczema — Itchy tail— Mallenders and Sallenders — Harness galls and sitfasts — Chapped or cracked heels — Swelled legs —Warts 582 CHAPTER XXXII FEVERS AND SPECIFIC DISEASES Specific fevers— Stable fever— Influenza— Strangles— Bastard strangles— Anthrax, or Loodiana fever — South African horse sickness — Glanders — Farcy — Inflam- matory cedema, or water farcy— Purpura Htemorrhagica- Scarlatina— Azoturia — Rheumatism ............. ."i^Q CHAPTER XXXIII DISEASES OF THE FEET Corns— Sandcrack— False quarter— Quittor — Thrush — Canker— Laminitis— Seedy toe— Brittle feet— Villitis— Tread— Pricked foot— Contraction of the foot— Navi- cular disease — Accidents to the legs and feet 598 xiv CONTEXTS CHAPTER XXXIV PARASITES PA(IK Worms — Bots 618 CHAPTER XXXV METHODS OF CO>-TKOL The twitch — The halter twitch— Side lines — Hobbles — Slings — Ansesthesia . . 621 CHAPTER XXXVI OPEKATIOSS Bleeding — Firing — Setons and rowels — Blistering — Castration — Docking — Un- nerving— Reduction of hernia — The administration of medicines — Clysters — Back-raking 627 OX THE ACTIOX OF MEDICTN'ES CHAPTER XXXVn THE ACTIOX OF MEDICTNES, AXD THE FORMS Ef %THICH THEY ARE PRESCRIBED Alteratives — Anjesthetics — Anodynes — Antacids — Anthelmintics — Antispasmodics — Aperients — Astringents — Blistei-s — Canstics — Charges — Clysters — Cordials — Demulcents — Diaphoretics — Digestives — Diuretics — Embrocations — Emulsions — Expectorants — Febrifuges — Lotions — Narcotics — Refrigerants — Sedatives — Stimulants — Stomachics — Styptics — Tonics — Vermifuges — Electuaries — Pes- saries— Suppositories .... ........ 639 CHAPTER XXXVIII Shoeing 655 CHAPTER XXXIX A list of veterinary drugs, with their actions and doses ..... 675 CHAPTER XL On soundness ; and on the purchase and sale of horses 681 THE ANATOMY OF THE HORSE CHAPTER XVII CLASSIFICATION OP THE VARIOUS ORGANS, AND PHYSIOLOGY OP THE SKELETON CLASSIFICATION OF THE VAKIOrS ORGANS — OF THE STRVCTUEE OF BONE — OF THE SKELETON IN GENERAL — THE ARTIFICIAL SKELETON— NUMBER OF BONES COMPOSING THE SKELETON — GENERAL ANATOMY OF THE SPINAL COLUMN — OF THE HEAD AND FACE AND OF THE HTOID ARCH — OF THE THORACIC ARCH AND ANTERIOR EXTREMITIES — OF THE PELVIC ARCH AND HIND EXTREMITIES— THE TAIL — THE FORE AND HIND EXTREMITIES CONSIDERED AS ORGANS OF LOCOMOTION. CLASSIFICATION OF THE VARIOUS ORGANS The body op the Horse, like all the vertebrate animals, may be con- sidered as made up of several distinct apparatuses or systems. Of these, the first is a machine composed of the bony skeleton, or framework, the various parts of which are united by joints and moved by muscles. Secondh/, there are contained within the thorax the organs which supply the whole body with the means of nutrition in the form of blood, and purify this fluid. Thirdly^ in the abdomen are presented to view the important organs which assimilate the food to the condition of the blood ; while in the adjoining cavity, the pelvis, are the urinary and generative apparatuses. Fourthly, the nervous system may be considered, as comprising the gi'and centre of the mental faculties, and, also, as presiding over and controlling the whole of the functions performed by the several organs ; and fifthly, certain special organs, as, for example, those of sense, and likewise the foot, will complete flie Avhole circle of systems to be reviewed. Each of these groups will, therefore, be described in a separate chapter. OF THE STRUCTURE OF BONE The bones are composed of a tissue peculiar to them, enveloped by a membrane, t\\Q periosteum. They contain a semi-fluid of a fatty nature, the viarroiL\ and are pierced in various directions by blood-vessels and nerves. 313 A A 344 THE STRUCTURE OF BONE The proper tissue of the bones is made up of two distinct substances, cither of which may be removed by artificial means, leaving the other entire. If, for instance, a bone is submitted to the heat of a furnace, it retains its shape and rigidit}^ but becomes much whiter in colour, and is rendered extremely brittle. In fact, the mineral salts entering into its composition are left, but the animal matter binding them together is completely decom- posed and carried off in a gaseous form. On the other hand, by immersing a Ijone for two or three weeks in diluted hydrochloric acid, the earthy salts are dissolved, while the animal matter is untouched. ITere the bone retains its original shape, but it is soft and flexible ; and instead of presenting its usual opaque yellowish-white colour, it is semi-transparent, and resembles the ordinary gelatine of the shops. According to Berzillius, bone is chemically composed of the following constituents — namely, cartilage, reducible to gelatine by boiling ; blood-vessels ; phosphate of lime ; carbonate of lime ; fluate of lime ; phosphate of magnesia ; soda and chloride of sodium. Considered mechanically, the bones form the framework of the animal machine. In the limbs they are hollow cylinders, admirably fitted by their shape and texture to resist violence and support weight. In the trunk and head they are flattened and arched, to protect the contents of the cavities they form, and to provide an extensive surface for the attachment of muscles. In certain situations their exterior is raised into projections called processes, which serve as levers for the muscles to act upon ; in others they are grooved into smooth surfaces for the easy gliding of tendons, when these are stretched between the fleshy part of a muscle and one of its attachments. Lastly, they sometimes present a large hollow for the lodgment of the belly of a muscle, as in the case of the scapula. These differently shaped bones may, therefore, be classed under the following three heads : — 1st. The long hones consist of the humerus, radius, ulna, femur, tibia, and fibula ; the metacarpal and metatarsal bones (called, in horsemen's language, the cannon bones), the phalanges (pastern bones), and the ribs. These bones ax'e all divisible into a central cylindrical shaft, and two heads or extremi- ties. The shaft is usually of a prismoid form, dense in texture, and presenting a longitudinal tube in the interior, called the medullary canal, which contains marrow. The heads are broad, to articulate with the next adjoining bones, and are covered with a thin layer of cartilage, which will be described in the chapter treating of the joints. Their outer surface is a liard osseous layer, within which is a mass of cells containing red medullary matter, to be presently described. 2nd. The Jlat hones are composed of two layers of dense tissue, one on each surface, having between them another of a cellular nature, called the diploe. As a matter of course, from their shape, they have surfaces, borders, and angles ; in addition to which they have projections, called processes, of various shapes. They consist of the chief bones of the head, the scapula, and pelvis. 3rd. The irregxdar hones comprise the lesser bones of the head and face, the vertebrae, sacrum, sternum, carpal and tarsal bones, the sesamoid bones, the bones of the foot, and the patella?. They resemble the flat bones in their structure. When microscopically examined, bone is seen to be made up of a dense and homogeneous substance (basis substance), in which are numberless THE ANATOMY OF THE HORSE 345 minute cells (corpuscles of Purkinjo). TIk; l);isi,s subsiaiicc^ is |).arti;Llly fibrous and slightly liimollatcd, the layers being concentric in l(jng bones and parallel in flat ; it is traversed in all directions (more especially in the long axis, where there is one) by canals (Haversian canals), which frequently branch and inosculate, giving passage to vessels and nerves. In certain situations the lamelhu separate, and leave between them spaces of various sizes, called cancelli. Besides entering into the composition of the basis substance, the lamelhc are collected concentrically round the Haversian canals, the boundaries of which they form, generally to the extent of ten to fifteen layers. l]oth the compact and spongy tissues are, therefore, com- posed of the same elementary structure, the former being especially intended to alTord resistance to violence with as little weight as is consistent with its oflice, for which reason it is hollowed into a tube; while the latter is enlarged as much as possible without unnecessarily adding to its weight, the problem being solved by its development in a cellular form. The periosteum is a dense fd)rous membrane which covers every part of the surface of the bones, excepting their extremities when they enter into the composition of a joint, its place being then occupied by cartilage (see Joints). When this membrane covers the bones of the skull it is called pericranium, and when it invests the cartilag(!S of the ribs it receives the name perichondrium. It is full of blood-vessels, especially in the young, and they freely communicate with those of the surrounding soft parts. Hence it is extremely liable to inflammation, either caused by injury to itself or to the parts which cover it. The marrow, or medullary substance, is containc^d in the cavities formed within the bones, being of a yellow colour and oily nature in the shafts of the long bones ; and more or less red, from tlu; admixture with blood, in the flat and irregular bones, and in the heads of the long bones. It is contained within the areolar meshes of a membrane, which lines these cavities, answering to the periosteum, which has been already described. This medullary membrane is of excessive tenuity, and is composed of blood-vessels ramifying in fine cellular tissues. The use of marrow in the animal economy is not very clearly demonstrated. In the embryo, all the bones originally exist in the state of cartilage, being soft and flexible. By degrees vascular canals are developed within its substance, by the union of its cells in rows. These concentrate towards some one or more points, which in a long bone are one in the centre of the shaft and one at each extremity. Starting from this point {punctum ossiji- cationif^), fibres run out, embracing clusters of cells, and sending branches between the individuals composing each group. In this manner the network, characteristic of bone, is formed, the cells uniting to form the permanent areolic and Haversian canals. At first the contents of the cells are transparent, then granular, and finally opaque, from the pressure of amorphous mineral matter. The several ossified portions are ((uite distinct for a long time in the young animal, and may readily be separated by boiling or maceration. 343 THE SKELETON IN GENERAL OF THE SKELETON IN GENERAL The name skeleton has been given from the Greek word (JKe'/Wco {to dry), it being the only part of the body which will bear desiccation without change of form. In the vertehrata it is an internal bony framework, but in the Crustacea it invests the soft parts, and forms an insensible covering to them, while at the same time it serves the purpose of locomotion. In both these divisions of the animal kingdom the skeleton forms a series of arches or rings, capable of mo\4ng on each other, but so firmly attached as to secure protection to the important organs contained witliin them. In the horse, as in all the higher mammalia, these rings or arches are double — one set, the superior, being continuous throughout the whole length of the animal from the head to tlie root of the tail, and containing the nervous system ; while the other lying below, but closely connected to them, is interrupted in certain localities, being found to exist chiefly in three regions : — 1st, where it forms the jaws and bone of the tongue; 2nd, where, by means of the ribs and sternum, it constitutes the thorax and its appendages, the anterior exti'emities ; and, 3rdly, where, in the shape of the pelvic arch, it protects the organs of generation, and, through the posterior extremities prolonged from it, assists in locomotion. The superior of these arches, from containing the brain, and its prolongation, the spinal coi'd, is called the neural arch. The inferior is termed the haemal arch (cufia, blood), because it protects the heart and its large blood-vessels as the latter pass from the thorax towards the head and posterior extremities. In all the vertebrata the neural arch consists of one continuous cavity, defended from end to end by bony plates, strongly joined together ; and in some of the lower forms (lizards) the hremal arch is nearly as complete, these animals having cervical ribs ; while the dugong and some others are furnished with ribs in their tails. Consequently, it is fair to consider the whole skeleton in the superior forms of the animal kingdom as composed of two series of arched plates, firmly united together, but still allowing more or less motion, and serving to protect the centres of the nervous and sanguineous systems, from which they have received their names. THE ARTIFICIAL SKELETON The bones of the Horse, as of the other mammalia, may be preserved with their natural ligamentous attachments connecting them in a dry state, in which condition the skeleton is called a natural one. It is usual, however, to macerate them so long that all the soft parts readily separate, leaving the bones without any of the ligaments or cartilages which are fii'mly fixed to them during life. They are then put together by wires, etc., the cartilages being represented by leather and cork. In this way it often happens that the proportions are not exactly preserved, and, on reference to an articu- lated skeleton in any museum, the inexperienced eye may be greatly misled. Thus it is very common to represent the thorax in the artificial skeleton as much shallower than it is in nature, where its lower margin is on the average about midway between the top of the withers and the ground. Again, THE ANATOMY OF THE HORSE Ills f-l eirf ^' lO ~ l- CC c: O r-; c-i M -* >«■ d t-: od" p'lN -j! o « t~"c-: d r^ C-; crft- OO d. d rtio d ti IfiS; NUMBER OF BONES COMPOSING THE SKELETON 319 in the fresh state, the intervertebral fibro-cartilage is in some parts of tlio spine of considerable thickness ; and if the proper substance is not artificially supplied, the skeleton will be too short, or if too thick a material is added it will be too long. In the engraving of the skeleton occupying the opposite page, which is drawn from the skeleton in the Museum of the Royal Veterinary College, London, the spine is correctly represented, but the thorax: is too shallow, and the scapula, together with the whole fore extremity, i^j placed too far forward. NUMBER OF BONES COMPOSING THE SKELETON The skeleton is composed of two hundred and forty-seven separate bones, which are united by joints to form the spine, thorax, pelvis, tail, and fore and hind extremities. The spine is finished anteriorly by the head, which is divided into the cranium and face, and contains the teeth. Separated from the head is the os hyoides, which completes the number of bones. Thus :— The spine consists of 7 cervical, 18 dorsal, and 6 lumbar vertebrse — Total 31 The thorax is made up of the dorsal vertebra?, with 18 ribs on each side, and the sternum in the middle — Total 37 The pelvis comprises 2 ossa innominata (or ilium, ischium, and pubes), and 1 sacrum — Total 3 The TAIL contains on the average 17 bones 17 The fore extremity is made up on each side of the scapula, humerus, OS brachii, and 8 carpal bones, 3 metacarpal, os suffraginis, os coronse, OS pedis, OS naviculare, 2 ossa sesamoidea — Total on both sides . . 40 The hind extremity has the femur, patella, tibia, fibula, 6 tai\sal bones, 3 metatarsals, os suffraginis, os coronse, os pedis, os naviculare, 2 ossa sesamoidea — Total 38 Bones op the cranium 10 Bones of the face and lower jaw 18 Teeth! 40 Bones of the internal ear, 4 in each organ 8 Os HYOIDES, OR BONE OF THE TONGUE, made up of five sections ... 5 Grand total 247 GENERAL ANATOMY OF THE SPINAL COLUMN The vertebral or spinal column is the first rudiment of internal skeleton seen in the lower vertebrate animals, and this constitutes the type of that great division of the animal kingdom. In the horse, also, it is the portion of the skeleton first developed in the embryo, and forms the centre around 1 The teeth are not strictly speaking bones, but as the general reader usually regards them as such, and the distinction is a purely scientific one, we have allowed them to count in the usual wa/ 350 THE ANATOMY OF THE HORSE which all the other parts are framed. At its first appearance it is a cartilaginous cylinder, surrounding and protecting the primitive trace of the nervous system ; but as the embryo increases in growth, points of ossification are developed corresponding to each vertebra, the whole tube being finally divided into distinct pieces called vertebrce, to which the bones of the head are a prolongation, corresponding in their nature, though difiering out- wardly in form. The vertebrce are divisible into true and false, the former reaching from the head to the pelvis, and the latter extending thence backward, being respectively called the sacram and coccyx. The true vertebrce comprise the 7 cervical, 18 dorsal, and 6 lumbar vertebi'se. Each consists of a body, from which two laminpe or plates project upwards, terminating in a spinous process. In addition to these are two lateral projections (transverse processes), which serve the purpose of firmly connecting the vei'tebrre together by means of the muscles attached to them, and. also to the ribs and extremities below. Lastly, each vertebra has two small surfaces before . and the same number behind (articular surfaces), which form distinct joints between them. The details of these parts, and the peculiarities met with in each set, will be described in the next chapter. Between the body, the laminae, and the spinous process is an opening more or less triangular in shape, in which lie the spinal cord and its investments. The edges of this opening are attached to those before and behind by ligamentous tissues {ligamenta siibjlavct), which, opposite each intervertebral space, are pierced by openings on each side to give exit to the vertebral nerves passing out to the exterior of the body and to the ex- tremities. Opposite to these openings the bone is notched above and below, and these hitervertebral notches complete the parts common to the whole series. Thus the vertebral or spinal column serves as a firmly secured but flexible tube for the lodgment of the spinal cord, while at the same time it gives passage to its nerves. By this formation it is far less liable to injur}'^, and also more useful as an aid to locomotion, than if it were made of one solid piece of bone, which, from its length, would be readily broken. OF THE HEAD AND FACE, AND OF THE HYOID ARCH Modern anatomists, following out the idea first suggested by Maclise and Owen, consider the head as made up of six vertebrae ; the posterior one, or that nearest to the neck, being the occipital bone, the next two being made up of the temporal bone, and the ultimate vertebrae consisting of the sphenoid and aethmoid bones. This is a somewhat fanciful hypothesis, when worked out in detail ; but it is obvious that the several bones of the skull subserve the same purposes as the vertebrae, and resemble those parts of the skeleton in forming a series of irregular arches to protect the brain, the division into separate pieces being far more secure than if the whole were in one. The boxes of the face, including the lower jaw and os hyoides, depend from the neural arch or brain-case much in the same way as the ribs and THE EXTREMITIES 351 pelvic bones posterior to them are attache I to tlie vertebrre, and though they inclose organs of less vital importance, yet they are perfectly analogous to these parts in their types and in the offices which they perform. OF THE THORACIC ARCH AND ANTERIOR EXTREMITIES Lying in the horse at some distance posteriorly to the three first segments of the haemal arch (the bones of the face, lower jaw, and os hyoides), and separated from them by the neck, where there is a hiatus, the thoracic arch and anterior extremities depend from the vertebrae corresponding to them. In many of the higher vertebrates the fore extremity is firmly united by a joint to the thorax, and may be considered with it ; but in the horse it is only attached by muscles, the thorax being slung between the upper edges of the blade-bones by means of two broad sheets of muscular fibres. Hence the collar-bone is entirely absent in this animal ; and thus, while he is free from dislocations and fractures of that bone, to which he would be constantly subject if it were present, he is rendered more liable to strains and rheumatic inflammations of the muscular sling, by which freedom of action is impaired. In the articulated skeleton it is usual to consider the thorax as made up by the eighteen dorsal vertebrae superiorly, the eighteen ribs and their cartilages on each side, and the sternum with its cartilages below. But the cavity of the thorax, as bounded by the diaphragm posteriorly, is not nearly so large as would be supposed from a consideration of the dry skeleton, for though the diaphragm is attached to the twelve posterior i-ibs near their cartilages, yet its surface is so convex towards the thoracic cavity, that a very large space within the bony thorax is really occupied by the abdominal organs. This will be hereafter more fully explained in examining these parts at page 456 ei seq. THE PELVIC ARCH AND HIND EXTREMITIES Behind the thorax occurs a second interval corresponding to the loins, where the hfemal arch is deficient ; but at the pelvis the circle is completed by the bones of the ischium, ilium, and pubes, united to the sacrum above, and having the hind extremities firmly articulated to them at the hip joints. The pelvis constitutes not only a firm and solid case for the protection of the large blood-vessels, and of the urinary and genital organs, but it is also intimately connected with locomotion, to which the posterior extremities largely contribute. THE TAIL This organ appears to be intended chiefly to protect the body from insects ; but it also serves to some extent as an aid in balancing the body when rapidly moving in any new direction. It is made up of from fifteen to eighteen bones, which will bo described in the next chapter. 352 THE ANATOMY OF THE HORSE THE FORE AND HIND EXTREMITIES CON SIDERED AS ORGANS OF LOCOMOTION The several bones which are connected together to form the extremities must be regarded, first, as organs of support, and, secondly, as the primary means of locomotion. Each extremity consists of corresponding divisions, the ilium being the analogue of the scapula ; the femur of the humerus ; the tibia and fibula of the ulna and radius ; the tarsus of the carpus ; and, lower down, the bones of the fore and hind extremities being precisely similar in their forms. There is, however, a want of exact correspondence in the form and direction of the joints, which has been much insisted on byhomolo- gists, and which Mr. Maclise has attempted to explain in his very interesting article on " The Skeleton," contained in the Cyclopcedia of Ayiatoyyiy and Physiology edited by Dr. Todd. It appears to me that this does not make matters more simple, but the reverse, and that the proper point of view is to regard the humerus and femur as homologous, and the tibia, with the patella, as analogous to the ulna and its olecranon process. The interven- tion of the ligament between the patella and tibia does not affect the use of the former as a lever ; and both joints being perfectly hinge-like in their actions, there is no other important difference. Descending to the next joint, the os calcis stands out as an important lever, and is represented in the carpus by the os pisiforme (called by Percivall os trapezium), each having important muscles inserted in their upper edges. It is true that the one is an agent in what is called extension, while the other is engaged in flexing the limb ; but this is only dependent upon the limit to motion in either direction. Below the carpus and tarsus there is no necessity for continuing the comparison. Regarding the limbs as means op support, it must be remembered that the fore-limbs are nearer the centre of gravity, and, therefore, sustain more weight than the hind. The fore-quarter is suspended between the bases of the two shoulder-blades, chiefly by the serrati magni, and in such a way as to require no special muscular contraction. The four parts of which the limb itself is composed being bent at various angles, are prevented from giving way by the muscular actions of the extensors of the humerus and ulna, the carpus (or knee) having little tendency to yield, and the pastern being supported by the flexor muscles and suspensory ligament. The hinder limbs, though sustaining less weight, are not so favourably circumstanced for this purpose, the angles between their several parts being generally more acute. But if these are attentively regarded, there is not so much difference as is generally supposed. Thus, the first joint, the ilio-femoral, forms a less acute angle than its analogue, the shoulder joint (see Fig. 1, R, m). Again, though the stifle joint is considerably bent, it is not more so than the elbow joint, which will be clear on comparing the two in the skeleton given at page 348. The chief disadvantage sustained by the hind-limbs as means of support will be found in the hock, as compared with the knee, the latter being nearly straight, while the former is much bent : but as it has a long lever to assist it (the os calcis), and as this is kept in position by the power- ful hamstring muscles, each of which serves its purposes far more completely than the flexor of the carpus inserted in the os pisiforme, it may readily be THE EXTREMITIES 353 understood that the hind-limb is not greatly at a disadvantage in supporting the weight of the body. As AGENTS OP LOCOMOTION, the offices of the fore and hind limbs are widely different. Each has been already described as consisting of four sections, bent at angles on each other. In the fore-limb these angles are framed to serve as springs, so that when the feet touch the ground, they are enabled to adapt themselves so as to avoid altering the line of progression of the body. In those animals which have small and short fore-legs, as the kangaroo and hare, the most rapid locomotion ever consists in a series of curves ; whereas, in the horse at full speed, the body progresses in one straight line, owing to this elastic structure of the anterior limbs. So, also, in descending from an extraordinary leap, the springy action of the fore- limbs of the horse is so powerful that he can get off again without dwelling, whereas the kangaroo and hare must depend almost entirely upon their hind- legs, and consequently stop for a second after their descent. On the other hand, the angular formation of the hind-limbs is intended to enable the animal to drive its whole body forward, by first flexing all the joints, and thus drawing their feet under the belly ; and then suddenly extending them with the feet fixed on the ground, the weight is necessarily propelled. Or if the feet are not fixed they are lashed out backwards, developing the action so well known as " kicking." The difference between the powers displayed by the two limbs, in straightening their component parts, is well displayed in comparing kicking with the striking out of the fore-foot, which is common enough among vicious horses. It is true that the latter will sometimes cause a severe blow ; but it could very rarely break a limb, which is the least amount of mischief to be apprehended from the full force of a lash out with the hinder-limb. 354 THE ANATOMY OF THE HORSE CHAPTER XVIII DESCRIPTIVE ANATOMY OF THE SEVERAL BONES THE HEAD — BONES OF THE CRANIUM— BONES OF THE FACE— THE LOWER JAW— THE TEETH — OS HYOIDES — CHARACTERS OF VERTEBRiE IN GENERAL — GENERAL CHARACTERS 05 THE CERVICAL VERTEBR.?;— PECULIARITIES OF CERTAIN CERVICAL VERTEBRA — GENERAL CHARACTERS OF THE DORSAL VERTEBR.5: — PECULIARITIES OF THE DORSAL VERTE- ER.^ — GENERAL CHARACTERS OF THE LUMBAR VERTEBR.E— PECULIARITIES OF THE LUMBAR VERTEBR-E— THE SACRUM — THE COCCYGEAL VERTEBRiE— THE RIBS AND THEIR CARTILAGES — THE STERNUM, OR BREAST-BONE — SCAPULA, BLADE-BONE OR SHOULDKR- BLADE— HUMERUS, THE UPPER ARM-BONE— THE BONES OF THE FORE-ARM (OS BRACIIIl) — THE CARPUS (knee) AND METACARPUS (CANNON) — THE PHALANGEAL BONES (PAS- TERNS AND foot) — THE PELVIS — THE FEMUR (ROUND-BONE) AND PATELLA — BONES OF THE LEG — METATARSAL AND POSTERIOR PHALANGEAL BONES, THE HEAD Is COMPOSED of the bones of the cranium, face, and jaw. 1 2 Fig. 2.— Profile View of the Head and Face. 1. Occipnt. 2. Parietal bone. 3. Frontal bone. 4. Petrous portion of temi>oral bone. 5. Zygomatic arch. 6. Laclirymal bone. 7. Malar bone. 8. Posterior maxillary bone. 9—11. Nasal bone. 10. Anterior maxillary bone. 11. Temporal fossa. 12, 13. Lower jaw. BONES OF THE CRANIUM The CRANIUM, or brain-case, is small as compared with that of man, and occupies less than one-fourth of the whole head. It is made up of nine bones, three of which are pairs and three single ones. These bones are in most parts made up of two tables, with a cellular structure interposed, called the di^jlue, which is in certain situations expanded into large cells, as in the frontal sinuses. They are connected together by serrated sutures, except where the temporal bone overlaps the parietal, and in that situation, on each side thp «kull one thin scale fsquama) overlaps the other. Tlie two BONES OF THE FACE 355 frontal bones unite to form the anterior part of the cranial cavity and the upper walls of the orbits, leaving a space between them for the reception of the a^thmoid bone. The ttco 2Mrietals are situated at the upper and lateral parts of the brain-case, and are of an irregularly quadrilateral figure — each meeting its fellow in the median line on the top of the head. The temporal hone overlaps the parietal on each side, with its squamous portion, while the petrous part runs in towards its fellow on the opposite side, con- stituting a part of the floor of the bi-ain-case, and separating that cavity into two. It contains within its bony structure the true organ of hearing. The occipital bone occupies the back part of the ci^anium, and makes up the base. It has a large opening (the foram3n magnum), for the passage of the medulla oblongata, and vertebral arteries ; and on each side of this are large smooth articulating"Surfaces, for the attachment of the atlas vertebra. The sphenoid hone is of a most remarkable shape, resembling slightly a bat, with its wings partially expanded. The body and wings complete the middle of the base of the skull, and the legs go to for.n part of the walls of the nasal cavity and mouth. Lastly, the a'thmoid bine is made up of a cribriform plate sup- porting the anterior lobes of the briin, and giving passage to the olfactory nerves, which spread over the cellu'ar structure that constitutes the whole substance of this bone. Another thin plate contiubutes to form the inner and posterior wall of the orbits. BONES OF THE FACE The pace is made up of the nasal, posterior, and anterior maxillary, molar, lachrymal, and palate bones, the four turbinated bones, vomer, and lower jaw. Fio. 3.— Longitudinal Section of Head. 1, 2, 3. The upper walls of the cranium. 10. Petrous portion of temporal bone. 4. Frontal sinus. 11. Vomer. 5. Nasal bones. 12. Inferior turbinated bone. C. Suiierior turbinated bone. 13. Palatine plate of posterior maxillary. 7. jEthmoidal cells. 14. Posterior maxillary bone, outer wall. 8. Sphenoid bone, uniting witli 15. Anterior maxillary bone. 9. Occipital bone. The nasal bones are long and thin, forming the roof of the nosti'ils. Posteriorly they are broad, and taper gradually forwards to a sharp point. The 2^oste7nor maxillary hones are triangular in shape, thick behind, and presenting thin edges in front. The anterior maxillary hones are of an irregular shape, being connected with the corresponding edges of the posterior maxillary and nasal bones, and completing with the former the roof of the mouth. The malar hone has an irregularly triangular shape, 356 THE ANATOMY OF THE HORSE presenting its broad base forwards, and is connected with the temporal, posterior maxillary, and lachrymal bones. The lachrymal hones form the internal corners of the orbits, where they are very thin, and are hollowed out to receive the lachrymal sac, and give passage to its duct. The pa^oYe hones are of a very irregular shape, and are connected with the frontal, jethmoid, sphenoid, posterior maxillaiy, inferior turbinated bones, and vomer. The turhinated hones, two in each nasal cavity, are attached to its outer walls one above the other, and appear to be intended merely for the purpose of extending the surface for the expansion of the olfactory nerve. The vomer resembles in shape the share of the plough, after which it is named, and rises up in the middle line of the back of the division between the nostrils. THE LOWER JAW The lower jaw resembles in general shape the letter V, the point being rounded off forwards and receiving the incisor teeth, while the two branches are broad, thin, and slightly cux'ved, being surmounted by the condyles for articulation with the glenoid cavity of the temporal bone, and giving lodgment to the tushes and grinders. The two lines of alveolar cavities are not so wide as those of the upper jaw, and consequently the two sets of teeth do not exactly correspond. THE TEETH The teeth are developed within their appropriate cavities or sockets, which are found exactly corresponding with their number in the upper and lower jaws, being narrower in the lower than in the upper. Before birth they are nearly all in a state of incomplete growth, covered and con- cealed by the gums, but soon afterwards they rise through it in pairs, the first set, or milk teeth, being in course of time superseded by the permanent teeth as in all the mammalia. The following is the formula of the com- plete dentition of the horse : — Incisors f , canine #, molars yi. Each tooth is developed within its corresponding cavity in the jaw, and is made up of three distinct substances — cement, enamel, and dentine. The cement of the horse's tooth (sometimes called crusta petrosa) closely corresponds in texture with his bone, and, like it, is traversed by vascular canals. The enamel is the hardest constituent of the tooth, and consists of earthy matter arranged in the animal matrix, but contained in canals, so as to give the striated appearance which it presents on splitting it open. Dentine has an organized animal basis, presenting extremely minute tubes and cells, and containing earthy particles, which are partly blended v/ith the animal matter in its interspaces, and partly contained in a granular state within its cells. These three substances are shown in the annexed sections of an incisor tooth, one of which, Fig. 4, is of the natural size, while the other. Fig. 5, is shown under the microscope. In the molar teeth the arrangement of these three substances is the THE TEETH 35) same, except that tlie cement and enamel dip down into two or more cavities instead of one, and are also reflected in a sinuous manner upon the sides. This inequality in the hardness of the component parts of these teeth causes them to wear away with different degrees of rapidity, and thus leaves a rough surface, which materially aids in grinding down the hard grain which forms a large portion of the animal's food. In the upper jaw, the table presented by each molar tooth is much larger than those of the corresponding lower teeth, and therefore it is easy to distinguish the one from the other. Fia. 4.— Section of Incisor. e. Cement on external surface. c. Cement reflected within tlie cavity. €. Enamel also reflected. d. Dentine. 8. Tartar, coloured black by decomposition of food, contained within the cavity. Pig. 5. Section of a Portion of Incisor (maonified). The temporary or milk incisors differ in shape a good deal from the permanent set. The milk teeth are altogether much smaller, but especially in the neck, which is constricted in them, whilst in the permanent set, which go on growing as they wear out, the diameter is nearly the same throughout. The former are also whiter in colour, and have grooves or indentations on their outer surfaces, running towards the gum. Lastly, the mark on the table is much slighter than in the permanent teeth. The temporary molars are not distinguishable from the permanent teeth of that class. As A consequence of this arrangement op parts, the teeth, as they wear down, present a different appearance according to the extent to which their attrition has reached. On this fact is founded a means of arriving at 358 THE ANATOMY OF THE HORSE a knowledge of the age of the horse after he has shed his milk teeth, whicli as a rule he does in pairs at certain fixed periods. In order, therefore, to be able to estimate the age of the horse from his teeth, it is necessary to ascertain, as nearly as may be, the exact time at which he puts up each pair of his milk or sucking teeth, and afterwards the periods at which they are replaced by the permanent teeth. Finally, it becomes the province of the veterinarian to lay down rules for ascertaining the age from the degree of attrition which the permanent teeth have undergone. For these several purposes, the horse's mouth must be studied from the earliest period of his life up to old age. In horseman's language the incisors are called nijypers, the canine teeth tushes, and the molars grinders. By the exd of the first year the colt has cut his twelve nippers and sixteen grinders, which usually pierce the gums at the following months. Before birth, the eight anterior grinders have generally shown themselves, followed about a week after foaling by the two central nippers. At the end of the first month another grinder makes its appearance all round, and in the middle of the second the next nipper shovvs itself. By the end of the second month the central nippers have attained their full size, and the second are about half-grown, requiring another month to overtake their fellows. Between the sixth and ninth months the corner nippers are cut, and towards the end of the first year reach their full size. This first set of nippers consists of teeth considerably smaller in size than the permanent teeth, and somewhat different in shape. They are more rounded in front, and hollow towards the mouth, the outer edge being at first much higher than the inner. As they wear down, these two edges soon become level, but the corner nippers maintain this appearance for a long time. At six months the central nippers are almost level, with the black " mark " in their middle wide and faint ; and about the ninth month the next nipper on each side above and below is also worn down almost to a level surface. During the second year the following changes take place : — In the first month, and sometimes towards the end of the first year, a fourth grinder is cut all round, which commences the set of permanent teeth, the three first molars only being shed. At a year and a half, the mark in the central nippers is much worn out, and has become very faint ; the second is also worn flat, but is not so faint ; and the corner nippers are flat, but present the mark clearly enough. In colts which have been reared on corn and much hay, the wearing down proceeds more rapidly than in those fed upon grass alone. The third year is occupied by the commencement of the second dentition, which is effected in the same order in which the milk teeth made their appearance. Both sets are contained within the jaw at birth, the permanent teeth being small and only partially developed, and lying deeper than the milk teeth. As the mouth grows, it becomes too large for its first set of teeth ; and the roots of these being pressed upon by the growth of the permanent set, their fangs are absorbed, and allow the new teeth to show themselves, either in the places of the former, or by their sides, in which case they are known by the name of rcolfs teeth. This change pi'oceeds in the same order as the cutting of the milk teeth, commencing with the first grinder, which is shed and I'eplaced by a permanent tooth early in the THE TEETH 359 third year, a fiftli grinder (permanent) making its appearance about the same time. Towards the end of this year the sixth grinder shows itself, but gi'ows vei'y slowly, and the central nippers above and below fall out, and are replaced by permanent ones, which, as before remarked, are considerably larger in size and somewhat diflFerent in foi-m. At three years the mouth presents the appearance shown in Fig. 6, the development of the permanent teeth varying a good deal in different individuals. At thi'ee years and four or six months, the next nipper all Fio. C— Tiirf.e-YeatvOi.d Mouth. B. Anterior maxillary bone. 3. 3. Corner milk tooth, stiU .showing central 1. 1. Central permanent nippers, nearly full- mark. grown. 4. i. Tushes concealed within the jaw. 2. 2. Milk teeth worn down. round falls out, and is replaced by the permanent tooth. The corner nippers are much worn, and the mark in them is nearly obliterated. About this time also the second grinder is shed. At four years of age the mouth should differ from that represented in Fig. 6 in the following particulars : — The central nippers begin to lose their sharp edges, and have grown considerably in substance. The next nipper all round has grown nearly to its full size, but not quite, and its edges are still sharp, with the mark deep and very plain. The corner milk nippers still remain, unless they have been knocked out for purposes of fraud, which is sometimes done to hasten the growth of the permanent teeth, and give the horse the appearance of being four or five months older than he is. 360 THE ANATOMY OF THE HORSE Between four and a half and five years, the corner nippers are shed, and the tush protrudes through the gum. These changes are shown in Fig. 7. At five tears the mouth is complete in the number of its teeth ; and from this date it becomes necessary to study their aspect in both jaws. Fig. 8 shows the upper teeth at tliis age, by comparing which with Fig. 7 the shght growth in the half-year may be traced. In the lower teeth of the same mouth, the edges of the central cavities are much more worn away. Fio. 7.— Mouth or the Colt at Fotje and a Half Yeaes. \. Anterior maxillary bone. growth, with the edges of the cavity 1.1. Central nippers, considerably worn down. sharp, and tlie mark verj' plain. 2. 2. The next pair, fully developed, with their 4. 4. The tushes showing themselves through edges slightly worn. the gum, but not full-grown. 3. 3. Comer permanent nippers, in a state oi the central nipper having only a small black speck in the middle of a smooth surface, while the next is much worn, and the corner teeth, though showing the mark very plainly, bear evidence of having been used. The tush is much grown, with its outer surface regularly convex, and its inner concave, the edges being sharp and well defined. The sixth molar is at its full growth, and the third is shed to make room for the permanent tooth in its place. These two kist-named teeth should always be examined in cases where there is any doubt about the age. After five years, no further shedding occurs in any of the teeth. The six- year-old mouth is the last upon which any great reliance can be THE TEETH 361 placed, if it is desired to ascertain the age of the horse to a nicety ; but by attentively studying both jaws, a near approximation to the truth may be arrived at. It is ascertained that the nippers of the upper jaw take about two years longer to wear out than those of the lower ; so that until the horse is eight years old, his age may be ascertained by referring to them, nearly as well as by the lower nippers at six. But as different hoi^ses wear out their teeth with varying rapidity, it is found that this test cannot be implicitly relied on ; and in crib-biters or wind-suckers the upper teeth I'ia. 8.— rpPER Nippers and Tushes at Five Teae=; Oijj Comer nipj "ishes wel groove on the outside plainly, 1. 1. Central nippers, with, the mark stiU un- obliterated. 2, 2. Next nippers, with the mark still plainer. with the edges very sligutiy woru. 4. 4. Tushes TveU developed, and still showing the wear out wonderfully soon. Fig. 10 is taken from the lower jaw of a six- year-old horse, showing the marks of the central nippers almost obliterated but still presenting concentric circles of discoloured bro^vn tartar in the middle ; next to which is the cement, then the enamel, and the dentine, with a thin layer of enamel outside. Up to this age the nippers stand nearly pei^pendicular to each other, the two sets presenting a slight convexity when viewed together, as seen in Fig. 2, page 354. Afterwards the nippers gradually extend themselves in a straight line from each jaw, and, in the very old horse, form an acute angle between them. 362 THE ANATOMY OF THE HORSE At about tile eighth year the upper nippers present the same appear- ance as already described in the lower nippers at six years old. Both tushes are considerably -worn away at their points, and the upper ones more so than the lower. At nine years of age the upper middle nippers are worn down com- pletely. The next pair have a slight mark left, but their surfaces are quite level, and the corner nippers have only a black stain, without any central depression. After nixe years the age of the horse can only be guessed at from his teeth, which gradually grow in length, and are more in a line ^vith the jaw. Fin. 9.— Lower Nippers and Toshes at Fi^t: Years Old. 1. 1. Central nippers, with their marks almost 3. 3. Comer nippers, with the mark plainly seen, entirely worn out. but the edges partially worn. 2. 2. Next nippers, showing marks partially 4. 4. Tushes, with the grooves inside almost worn. obliterated. The section of each nipper presented to the eye becomes more and more triangular instead of being oval, as seen in Figs. 10 and 11 ; but after about the twelfth year the triangular section disappears, and the tooth becomes nearly round. In accordance with the increase of length is the colour of the tooth altered, being of a dirty yellow in very old horses, with occasional streaks of bro^vn and black. The tushes wear down to a very small size, and very often one or both di'op out. Allusion has already been made to the practice of removing the milk nippers for the purpose of inducing a more rapid growth of the next set, which, however, is not materially affected by the operation, but dishonest dealers have recourse to another deception, called bishoping, by which an THE TEETH 363 aged horse may be passed off upon an inexperienced person for a six-year-old. The plan adoped is to cut oflf all the nippers with a saw to the proper length, and then with a cutting instrument the operator scoops out an oval cavity in the corner nippers which is afterwards burnt with a hot iron until it is quite black. It is extremely easy to detect the imposition by carefully comparing the corner nippers with the next, when it will be seen that there is no gradation from the centre to the corner nippers, but that the four middle ones are exactly alike, while the corners present a large black cavity, without a distinct white edge to it, the dentine being generally encroached Fig. 10.— The Lower XiPfERS and Tushes of a Sis- Year-Old Horse. B. Tlie lower jaw. 1. 1. The central nippers, with the marks worn out. 2. 2. The next nippers, with the marks disappear- ing. 3. 3. The comer nippers, showing the mark plainly enough, but with the edges of the cavity considerably worn. 4. 4. The tushes, sta'nding up three-quarters of an inch, with their points only slightly blunted. upon without any I'egularity in the concentric rings. Moreover, on compai-- ing the lower with the upper nippers, unless the operator has performed on the latter also, they will be found to be considerably more worn than the lower, the reverse of which ought naturally to be the case. Occasionally a clever operator will burn all the teeth to a properly regulated depth, and then a practised eye alone will detect the imposition. In the present day there is not so great a demand for six-year-old horses as was formerly the case, and purchasers are contented with a nine or ten-year-old mouth if the legs and constitution are fresh. Hence bishoping is seldom attempted excepting with horses beyond the age of eleven or twelve ; and the mere use 364 THE ANATOMY OF THE HORSE of the burning-iron without cutting off the teeth will seldom answer the pui-poses of the " coper." Formerly it was very common to see mouths with the corner nippers burnt to show a " good mark," and nothing else done to them ; but, for the reasons given above, the plan is now almost entirely abandoned. Irregularities in the growth of teeth are by no means uncommon in the horse, often caused by the practice of punching out the milk teeth to hasten the growth of the permanent set. Instead of having this effect, however, "iG. 11. —Upper Nippers ik the Kigut-Year-Old Horse. A. Anterior maxillary bone. 1. 1. Central nippers, worn to a plane surface. 2. 2. Next pair, still showing a slight remnant of the cavity. 3. 3. Comer nippers, showing the mark jilainly enough. 4. 4. Tuslies, more worn down than in the lower jaw of the six-year-old mouth. Fio. 11a.— Lower Niitees and Left Tush OF A VERY Old Horse, the Bight hav- INQ FALLEN ODT. the teeth are induced to take a wrong direction, and not meeting their fellows they do not wear down as they naturally should. In punching out the comer nipper it is very often broken off, and the fang is allowed to remain in the socket. The consequence is that the picking up of the food does not hasten the removal of the fang of the milk tooth, and instead of accelerating the growth of the permanent tooth in the natural position, it retards it and sometimes drives it to seek a passage through the gums behind its proper socket. Here, not meeting the corresponding nipper of the upper THE VERTEBRA IN GENERAL 365 jaw, it grows like a tush, and has sometimes been mistaken for a second tooth of that kind. Some horses are naturally formed with " pig jaws " — that is to say, with the upper longer than the lower — and in these cases the whole set of teeth grow to a great length, and interfere with the prehension of the food. OS HYOIDES The OS hyoides in the horse consists of five distinct pieces, contributing to the support of the tongue and larynx. One of these (the body) is central, the other four are in pairs called the greater and lesser horns. They are connected by ligaments. The body resembles a two-pronged fork in form, having a central portion flat, an apjoendix, or spur, which lies in the centre of the muscles of the tongue, and two branches. At the sides of the central portion are two little knobs for the articulation of the lesser cornua. The horns are four in number, two short and two long; the former ascend obliquely from the sides of the bodies, and end in oblong flattened smooth surfaces for the attachment of the long horns. These are much larger than the short horns, constituting two long, flat, thin bones, which give attachment to the stylo-hyoideus and hyoideus magnus muscles, and also to the constrictors of the pharynx. The bones composing the os hyoides are delineated in connection with the larynx in the twenty-first chapter. CHARACTERS OF VERTEBRiE IN GENERAL Every vertebra from the head to the sacrum is made up of certain parts, to the uses of which in the animal economy attention has been already drawn at page 350. These are — 1st, a body, which may at once be recog- nized as the central and most substantial part ; 2nd, projecting upwards from its upper edges are the two lamince, or sides of the ring, in which lies the spinal cord ; 3rd, at the upper part of the ring is a projection, more or less marked, called the spinous process ; -ith, projecting outwards from each side of the body is a lateral process, intended to give insertion to muscles, and in the region of the back affording a firm attachment to the ribs. In addition to the connection between the bodies of the contiguous vertebrte by means of a tliick fibro-cartilage, there is also a distinct articular sui-face on each side of the anterior and posterior faces of the body, which is placed upon a projection called the articular or oblique process. Thus, each vertebra has four oblique processes, two transverse processes, a spinous process, and two laminsB or sides to its large foramen, in addition to its body. This last part presents an anterior and a posterior surface, more or less oval, by which it is united to the next adjacent vertebrjB ; a superior face, which forms tlie floor of the spinal canal, and an inferior face, which is clothed with muscle on each side of a projecting x'ough line, called, wherever it is marked, the inferior spine. Throughout the spine no two vertebrae are exactly alike, even the sixth 366 THE ANATOMY OF THE HORSE and seventh dorsal showing a slight change of form in the inclination of their spinous processes. But between the first and second cervical and the last lumbar the difference is so marked, that they are not at once perceived by the casual observer to belong to the same class of bones. Tn this change the transition is gi-adual, the sixth and seventh cervical °gs g ^ g bo« 5, a eft true or sternal rib. 2. Tubi^rclp for altachment to transverse process of vertebra. 3. Head, true. 4. Body. 5. Junction of rib and its corresponding sternal cartilage. 0. Sternal cartilago^ B. Profile view of left false or asternal rib (eigh- teenth). 2. Tubercle fused in one witli the head. 3. Head. 4. Body. 5. Junction of false rib and asternal cartilage. G. Asternal cartilage. C. View of the upper extremity of sternal rib inverted to show tlie mode by wiiich tlie articulating surfaces on the upper part of tlie rib corre- spond to the nine anterior dorsal vertebrse. 1. Body. 2. Tubercle, separate. 3. 4. Head (true), showing the two surfaces of articulation, and the notch in which tlie round ligament is attached. D. View of the last asternal rib, also inverted to show the fusion of tubercle and head together. 1. Body. 2, 3. Tubercle fused with head. engraving (Fig. 21), where one of each kind is delineated. The cartilages are all attached to the ribs by firm union of their fibres to a deejD pit in the extremity of each rib. They serve the double purpose of giving elasticity to the thorax in the act of respiration and of enabling it to bear severe shocks without fracture. Among the several ribs, the first is the thickest and shortest, and is irregularly arched ; the second is very slightly curved : from this point they STERNUM, OR BREAST-BONE 375 increase in length and breadth to the ninth ; from the ninth to the last they become more curved and short. In the seventeenth and eighteenth the articulatory surface of the tubercle becomes confounded with that of the head, and the neck is wanting (see .,^ ., B, Fig. 21). THE STERNUM, OR BREAST BONE The sternum, which forms the inferior boundary of the thorax (see page 403), forms in the adult one long keel-like bone, of a spongy or cellular nature, more or less divided by cartilage ; but in the embryo it, like the sacrum, is made up of distinct pieces, six or seven in number. Anteriorly Fig. 22.— Profile View of Sternum (Breast-bone). 1. 1. 1. etc. Pits for attachment of costal cartilages. 3. 3. Posterior extremity witli its ensiform car- 2. 2. Anterior extremity ending in cariniform tilage. cartilage. the breast-bone is prolonged in a manner resembling the keel and figure-head of a ship, being clothed with cartilage, which is hence called cariniform (carina, a keel) (o, 2, P'ig- 22). Posteriorly it terminates also in a cartilage of a thinner and more flexible form, and called, from its resemblance to a sword, ensiform (ensis, Lat. sword) or xiphoid {^i^os, Gk. sword). The sides are occupied above by ,the cavities for the insertion of the costal cartilages, and below by a rough surface, to which the fibres of the pectoi"al muscles are attached. The superior face forms a very lengthened isosceles triangle, having its apex forward. It is slightly hollowed from before backwards. The three anterior divisions of the sternum present broad lateral surfaces ; the three posterior have projecting sides inclining downwards, and forming the boundaries between the inferior surface and the sides. The ribs are received into cavities in the cartilage existing between the separate bones, the last posteriorly having, however, an additional pit in its middle for the cartilage of the eighth rib. SCAPULA, BLADE-BONE OR SHOULDER-BLADE Intervening between the thorax and the fore extremity, and presenting large surfaces for the attachment of muscles to connect these two parts of the skeleton, is the scapula or shoulder-blade. It is a triangular flat bone, and lies obliquely on each side of the anterior part of the thorax, with ita 376 THE ANATOMY OF THE HORSE apex looking downwards and forwards, and its base upwards and backwards (see page 348). It presents three fossae, three borders, and three angles ; in addition to which there are the spine, the coracoid process, and the glenoid cavity. The FOSS.E are two externally, (a) the anterior, and (b) the posterior fossa, diAdded by the spine (^^ Fig. 23). These lodge and give attachment to the fibres of the supra and infra-spinatus muscles, while the internal fossa, sometimes called the venter scapulae (belly of the scapula), in the same way subserves the use of the subscapularis. 1. Spine. 2. Coracoid process. 3. Glenoid cavity, a. Anterior fossa. -Outer Surface of Left Scapula- 6. Posterior fossa. iperior costa, to which the cartilage ie attached. The SDPEiiiOR border is rough for the attachment of the broad strip of cartilage, which increases the length of the blade. The anterior border is thin, while the posterior is comparatively thick. Tee two superior angles present nothing very remarkable, but the inferior is occupied by the coracoid process anteriorly, and by the glenoid cavity posteriorly — which latter is a smooth oval cavity, lined with cartilage. It receives the head of the humerus. On account op the important offices belonging to the muscles which occupy the fossae on this bone, and since it is found that in proportion to the extent of the latter will be the muscular power, horsemen examine with great care the due development of the scapula. Unless it is long and broad it may always be predicted that the hunter will be powerless in using his fore-legs " in dirt," or in getting out of other difficulties ; and though some hacks with short shoulders may go well enough, yet, in the majority, such will not be the case. Heavy draught-horses, in which a great thickness of muscle is heaped upon the blade, are not so dependent upon its length and breadth, as has been already shown in treating of the external form of the horae at i)age 107. HUMERUS, THE UPPER ARM-BONE 577 HUMERUS, THE UPPER ARM-BON Lies between the scapula and elbow, in an oblique direction from the point of the shoulder downwai"ds and backwards. Like all the long bones, the humerus may be described as consisting of a body or shaft and two extremities. The body, which has a prismatic section, looks as if it had been twisted on itself. In the upper pai^t it is expanded laterally to form the extei-nal tuberosity (r,, Fig. 24) on the outside and the scabrous tubercle (4, Fig. 25) internally, both being for the attachment of muscles. Towards the lower extremity it becomes rounded, and then suddenly spreads out to present the 4' Fig. 24.— Extkrnal Vp . 1. Body of humerus with mnsculo-spiral groove. 2. Head. 3. External tubercle. 4. Tubercles in front of head. 5. External tuberosity. 6. Sigmoid fossa. 7. Olecranon fossa. 8. External condyle. 9. Internal condyle. wide surface which ends in the condyles on each side with the intervening articular surfaces. The superior extremity, larger than the inferior, presents for consideration a head and four tubercles. The head is the hemispherical smooth part, pro- jecting posteriorly. It articulates with the glenoid cavity of the scapula, which it much exceeds in extent of superficies. Anteriorly, the head is surmounted by four tubercles ; three directly in front are between two smooth grooves, which are covered with cartilage. The outer, or fourth tubercle, is joined with the tuberosities by a protuberant ridge, the external edge of which serves to guard against dislocation. The inferior extremity is made up of two condyles, or knuckle-like projections (g, c,, Pig- 24), having between them the smooth articular sui'face for the elbow joint. This surface is broad, and assumes a segmental form, being 378 THE ANATOMY OF THE HORSE divided into three portions by projecting lines — First, a middle groove, which terminates in front in the coronoid fossa and behind in the olecranon fossa, each being for the reception of the corresponding processes of the ulna and radius, thereby checking the motion of the joint. Second, the external 7 Flu. 25.— Internal View of left HuMERrs. A. Body or shaft. 5. Internal depression to which the internal lateral 1. Tlie head. ligament is attached. 2. Tubercles on the head. 6. Back jiart of inner condyle. 3. Internal tubercle. 7. Internal condyle. 4. Scabrous tubercle. groove, which is comparatively slightly marked ; and third, the smooth surface lining the internal condyle. All of these fit accurately into the articular surface of the ulna and radius, to be presently described, allowing of nothing but a hinge-like motion. Of the condyles, the inner is larger and more projecting than the outer. In the young foal the two extremities arc distinct epiphyses, united to the shaft b}- cartilage only. THE BONES OF THE FORE-ARM (OS BRACHII) In the hujian subject, and in the dog and cat among our domestic animals, the bones of the fore-arm are distinct, and may readily be separated from each other as the ulna and radius. In the early periods also of the life of the horse the same condition obtains, but when he is matured, these bones are indissolubly united by ossification. The line of junction can always be traced, and there is an opening left which is called the radio- cuhital arcade, and gives passage to an artery and vein. It will be therefore understood that the term os hrachii means the bone composed of the united ulna and radius, and that in alluding to each of these divisions we only speak of tlicm, in analogy with human anatomy, as separate bones. By THE FOREARM 379 drawing a line from llic back of the condyle of tlie humerus till it cuts the posterior edge of the sliaft of the os brachii about its middle, the line of demarcation may easily be arrived at. The Radius forms the bulk of the os hraehii, supporting the weight of thr; body upon its head, and conveying it to the carpus through its lower extremity. Its shaft is long, smooth, and convex anteriorly ; rough for the attachment of muscles, and concave posteriorly. The superior extramity is expanded and presents an articular surface divided into two fossae by a slight ridge, the inner of the two being broader and more circular. On each side of these pits is a slight projection, called the lateral process, to which the corresponding ligaments are attached. The hiferior extremity, which is also expanded, is remarkable for the variously shaped pits slightly marked on its articular surface, each being intended to fit one of the carpal bones of which the knee is made up. There is a prominent internal lateral pro- cess, and one less distinct on the outside marked with a groove. The ulna (or ulnar division of the os brachii) is much shorter than the radius, and can scarcely be considered as having two extremities, its lower end being cut off in an oblique direction and terminating in a sharp point, so as to look like a splicing of the one bone to the other. It may be considered as consisting of a short body (o, Fig. 26), surmounting which is the olecranon process (3) behind, and the articular surface (4) Fio. 26.— Bones ok the Foue-Aum, Knee, Cannon, Pa8TEp.n3, AND Foot. 1. Semicircular fossa fjnned by the radius and ulna for tlie elbow joint. 2. Body of the ulna. 3. Olecranon process. 4. Articulating surface. 5. Body of the radius. 6. Surface articulating witli the condyle of the hunicnis. 7. Tubercle to which the coraco-radialis muscle is attached. 8. Articulatory surfaces corresponding to tlie ujii^er row of knee- bones. 9. Ospisifonne. "\ 10. — cuneifonne. | 11. — lunare. ,- Bones of the knee. 12. — unciforme. i 13. — magnurn. ; 14. Metacarjjus or cannon-bone. 1j. External small metacarpal bone. 16. Tubercle to which the tendon of the muscle (extensor metacarpl rnagnus) is attached. 17. Joint uniting with the os sufEraginis. 18. Os suffraginis. 19. External sesamoid bone. 20. Os corona. 21. Os pedis. 22. 22. Wings of pedal bone. 23. Os naviculare. 380 THE ANATOMY OF THE HORSE in front. Descending from the bocl}^ is the thin wedge of bone which is united iudissolubl}^ with the shaft of the radius at the point marked 5, and may be traced down to the carpal joint. The articular surface comprises part of the elbow joint, and has below it some roughened inequalities for the attachment of ligaments. The olecranon process, or elbow, is of considerable size and strength, form- ing a strong lever for the action of the triceps muscle, which is inserted in its point. Its anterior edge has a sharp point, which deepens the articular cavity, and checks the motion of the joint from being carried too far. THE CARPUS (KNEE) AND METACARPUS (CANNON) The knee of the horse corresponds with the wrist of man, and though the name so well known to horsemen will probably always be maintained, yet scientifically each of the bones receives the corre- sponding names, and the whole group is called the carpus. The anterior surface of the carpus is convex ; the posterioi', concave and irregular, and marked by bony prominences. It consists of eight bones, disposed in two rows, one above the other, as follows : — The first, or top row, beginning to enumerate from within outwards, consists of the scaphoid, lunar, cuneiforme, and pisiforme bones. The second, or lower row, consists of the essa tra- pezoid, magnum, and unciforme, and sometimes of a small floating bone situated behind the trapezoid. The superior row may be described as follows : — Os ScAPHOiDES (o-Kci^r;, a cradle), the largest of this row, articulates superiorly with the infeiior and inner extremity of the radius, internally by means of two distinct facettes with the os lunare, and inferi- orly Avith the os trapezoides and os magnum. Os Lunare (luna, the moon) articulates superi- orly with the radius, internally as before mentioned with the OS scaphoides, and externally through the medium of two facettes with the os cuneiforme. Os Cuneiforme (cuneus, a wedge) articulates supe- riorly with fehe inferior and outer extremity of the radius, inferiorly with the os unciforme, and pos- teriori}'^ with the OS pisiforme. Os Pisiforme (pisum, a pea) is situated at the postero-external side of the top row, and presents for description two surfaces and four borders. The external surface is unevenly convex, and elevated for ligamentous attachment. The internal surface is concave and porous, and also roughened for ligamentous attachment. The anterior border rio. 27. — FoiiE View oi- TUE Carpal Bones, cosi- MONLY CALLED THE KnEE. •2. Lower extremity i,f radius. 3. Ulna, lower extruniil\' of. 4. Os pisiforme. 5. — cuneiforme. 6. — lunare. 7. — scaphoides. 8. — unciforme. 9. — magnum. 10. Large metacariial bone. 11. Small metafarjuil bone. THE CAllPUS AND I\l]']TACAKPUS 3X1 FlO, S PiSIlORMK. 1. Body of OS pisiforme. 2. Surface articulating with inferior ex- tremity of the ra- dius. 3. Surface articulating with the cuneiforni bone. presents two smooth ovoid surfaces : the superior one articulates with the radius ; the inferior with a corresponding surface, mentioned as occurring on the posterior surface of tlie os cuneiforme. The three other borders, namely, the superior, posterior, the inferior, are unevenly convex, and roughened for the attachment of ligaments. The bones of the inferior row, viz. the Os Trape- zoiDES {TpdireCa, a table), Os Magnum (the large bone), and Os Unciforme (uncus, a hook), articulate laterally one with the other, supei'ioi-ly with the top row of bones, and inferiorly with the three metacarpal bones. The Metacarpal Bones, answering to the bones in the palm of the hand of man, are three. One (metacarpus magnus) is much larger than the other two, which, from thus supporting, "are sometimes called splint-bones. The Metacarpus Magnus, or cannon-bone, has a body and two extremities, the superior of which articulates with the carpus while the inferior rests upon the next phalanx, or great posterior bone (see Fig. 26). The body is convex and smooth, anteriorly and laterally ; thus forming two-thirds of a cylinder. Posteriorly it is flattened ; its sides, extending from above, downwards, to about three inches above its inferior extremity, present two triangular scabrous surfaces, on the upper parts of which two smooth articulatory spots occur, to which the small meta- carpal bones are attached. The superior extremity presents a smooth ar- ticulatory surface which is, for the most part, flat; it slopes ofi^, however, on its outer side for ai'ticulation with the OS unciforme. There is also another small spot which slightly declines, situated at the outer side of the head of the inner small metacarpal bone. This spot articulates with the postero-inferior surface of the OS trapezoides. The flat surface articulates with the OS magnum, to which it corresponds in figure. Its anterior and lateral edges are somewhat roughened. The inferior extremity presents two smooth condyloid surfaces, separated by a smooth semicircular eminence, which articulate with a corresponding for- mation on the superior extremity of the os suffraginis. On the sides of each of the condyles a depression occurs. OssA Metacarpi Parva are in number, two ; external and internal. In form they are pyramidal, presenting bases turned upwards, apices down- wards, and bodies or middles. Fm. 29.— Back View of THE Large and Small Metacarpal Bones. 2. Metacarpus magnus. 3. The surfaces above ar- ticulate with the lower carpal bones. ■J. 4. External and internal snjall metacarpal bones 5. 5. Condyloid surfaces ar ticulating witli corre spending ones on the upper extremity of tlie os suffraginis. 0. Eminence articulating with a corresponding depression on the upper extremity of the os suf- fraginis. 382 THE ANATOMY OF THE HORSE The base is surmounted by a smooth articulatory surface, surrounded iuferiorly by roughened tuberosities, except anteriorly, where two smooth articular surfaces occur, which articulate with corresponding surfaces mentioned as existing on the metacarpus magnus. The body is trifacial. The anterior surface is rough, and articulates with the metacarpus magnus. The inner surface is excavated. The outer surface is convex and smooth. The apex terminates in a bulbous extremity, which looks posteriorly, and does not articulate with the metacarpus magnus. THE PHALANGEAL BONES (PASTERNS AND FOOT) Beyond the metacarpus in the horse, there is only a single bone in each joint, the five fingers being merged in one. The same number of phalanges, however, is maintained, counting from the metacarpus to the distal phalanx, which is the pedal bone. The whole may, therefore, be considered as analogous to one human finger, with the addition of the two sesamoid bones, and the navicular bone, all three of which are intended to assist in giving leverage to the tendons moving these parts. The highest of these is the OS suffroginis or larger pastern, the next the os co7'ona or lesser pastern, and the lowest the os jj^dis or coffin-bone. The Os Suffraginis and its Ossa Sesamoidea may be taken together, the latter lying on each side of the back of its superior extremity, but play- ing only on the large metacarpal. They are separately shown at Fig. 30. The os suflfraginis has a body and two extremities. The body shows an anterior surface, which is con- -OssA Sesamoidea. ^^^ ^^^ smooth ; and a posterior which is rough and flattened, and presents superiorly a triangular space, bounded lateral!}^ by two roughened ridges, which meet at a point inferiorly. The superior extremity presents two shallow concavities, which are separated one from the other by a deep transverse canal. Behind these concavities, two tuberosities exist for the attachment of the crucial ligaments. The inferior extremity has two semi-cylindroid convexities, divided transversely by a shallow depression, which is widened posteriorly. Os CoRONiE (corona, a coronet) is in form a parallelogram with four surfaces. The anterior surface is convex and roughened, presenting two tuber- osities below. The posterior surface is smooth, and has superiorly a semilunar smooth surface. The superior surface presents two ovoid concavities, divided by an eminence running from behind forwards, and bounded, anteriorly and posteriorly, by two roughened projections. These form the lesser fetlock joint with the bone above. The inferior surface i^esembles the corresponding part of the oa sufFraginis. THE PHALANGEAL BONES 383 Ujs vEDis (the bone of the foot, foruicily called the coffin-bone). In form it is semilunar, divided into wall, sole, articulatory surface, and retrossal processes, commonly called wings (see Fig. 31). The wall, the semicircular prominent part, possesses some degree of declivity, increasing in circumference from above, downwards. It is full of foramina, and rough. Superiorly, the bone bulges out, forming the coronal process (8, 8). The middle part of it terminates in a peak, which looks slightly backwards — the cacumen coronse {the peak of the coronet). The wall terminates posteriorly in wings ; the retrossal processes Pia. 31.— Posterior View of Phalanoes. B. Os 5. 0. C. Os D. Os 12. 114. siiffraginis. 1. Surfaces articulating witli the lower extremity of the large meta- carpal bone. Groove. Rough surface for the implantation of ligaments. 4. Inferior extremity articulating with coronse. 5. Superior articulatory surfaces. 6. Inferior articulatory surfaces, pedis. 7. Articulatory surfaces. 8. Coronal jirocess. 9. Scutiform processes. 10. Retrossal processes. Surface articulating with a corre- sponding one on tlie navicular bone (12.) naviculare. Surface articulating with the os coronte. Surface over which the flexor pedis lierforans tendon glides. 14. Points attached to the i^edal bone by ligaments. (10,10); each wing is divided into two parts by a groove, which runs through it from before, backwards. The inferior surface or sole is divided into an antei'ior semilunar plantar surface, and into a posterior sharp semicircular edge which divides it from the tendinous portion. The former is slightly concave, porous, and bounded by the inferior circumferent edge of the wall. The superior articulatory surface, semilunar in form, presents two lateral concavities, separated by an eminence. The eminence is bounded anteriorly by the cacumen coronje, which stands before it, the point looking backwards. Posteriorly, it is bevelled off for articulation with the os naviculare. Os Naviculare (navis, a shi^j), sometimes called the shuttle-bone, in form is semilunar and elongated. It is divided into four surfaces and two extremities. The superior surface presents, in its centre, an eminence, which declines laterally, leaving two slight concavities. 384 THE ANATOMY OF THE HORSE The inferior surface presents two slightly convex divisions, with a prominent smooth ridge dividing them, running from behind forwards. The anterior surface presents superiorly a smooth triangular articula- tory surface, and inferiorly a porous, roughened face. The posterior surface is triangular, roughened, and porous. The extremities, the internal and external, turned upwards, terminate obtusely. THE PELVIS The general features belonging to the pelvis have been alluded to in the last chapter, and the sacrum which forms its upper wall has been described in this. It remains now to ascertain the shape and anatomical Fia. 32.— Pkoi-ile View of tiik two Ossa Insominata. 1. 1. Wings of the iliac bones. 2. 8. Pubic bone. 3. Ischiac bone. 4. 4. Superij-posterior spinous process of the two ossa ilii. 5. An tero- inferior spinous process of the left ilir 6. Tlie narrow part or neck of the ilium. 7. 7. Obturator holes (foramina). 9. 9. Tuberosity of each ischium. 10. Acetabulum. bearings of the bones which complete the arch. These in the embryo are three on each side, uniting below in the median line by symphysis, and above to the rough surface on the side of the sacrum. These three are 1st, Os ischi ; 2nd, Os ilii, and 3rd, Os j^uhis. The whole bone, which is firmly united in the adult, receives the somewhat paradoxical denomination of Os innominatum, or the unnamed bone. On referring to the skeleton at page 348 it will be apparent that the attachment of this bone to the sacrum is so arranged that it shall act as a THE FEMUR 385 spring in breaking the jars receivud by the hind extremity from the ground. Its oblique direction, its comparatively short surface of attachment to the sacrum, and its own great length show this most plainly, especially when compared with the human pelvis, in which a very different formation prevails. In the horse it forms, with the sacrum, the first of a series of angles, the second being between it and the femur, the third at the stifle joint, and the fourth at the hock. In the embryo the three bones are quite distinct, the cartilaginous lines of separation being visible for some time after birth, running through the cup-like cavity which forms the socket of the hip joint. The portion lying above and in front of this cavity, and taking in also two-thirds of its own cup, is the OS ilii. Posteriorly to the cavity, the bone is divided into two strong branches by a large opening, the obturator foramen, and that portion which lies above it is the os ischii, while the lower division is the os pubis. It is needless to describe these bones separately. The bone as a whole may be considered as divided into two parts by the contracted neck which forms its middle. The anterior of them is hollowed out externally for the reception and attachment of the glutei muscles. Internally it is rough, and gives attachment to the strong car- tilage and ligaments which bind it to the sacrum. The processes extending forwards are called the spinous processes of the ilium (see Fig. 44). Behind the neck the bone swells out slightly for the development of the cotyloid (KOTvXrj, a cup) cavity, or acetabulum. This is nearly three inches in diameter, and is surrounded on all sides but that looking towards the obturator foramen by a prominent lip. The interval is called the notch, and corresponding with it is a rough depression in the cotyloid cavity, where the cartilage is absent, and to which the round ligament of the hip is attached. Behind the cotyloid cavity is the obturator hole, apparently intended to lighten the bone, being filled up by a strong membrane, the obturator ligament. Above this opening is the ramus of the ischium, which bone also enters into the composition of the hip joint as already described. Posteriorly the ischium terminates in a rough protuberance, the tuberosity (9-9, Fig. 32), which is the rounded projection felt and seen on each side the root of the tail in the living horse. Below the foramen is the os pubis, the anterior part of which is the ramus, and the small section of the cotyloid cavity which it forms, while posteriorly the body unites with the os ischii, to form, with the corresponding bones of the opposite side, the symphysis, or connecting joint between them. By THE CONJUNCTION of the two ossa innominata an oval ring is nearly completed, the deficiency being supplied by the sacrum above. The anterior margin of this ring is the brim of the pelvis, and it is upon the size of this as compared with the foal that parturition is in general rendered easy or difficult. THE FEMUR (ROUND-BONE) AND PATELLA The Os Femoris, the strongest and heaviest bone in the body, is situated between the os innominatum and the tibia. It takes an oblique direction from above downwards and forwards, and presents a central part or body, 386 THE ANATOMY 01 THE HORSE and two extremities. It Wtas formerly called the round-bone, froiij being in the centre of the part called by butchers " the round." The body, although compressed, is nearly cylindrical towards its centre ; anteriorly, the bone is convex and smooth ; posteriorly, flattened and rough ; superiorly and inferiorly, it is expanded to meet the enlarged extremities. The superior extremity is prolonged into a thiok, flattened neck, FiP. 33.— The Fe.mur, pautiallt detached from xnn Cotyloid Cavity. A. External view of posterior half of tlio os iii- iiominatum. 0. Rough surface for the attachment of muscles. b. Cotyloid rim. c. Tuberosity of the ischium. 1. Cotyloid cavity. 2. Depression in which the round ligiuiieiit (ligamentum teres) is fixed. 3. Obturator hole. R. External view of the right femur. 4. Head of the femur (round-bone). 5. Trochanter major externus. (.1. Tubercle on the head of the femur. V. Trochanter minor externus. S. Fossa for muscular Insertion. 0. 0. Trochlear surfaces for articulation with the patella (knee-cap). ] 0. External condyle. articulating with ujtper extremity of the tibia, or leg-bone. directed upwards and inwards, so as to form an obtuse angle with the rihaft. At the point of union are two eminences (trochanters, rpoxoiv, to run or roll) ; one on the outer, and the other on the inner side ; and it is from between these that the neck arises. The trochanter major is prolonged from the postero-external margin of the body, and nearly in a line with its axis : it is a large irregular projec- tion, rising into a pyramidal eminence. I'osteriorly, at its base, it presents THE FEMUR 387 an oval cavity, the digital fossa, for the attachment of several small muscles. Inwardly it presents a concavo-convex smooth surface ; outwardly, a convex and rough one. From the back of the great trochanter a prominent line runs vertically down, terminating in the trochanter minor e«ternu.s (t. Fig. 33) ; and from this again a roughened ridge descends, taking a course downwai'ds and slightly forwards to the oval fossa situated above the external condyle (8). The neck is surmounted by a hemispherical smooth head, coated with cartilage, and lodged in the acetabulum ; on it is a deep ovoid fossa, which gives attachment to the ligamentum teres. Tlie trochanter minor internus, a conical rounded eminence, arises from the posterior and internal side of the bone. It is placed above the tro- chanter minor externus, which is on the opposite side. The inferior extremity has on each side an eminence (the external and internal condyles), separated by a deep fossa. Between these anteriorly two articular surfaces occur (external and internal), separated by a semicircular groove, in which the patella plays. The external condyle is larger and projects more forwards than the internal ; its articular surface is also broader : the internal presents a tuberosity on its inner surface. The articular surfaces of both condyles are covered with cartilage, and united anteriorly to the prominences before mentioned, where they form a pulley-like surface, concave from side to side, over which the patella glides. Inferiorly, from before backwards, these prominences converge together, and terminate abruptly on the postero-interior surface of the bone ; thus leaving a space between them and this interval, which has been denominated the intercondyloid fossa. The patella, stifle-bone, or knee-cap, lies on the lower extremity of the femur, at the anterior part of the stifle joint. It is quadrangular in form ; its anterior surface is converse and rough ; its posterior being covered with cartilage is smooth, and is divided by an eminence running over it into two shallow cavities (the super- ficies of the internal being the larger), which corre- spond with the trochlear prominences, situated ante- riorly to the condyles of the femur. Superiorly it Fm. 34.— Posterior View presents a triangular roughened space, bounded by its two lateral angles, which gives attachment to muscles, 2.' ^"sMrfaceTfiidingontiie and inferiorly we notice a fourth angle. These angles trochiese of the fe- are all blunt and slightly rounded off. BONES OF THE LEG The TiniA (so called because the ancient shepherds used this bone as a tlute) lies between the femur and tarsus (hock), forming an angle with each. It is broad, and of a spongy texture above ; contracted and dense below, wher(! it is felt imm.efliately beneath the skin and tendons. The body is of a triangular or prismatic shape above, its angles gradually rounriing off below, and then expanding laterally to meet the condyles of the 388 THE ANATOMY OF THE HORSE lower extremity. The anterior angle is the shin, and at the upper part of this is a strong tubercle (3, Fig. 35). The superior extremity has two irregular^ oval and slightly hollowed articulatory surfaces, which revolve upon the condyles of the femur, the cavity being deepened in each by the intervention of the semilunar cartilage. Between them are to be seen a sharp elevation and two pits to which the Fig. "5.— Tibia, FinL'i,A, and Tarsus. A. Tibia. 1. 2. Articulfttory snrfanflR. 3. Tuberosity. 4. Sijine. 5. External malleolus. 6. Surfaces articulating with astraj B. Fibula. C. Os calcis. 7. Point of hock. ]). Astragalus. E. Os scaphoides. F. Os cuneiforme mnguum. Q. Os cuboidcs. H. Os cuneiforme parvum. I. Upper part of large metatarsal bone. K. Upper portion of the external small mntatai-snJ bone. crucial ligaments are attached. In front is the tuberosity to which the ligament of the patella is fixed. On the sides of the head are the condyles, rough for the attachment of the corresponding ligaments, and the external having an oval articular fossa for the head of the fibula. The inferior or tarsal extremity is much smaller than the superior, but wider than the body, and neai^ly quadrilateral ; its anterior border is flat and rough; its posterior border is also flat, and presents numerous foramina. THE HOCK 389 The external border is prominent and rough, and has a groove in its centre. Depending from each side is a process (the internal and external malleolus of human anatomy), serving to strengthen the articulation with the astragalus, and the internal being considerably the longer. Between these are two deep grooves, smoothly covered with cartilage, and having a projection in the middle similarly clothed. The direction of these grooves is obliquely forwards and outwai'ds. Both the malleoli are lined with cartilage, which enters into the joint. The Fibula is a slender bone, having a slight enlargement at its superior extremity to form the head. On its inner surface there is a layer of articular cartilage to form the joint with the tibia. Below it has a bulbous end, which is free, and affords attachment to the ligamentous fibres which connect it with the tibia. Between the two bones there is a considerable space, occupied by a thin membrane. The Tarsus, or hock, is made up of several bones connecting the tibia above with the metatarsus below. It corre- sponds with the ankle of man ; and if the term wrist were to be applied to the knee of the horse, as suggested by certain writers, in order to be consistent the hock must be called the ankle, which would lead to endless confusion. The better plan is to retain the names by which these parts ai^e known in our ordin- ary language, and to adopt the nomencla- ture of the anatomical school for any scientific description. Thus the carpus and tarsus of the anatomist are rendered into the knee and hock of the horseman without impropriety, and at the same time without any chance of a misunderstanding. The tarsus consists of six bones, dis- posed in two rows, the astragalus and os calcis forming the upper one, but the former bone alone entering into the tibio tarsal, or hock joint, with the tibia. The Astragalus (aarpdyakos, a die) is an irregular bone, situated in front of the OS calcis, between the tibia and the os scaphoides : it is divided into five sur- faces : first, the supero-anterior surface, pulley-like and articulatory, cor- responds with the inferior extremity of the tibia, and consists of two semicircular prominences, separated by a deep groove, taking a course obliquely outwards and forwards ; secondly, the inferior presents a smooth convex surface with a roughened depression posteriorly, for ligamentous attachment, and articulates with the superior face of the os scaphoides; Fio. 36.— Internal View of Tarsal Bokbs. 2. Inferior extremity of the tibia. a. Internal malleolus. 6. External malleolus, 3. ips calcis. 4 aifti 6. Surfaces of articulation on the astragalus, which, together with corresponding ones on the tibia, form the great hinge-joint of th« skeleton. e. Tubercle on the astragalus for the attach- ment of ligaments 6. Os scaphoides. 7. — cuneiforme magnum 8. — cuneiform parvum. 9. — Large metatarsal bone. 10. Internal small metatarsal bone. S90 THE ANATOMY OF THE HORSE thirdly, the posterior is irregular, and presents on its surface four smooth faces for articulation with the os calcis, which are separated by roughened excavations. The external side is marked by ligamentous impressions ; the internal, smoother than the external, presents behind and below a little tubercle, which gives attachment to ligaments. The Os Calcis {the heel-hone). — This bone, forming the point of the hock, presents two surfaces, two borders, and two extremities ; the external 8U rf ace is almost plain ; the internal is excavated as a groove ; the anterior is slightly concave ; the posterior is straight and roughened ; on the superior extremity is a thick tuberous termination, to which the hamstrings are attached ; its inferior extremity is large and concave, and presents four surfaces for articulation with the astragalus, os cuboides, and os scaphoides, and a median rough interspace to which ligaments are attached. The Os Cuboides (kvIBos, a cube) is situated on the postero-external sides of OS cuneiforme magnum and os scaphoides, between the inferior exti'emity of the OS calcis and the head of the external small metatarsal bone and also a portion of the superior extremity of the large metatarsal bone. It presents six surfaces : a superior, which articulates with the os calcis : an inferior by two facettes corresponds to similar ones situated on the large and external small metatarsal bones just mentioned ; internally two arthrodial surfaces occur, which face with similar surfaces on the os cuneiforme magnum and OS scaphoides. The external, anterior, and posterior surfaces are roughened for ligamentous attachment. The Os Scaphoides is in figure triangular ; the superior surface, smooth and slightly concave, is entirely articulatory, with the exception of a little groove, running to its middle from the outer side ; this surface corresponds with the under surface of the astragalus. The inferior surface is similar to the superior, except that it is slightly convex, and articulates with the superior surface of the os cuneiforme magnum, and also on its internal angle with the os cuneiforme parvum ; it offers also, on its postero-external face, two small diarthrodial surfaces for articulation with the os cuboides ; in the rest of its extent, it is roughened for ligamentous attachment. The Os Cuneiforme Magnum. — This bone, although smaller than the scaphoid, at the same time greatly resembles it ; its superior surface articu- lates with the inferior surface of that bone ; the inferior surface articulates with the large metatarsal bone ; its external border is provided with two arthrodial spots for articulation with corresponding ones on the os cuboides. The internal border also offers a spot which articulates with a similar one on the OS cuneiforme parvum ; its anterior border is roughened throughout. The Os Cuneiforme Parvum is situated on the internal side of the tarsus This bone, smaller than all, is prolonged from before backwards, flatten' d from one side to the other, and articulates with the os cuneiforme magnum and with the large and internal small metatarsal bones, to which it corresponds by four surfaces covered with cartil;i;,''>. METATARSAL AND PHALANGEAL BONE.S 391 METATARSAL AND PHALANGEAL BONES The Metatarsal and Plialangeal bones, known to the horseman iis tho cannon-bones, the pasterns, and the hind-feet, resemble so closely those of the fore extremity, that it is unnecessary to repeat the description of them licre. CHAPTER XIX OF THE JOINTS, AND THE TISSUES ENTERING INTO THEIR COMPOSITION GENERAL REMARKS— CARTILAGE— FIBROUS TISSUE— FIBRO-CARTILAGE— SYNOVIAL MEM- BRANES— CLASSIFICATION OF THE JOINTS — MOVEMENTS OF THE JOINTS — ARTICULATIONS OF THE VERTEBRAL COLUMN— THE LIGAMENTUM NUCHfE, OR GREAT CERVICAL LIGA- MENT, AND OTHER PECULIARITIES IN THE LIGAMENTS OF THE NECK — MOVEMENTS OF THE VERTEBRAE IN GENERAL, AND OF CERTAIN OF THEIR JOINTS IN PARTICULAR — THORACIC ARTICULATIONS — PECULIARITIES IN THE ARTICULATIONS OF THE LUMBAR VERTEBR^?: — THE LUMBO-SACRAL ARTICULATION AND SACRAL LIGAMENTS — THE COCCY- GEAL JOINTS — THE TEMPORO-MAXILLARY ARTICULATION — THE SACRO-ILIAC ARTICULA- TION ^ ISCHIO-PUBIC SYMPHYSIS — THE SHOULDER JOINT — THE ELBOW JOINT — THE KNEE JOINT (CARPUS, OR WRIST). — INTER-METACARPAL ARTICULATIONS — FETLOCK JOINT^THE PASTERN JOINT — THE COFFIN JOINT — THE HIP JOINT — STIFLE JOINT OR COXO-FEMOR.\L ARTICULATION— TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT— TARSO-METATARSAL ARTICULATION — TERMINAL ARTICULATION OF THE POSTERIOR LIMBS. GENERAL REMARKS The JOINTS are all formed between two or more separate bones, having a soft and elastic substance interposed, whose structure varies with the amount of motion. Where this is extensive, as in the joints of the limbs, the adjacent surfaces are covered with a peculiar kind of cartilage arranged in a thin and very smooth layer upon them. In addition to this protection against friction and vibration, the bones are firmly bound together by strong bands of white fibrous inelastic tissue under the general name of ligaments, each bundle receiving a distinct appellation. In those situations where the motion is limited, a mixture of cartilage and fibrous tissue is inserted between the ends of the bones and attached to both, as in the vertebrfp, ischio-pubic symphysis, etc. ; while in order to reduce the vibration and friction in certain important joints fibro-cartilages are introduced, with both surfaces free, and in contact only with the usual layer of cartilage, as in the stifle and jaw. A lubricating fluid (called synovia) is required to reduce the amount of friction ; and to produce it, as well as to keep it within proper limits, a membrane (synovial) is developed. This is -attached to each D D 392 THE ANATOMY OF THE HORSE bone in a peculiar manner, to be presently described. Lastly, an elastic fibrous tissue (yellow) is met with in certain situations, the most remarkable being the great ligament of the neck. Each of these different structures will require a separate description ; for as the diseases of the joints are of great importance, a knowledge of the structure of their component parts must be carefully obtained before entering upon the treatment with any hope of success. CARTILAGE True cartilage (which is familiarly known to all when it shows the large white masses in a breast of veal, as dressed for the table) is a homo- geneous, white, semi-transparent substance, possessing a certain amount of elasticity, and easily cut with a knife. In the early embryo it exists as the sole foundation of the skeleton, bone being afterwards deposited in its meshes and finally substituted for it. This is called the temporary cartilage. In after life it invests those parts of the bones which enter into the com- position of the joints (articular cartilage, which is what we are considering just now), and also forms the costal cartilages, the ensiform and cariniform cartilages, and those of the larynx, trachea, and nose. Reticular or memhraniform cartilage, diffei'ing slightly from true cartilage, is met with in the Eustachean tube, the external ear, and the epiglottis. Structure. — On putting a slice of true cartilage under the microscope, it is seen to consist of a number of minute cells disseminated through a vitreous substance. The cells are oval, oblong, or polyhedral in shape, and more or less flattened by packing. The membrane forming the cell- wall is • usually blended with the matrix, but sometimes consists of concentric layers. White fibres usually enclose the mass of cells, and even dip sometimes into those cells more superficially placed. The cells or corpuscles are contained in hollow cavities, called lacunae. Sometimes they do not entirely fill up the lacunte, so that a vacant space is left. The corpuscles are usually dispersed in groups, A^arjdng in size and form, through the matrix ; the groups towards the surface of the cartilage are generally flattened conformably with the surface. In articular cartilage, the matrix in a thin section appears dim and presents a granular aspect, the cells and nuclei of which are small. The parent-cells enclose two or three younger cells. The groups they form are flattened near the surface and lie parallel with it. In the internal part of this cartilage the cells assume a linear direction, and point towards the surface. Near its attached surface cartilage blends with the bone, the cells and nuclei of which become surrounded by little granular bodies, which seem to be the rudimentary deposit of bone. In costal cartilage the cells are very large ; they contain two or more nuclei, which arc clear and transparent, and some contain a few oil globules. The cells, internally situated, form oblong groups, disposed in lines radiating to the cii'- cumference. We observe a great quantity of intercellular tissue, in the form of white fibrous structure, the fibres of which are parallel and straight. Perichondrium ("Trept, around, and xovhpos, cartilage}) is a white fibrous Bubstance, which covers the external surface of all cartilages, except those FIBROUS TISSUE 393 of the joints. In this membrane the blood-vessels which supply the carti- lage with blood, ramify. It is analogous to the periosteum which covers the external surface of bones. Nerves. — No nerves have been traced into any of the cartilages ; they are destitute of sensation while free from inflammation. Blood-vessels. — Cartilage is non- vascular ; it receives its nourishment from the bone and pez'ichondrium by imbibition. The law of endosmose coming into operation when the tissue is thick, as in the costal cartilages, canals are formed through which the vessels pass to supply the parts which are too far removed from the j)erichondrium. In articular carti- lages no vessels enter. When cai'tilage is removed by mechanical means, or by absorption, it is not regenerated, and when fractured, as in the ribs, there is no reunion by cartilage, but by fibrous, or most frequently by osseous deposition. Chemical Composition. — True cartilage contains three-fifths of its weight of water. It is ascertained that the cells and the intermediate substance are composed of different materials. The membranes of the cartilage cells are not resolved by boiling, and offer a lengthened resistance to alkalies and acids. The contents of the cells coagulate in water and dilute acids, and are dissolved by alkalies. The intermediate substance consists of chondrine, which differs from gelatine in not being precipitated by the mineral acids. FIBROUS TISSUE Fibrous tissue exists very generally throughout the body, being com- posed of fibres of extreme minuteness. It is found under three forms, as white fibrous tissue, yellow fibrous tissue, and red fibrous tissue. White fibrous tissue is composed of cylindrical fibres of exceeding iijinuteness, transparent, and undulating. They are collected first into small fasciculi and then into larger bundles, which, according to their arrangement, compose thin layei-s or membranes, ligamentous bands or tendons. The viemhranous form is seen in the periosteum and peri- chondrium, the fascise covering various organs, the membrane of the brain, ■etc. — Ligaments are glistening and inelastic bands, composed of fasciculi of librous tissue genei'ally ranged side by side, sometimes interwoven with each other. These fasciculi are held together by separate fibres, or by ai^eolar tissue. They are of all foi-ms, from the round band to the expanded membx'ane known as a capsular ligament. — Tendons are constructed like ligaments, but usually in larger and more rounded bundles. Sometimes they are spread out in the form of aponeuroses. Yellow fibrous tissue is also known as elastic tissue, from its most prominent physical characteristic, in which it differs from white fibrous tissue. It is so elastic that it may be drawn out to double its natural length, without losing its power of returning to its original dimensions. Its fibres are transparent, brittle, flat or polyhedral in shape, colourless when single, but yellowish when aggregated in masses. When this tissue is cut or torn, the fibres become curved at their extremities in a peculiar auanner. It is met with in the ligamenta subflava of the vertebrae, the 394 THE ANAT02k[Y OF THE HORSE ligamentum colli, the cliordise vocales, and membranes of the larnyx and trachea, and the middle coat of the arteries. Red fibrous tissue, also called contractile tissue from its possessing the power of contracting under certain stimulants, is intermediate between 3-ellow fibrous tissue and muscular fibre. Its fibres are cylindrical, trans- parent, of a reddish colour, and collected in bundles. It has no connection with the joints, but is met with in the iris, around certain excretory ducts, and in the coats of the veins. Chemical Comjjosition.^ — The flexibility of fibrous tissue is owing to the presence of water in it, of which it contains about two-thirds of its weight. A tendon or ligament will readily dry and become brittle. Acetic acid causes it to swell up, and here the acid discloses the existence of nuclei and elastic fibres. It is chiefly composed of gelatine, which is extracted by boiling. Blood-vessels. — White fibrous tissue contains few blood-vessels. They usually follow the course of the fasciculi ; in ligaments they run in a longitudinal direction, sending off communicating branches across the fasciculi, and eventually forming an open network. The periosteum is much more vascular, but the vessels do not strictly belong to the membrane, as the ramifications found in it are chiefly intended for supplying blood to the Ijone which it covers. Nerves. — Small tendons contain no nerves, and large ones only small filaments. In the periosteum, nerves are abundant ; they exist there chiefly for supplying the bones with sensibility. The pain caused in rheu- matism, which is an intensely painful disease, is a proof of the sensibility of white fibrous tissue. FIBRO-CARTILAGE This substance, intermediate in structure and uses between cartilage and fibrous tissue, is composed of a network of white glistening fibres col- lected into fasciculi of various sizes, and containing within its meshes cells and a sub-fibrous tissue resembling that of true cartilage. Fibro-cartilage admits of arrangement in four groups : — 1. Interarticular fibro-cartilage is placed between the moving surfaces of bones. It serves to connect them together, to facilitate their gliding motion, and to act as a cushion, thus preserving the articular sur- faces from attrition, and the bones from the efiects of sudden concussion. It is usually placed where much motion is enjoyed, as in the lower jaw and knee, in the form of round oval plates growing thinner in the centre. Marginal cartilages such as that around the cotyloid cavity are of the same kind. 2. Stratiform fibro cartilages form a thin coating to the bony grooves over which tendons play. 3. Interosseous fibro-cartilage occurs between the vertebra?, at the ischio-pubic symphysis, etc. 4. Free fibro-cartilages are met with in the tarsal cartilages of the eyelids, etc. SYNOVIAL ME^[BRANES 395 SYNOVIAL MEMBRANES The synovial membrane is a thin layer, which invests tne articular cartilages of opposite bones, and is continued from one to the other by being reflected beneath the ligaments which connect ttiem. It resembles ;he serous membrane in being a shut sac or bladder, and a synovial capsule may be compared to a small bladder, containing only as much fluid as will adhere to its interior, placed between the opposite ends of two bones forming a joint. The secretion formed by it, synovia (avv, together, u)uv, an tgg), is alkaline, and contains albumen, which is coagulable by boiling- Heale has ascertained, by the aid of the microscope, that this membrane is actually reflected over the articular cartilage, a point which has been long disputed. Besides the joints, the synovial membranes also form smaller sacs which lubricate the tendons as they pass over the ends of the bones, and which are called hursce mucosce. The epithelium lining these mem- branes is of the kind called tesselated ; it is developed in the same manner with that of other free surfaces, being continually reproduced as it is worn away. Synovial membranes, in many situations, are closely and completely invested externally by fibrous layers — the fibrous capsules, as they ai'e termed. These fibrous coats are met with especially in situations where the articulation is either wholly unprotected or but thinly covered by 8oft parts ; or where a very firm connection is required, as in the hip joint. The}' are absent where muscles or ligaments rest upon the articu- lation ; or where, for special purposes, the synovial membrane is exposed to more considerable movements, as in the knees. The synovial capsule is attached, either simply to the cartilaginous surface, extending thence directly to the other bone, or it may, in the first place, besides the cartilage, also invest a larger or smaller extent of the surface of the bone itself, and then pass to the second bone, with wdiich it is connected in the one way or the other. Synovia is a viscid transparent fluid, of a pale straw colour, slightly alkaline. In chemical and general characters it is like the serum of the olood. A drop of synovia is found to contain — fat molecules, epithelial cells, and small granular corpuscles, bearing a close resemblance to the white corpuscles of the blood. This fluid od account of the presence of albumen, is coagulable by heat. CLASSIFICATION OF THE JOINTS The skeleton lias already been described as composed of diiferent pieces of bone, united to each other in various manners : from this union result the articulations, which are sometimes very movable ; sometimes joined to each other through the medium of long digitations or teeth, which fix them, if not to iimnobility, at least to a very constrained movement ; and, lastly, united together through the medium of cartilage, the elasticity of which permits latitude of movement. In the first case, the articulations take the name of diarthrosis or movable articulations (5ia, through, and apdpov, a limb) ; in the second, synarthrosis {(tvv, together, and &p0pov, a limb) ; and 396 THE ANATOMY OF THE HORSE thirdly, amphiarthrosis (a.fJLcf>L, about, and apdpov), partaking, at the same time, of the two classes of articulation above mentioned — namely, synar- throsis, in the continuity established by the articular sui'faces ; and diarthrosis, in the limited extent of movement it permits. The guide to the classification of joints is the configuration of their articular sui'faces, and the movements they allow. DiARTHRODiAL JOINTS are arranged under three distinct classes : — 1. Enarthrosis. This kind of joint is characterized by the reception of an articular head into a cavity of appi'opriate form. It is the seat of most extensive movements ; namely, flexion, extension, adduction, abduction^ circumduction, and rotation. Example : Acetabulum with femur. 2. Ginglymus. A perfect hinge-joint, the articular surfaces of which are configured in a trochlear arrangement, in such a manner that two or more prominences may fit into two or more excavations of appropriate form for their reception. Their only movements are flexion and extension. Example : Tibia with the astragalus. 3. Arthrodia (a kind of shallow articulation), consisting almost of plain surfaces. Gliding is the only possible movement. Example : the Carpo- metacarpal articulation. Synarthrodial joints are included under four heads, all of which should be examined as parts of the bony skeleton : — 1. Hai^monia, in Avhich the bones are joined by apposition, as in the nasal bones. 2. Schindylesis, in which a ridge or keel projects into a cleft. Example : Vomer with sphenoid. 3. Gomphosis. Like a nail in its socket, as the teeth in the alveoli. 4. Sutura. Indented, and subdivided into sutura seirata, as in the frontal bones, and sutura squamosa, as in the union of the parietal and temporal bones. The amphiarthrodial joints are often smooth, and formed after the manner of diarthrodial surfaces. At other times they are more or less rough. These joints are united together for the most part by fibro-cartilage. Their extent of movement depends on the thickness and elasticity of the interarticular fibro-cartilage. They do not glide, therefore, one over the other. Only one species of amphiarthrosis exists of which the articulations of the vertebrae, the ischio-pubic symphysis, and the intermetacarpal joints are examples. MOVEMENTS OF THE JOINTS Thk motions permitted in the joints are four — namely, gliding, angular motion, circumduction, and rotation. 1. Gliding is the simple motion of one bone upon the other, without materially altering their relations. 2. Angular motion may be either limited to one plane, as in the trace- hinge, or it may be extended to more, when the motion becomes nearly allied to circumduction.- The elbow and hock are examples of the former, us, indeed, are most of the horse's joints. 3. Circumduction is a motion very little seen in the large joints of this ARTICULATIONS OF THE VERTEBRA 397 animal, and is confined to the hip and shoulder joints, in which it is far more limited than in the corresponding joints of the human frame. It is displayed when a limb is made to describe a segment of a lai^ge circle around the joint which connects it to the body. 4. Rotation is the movement of a bone on its own axis, and is only seen in the horse in the joint between the two first vertebrae of the neck. ARTICULATIONS OF THE VERTEBRAL COLUMN The vertebra are connected together by ligaments, fibro-cartilage, and synovial membranes ; the first two serving to retain them in position ; the last to facilitate motion. They correspond, fii^stly, by their bodies ; secondly, by their spines ; and thirdly, by their oblique and transverse processes. It is necessary to state, that the general details into which this study leads us will apply only to the articulations which unite the six lower cervical vertebi-se, the dorsal and lumbar vertebrae, and the sacrum. The bodies connect themselves by their surfaces, which in the cervical region represent, 1st, the anterior, or true head; 2nd, the posterior, or glenoid cavity, which receives the head of the vertebra immediately behind it. In passing from the first dorsal to the sacrum, these tend to efface them- selves, and become plainer ; nevertheless, they preserve throughout the one its convexity, and the other its concavity. Their means of union are — (1) fibro-cartilages, intei'posed between the ai'ticular surfaces ; (2) a common superior vei-tebral ligament ; (3) a common inferior vertebral ligament. The intervertebral fibro-cartilages are circular or elliptical discs, convex before, concave behind ; firmly fixed to the surfaces of the bones which they separate. The fibro-cartilaginous substance which forms them is composed of an external laminar part, constituting the circumference of an internal soft or pulpy part, which occupies the centre. The laminar part forms more than half the whole mass, and consists of laminse, or plates of fibro-cartilage, and fibrous tissue, alternating one with the other. The central part is a pulpy, elastic material, which is of a yellowish colour, and destitute of the concentric arrangement seen external^. The fibro-cartilages join at their circumference the two common vertebral ligaments, and in the vertebree of the back help to form the intervertebral cavities destined for the reception of the heads of the ribs. The su2')erior vertebral ligament ^y'lihin the spinal canal, and attached to the posterior surface of the bodies of the vertebrae, extends from the dentata to the sacrum. In the neck, it spreads across the bodies ; but in the back and loins it is broader opposite the intervertebral cartilage than opposite the bodies of the bones. It adheres firmly to the fibro-cartilages and to the contiguous margins of the bodies of the vertebrae ; but it is separated from their middles by a transverse venous plexus. 7'Ae inferior vertebral ligament reaches from the fifth dorsal vertebra to the first bone of the sacrum ; becoming broader and broader as it approaches the sacrum, along its course it connects itself to the inferior spines of the )x)dies of the vertebrae and to the intervertebral discs. The UNION" of the vertebra through their spinal part is effected by a superior spinal ligament and an interspinal ligament. 398 THE ANATOMY OF THE HORSE The supraspinous ligament consists of small compressed bundles of longi tudinal fibres, extending from the last cervical spine to the spine of the anterior coccygeal bone, and thus forms a continuous chain. The interspinal ligaments consist of fibrous plates, filling up the spaces between the spines, and attached before and behind to their opposite borders. One set of these fibres passes from the anterior border of one spine to the posterior border of the one before it, taking a direction from below, forwards and upwards ; another set runs from the posterior border of the spine to tlie anterior border of that situated behind it, taking a direction from below, upwards and backwards. The arches or plates are connected together by the ligamenta vertebra- tum subflava. These ligaments consist of yellow and white 'fibrous tissue. Their attachment extends from the roots of the oblique processes to the origin of the spinous processes. Their anterior edges are attached to the posterior edges of the vertebral plates which are in front. Their posterior edges are attached to the anterior edges and inferior faces of the plates Avhich are l"iG. 37. — Profile View of the Ligaments COMMON TO THE VEBTEBR.E. 2. 2. Bodies of vertebra;. ;.'.. 3. Spines. 4. 4. Transverse processes. b. Head of the body. (i. Oblique process. 7. Hole of conjugation. 8. Glenoid cavity. 9. Supra-spinous ligament. 10. lutra-spinous ligament. 11. Inter\'ertebral fibro-cartilnge. 12. 12. Inferior common vertebral ligament. behind. The ligamenta subflava do not exist between the occiput and atlas, or between the atlas and dentata. Inter-transverse ligaments are situated between the transverse processes, running from the transverse process of one vertebra to the same process of the one next to it. The oblique processes ai'e united by synovial capsules one to the other. These capsules, throughout the vertebrcne of the back, are pro- tected by white fibrous tissue, but in the cervical region the fibres covering the capsules are yellow and elastic, and on this account, and owing to the size of their arthrodial surfaces, latitude of movement is permitted to a greater extent than is noticed in any other vertebi'al leffion. THE LIGAMENTUM NUCHCE, OR GREAT CERVI- CAL LIGAMENT, AND OTHER PECULIARITIES IN THE LIGAMENTS OF THE NECK In the neck a much greater latitude of motion is required, to admit of the lowering of the head in grazing, and of raising it for various purposes, a.s well as balancing its gi'eat Aveight at all times. Lateral flexion and LIGAMENTS OF THE NECK 399 rotation on its (twn axis are also nei essitaied for tlie puri)Of-;e of d/rectin.i? the muzrle right and left of the straight line, an I for these severa' motions the following deviations from the ordinary vertebral joints are developed. The ligamextuji nuciice, or great cervical ligament, is intended to relieve the muscles of the neck in supporting the head by its natural or inherent elasticity. It is entirely formed of yellow elastic tissue, and occupies the angle formed posteriorly by the anterior dorsal spines, and inferiorly by the cervical spinous processes, thus separating the cervical rauacles of the right side from those of the left. Profile View of the Great Ligament of the Neck. 1. Crest of the occiput. 2: 2. Cervical vertebrae. 3. 3. Dorsal vertebrre. 4. 4. 4. Dorsal spines. 5. 5. 5. Cordiform or funicular portion (f the ligamentum nucha. 6. Cordiform portion of tlie ligamentum colli mix- ing with the supra-spinous ligament. 7. 7. Lamellary portion of tlie ligamentinn nuchoe. 8. 8. 8. Interspinous ligaments. It is divided for description into two parts — a funicular and lamellary portion. The first, designated under the name of the cord of the cervical ligament, is represented by a large band, which extends immediately from the dorsal spinous processes to the top of the head, divided into two lateral lips by a mesian line. The cord is connected posteriorly with the suprasiDinous ligament, and is inserted anteriorly into the scabrous pit, situated just below the crest of the occiput. It is covered superiorly by a mass of thick adipo-fibrous tissue, much developed in low-bred animals. Inferiorly it gives off the lamellary portion, which is composed of two plates united b}' cellular membrane. These lie between the tAvo sets of muscles, and give off six tongues or slips, which unite with the spines of the six posterior cervical vertebree, mixing with the fibres of the inter- spinous ligaments. The Atlas is united to the occiput by lateral ligaments, which bind ito articular surfaces to the condyles of the bone — also by two inferior ligaments and sj^novial capsules. The two lateral ligaments, broad and membranous, arise from the supero- iOO THE ANATOMY OF THE HORSE lateral border of the arch of the atlas, and ai^e attached to the sides of thj condyles of the occiput, or rather between the condyles and the styloM processes. The long inferior ligament arises from the tubercle on the inferior surface of the atlas, and is attached to the basilar process of the occiput. The short inferior ligament arises from the tubercle on the inferior sui'face of the atlas, is attached to the foramen magnum of the occiput, and is con- nected with the theca vertebralis. A thin fibrous ligament (the occipito-atlo'ul) surrounds the entire articula- tion ; it is attached anteriorly to the condyles of the occiput, and posteriorly to the articulatory surface of the atlas. This membrane is thin and clastic in- feriorly ; superiorly it is formed of two bundles of fibres, which cross one another like the letter X. Internally it is lined by synovial membrane. The axis, or vertebra deJjtata, is united to the atlas, and partially also to the occiput, as follows : — 1. Articular surfaces are formed on tlie odontoid process of the axis, and also on the sides of its body close to the root of that part. These correspond with similar faces on the inside of the ring of the atlas, and also on its posterior side. 2. The ligaments connecting the rings of the tiro vertebrce together, or the srq^erior and inferior alio- axoid ligaments. The former represent the inter- spinous ligaments of the other vertebrse — being yellow, elastic, and formed of two layers, which are con- tinuous with the capsular ligaments — the latter is a large thin band, which is stretched from the infei'ior face of the axis to the inferior spine of the atlas, lying concealed by the longus colli muscle. Besides these two ligaments, there is also a capsular liga- ment, which commences from the sides of the superior atlo-axoid ligament, and after uniting with the borders of the odontoid ligament is confounded with the fibres of the inferior atlo-axoid. In fact, it is a mesh of white fibrous tissue connecting the three together. 3. The odontoid ligaments, which are covered by the superior atlo-axoid ligament. On cutting through these the following sets of fibres will be made apparent : — First, a transverse band arises from the root of the odontoid process, and dividing into two like the letter V, is attached on each side to the ridge on the inferior part of the fin"- of the at'las, a few thin fibres passing on to be attached to the basilar process and condyles of the occiput. Secondly, a strong band arises from the point of the odontoid process, and is attached to the middle of the ridge on the inferior part of the atlas. Thirdly, a few fibres pass across from the inside of the ring of the atlas on one side to the corresponding part of the other. These serve to strengthen tlie capsule, but they luavr; not the sub- itanco of the corresponding ligament in th 5 human fiaiio. Fia. 30.— Superior View of THE Joints roRMEn be- tween TUB First Tw» Vertebr.« of the Neck AND BETWEEN THE ATLA3 AND Occiput. a. Superior fibres of the occi- pito-atloid ligament. H. Atlas. C. Vertebra dentata, showing the superior atlo-axoid ligament. 1>. Third cervical vertebra. 1'. K. Transverse processes ofdentata. 1. 1. Odontoid ligament. THORACIC ARTICULATIONS 401 MOVEMENTS OF THE VERTEBRiE IN GENERAL AND OF CERTAIN OF THEIR JOINTS IN PAR- TICULAR The amount of motion between any two vertebra? is extremely limited, with the exception of the atlo-axoid articulation, in which the degree of rotation is considerable. But when the spine is viewed as a whole, these slight individual movements multiplied together are sufficient to allow of flexion and extension, as well as of inclination to either side. In the region of the back the joints are rigid, in the loins less so, but in the neck and tail great liberty is allowed. Flexion and extension, as well as lateral motion, are dependent entirely upon the elasticity of the intervertebral substance, which allows of one part being compressed while the other is extended. Thus, when the loins are arched upwards the lower edge of this substance is compressed, while the upper part assumes a moi'e expanded condition, and at the same time the spinous processes are separated more v/idely, and their ligaments are stretched. The reverse of this takes place when these bones are arched downwards, while in lateral inclination the sides are compressed and expanded in a corresponding manner. Very slight rotation of the whole spine, or more proj^erly twisting, is permitted by the elastic nature of the intervertebral substance ; but in the atlo-axoid articulation a perfect I'otation occurs around the centre of the odontoid pi^ocess, allowing the muzzle to be turned in either direction, which could not be done without an arrangement of this nature. The capsular ligaments and the supei'ior and infei'ior atlo-axoid ligaments are necessarily lax to allow of this motion. Lastly, the great ligament of the neck serves to support the weight of the head, which would be too great for the muscles of the neck, in consequence of the length of leverage which is presented. THORACIC ARTICULATIONS The articulations which unite the bones composing the thorax may be divided first into costo- vertebral articulations, or those which unite the ribs with the spine ; secondly, chondro- costal, or those which unite the ribs with their cartilages ; thirdly, the chondro-sternal, or those which unite the cartilages with the sternum ; fourthly, the articulations of the cartilages cmong themselves. Each rib (with the exception of the first and last) is connected with the bodies of two vertebrte, the three bones, together with the intei'vertebral substance, forming two joints which are sepai\ated from each other by a band of fibres passing from the head of the rib to the intervertebral sub- stance. Besides these there is also an articulation between the rib and the transverse process of the vertebra behind it. The superior costo-vertehral ligament connects the head of each rib to the sides of the bodies of the vertebrae, and is divided into three bundles, of MJiich one bundle (the middle) passes to the corresponding intervertebral fibro-cartilage, whilst the anterior passes to the body of the vei'tebra before, the posterior to the body of the vertebra behind. This ligament is called 402 THE ANATOMY OF THE HORSE the suj)erior stellate ligament. From the inferior surface of the neck there is a ligament, Avhich is disposed in the same way inferiorly as the foregoing is superiorly, in attaching the ribs to the bodies of the vertebrse. This is called the inferior stellate ligament. The inter-articidar ligament, or ligamentum teres, consists of a thin bundle of longitudinal fibres, and arises from the ridge dividing the two articular Fig. 40. — SuPERiOE View of Costo-Vertedral Articulations. A. A. A. etc. Points where the vertebral arches are removed in order to expose. 1. 1. etc. Suiierior common vertebral ligament. 13. B. etc. Transverse processes. 2. 2. etc. Superior costo - vertebral or stellate ligament. 3. 3. 3. etc. Superior costo-transverse ligament. surfaces on the head of the rib from which it passes to be implanted on the side of the intervertebral substance. There are two distinct synovial capsules — an anterior and a posterior — set back to back, and separated by the inter-articular ligament. The costo-traxsverse articulation. — On the superior surface of the tubercle of the rib is a smooth convex articular surface, which is in apposition with a smooth concave surface^ situated on the transverse process. Two ligaments strengthen this articulation. First, the posterior costo- transverse ligament consists of a short fasciculus of fibres, which passes from the posterior surface of the summit of the transverse process, to the rough surface uncovered by cartilage at the postero-lateral part of the tuber- cle. Secondly, the anterior transverse costal ligament is formed of a bundle of white, thick, short fibres, which take a course from the anterior surface of the transverse process near its base, to the excavation which is close to the neck of the rib. This ligament is clothed behind b}' synovial membrane and in front by adipose tissue, which separates it from the costo-vertebral articulation. The last two, namelj^ the 17th and 18th costotransverse articulations, are confounded with the corresponding costo-vertebral joints. The cuoxdrocostal articulation may be referi'ed to the subdivision gomphosis of the synarthrodial joints. It is formed by the implantation of the inferior extremity of the rib into the superior extremity of the cartilage, THORACIC ARTICULATIONS 403 which presents a surface corresponding with the rough depression in the end cf the rib. Further sti^ength is given to this articulation by the periosteum, Fig. 41. — Inferior View of the Costo-Vertebral Articulations. 1. 1. etc. Inferior common vertebral ligament. 2. 2. etc. Inter-fibro-cartilaginous disc. 3. 3. etc. Inferior costo-transverse ligament. 4. 4. etc. Inferior costo-vertebral ligament. which, in passing from the bone to the cartilage, forms a strong uniting band. The chondro-sternal articulations occur between the inferior extremity of the cartilage of each rib, and the oblong cavities existing along each side of the sternum. The eight anterior cartilages forai, with the fossae in the sternum, eight corresponding articulations. The joints which result from the union of these two surfaces are Fig. 42.— Profile View of Sterno-Costal and Chondro-Costal Articulations. 1. 1. Anterior end of sternum and cariniform car- tilage. 2. Ensiform cartilage. 3. 3. etc. Sternal cartilages. 4. etc. Chondro-stenial articulati' ns. 5. etc. Ends of the true ribs with the articula- tions between them, and the cartilages seen between 3 and 5. enveloped on all sides by fasciculi of white and extended fibres, the whole of which constitute a ligamentous capsule. The superior fibres are sometimes described as the superior chondro-sternal ligament. The inferior are continu- ous with the origin of the pectoral muscles. The foremost chondro-sternal articulation is not separated from the corre- sponding one on the opposite side. The two cartilages being close together, 404 THE ANATOMY OF THE HORSE their synovial capsule is continuous, and the two oblong ybss«j on the sternuin unite one with the other. It must be fui'ther noticed that this articulation frequently occurs on the cariniform cartilage, which is anterior to the first bone of the sternum. As regards the two posterior sternal cartilages, they are in close apposition one with the other, and fit into one common fossa situated on the posterior bone of the sternum, and with it form one synovial joint. A thin fasciculus of fibres connects the cartilages of the 8th and 9th ribs to the ensiform or xiphoid cartilage, called the chonclro-.ciphoid ligament. A similar fasciculus to the foregoing connects the cariniform and xiphoid cartilages together — the carino-xiphoid ligament. The asternal or false cartilages are united one to the other by a yellow elastic ligament, which extends from the fore extremity of each to the posterior border of the preceding cartilage. Ox THE SUPERIOR AXD INFERIOR SURFACES of the sternum, ligamentous fibres may be observed running longitudinally, called the superior and inferior sternal ligaments. The longitudinal fibres are mixed with those radiating from the costal cartilages, especially inferiorly, where they blend with aponeuroses of the pectoral muscles. PECULIARITIES IN THE ARTICULATIONS OF THE LUMBAR VERTEBRAE The four anterior lumbar vertebra have nothing remax-kable about them, but the fifth differs in having on the posterior part of each trans- verse process an articular surface furnished with a synovial capsule, for uniting it with the sixth. This last has also four articulatory surfaces on its transverse processes — two anteriorly, which unite with the correspond- ing ones on the fifth vertebra just described, and two posteriorly, which are similarly furnished with synovial capsules, and which unite it with the sacrum. THE LUMBRO-SACRAL ARTICULATION AND SACRAL LIGAMENTS TuE FIBRO-CARTILAGE intervening between the last lumbar vertebra and the sacrum is unusually thick, and the joint is protected also ex- ternally by some strong longitudinal fibres passing from bone to bone. Tlio last lumbar vertebra joins the sacrum not only by its body and articular processes (which latter are oval, with their long diameter from side to side), but also by two oval and slightly concave articular surfaces, which articulate with corresponding faces on the last lumbar vertebra already alluded to. Besides the articulations between the lumbar vertebrise and the sacrum, there are also ligaments between the spines of the sacrum itself, which are no longer of much use after the separate bones of which it is composed are united by ossification. THE COCCYGEAL JOINTS 405 THE COCCYGEAL JOINTS The sacro- coccygeal and inter -coccygeal articulations are con- structed much after the same principle as the other vertebral articula- tions. The coccygeal bones, however, are only united together by their bodies. The anterior and i:)osterior articulatory surfaces of each vertebra Fig. 43.— Articulations of the Lumbar Vertebr.e with the Sacrum. A. Last three lumbar vertebrte. B. Sacrum. C. C. Iliac bones. 1. 1. Transverse process of fourtli lumbar vertebra. 2. 2. Transverse process of fifth lumbar vertebra. 3. 3. Transverse jirocess of sixth lumbar ver- tebra. 4. 4. etc. Inferior common vertebral ligament. 5. 5. Ligamentous fibres covering the capsules oe- tween the transverse processes of the foi.ith and fifth lumbar vertebras. 6. 0. Capsular ligaments «aiting together the fiftli and sixth lumbar vertebrae. 7. 7. Lumbo-sacral ligaments. 8. S. Sacro-iliac ligaments. are both convex, and their inter-articular fibro-cartilage is hollow on both surfaces. As to ligaments, they are represented by bundles of longitudinal fibres spread on the surfaces of these bones, which they envelop in a common sheath. THE TEMPORO-MAXILLARY ARTICULATION The lower jaw articulates on each side by one of its condyles with the glenoid cavity of the temporal bone. Between them is placed an inter -articular fibro-cartilage, with one synovial membrane above and another below it. I'Ae articular surfaces above mentioned do not exactly fit one into the other. This, however, is corrected through the interposition of a fibro- cartilaginous disc between them. This disc represents an irregular plate, flattened above and below, thicker in front than behind, moulded on each 406 THE AKATOMY OF THE HORSE surface, which it separates, so that its superior face presents in front a con- cavity to receive the tubercle on the zygomatic process of the temporal bone, and a convexity behind, which is lodged in its glenoid cavity. As to its inferior face, it is indented by an oblong furrow, in which the condyle of the inferior maxiDary bone is imbedded. These hones are united hy a capsular ligament, covering a synovial capsule, and two lateral ligaments, one external and the other internal. A Jibrous cover, a true capsular ligament, surrounds this articulation, and is attached by its edges to the articular surfaces which it unites, as well as to the borders of the inter-articular fibro-cartilage ; thus forming two distinct capsules, namely, one supei'iorly, and one inferiorly, which are lined inter- nally by synovial membranes. The larger of the two, after lining the upper surface of the disc, is reflected upward to the glenoid cavity of the temporal bone. The inferior sjmovial membrane is interposed between the inferior surface of the cartilage and the condyle of the lower jaw ; and thus a double joint is constituted. The external lateral ligament is a short fasciculus of fibres, attached superiorly to a tubercular prominence, situate on the supero-external part of the squamous temporal bone, and inferiorly to the external surface of the condyle, and to the postero-external surface of the neck of the lower jaw, just below the condyle ; its fibres take a backwai-d and downward course. The internal lateral ligament is looser and more elongated than the external. It extends from the inner surface of the squamous temporal bone to the cartilage and inner surface of the condyle of the superior maxillary bone, reaching down to the inner part of its angle. Movement. — The temporo-maxillary az'ticulation is the centre of every movement of the lower jaw. These are — elevation, lowering, lateral movement, and horizontal sliding, which motions together accomplish the grinding action necessary to triturate the hard grain upon which the horse feeds. THE SACRO-ILIAC ARTICULATION This joint establishes the union of the posterior members with the spine, and is formed by the sacrum and os innominatum. It belongs to the arthro- dial order of joints. On each of these two bones is a large and irregular articular surface, lined with a thick layer of cartilage, which is firmly united to them. The joint thus formed is strengthened by four ligaments, namely — 1, the sacro-iliac ; 2, the superior ilio-sacral; 3, the inferior ilio-sacral ; and 4, the sacro-sciatic. The sacro-iliac ligament is composed of large ligamentous fibres, which everywhere envelop the articulation, by firmly attaching themselves at their extremities to the impressions around the articular surfaces, situated on the sacrum and internal border of the iUum. The inferior half of this ligament is covered by the psoas muscles. Its posterior half, much stronger than the former, is hidden by the ilium. The superior ilio-sacral ligament is a large, strong, short ligament, which, arising from the internal part of the ilium, is carried backwards and fixes THE SACRO-ILIAC ARTICULATION 407 itself upon the sacral spines, where it mixes its fibres with the supra-spinous ligament of the lumbar vertebra?. The inferior ilio-sacral ligament is a triangular and very resisting mem- branous band, formed of parallel fibres running obliquely from above (lownwai'ds, and from before backwards. It is attached by its antero- inferior edge to the superior half of the ischiatic border and the internal angle of the ilium, mixing itself with the preceding ligament ; its superior Fio. 44. — Profile View of the Ilio-Sacral and Sacro-Sciatic Ligaments. A. Os ilium. H. Rim of the cotyloid cavity. B. Os pubis. K. K. Sacral spines. C. Os ischium. N. M. O. Tubercles on the antero-inferior D. Femur. spinous process of the ilium. E. Trochanter major extemus. 1. 1. Superior ilio-sacral lignnient. F. Large tubercle at the head of femur. 2. 3. -4. Sacro-sciatic ligament. G. Head of the femur. border inserts itself upon the roughened ridge which bounds tlie sacrum laterally ; its posterior border is united to the aponeuroses which cover the coccygeal muscles. The sacro-sciatic ligament is a vast membranous expansion, stretched upon the side of the pelvis, between the sacrum and the os innominatum ; it serves rather as an inclosure for the pelvic cavity than as a means of securing the firmness of the sacro-iliac articulation. Its form is irregu- larly quadrilateral, presenting four borders — a superior, attached to the lateral roughened edge of the sacrum ; an inferior, inserted in the ridge beluw the cotyloid cavity ; an anterior, unattached in a great part of its course, and serving as a protection to the large vessels and nerves which pass through the sciatic notch ; and lastly, a posterior margin, which splits into two laminse, between which the semi-membranous muscle takes its origin. A synovial memhrane covers the sacro-iliac ligament, but furnishes a small quantity of synovia. INIovEMENTS. — The two sacro-iliac articulations, through which all the 408 THE ANATOMY OF THE HORSE efforts of impulsion are communicated to the trunk b})- the posterior members, without interfei'ing with the transmission of locomotive force, permit but a slight gliding movement of their arthrodial surfaces. Indeed, this articula- tion seems exclusively designed to prevent the fractures to which these bones would be incessantly exposed, were they attached in a more intimate manner, as, for example, by bony union. ISCHIO-PUBIC SYMPHYSIS The two ossa innomixata are firmly united together in the median line below, by the corresponding edges of the ischium and pubes. In the foal this is a distinct joint, possessing an inter-articular cartilage, and some transverse ligamentous fibres above and below ; but in the adult horse the two bones are firmly united by ossification, and the ossa inno- minata together form a complete arch, without the slightest movement between them. THE SHOULDER JOINT The scapulo-humeral articulation, commonly known as the shoulder joint, belongs to the division Diarthrosis ; subdivision, Enarthrosis. It is formed by the scapula uniting with the humerus, at an obtuse angle. The articular surfaces which compose this joint are the head of the humerus, and the glenoid cavity of the scapula. On examining these bones, described and illusti^ated at pages 376-7, it will be seen that the head of the humerus is semi-globular, while the cavity in the scapula is very superficial, and incapable of maintaining the former in its place without some collateral aid. It is somewhat remarkable that the ligaments of this joint are ex- tremely weak, being confined to the lax fibres surrounding the synovial capsule, which is so loose that after removing all the other soft parts, and making a small opening into the joint, the two bones may be readily separated for some distance ; these fibres are superiorly fixed around the margin of the glenoid cavity, and infeiiorly round the head of the humerus. Chauveau states that a ligament descends from the coracoid process of the scapula, which diverges and becomes inserted into the tubercles at the anterior part of the head of the humerus. He also states that it is loose, and therefore facilitates jnuch motion, but it is not easy to separate it from the capsular ligament. This is longer posteriorly than anteriorly, and presents postero- laterally two stays, similar to two pieces of tape. The external one, arising from the outer lip of the glenoid cavity, is attached to the outer and back part of the head of the humerus. The internal one arises from the inner edge of the glenoid cavity, and is attached to the inner and back part of the head of the humerus. But this deficiency in ligaments is made up by a much more powerful material in resisting dislocations. The whole joint is surrounded by elastic muscular fibre or by tendinous bands, having the same kind of support — thus it has in close apposition the following muscles, viz. — TPIE SHOULDER JOINT 409 Anteriorly, the Coraco Hunieralis, and Flexor Brachii. Extei'nally, the Antea Spinatus, and Postea Spinatus. Posteriorly, the Scapulo-Humeralis Posticus, etc. Internally, the Subscapularis, etc. Whenever, therefore, any violent strain is thrown upon the joint, which would force the head of the humerus forwards, the Coraco Hunieralis and Flexor Brachii contract and prevent the accident. In the same manner, each of the above muscles acts in its own direction, and the result is that dislocation of the humerus in the horse is extremely rare. The movements op the shoulder joint in the horse are much more limited than in man, and indeed they are almost confined to flexion and extension. When all the muscles are cut away from the joint, rotation and circumduction may be easily effected ; but in examining its movements during life, it will be evident that neither one nor the other of these acts can be effected in any appreciable degree ; this is at once proved if it is attempted to turn the foot in- wards or outwards, when it is flexed at the knee, during the life of the horse, for beyond the slight motion of the whole limb, including the scapula, the foot is firmly fixed, and there is not the slightest rotation or circumduction at the shoulder joint. With- out the power of pronation and supination possessed by man, and partially by the dog and cat, the above actions would be worse than useless, and it is alto- gether a mistake to ascribe to any other of the domestic animals, as Chauveau has done, in addition to flexion and extension of the shoulder joint, the four move- ments of abduction, adduction, circumduction, and rotation.^ It would much puzzle that generally accu- rate anatomist to turn the horse's foot up in front so that its possessor could see the sole ; yet if circum- duction and adduction were permitted, this could readily be done as by the domestic cat or dog in licking the inside of the fore-[ The shoulder joint is, in fact, a true hinge (ginglymus) in the horse, ass, cow, sheep, and goat, but in the first of these animals it is more especially limited in its movements, by the enormously powerful muscles which surround the joint, and which are constantly tense, though extremely elastic, and giving way to every voluntary movement. It is a beautiful provision of nature, to enable the horse to bear the shocks which his shoulders have to sustain in coming down from a leap with a great weight on his back, a,nd without it he would be rendered comparatively useless to man. Fig. 45. — Profilk View of the scapulo-humeral, OR Shoulder Joint. A. Inferior third of sca- pula. B. Coracoicl process of scaiiula. C. Analogue of the aero- niion process. D. Rim of glenoid cavity. E. Superior third of hu- merus. 1. Capsular ligament. 2. Tendon of the coraco- radialis muscle. 1 Under certain circumstances, lame and otherwise injured horses prove the possession of those movements claimed by Chauveau, but only to a very limited extent. — Editok. 410 THE ANATOMY OF THE HORSE THE ELBOW JOINT Or the HUMEno-RADio-ULNAR ARTICULATION. — This joiiit is formed between the lower extremity of the humerus above, and the junction of the radius and ulna below. It is a complete hinge, and has no power of pronation or supination as in man, consequently there is no necessity for the peculiar additional joint between the radius and ulna, observ- able in man and partially in the dog and cat ; but the two bones are firmly ossified together in the adult, as already described at page 379. These hones are connected together by three liga- ments, two lateral (an internal and an external), a capsular ligament, and a synovial capsule. The internal lateral ligament arises from a fossa on the side of the internal condyle of the humerus ; it takes a vertical course, expanding as it descends : and is inserted partly on the roughened inner border of the articular cavity of the radius. Its middle fibres, which are the longest, take the same course as the former, assuming while passing over the radius the shape of a cord, which is inserted into the inner and fore part of the radius about three inches below the former insertion. The external lateral ligament is shorter but sti^onger than the internal. It ai^ises from the superior fossa and ridge surrounding it, on the outer surface of the external condyle of the humerus, and is inserted into the tuberosity on the upper and external part of the radius. Its superficial fibres take a vertical course, whilst its internal fibres take an oblique direction, from top to bottom and from back to front. TAe capsular ligament is attached by its superior boi'der to the surfaces surrounding the condyles of the humerus ; by its inferior border, to the circumference of the superior part of the radius ; and by its posterior border to the circumference of the articular surface of the ulna. The synovial membrane is shoi't anteriorly, very extended, and spread out posteriorly ; where it forms three sacs, which tend to facilitate flexion of the joint. TuE MOVEMENTS of the elbow joint are confined to flexion and extension, it being a pure hinge, but these actions do not take place exactly in the same plane. For instance, if the knee is bent and the foot brought up to the elbow, the frog will not correspond with that projection, but will be almost entirely outside it, while the knees will also be wider apart when both are flexed and raised towards the bosom, than when the horse is stand- ing. This arrangement is brought about by the oblique direction of the pulley-like articular surfaces on the humerus, ulna, and radius, and appears to be designed to prevent the foot from hitting the opposite leg as it passes it in trotting. When the obliquity is insuflicient, either cutting of the Fig. 46.— Posterior \'iew OF LEFT Elbow Joint. A. Inferiorthird of the liu- menis. B. B. External and internal condyles. C. Oleeranou process of ulna. r>. Tiadius. 1. External lateral liga- ment. 2. Internal lateral liga- ment. 3. 3. Fibro - cartilaginous substance uniti iig the ulna to the radium. THE KNEE JOINT 411 fetlocks or speedy cutting is sure to be manifested ; if too great, the awkward gait known as "dishing" is established. Extension is not nearly so com- plete as in the human subject, being limited by the greater length and breadth of the olecranon pi'ocess, the upper part of which forms a prominence which fits into the corresponding fossa of the humerus, and thus serves as a check to the extension of the fore-arm. In most men the upper arm and fore-arm can be made to fall into one straight line, but in the horse there is always a considerable angle. THE KNEE JOINT (CARPUS, OR WRIST) This articulation is a very complicated one, and in order to understand it thoroughly, it will be necessary to examine the parts composing it under three divisions. 1st. The articulations between the several carpal bones. 2nd. The Eadio-carpal articulation ; and 3rd. The Carpo-metacarpal joint ; to which must be added (4) the examination of certain ligaments, common to all three. 1. The two rows of carpal bones, which have been described in the dry state at page 380, are furnished with cartilages on the faces, by which they correspond, thus forming a series of nearly plane arthrodial surfaces, having .synovial capsules, but embracing several of them in one. It may be remem- bered that these bones are arranged in two rows, the upper one consisting of the scaphoid, lunar, cuneiform, and pisiform bones, while the lower com- prehends the OS magnum, the trapezoid, and the unciform bones. The upper roiv is united together by six ligaments, three anterior and tltree interosseous. The anterior ligaments consist of flattened bands of fibres which lie in front of the knee, and connect the four bones together, passing laterally from one to the other. The interosseous are strong and short fibres concealed between these bones, and attached to the rough excavations between the distinct facettes on the several bones to which allusion has been made at page 380, the ligament connecting the pisiform bone with the :Scaphoid being particularly well marked. The hones of the second rotv are, in a similar way, united by anterior and interosseous ligaments, but instead of being three, there are only two of •each, in correspondence with the diminished number of bones. It is un- necessary to describe them more minutely. The tivo roivs again, between which is a partial hinge joint, are united by three sjyecial ligaments, in addition to those common to the whole knee joint, which will be presently described. Two of the special ligaments ■consist of very short fibres lying behind the carpal bones, and covered by the great posterior ligament. The third is larger than these, and extends from the pisiform bone to the unciform, and to the head of the external small metacarpal bone (see ^^ Fig. 48). It is united on the outer side with the external lateral ligament, and internally with the common posterior ligament. To its posterior border are attached the outer fibres of the sheath of the flexor tendons. The synovial capsules proper to these articulations line all the above ligaments and articular surfaces, being reflected from one to the other, and forming also pouch-like prolongations upwards between the bones of each 412 THE ANATOMY OF THE HORSE row, as fai' as the interosseous ligaments, and downwards in a similar manner Neither of the ascending pouches is continuous with the radio-carpal capsule, but the external of the two lower communicates with that of the carpo- metacarpal joint. This fact is sometimes important in punctured wounds of the knee joint. 2. The kadio-carpal articulation, formed by the union of the lower end of the radius with the upper surfaces of the scaphoid, lunar, cuneiform, and pisiform bones, is a true hinge, but somewhat limited in the amount of its motion. The lower end of the cannon-bone can describe fully ninety degrees of a circle around the knee joint as a centre ; but the full extent of this motion is divided between the three several articu- lations to which I have alluded, the radio-carpal taking considerably the largest share. The lower end of the radius presents an irregular articular sur- face, longer from side to side than from before backwards, and a non-articular pit or fossa hollowed out to receive a projection of the lunar bone during the flexion of the joint. On each side of these ai^e the lateral processes. The upper surfaces of the carjml bones are moulded exactly to fit the inferior extremity of the radius, and a loose synovial capside passes from one to the other, extending downwards between the three innermost carpal bones as far as their interosseous ligaments, and sometimes also to the capsule between the pisiform and cuneiform bones. The ligaments proper to this articulation, in ad- dition to those common to the whole knee joint, are three. Of these one forms a large rounded cord, attaclied to the radius above, and to the cuneiform bone below, taking an oblique direction downwards, and inwards beneath the common posterior liga- ment. The second, much smaller in size, is ex- tended between the external lateral process of the radius and the pisiform bone, being partially covered by the common external lateral ligament, but allow- ing a small triangular space to intervene, through which the synovial capsule is sometimes protruded in diseased conditions of this joint. The third, still more thin and weak in its fibres, is situated beneath _ from the radius is inserted in the lunar bone, and into the interosseous ligament which unites the pisiform and the scaphoid bones (see 3, Fig. 49). 3. The carpo-metacarpal articulation is formed above by the three inferior carpal bones, and below by the heads of the three metacarpal bones, together constituting a limited hinge joint. These surfaces above and below are in close apposition, and are lined by one common syno/ial capsule, which, as already mentioned, communicates with that between the two rows of carpal bones. Fic. 47. — Anterior View of THE Left Knee Joint. A. Inferior third of the ra- dius. B. Cuneiform bone. C. Lunar bone. D. Scai>hoid bone. E. Unciform bone. G. The great bone. H. Trapezoid bono. K. Superior third of meta- carpus. 1. Scapho-radial ligament. 2. Externallateralligament. 3. 3. Internal lateral liga- ment. 4. 4. Ligaments existing be- tween upper row of carpal bones. 5. 5. Caqio-metacarpal liga- ment. the second, and arising THE KNEE JOINT 413 Besides the c6mmon ligaments, there are seven proper to this joint — three anterior, two posterior, and two interosseous. Of the three anterior ligaments, the external one, covered by the external lateral ligament, unites the unciform bone to the outer small metacarpal bone. The middle one unites the os magnum to the large metacarpal bone. The internal one unites the trapezoid to the inner small metacarpal bone. Fio. 4S.— Back View of Left Knee Joint, seen oblique- ly FROM THE Bight, add showing the deep-seated Ligaments. A. Inferior third of radius. B. Pisiform bone. C. External small metacarpal bone. D. Internal small metacarpal bone. 1. External lateral ligament. 'J. 3. Scapho - metacarpal liga- ment. 4. Eadio-lunar ligament. £/. Ligament between the pisi- form, unciform, and ex- ternal small metacarpal bone. Fio. 49. — Bapk View of Right Knee Joint, show- ing THE SUPERFICIAL LIGA- MENTS. A. Inferior third of radius. B. Superior third of large metacarpal bone. C. Internal small metacarpus. D. External small mwtaeariial bone. 1. Internal lateral ligament. 2. External lateral ligament. 3. Ligament between the ra- dius, lunar, and pisi- form bones. 4. 5. Ligament between the unciform, jiisiform, and between the ex- ternal small metacar- pal bones. 6. Strong band of ligamentous fibres, binding down the flexor tendons in their sheath or groove. 7. 7. Groove for the passage of the perforans and perforatus tendons. The two iwsterior ligaments, described by Rigot, are very difficult of demonstration, being only with the greatest care separated from the common posterior ligament. One of them, however, is capable of being made out by dissection, as a strong band of fibres passing from the back of the scaphoid bone to the inner small metacarpal bone (see o^ 3 Fig. 48). The tivo interosseous ligaments ascend from the roughened depressions existing between the three metacarpal bones to the interosseous ligaments of the second row. 414 THE ANATOMY OF THE HORSE 4. The ligaments common to the avhole knee joint are four — two lateral, an anterioi', and a posterior. The external lateral Vuiament is a thick cord, formed of two kinds of libres, a deep-seated and a superficial set, which take a crucial direction. It arises from the external lateral process of the radius, and descends vertically on the side of the knee joint. In its passage, it gives off a band to th(^ pisiform bone, and also to the os unciforme, and terminates at the head of the external small metacarpal bone. This ligament lies on the carpal bones and capsular ligament. The internal lateral ligament, analogous to the preceding, and situated on the opposite side, is thicker and larger. It arises from the internal lateral process of the radius, and terminates on the supero-antei'ior and internal surface of the large metacarpal and head of the internal small metacarpal bones. The fibres of this ligament take a crucial direction ; in its passage downwards, it gives off three little bands, namely, one to the scaphoid bone, one to the os magnum, and one to the trapezoid. The anterior or capsular ligament covers the anterior face of the carpal articulations. Its superior edge is attached to the inferior extremity of the radius ; its inferior edge is attached to the superior extremity of the large metacarpal bone ; its right and left borders are in contact with the lateral ligaments ; its external face is connected with tendons, etc. ; its internal face is lined, at certain points, by synovial membrane. This ligament is formed of transverse fibres, more or less oblique, crossed and i-e-crossed. The posterior ligament — one of the strongest of the animal economy — covers the posterior surface of the knee. It is inserted superiorly into the transverse ridge which bounds the articular surface of the i^adius. At the posterior part of the carpal bones, it becomes attached to the inner border of the pisiform bone, the posterior sui'face of the os magnum, the cuneiform and scaphoid bones terminating on the postero-superior extremity of the large metacarpal bone. The scapho-metacarpal ligament, described as part of the posterior ligament of the carpo-metacarpal joint, is with difficulty separated from this ligament. The knee is the centre of two very extensive movements, namely, extension and flexion ; to which three others, very limited in their extent, may be added, namely, adduction, abduction, and circumduction. As already mentioned, all the carpal articulations do not take an equal part in the execution of these movements ; in fact, it is evident that they chiefly take place in the radio-carpal ginglymus, and in the imperfect hinge formed between the two rows of carpal bones. Each of these articulations participates in the movements of the knee, nearly in the same joroportion, the superior perhaps being slightly the more extensive, and both perform their office in the same manner. In flexion, the first row of bones turns from before backwards on the radius ; the inferior row moves in the same way on the superior i*ow. The metacarpus is carried backwards and upwards, thus relaxing the common posterior ligament. The anterior ligament, on the contrary, is rendei-ed tense. The articular surfaces, especially those of the second joint, separate in front from one another. In extension, the metacarpus is carried below and forwards by an inverse FETLOCK JOINT 415 meclumisai. This movement is arrested when the radius and the meta carpus are placed in the same vertical line, as in the standing position. In ^flexion, the bony radii do not directly approach each other ; the inferior extremity of the metacarpus is always carried outwards. The movements of abduction, adduction, and circumduction are not able to be performed until the foot is bent up under the fore-arm, and are then only capable of being very partially carried out. 71ie plain arthrodial surfaces existing between the lower row of carpal bones and the superior metacarpal extremity, only admit of a simple sliding of the surfaces in contact. The limited motion of this articulation can have but a secondary influence over the general movements of the knee ; but it favours them by permitting the carpal bones to change their reciprocal connections, and thence lends itself, through the medium of the radio-carpal and inter-carpal ginglymi, to a more exact coaptation of the articular surfaces which constitute them. INTER-METACARPAL ARTICULATIONS Each small metacarpal bone articulates with the large metacarpal bone through the medium of two diarthrodial surfaces, situated on the inner part of their heads ; a third, of a synarthrodial character, occurs on the anterior jmrt of the body. Each of these articulates with corresponding surfaces on the large metacarpal bone. An interosseous ligament, composed of very short and strong bundles, is interposed between the synarthrodial surfaces, and fixes them solidly one on the other. The INTER-METACARPAL ARTICULATIONS allow Only of a very slight vertical slidina: movement. FETLOCK JOINT The fetlock joint is formed by the junction of the inferior condyloid extremity of the large metacai^pal bone with the biconcave surface of the OS sufi"raginis, and by the anterior smooth surfaces of the ossa sesamoidea with the posterior part of the condyles of the same metacarpal bone. It is a perfect hinge. The ligaments forming the bond of union between these surfaces are as follow : — First, those which belong to the ossa sesamoidea ; secondly, those which connect the os coronse and pastern together; thirdly, a ligament common to both. Besides which, there is a synovial capsule. 1. The first have received the general names of the sesamoideal liga- ments, and are six in number, namely, three inferior, two lateral, and an inter- sesamoideal. The inferior sesamoideal ligaments are divided into three, namely, the superficial, the middle, and the deep. Of these the first is a narrow band, flattened behind and before ; arising from the middle of the fibro-cartilagin- ous mass, which completes behind the superior articular surface of the os coronse, it continues slightly expanding as it ascends, until it reaches the 416 THE ANATOMY OF THE HORSE bases of the ossa sesamoidea, to which it is inserted, mixing also with the inter-sesamoidea] ligament. The middle is of a triangular shape, and is formed of three bands, two lateral and a median. It is often confounded with the first ligament, although easily distinguishable from it by its lower insertion. Fixed in common, inferiorly, to the apex of the triangular ridge situated on the posterior surface of the os suffraginis, these three I'i'j. 50— Antkkkir Vikw of Feixock AND Pastern Joints. 1. 1. 1. Lower row of carpal bones. 2. Metacarpal bone. S. External sesamoid bone. 4. Suffragineal bone. 5. Coronal bone. 6. Pedal bone. 7. Tendon of the extensor pedis. li. Long ligament which blends inferiorly with the tendon of the extensor pedis. 9. Point where the extensor tendon be- gins to expand. 10 & 11. Points to which the extensor tendon is attached. 12. 12. Lateral cartilages. Fio. 51.— Posterior View of Fetlock and Pastern Joints. A. Metacarpal bone. B. B. Sesamoid bones. C. Suffragineal bone. i D. Coronal bone. B. B. Lateral cartilages. F. Navicular bone. 1. 1. 1. Lower row of carpal bonoa. 2. 2. Suspensory ligament. 3. 3. Bifurcation of same, in order to join the sesamoid bones. 4. 4. Inter - sesamoideal fibro - cartilaginous sub- stance. 5. Point over which the tendon of the flexor pedis ]iprforaiis ]ilavR. 6. InfiTinv sii|MTiici;d sesamoideal ligament. 7. 7. Mi