Skeleton.—The skull as a whole is greatly elongated, chiefly in consequence of the immense size of the face as compared with the hinder or true cranial portion. The basal line of the cranium from the lower border of the foramen magnum to the incisor border of the palate is nearly straight. The orbit, of nearly circular form, though small in proportion to the size of the whole skull, is distinctly marked, being completely surrounded by a strong ring of bone with prominent edges. Behind it, and freely communicating with it beneath the osseous bridge (the post-orbital process of the frontal) forming the boundary between them, is the small temporal fossa occupying the whole of the side of the cranium proper, and in front is the great flattened expanse of the “cheek,” formed chiefly by the maxilla, giving support to the long row of cheek-teeth, and having a prominent ridge running forward from below the orbit for the attachment of the masseter muscle. The lachrymal occupies a considerable space on the flat surface of the cheek in front of the orbit, and below it the jugal does the same. The latter sends a horizontal or slightly ascending process backwards below the orbit to join the under surface of the zygomatic process of the squamosal, which is remarkably large, and instead of ending as usual behind the orbit, runs forwards to join the greatly developed post-orbital process of the frontal, and even forms part of the posterior and inferior boundary of the orbit, an arrangement not met with in other mammals. The closure of the orbit behind distinguishes the skull of the horse from that of its allies the rhinoceros and tapir, and also from all of the perissodactyles of the Eocene period. In front of the brain cavity, the great tubular nasal cavities are provided with well-developed turbinal bones, and are roofed over by large nasals, broad behind, and ending in front in a narrow decurved point. The opening of the anterior nostrils is prolonged backwards on each side of the face between the nasals and the elongated slender premaxillae. The latter expand in front, and are curved downwards to form the semicircular alveolar border which supports the large incisor teeth. The palate is narrow in the interval between the incisor and molar teeth, in which are situated the large anterior palatine foramina. Between the molar teeth it is broader, and it ends posteriorly in a rounded excavated border opposite the hinder border of the penultimate molar tooth. It is mainly formed by the maxillae, as the palatines are very narrow. The pterygoids are delicate slender slips of bone attached to the hinder border of the palatines, and supported externally by, and generally welded with, the rough pterygoid plates of the alisphenoid, with no pterygoid fossa between. They slope obliquely forwards, and end in curved, compressed, hamular processes. There is a distinct alisphenoid canal for the passage of the internal maxillary artery. The base of the cranium is long and narrow; the alisphenoid is very obliquely perforated by the foramen rotundum, but the foramen ovale is confluent with the large foramen lacerum medium behind. The glenoid surface for the articulation of the mandible is greatly extended transversely, concave from side to side, convex from before backwards in front, and hollow behind, and is bounded posteriorly at its inner part by a prominent post-glenoid process. The squamosal enters considerably into the formation of the temporal fossa, and, besides sending the zygomatic process forwards, it sends down behind the meatus auditorius a post-tympanic process which aids to hold in place the otherwise loose tympano-periotic bone. Behind this the exoccipital gives off a long paroccipital process. The periotic and tympanic are welded together, but not with the squamosal. The former has a wide but shallow floccular fossa on its inner side, and sends backwards a considerable “pars mastoidea,” which appears on the outer surface of the skull between the post-tympanic process of the squamosal and the exoccipital. The tympanic forms a tubular meatus auditorius externus directed outwards and slightly backwards. It is not dilated into a distinct bulla, but ends in front in a pointed rod-like process. It completely embraces the truncated cylindrical tympanohyal, which is of great size, corresponding with the large development of the whole anterior arch of the hyoid. This consists mainly of a long and compressed stylohyal, expanded at the upper end, where it sends off a triangular posterior process. The basi-hyal is remarkable for the long, median, pointed, compressed “glossohyal” process, which it sends forward from its anterior border into the base of the tongue. A similar but less developed process is found in the rhinoceros and tapir. The lower jaw is large, especially the region of the angle, which is expanded and flattened, giving great surface for the attachment of the masseter muscle. The condyle is greatly elevated above the alveolar border; its articular surface is very wide transversely, and narrow and convex from before backwards. The coronoid process is slender, straight, and inclined backwards. The horizontal ramus, long, straight, and compressed, gradually narrows towards the symphysis, where it expands laterally to form with the ankylosed opposite ramus the wide, semicircular, shallow alveolar border for the incisor teeth.Fig. 1.—Side view of Skull of Horse, with the bone removed so as to expose the whole of the teeth.PMx, Premaxilla.Mx, Maxilla.Na, Nasal bone.Ma, Jugal or malar bone.L, Lacrymal bone.Fr, Frontal bone.Sq, Squamosal bone.Pa, Parietal bone.oc, Occipital condyle.pp, Paroccipital process.i¹,i², andi³, The three incisor teeth.c, The canine tooth.pm¹, The situation of the rudimentary first premolar, which has been lost in the lower, but is present in the upper jaw.pm²,pm³, and pm4, The three fully developed premolar teeth.m¹,m², andm³, The three true molar teeth.The vertebral column consists of seven cervical, eighteen dorsal, six lumbar, five sacral, and fifteen to eighteen caudal vertebraeThere may be nineteen rib-bearing vertebrae, in which case five only will be reckoned as belonging to the lumbar series. The odontoid process of the axis is wide, flat, and hollowed above, as in the ruminants. The bodies of the cervical vertebrae are elongated, strongly keeled, and markedly opisthocoelous, or concave behind and convex in front. The neural laminae are broad, the spines almost obsolete, except in the seventh, and the transverse processes not largely developed. In the trunk vertebrae the opisthocoelous character of the centrum gradually diminishes. The spinous processes of the anterior thoracic region are high and compressed. To these is attached the powerful elastic ligament (ligamentum nuchae, or “paxwax”) which, passing forwards in the middle line of the neck above the neural arches of the cervical vertebrae—to which it is also connected—is attached to the occiput and supports the weight of the head. The transverse processes of the lumbar vertebrae are long, flattened, and project horizontally outwards or slightly forward from the arch. The metapophyses are moderately developed, and there are no anapophyses. The caudal vertebrae, except those quite at the base, are slender and cylindrical, without processes and without chevron bones beneath. The ribs are eighteen or nineteen in number on each side, flattened, and united to the sternum by short, stout, tolerably well ossified sternal ribs. The sternum consists of six pieces; the anterior or presternum is compressed and projects forwards like the prow of a boat. The segments which follow gradually widen, and the hinder part of the sternum is broad and flat.As in all other ungulates, there are no clavicles. The scapula is long and slender, the supra-scapular border being rounded, and slowly and imperfectly ossified. The spine is very slightly developed; rather above the middle its edge is thickened and somewhat turned backwards, but it gradually subsides at the lower extremity without forming any acromial process. The coracoid is a prominent rounded nodule. The humerus is stout and rather short. The ulna is rudimentary, being represented by little more than the olecranon. The shaft gradually tapers below and is firmly welded to the radius. The latter bone is of nearly equal width throughout. The three bones of the first row of the carpus (scaphoid, lunar and cuneiform) are subequal in size. The second row consists of a broad and flat magnum, supporting the great third metacarpal, having to its radial side the trapezoid, and to its ulnar side the unciform, which are both small, and articulate inferiorally with the rudimentary second and fourth metacarpals. The pisiform is large and prominent, flattened and curved; it articulates partly with the cuneiform and partly with the lower end of the radius. The large metacarpal is called in veterinary anatomy “cannon bone”; the small lateral metacarpals, which gradually taper towards their lower extremities, and lie in close contact with the large one, are called “splint bones.” The single digit consists of a moderate-sized proximal (os suffraginis, or large pastern), a short middle (os coronae, or small pastern), and a wide, semi-lunar, ungual phalanx (os pedis, or coffin bone). There is a pair of large nodular sesamoids behind the metacarpo-phalangeal articulation, and a single large transversely-extended sesamoid behind the joint between the second and third phalanx, called the “navicular bone.”The carpal joint, corresponding to the wrist of man, is commonly called the “knee” of the horse, the joint between the metacarpal and the first phalanx the “fetlock,” that between the first and second phalanges the “pastern,” and that between the second and third phalanges the “coffin joint.”In the hinder limb the femur is marked, as in other perissodactyles, by the presence of a “third trochanter,” a flattened process, curving forwards and arising from the outer side of the bone, about one-third of the distance from the upper end. The fibula is reduced to a mere rod-like rudiment of the upper end. The lower part is absent or completely fused with the tibia. The calcaneum has a long and compressed calcaneal process. The astragalus has a large flat articular surface in front for the navicular, and a small one for the cuboid. The navicular and the external cuneiform bones are broad and flat. The cuboid is small, and the internal and middle cuneiform bones are small and united together. The metapodals and phalanges resemble very closely those of the fore limb, but the principal metatarsal is more laterally compressed at its upper end than is the corresponding metacarpal. The joint between the femur and tibia, corresponding to the knee of man, is called the “stifle-joint”; that between the tibia and tarsus, corresponding to the ankle of man, the “hock.” The bones and joints of the foot have the same names as in the fore limb. The horse is eminently “digitigrade,” standing on the extremity of the single digit of each foot, which is kept habitually in a position approaching to vertical.The muscles of the limbs are modified from those of the ordinary mammalian type in accordance with the reduced condition of the bones and the simple requirements of flexion and extension of the joints, no such actions as pronation and supination, or opposition of digits, being possible or needed. The muscles therefore which perform these functions in other quadrupeds are absent or rudimentary.Below the carpal and tarsal joints, the fore and hind limbs correspond almost exactly in structure as well as function. On the anterior or extensor surface of the limb a powerful tendon (7 in fig. 2), that of the anterior extensor of the phalanges (corresponding to theextensor communis digitorumof the arm andextensor longus digitorumof the foot of man) passes down over the metacarpal bone and phalanges, to be inserted mainly into the upper edge of the anterior surface of the last phalanx or pedal bone. There is also a much smaller second extensor on the outer side of this in each limb, the lateral extensor of the phalanges. In the fore-leg the tendon of this muscle (which corresponds with theextensor minimi digitiof man) receives a slip from that of the principal extensor, and is inserted into the first phalanx. In the hind-leg (where it is the homologue apparently of theperoneus brevisof man) the tendon becomes blended with that of the large extensor.Fig. 2.—Section of Foot of Horse.1, Metacarpal bone.2, First phalanx (os suffraginis).3, Second phalanx (os coronae).4, Third or ungual phalanx (os pedis, or coffin bone).5, One of the upper sesamoid bones.6, Lower sesamoid or navicular bone.7, Tendon of anterior extensor of the phalanges.8, Tendon of superficial flexor (fl. perforatus).9, Tendon of deep flexor (fl. perforans).10, Suspensory ligament of fetlock.11, Inferior or short sesamoid ligament.12, Derma or skin of the foot, covered with hair, and continued into13, The coronary cushion,14, The podophyllous or laminar membrane, and15, The keratogenous membrane of the sole.16, Plantar cushion.17, Hoof.18, Fatty cushion of fetlock.A strong ligamentous band behind the metapodium, arising from near the upper extremity of its posterior surface, divides into two at its lower end, and each division, being first connected with one of the paired upper sesamoid bones, passes by the side of the first phalanx to join the extensor tendon of the phalanges. This is called in veterinary anatomy the “suspensory ligament of the sesamoids,” or of the “fetlock” (10 in fig. 2); but its attachments and relations, as well as the occasional presence of muscular fibres in its substance, show that it is the homologue of the interosseous muscles of other mammals, modified in structure and function, to suit the requirements of the horse’s foot. Behind or superficial to this are placed the two strong tendons of the flexor muscles, the most superficial, orflexor perforatus(8) dividing to allow the other to pass through, and then inserted into the middle phalanx. Theflexor perforans(9) is as usual inserted into the terminal phalange. In the fore-leg these muscles correspond with those similarly named in man. In the hind-leg, the perforated tendon is a continuation of that of the plantaris, passing pulley-wise over the tuberosity of the calcaneum. The perforating tendon is derived from the muscle corresponding with the long flexor of man, and the smaller tendon of the oblique flexor (tibialis porticusof man) is united with it.The hoof of the horse corresponds to the nail or claw of other mammals, but is so constructed as to form a complete and solid case to the expanded termination of the toe, giving a firm basis of support formed of a non-sensitive substance, which is continually renewed by the addition of material from within, as its surface wears away by friction. The terminal phalange of the toe is greatly enlarged and modified in form to support this hoof, and the size of the internal framework of the foot is increased by a pair of lateral fibro-cartilaginous masses attached on each side to the hinder edges of the bone, and by a fibro-cellular and fatty plantar cushion in the median part. These structures are all enclosed in the middle subcorneous integument, a continuation of the ordinary skin of the limb, but extremely vascular, and having its superficial extent greatly increased by being developed into papillae or laminae. From this the horny material which constitutes the hoof is exuded. A thickened ring encircling the upper part, called coronary cushion (13) and the sole (15), are covered with numerous thickly-setpapillae or villi, and take the greatest share in the formation of the hoof; the intermediate part constituting the front and side of the foot (14), corresponding with the wall of the hoof, is covered with parallel, fine longitudinal laminae, which fit into corresponding depressions in the inner side of the horny hoof.The horny hoof is divided into a wall or crust consisting of the front and sides, the flattened or concave sole, and the frog, a triangular median prominence, notched posteriorly, with the apex turned forwards, situated in the hinder part of the sole. It is formed of pavement epithelial cells, mainly grouped in a concentric manner around the vascular papillae of the subcorneous integument, so that a section near the base of the hoof, cut transversely to the long axis of these papillae, shows a number of small circular or oval orifices, with cells arranged concentrically round them. The nearer the surface of the hoof, or farther removed from the seat of growth, the more indistinct the structure becomes.Small round or oval plates of horny epithelium called “chestnuts,” callosities growing like the hoof from enlarged papillae of the skin, are found on the inner face of the fore-arm, above the carpal joint in all species of Equidae, and in the horse (E. caballus) similar structures occur near the upper extremity of the inner face of the metatarsus. They are evidently rudimentary structures which it is suggested may represent glands (Lydekker,Proc. Zool. Soc. London, 1903, vol. i.).Fig. 3.—Longitudinal and Transverse Section of Upper Incisor of Horse.p, Pulp cavity.d, Dentine or ivory.e, Enamel.c, Outer layer of cementum or crusta petrosa.c′, Inner layer of cementum, lininga, the pit or cavity of the crown of the tooth.Dentition.—The dentition of the horse, when all the teeth are in place, is expressed by the formulai.3⁄3,c.1⁄1,p.4⁄4m.3⁄3= 44. The incisors of each jaw are placed in close contact, forming a semicircle. The crowns are broad, somewhat awl-shaped, and of nearly equal size. They have all the great peculiarity, not found in the teeth of any other mammal, and only in the Equidae of comparatively recent geological periods (see alsoPalaeontology), of an involution of the external surface of the tooth (see fig. 3), by which what should properly be the apex is carried deeply into the interior of the crown, forming a pit, the bottom of which becomes partially filled with cement. As the tooth wears, the surface, besides the external enamel layer as in an ordinary simple tooth, shows in addition a second inner ring of the same hard substance surrounding the pit, which adds greatly to the efficiency of the tooth as an organ for biting tough, fibrous substances. This pit, generally filled in the living animal with particles of food, is conspicuous from its dark colour, and constitutes the “mark” by which the age of the horse is judged, as in consequence of its only extending to a certain depth in the crown it becomes obliterated as the latter wears away, and then the tooth assumes the character of that of an ordinary incisor, consisting only of a core of dentine, surrounded by the external enamel layer. It is not quite so deep in the lower as in the upper teeth. The canines are either rudimentary or absent in the female. In the male they are compressed, pointed, and smaller than the incisors, from which they are separated by a slight interval. The teeth of the cheek series are all in contact with each other, but separated from the canines by a considerable toothless space. The anterior premolars are quite rudimentary, sometimes not developed at all, and generally fall by the time the animal attains maturity, so that there are but six functional cheek teeth,—three that have predecessors in the milk-dentition, and hence are considered as premolars, and three molars, but otherwise, except the first and last of the series, not distinguishable in form or structure. These teeth in both upper and lower jaws are extremely long-crowned or hypsodont, successive portions being pushed out as the surface wears away, a process which continues until the animal becomes advanced in age. The enamelled surface is infolded in a complex manner (a modification of that found in other perissodactyles), the folds extending quite to the base of the crown, and the interstices being filled and the surface covered with a considerable mass of cement, which binds together and strengthens the whole tooth. As the teeth wear, the folded enamel, being harder than the other constituents, the dentine and cement, forms projecting ridges on the surface arranged in a definite pattern, which give it great efficiency as a grinding instrument (see fig. 2, in articleEquidae). The free surfaces of the upper teeth are quadrate, except the first and last, which are nearly triangular. The lower teeth are much narrower than the upper.The milk-dentition consists of i.3⁄3, c.0⁄0, m.3⁄3= 24,—the canines and first or rudimentary premolars having apparently no predecessors. In form and structure the milk-teeth much resemble the permanent ones, having the same characteristic enamel-foldings. Their eruption commences a few days after birth, and is complete before the end of the first year, the upper teeth usually appearing somewhat earlier than the lower. The first teeth which appear are the first and second milk-molars (about five days), then the central incisor (from seven to ten days); this is followed by the second incisor (at one month), then the third molar, and finally the third incisor. Of the permanent teeth the first molar appears a little after the end of the first year, followed by the second molar before the end of the second year. At about two and a half years the first premolar replaces its predecessor. Between two and a half and three years the first incisor appears. At three years the second and third premolars, and the third molar have appeared, at from three and a half to four years the second incisor, at four to four and a half years the canine, and, finally, at five years, the third incisor, completing the permanent dentition. Up to this period the age of the horse is clearly shown by the condition of dentition, and for some time longer indications can be obtained from the wear of the incisors, though this depends to a certain extent upon the hardness of the food or other circumstances. As a general rule, the depression caused by the infolding of the surface of the incisor (the “mark”) is obliterated in the first or central incisor at six years, in the second at seven years, and in the third at eight years. In the upper teeth, as the depressions are deeper, this obliteration does not take place until about two years later. After this period no certain indications can be obtained of the age of the horse from the teeth.Digestive Organs.—The lips are flexible and prehensile; and the membrane that lines them and the cheeks smooth. The palate is long and narrow; its mucous surface has seventeen pairs of not very sharply defined oblique ridges, extending as far back as the last molar tooth, beyond which thevelum palatiextends for about 3 in., having a soft corrugated surface, and ending posteriorly in an arched border without a uvula. This embraces the base of the epiglottis, and, except while swallowing food, shuts off all communication between the cavity of the mouth and the pharynx, respiration being, under ordinary circumstances, exclusively through the nostrils. Between the mucous membrane and the bone of the hard palate is a dense vascular and nervous plexus. The membrane lining the jaws is soft and corrugated. An elongated raised glandular mass, 3 in. long and 1 in. from above downwards, extending backwards from the root of the tongue along the side of the jaws, with openings on the surface leading into crypts with glandular walls, represents the tonsil. The tongue, corresponding to the form of the mouth, is long and narrow. It consists of a compressed intermolar portion with a flat upper surface, broad behind and becoming narrower in front, and of a depressed anterior part rather shorter than the former, which is narrow behind and widens towards the evenly rounded apex. The dorsal surface generally is soft and smooth. There are two large circumvallate papillae near the base, rather irregular in form, about a quarter of an inch in diameter and half an inch apart. The conical papillae are small and close set, though longer and more filamentous on the intermolar portion. There are no fungiform papillae on the dorsum, but a few inconspicuous ones scattered along the sides of the organ.Of the salivary glands the parotid is by far the largest, elongated in the vertical direction, and narrower in the middle than at either end. Its upper extremity embraces the lower surface of the cartilaginous ear-conch; its lower end reaches the level of the inferior margin of the mandible, along the posterior margin of which it is placed. Its duct leaves the inferior anterior angle, at first descends a little, and runs forward under cover of the rounded inferior border of the lower jaw, then curves up along the anterior margin of the masseter muscle, becoming superficial, pierces the buccinator, and enters the mouth by a simple aperture opposite the middle of the crown of the third premolar tooth. It is not quite so thick as a goose-quill when distended, and nearly a foot in length.The submaxillary gland is of very similar texture to the last, but much smaller; it is placed deeper, and lies with its main axis horizontal. It is elongated and slender, and flattened from within outwards. Its posterior end rests against the anterior surface of the transverse process of the atlas, from which it extends forwards and downwards, slightly curved, to beneath the ramus of the jaw. The duct which runs along its upper and internal border passes forwards in the usual course, lying in the inner side of the sublingual gland, to open on the outer surface of a distinct papilla, situated on the floor of the mouth, half an inch from the middle line, and midway between the lower incisor teeth and the attachment of the fraenum linguae. The sublingual is represented by a mass of glands lying just beneath the mucous membrane of the floor of the mouth on the side of the tongue, causing a distinct ridge, extending from the fraenum backwards, the numerous ducts opening separately along the summit of the ridge. The buccal glands are arranged in tworows parallel with the molar teeth. The upper ones are the largest, and are continuous anteriorly with the labial glands, the ducts of which open on the mucous membrane of the upper lip.The stomach of the horse is simple in its external form, with a largely developed rightcul de sac, and is a good deal curved on itself, so that the cardiac and pyloric orifices are brought near together. Theantrum pyloricumis small and not very distinctly marked. The interior is divided by the character of the lining membrane into two distinct portions, right and left. Over the latter the dense white smooth epithelial lining of the œsophagus is continued, terminating abruptly by a raised crenulated border. Over the right part the mucous membrane has a greyish-red colour and a velvety appearance, and contains numerous peptic glands, which are wanting in the cardiac portion. The œsophageal orifice is small, and guarded by a strong crescentic or horseshoe-like band of muscular fibres, supposed to be the cause of the difficulty of vomiting in the horse. The small intestine is of great length (80 to 90 ft.), its mucous membrane being covered with numerous fine villi. The caecum is of conical form, about 2 ft. long and nearly a foot in diameter; its walls are sacculated, especially near the base, having four longitudinal muscular bands; and its capacity is about twice that of the stomach. It lies with its base near the lower part of the abdomen, and its apex directed towards the thorax. The colon is about one-third the length of the small intestine, and very capacious in the greater part of its course. As usual it may be divided into an ascending, transverse, and descending portion; but the middle or transverse portion is folded into a great loop, which descends as low as the pubis; so that the colon forms altogether four folds, generally parallel to the long axis of the body. The descending colon is much narrower than the rest, and not sacculated, and, being considerably longer than the distance it has to traverse, is thrown into numerous folds.The liver is tolerably symmetrical in general arrangement, being divided nearly equally into segments by a well-marked umbilical fissure. Each segment is again divided by lateral fissures, which do not extend quite to the posterior border of the organ; of the central lobes thus cut off, the right is rather the larger, and has two fissures in its free border dividing it into lobules. The extent of these varies, however, in different individuals. The two lateral lobes are subtriangular in form. The Spigelian lobe is represented by a flat surface between the postal fissure and the posterior border, not distinctly marked off from the left lateral by a fissure of the ductus venosus, as this vessel is buried deep in the hepatic substance, but the caudate lobe is distinct and tongue-shaped, its free apex reaching nearly to the border of the right lateral lobe. There is no gall-bladder, and the biliary duct enters the duodenum about 6 in. from the pylorus. The pancreas has two lobes or branches, a long one passing to the left and reaching the spleen, and a shorter right lobe. The principal duct enters the duedenum with the bile-duct, and there is often a second small duct opening separately.Circulatory and Respiratory Organs.—The heart has the form of a rather elongated and pointed cone. There is one anterior vena cava, formed by the union of the two jugular and two axillary veins. The aorta gives off a large branch (the anterior aorta) very near its origin, from which arise—first, the left axillary, and afterwards the right axillary and the two carotid arteries.Under ordinary circumstances the horse breathes entirely by the nasal passages, the communication between the larynx and the mouth being closed by the velum palati. The nostrils are placed laterally, near the termination of the muzzle, and are large and dilatable, being bordered by cartilages upon which several muscles act. Immediately within the opening of the nostril, the respiratory canal sends off on its upper and outer side a blind pouch (“false nostril”) of conical form, and curved, 2 to 3 in. in depth, lying in the notch formed between the nasal and premaxillary bones. It is lined by mucous membrane continuous with that of the nasal passage; its use is not apparent. It is longer in the ass than in the horse. Here may be mentioned the guttural pouches, large air-sacs from the Eustachian tubes, and lying behind the upper part of the pharynx, the function of which is also not understood. The larynx has the lateral sacculi well developed, though entirely concealed within the alae of the thyroid cartilage. The trachea divides into two bronchi.Nervous System.—The brain differs little, except in details of arrangement of convolutions, from that of other ungulates. The hemispheres are rather elongated and subcylindrical, the olfactory lobes are large and project freely in front of the hemispheres, and the greater part of the cerebellum is uncovered. The eye is provided with a nictitating membrane or third eyelid, at the base of which open the ducts of the Harderian gland.Reproductive System.—The testes are situated in a distinct sessile or slightly pedunculated scrotum, into which they descend from the sixth to the tenth month after birth. The accessory generative glands are the two vesiculae seminales, with the median third vesicle, oruterus masculinus, lying between them, the single bilobed prostate, and a pair of globular Cowper’s glands. The penis is very large, cylindrical, with a truncated, expanded, flattened termination. When in a state of repose it is retracted, by a muscle arising from the sacrum, within the prepuce, a cutaneous fold attached below the symphysis pubis.The uterus is bicornuate. The vagina is often partially divided by a membraneous septum or hymen. The teats are two, inguinally placed. The surface of the chorion is covered evenly with minute villi, constituting a diffuse non-deciduate placenta. The period of gestation is eleven months.Authorities.—R. I. Pocock, “The Species and Subspecies of Zebras,”Ann. Mag. Nat. Hist.ser. 6, vol. xx., 1897, and “A New Arrangement of the Existing Species of Equidae,”Op. cit.ser. 7, vol. x., 1902; R. Lydekker, “Notes on the specimens of Wild Asses in English Collections,”Novitates Zoologicae, vol. xi., 1904; B. Salensky, “On Equus przewalskii,”Mém. Acad. St Pétersburg, 1902; M. S. Arloing, “Organisation du pied chez le cheval,”Ann. Sci. Nat., 1867, viii. 55-81; H. Burmeister,Los caballos fosiles de la Pampa Argentina(Buenos Aires, 1875); Chauveau and Arloing,Traité d’anatomie comparée des animaux domestiques(Paris, 1871), and English edition by G. Fleming (1873); A. Ecker, “Das Europäische Wildpferd und dessen Beziehungen zum domesticirten Pferd,”Globus, Bd. xxxiv. (Brunswick, 1878); Major Forsyth, “Beiträge zur Geschichte der fossilen Pferde besonders Italiens,”Abh. Schw. Pal. Ges.iv. 1-16, pt. iv.; George, “Études zool. sur les Hémiones et quelques autres espèces chevalines,”Ann. Sci. Nat., 1869, xii. 5; E. F. Gurlt,Anatomische Abbildungen der Haussäugethiere(1824), andHand. der vergleich. Anat. der Haussäugethiere(2 vols., 1822); Huet, “Croisement des diverses espèces du genre cheval,”Nouv. Archives du Muséum, 2nd ser., tom. ii. p. 46, 1879; Leisering,Atlas der Anatomie des Pferdes(Leipzig, 1861); O. C. Marsh, “Notice of New Equine Mammals from the Tertiary Formation,”Am. Journ. of Science and Arts, vol. vii., March 1874;Id., “Fossil Horses in America,”Amer. Naturalist, vol. viii., May 1874;Id., “Polydactyle Horses,”Am. Journ. Sci. and Arts, vol. xvii., June 1879; Franz Müller,Lehrbuch der Anatomie des Pferdes(Vienna, 1853); R. Owen, “Equine Remains in Cavern of Bruniquel,”Phil. Trans.vol. clix., 1870, p. 535; W. Percivall,The Anatomy of the Horse(1832); G. Stubbs,Anatomy of the Horse(1766); W. H. Flower,The Horse(London, 1891); Ridgeway,Origin of the Thoroughbred Horse(1905).
Skeleton.—The skull as a whole is greatly elongated, chiefly in consequence of the immense size of the face as compared with the hinder or true cranial portion. The basal line of the cranium from the lower border of the foramen magnum to the incisor border of the palate is nearly straight. The orbit, of nearly circular form, though small in proportion to the size of the whole skull, is distinctly marked, being completely surrounded by a strong ring of bone with prominent edges. Behind it, and freely communicating with it beneath the osseous bridge (the post-orbital process of the frontal) forming the boundary between them, is the small temporal fossa occupying the whole of the side of the cranium proper, and in front is the great flattened expanse of the “cheek,” formed chiefly by the maxilla, giving support to the long row of cheek-teeth, and having a prominent ridge running forward from below the orbit for the attachment of the masseter muscle. The lachrymal occupies a considerable space on the flat surface of the cheek in front of the orbit, and below it the jugal does the same. The latter sends a horizontal or slightly ascending process backwards below the orbit to join the under surface of the zygomatic process of the squamosal, which is remarkably large, and instead of ending as usual behind the orbit, runs forwards to join the greatly developed post-orbital process of the frontal, and even forms part of the posterior and inferior boundary of the orbit, an arrangement not met with in other mammals. The closure of the orbit behind distinguishes the skull of the horse from that of its allies the rhinoceros and tapir, and also from all of the perissodactyles of the Eocene period. In front of the brain cavity, the great tubular nasal cavities are provided with well-developed turbinal bones, and are roofed over by large nasals, broad behind, and ending in front in a narrow decurved point. The opening of the anterior nostrils is prolonged backwards on each side of the face between the nasals and the elongated slender premaxillae. The latter expand in front, and are curved downwards to form the semicircular alveolar border which supports the large incisor teeth. The palate is narrow in the interval between the incisor and molar teeth, in which are situated the large anterior palatine foramina. Between the molar teeth it is broader, and it ends posteriorly in a rounded excavated border opposite the hinder border of the penultimate molar tooth. It is mainly formed by the maxillae, as the palatines are very narrow. The pterygoids are delicate slender slips of bone attached to the hinder border of the palatines, and supported externally by, and generally welded with, the rough pterygoid plates of the alisphenoid, with no pterygoid fossa between. They slope obliquely forwards, and end in curved, compressed, hamular processes. There is a distinct alisphenoid canal for the passage of the internal maxillary artery. The base of the cranium is long and narrow; the alisphenoid is very obliquely perforated by the foramen rotundum, but the foramen ovale is confluent with the large foramen lacerum medium behind. The glenoid surface for the articulation of the mandible is greatly extended transversely, concave from side to side, convex from before backwards in front, and hollow behind, and is bounded posteriorly at its inner part by a prominent post-glenoid process. The squamosal enters considerably into the formation of the temporal fossa, and, besides sending the zygomatic process forwards, it sends down behind the meatus auditorius a post-tympanic process which aids to hold in place the otherwise loose tympano-periotic bone. Behind this the exoccipital gives off a long paroccipital process. The periotic and tympanic are welded together, but not with the squamosal. The former has a wide but shallow floccular fossa on its inner side, and sends backwards a considerable “pars mastoidea,” which appears on the outer surface of the skull between the post-tympanic process of the squamosal and the exoccipital. The tympanic forms a tubular meatus auditorius externus directed outwards and slightly backwards. It is not dilated into a distinct bulla, but ends in front in a pointed rod-like process. It completely embraces the truncated cylindrical tympanohyal, which is of great size, corresponding with the large development of the whole anterior arch of the hyoid. This consists mainly of a long and compressed stylohyal, expanded at the upper end, where it sends off a triangular posterior process. The basi-hyal is remarkable for the long, median, pointed, compressed “glossohyal” process, which it sends forward from its anterior border into the base of the tongue. A similar but less developed process is found in the rhinoceros and tapir. The lower jaw is large, especially the region of the angle, which is expanded and flattened, giving great surface for the attachment of the masseter muscle. The condyle is greatly elevated above the alveolar border; its articular surface is very wide transversely, and narrow and convex from before backwards. The coronoid process is slender, straight, and inclined backwards. The horizontal ramus, long, straight, and compressed, gradually narrows towards the symphysis, where it expands laterally to form with the ankylosed opposite ramus the wide, semicircular, shallow alveolar border for the incisor teeth.
PMx, Premaxilla.
Mx, Maxilla.
Na, Nasal bone.
Ma, Jugal or malar bone.
L, Lacrymal bone.
Fr, Frontal bone.
Sq, Squamosal bone.
Pa, Parietal bone.
oc, Occipital condyle.
pp, Paroccipital process.
i¹,i², andi³, The three incisor teeth.
c, The canine tooth.
pm¹, The situation of the rudimentary first premolar, which has been lost in the lower, but is present in the upper jaw.
pm²,pm³, and pm4, The three fully developed premolar teeth.
m¹,m², andm³, The three true molar teeth.
The vertebral column consists of seven cervical, eighteen dorsal, six lumbar, five sacral, and fifteen to eighteen caudal vertebraeThere may be nineteen rib-bearing vertebrae, in which case five only will be reckoned as belonging to the lumbar series. The odontoid process of the axis is wide, flat, and hollowed above, as in the ruminants. The bodies of the cervical vertebrae are elongated, strongly keeled, and markedly opisthocoelous, or concave behind and convex in front. The neural laminae are broad, the spines almost obsolete, except in the seventh, and the transverse processes not largely developed. In the trunk vertebrae the opisthocoelous character of the centrum gradually diminishes. The spinous processes of the anterior thoracic region are high and compressed. To these is attached the powerful elastic ligament (ligamentum nuchae, or “paxwax”) which, passing forwards in the middle line of the neck above the neural arches of the cervical vertebrae—to which it is also connected—is attached to the occiput and supports the weight of the head. The transverse processes of the lumbar vertebrae are long, flattened, and project horizontally outwards or slightly forward from the arch. The metapophyses are moderately developed, and there are no anapophyses. The caudal vertebrae, except those quite at the base, are slender and cylindrical, without processes and without chevron bones beneath. The ribs are eighteen or nineteen in number on each side, flattened, and united to the sternum by short, stout, tolerably well ossified sternal ribs. The sternum consists of six pieces; the anterior or presternum is compressed and projects forwards like the prow of a boat. The segments which follow gradually widen, and the hinder part of the sternum is broad and flat.
As in all other ungulates, there are no clavicles. The scapula is long and slender, the supra-scapular border being rounded, and slowly and imperfectly ossified. The spine is very slightly developed; rather above the middle its edge is thickened and somewhat turned backwards, but it gradually subsides at the lower extremity without forming any acromial process. The coracoid is a prominent rounded nodule. The humerus is stout and rather short. The ulna is rudimentary, being represented by little more than the olecranon. The shaft gradually tapers below and is firmly welded to the radius. The latter bone is of nearly equal width throughout. The three bones of the first row of the carpus (scaphoid, lunar and cuneiform) are subequal in size. The second row consists of a broad and flat magnum, supporting the great third metacarpal, having to its radial side the trapezoid, and to its ulnar side the unciform, which are both small, and articulate inferiorally with the rudimentary second and fourth metacarpals. The pisiform is large and prominent, flattened and curved; it articulates partly with the cuneiform and partly with the lower end of the radius. The large metacarpal is called in veterinary anatomy “cannon bone”; the small lateral metacarpals, which gradually taper towards their lower extremities, and lie in close contact with the large one, are called “splint bones.” The single digit consists of a moderate-sized proximal (os suffraginis, or large pastern), a short middle (os coronae, or small pastern), and a wide, semi-lunar, ungual phalanx (os pedis, or coffin bone). There is a pair of large nodular sesamoids behind the metacarpo-phalangeal articulation, and a single large transversely-extended sesamoid behind the joint between the second and third phalanx, called the “navicular bone.”
The carpal joint, corresponding to the wrist of man, is commonly called the “knee” of the horse, the joint between the metacarpal and the first phalanx the “fetlock,” that between the first and second phalanges the “pastern,” and that between the second and third phalanges the “coffin joint.”
In the hinder limb the femur is marked, as in other perissodactyles, by the presence of a “third trochanter,” a flattened process, curving forwards and arising from the outer side of the bone, about one-third of the distance from the upper end. The fibula is reduced to a mere rod-like rudiment of the upper end. The lower part is absent or completely fused with the tibia. The calcaneum has a long and compressed calcaneal process. The astragalus has a large flat articular surface in front for the navicular, and a small one for the cuboid. The navicular and the external cuneiform bones are broad and flat. The cuboid is small, and the internal and middle cuneiform bones are small and united together. The metapodals and phalanges resemble very closely those of the fore limb, but the principal metatarsal is more laterally compressed at its upper end than is the corresponding metacarpal. The joint between the femur and tibia, corresponding to the knee of man, is called the “stifle-joint”; that between the tibia and tarsus, corresponding to the ankle of man, the “hock.” The bones and joints of the foot have the same names as in the fore limb. The horse is eminently “digitigrade,” standing on the extremity of the single digit of each foot, which is kept habitually in a position approaching to vertical.
The muscles of the limbs are modified from those of the ordinary mammalian type in accordance with the reduced condition of the bones and the simple requirements of flexion and extension of the joints, no such actions as pronation and supination, or opposition of digits, being possible or needed. The muscles therefore which perform these functions in other quadrupeds are absent or rudimentary.
Below the carpal and tarsal joints, the fore and hind limbs correspond almost exactly in structure as well as function. On the anterior or extensor surface of the limb a powerful tendon (7 in fig. 2), that of the anterior extensor of the phalanges (corresponding to theextensor communis digitorumof the arm andextensor longus digitorumof the foot of man) passes down over the metacarpal bone and phalanges, to be inserted mainly into the upper edge of the anterior surface of the last phalanx or pedal bone. There is also a much smaller second extensor on the outer side of this in each limb, the lateral extensor of the phalanges. In the fore-leg the tendon of this muscle (which corresponds with theextensor minimi digitiof man) receives a slip from that of the principal extensor, and is inserted into the first phalanx. In the hind-leg (where it is the homologue apparently of theperoneus brevisof man) the tendon becomes blended with that of the large extensor.
1, Metacarpal bone.
2, First phalanx (os suffraginis).
3, Second phalanx (os coronae).
4, Third or ungual phalanx (os pedis, or coffin bone).
5, One of the upper sesamoid bones.
6, Lower sesamoid or navicular bone.
7, Tendon of anterior extensor of the phalanges.
8, Tendon of superficial flexor (fl. perforatus).
9, Tendon of deep flexor (fl. perforans).
10, Suspensory ligament of fetlock.
11, Inferior or short sesamoid ligament.
12, Derma or skin of the foot, covered with hair, and continued into
13, The coronary cushion,
14, The podophyllous or laminar membrane, and
15, The keratogenous membrane of the sole.
16, Plantar cushion.
17, Hoof.
18, Fatty cushion of fetlock.
A strong ligamentous band behind the metapodium, arising from near the upper extremity of its posterior surface, divides into two at its lower end, and each division, being first connected with one of the paired upper sesamoid bones, passes by the side of the first phalanx to join the extensor tendon of the phalanges. This is called in veterinary anatomy the “suspensory ligament of the sesamoids,” or of the “fetlock” (10 in fig. 2); but its attachments and relations, as well as the occasional presence of muscular fibres in its substance, show that it is the homologue of the interosseous muscles of other mammals, modified in structure and function, to suit the requirements of the horse’s foot. Behind or superficial to this are placed the two strong tendons of the flexor muscles, the most superficial, orflexor perforatus(8) dividing to allow the other to pass through, and then inserted into the middle phalanx. Theflexor perforans(9) is as usual inserted into the terminal phalange. In the fore-leg these muscles correspond with those similarly named in man. In the hind-leg, the perforated tendon is a continuation of that of the plantaris, passing pulley-wise over the tuberosity of the calcaneum. The perforating tendon is derived from the muscle corresponding with the long flexor of man, and the smaller tendon of the oblique flexor (tibialis porticusof man) is united with it.
The hoof of the horse corresponds to the nail or claw of other mammals, but is so constructed as to form a complete and solid case to the expanded termination of the toe, giving a firm basis of support formed of a non-sensitive substance, which is continually renewed by the addition of material from within, as its surface wears away by friction. The terminal phalange of the toe is greatly enlarged and modified in form to support this hoof, and the size of the internal framework of the foot is increased by a pair of lateral fibro-cartilaginous masses attached on each side to the hinder edges of the bone, and by a fibro-cellular and fatty plantar cushion in the median part. These structures are all enclosed in the middle subcorneous integument, a continuation of the ordinary skin of the limb, but extremely vascular, and having its superficial extent greatly increased by being developed into papillae or laminae. From this the horny material which constitutes the hoof is exuded. A thickened ring encircling the upper part, called coronary cushion (13) and the sole (15), are covered with numerous thickly-setpapillae or villi, and take the greatest share in the formation of the hoof; the intermediate part constituting the front and side of the foot (14), corresponding with the wall of the hoof, is covered with parallel, fine longitudinal laminae, which fit into corresponding depressions in the inner side of the horny hoof.
The horny hoof is divided into a wall or crust consisting of the front and sides, the flattened or concave sole, and the frog, a triangular median prominence, notched posteriorly, with the apex turned forwards, situated in the hinder part of the sole. It is formed of pavement epithelial cells, mainly grouped in a concentric manner around the vascular papillae of the subcorneous integument, so that a section near the base of the hoof, cut transversely to the long axis of these papillae, shows a number of small circular or oval orifices, with cells arranged concentrically round them. The nearer the surface of the hoof, or farther removed from the seat of growth, the more indistinct the structure becomes.
Small round or oval plates of horny epithelium called “chestnuts,” callosities growing like the hoof from enlarged papillae of the skin, are found on the inner face of the fore-arm, above the carpal joint in all species of Equidae, and in the horse (E. caballus) similar structures occur near the upper extremity of the inner face of the metatarsus. They are evidently rudimentary structures which it is suggested may represent glands (Lydekker,Proc. Zool. Soc. London, 1903, vol. i.).
p, Pulp cavity.
d, Dentine or ivory.
e, Enamel.
c, Outer layer of cementum or crusta petrosa.
c′, Inner layer of cementum, lininga, the pit or cavity of the crown of the tooth.
Dentition.—The dentition of the horse, when all the teeth are in place, is expressed by the formulai.3⁄3,c.1⁄1,p.4⁄4m.3⁄3= 44. The incisors of each jaw are placed in close contact, forming a semicircle. The crowns are broad, somewhat awl-shaped, and of nearly equal size. They have all the great peculiarity, not found in the teeth of any other mammal, and only in the Equidae of comparatively recent geological periods (see alsoPalaeontology), of an involution of the external surface of the tooth (see fig. 3), by which what should properly be the apex is carried deeply into the interior of the crown, forming a pit, the bottom of which becomes partially filled with cement. As the tooth wears, the surface, besides the external enamel layer as in an ordinary simple tooth, shows in addition a second inner ring of the same hard substance surrounding the pit, which adds greatly to the efficiency of the tooth as an organ for biting tough, fibrous substances. This pit, generally filled in the living animal with particles of food, is conspicuous from its dark colour, and constitutes the “mark” by which the age of the horse is judged, as in consequence of its only extending to a certain depth in the crown it becomes obliterated as the latter wears away, and then the tooth assumes the character of that of an ordinary incisor, consisting only of a core of dentine, surrounded by the external enamel layer. It is not quite so deep in the lower as in the upper teeth. The canines are either rudimentary or absent in the female. In the male they are compressed, pointed, and smaller than the incisors, from which they are separated by a slight interval. The teeth of the cheek series are all in contact with each other, but separated from the canines by a considerable toothless space. The anterior premolars are quite rudimentary, sometimes not developed at all, and generally fall by the time the animal attains maturity, so that there are but six functional cheek teeth,—three that have predecessors in the milk-dentition, and hence are considered as premolars, and three molars, but otherwise, except the first and last of the series, not distinguishable in form or structure. These teeth in both upper and lower jaws are extremely long-crowned or hypsodont, successive portions being pushed out as the surface wears away, a process which continues until the animal becomes advanced in age. The enamelled surface is infolded in a complex manner (a modification of that found in other perissodactyles), the folds extending quite to the base of the crown, and the interstices being filled and the surface covered with a considerable mass of cement, which binds together and strengthens the whole tooth. As the teeth wear, the folded enamel, being harder than the other constituents, the dentine and cement, forms projecting ridges on the surface arranged in a definite pattern, which give it great efficiency as a grinding instrument (see fig. 2, in articleEquidae). The free surfaces of the upper teeth are quadrate, except the first and last, which are nearly triangular. The lower teeth are much narrower than the upper.
The milk-dentition consists of i.3⁄3, c.0⁄0, m.3⁄3= 24,—the canines and first or rudimentary premolars having apparently no predecessors. In form and structure the milk-teeth much resemble the permanent ones, having the same characteristic enamel-foldings. Their eruption commences a few days after birth, and is complete before the end of the first year, the upper teeth usually appearing somewhat earlier than the lower. The first teeth which appear are the first and second milk-molars (about five days), then the central incisor (from seven to ten days); this is followed by the second incisor (at one month), then the third molar, and finally the third incisor. Of the permanent teeth the first molar appears a little after the end of the first year, followed by the second molar before the end of the second year. At about two and a half years the first premolar replaces its predecessor. Between two and a half and three years the first incisor appears. At three years the second and third premolars, and the third molar have appeared, at from three and a half to four years the second incisor, at four to four and a half years the canine, and, finally, at five years, the third incisor, completing the permanent dentition. Up to this period the age of the horse is clearly shown by the condition of dentition, and for some time longer indications can be obtained from the wear of the incisors, though this depends to a certain extent upon the hardness of the food or other circumstances. As a general rule, the depression caused by the infolding of the surface of the incisor (the “mark”) is obliterated in the first or central incisor at six years, in the second at seven years, and in the third at eight years. In the upper teeth, as the depressions are deeper, this obliteration does not take place until about two years later. After this period no certain indications can be obtained of the age of the horse from the teeth.
Digestive Organs.—The lips are flexible and prehensile; and the membrane that lines them and the cheeks smooth. The palate is long and narrow; its mucous surface has seventeen pairs of not very sharply defined oblique ridges, extending as far back as the last molar tooth, beyond which thevelum palatiextends for about 3 in., having a soft corrugated surface, and ending posteriorly in an arched border without a uvula. This embraces the base of the epiglottis, and, except while swallowing food, shuts off all communication between the cavity of the mouth and the pharynx, respiration being, under ordinary circumstances, exclusively through the nostrils. Between the mucous membrane and the bone of the hard palate is a dense vascular and nervous plexus. The membrane lining the jaws is soft and corrugated. An elongated raised glandular mass, 3 in. long and 1 in. from above downwards, extending backwards from the root of the tongue along the side of the jaws, with openings on the surface leading into crypts with glandular walls, represents the tonsil. The tongue, corresponding to the form of the mouth, is long and narrow. It consists of a compressed intermolar portion with a flat upper surface, broad behind and becoming narrower in front, and of a depressed anterior part rather shorter than the former, which is narrow behind and widens towards the evenly rounded apex. The dorsal surface generally is soft and smooth. There are two large circumvallate papillae near the base, rather irregular in form, about a quarter of an inch in diameter and half an inch apart. The conical papillae are small and close set, though longer and more filamentous on the intermolar portion. There are no fungiform papillae on the dorsum, but a few inconspicuous ones scattered along the sides of the organ.
Of the salivary glands the parotid is by far the largest, elongated in the vertical direction, and narrower in the middle than at either end. Its upper extremity embraces the lower surface of the cartilaginous ear-conch; its lower end reaches the level of the inferior margin of the mandible, along the posterior margin of which it is placed. Its duct leaves the inferior anterior angle, at first descends a little, and runs forward under cover of the rounded inferior border of the lower jaw, then curves up along the anterior margin of the masseter muscle, becoming superficial, pierces the buccinator, and enters the mouth by a simple aperture opposite the middle of the crown of the third premolar tooth. It is not quite so thick as a goose-quill when distended, and nearly a foot in length.
The submaxillary gland is of very similar texture to the last, but much smaller; it is placed deeper, and lies with its main axis horizontal. It is elongated and slender, and flattened from within outwards. Its posterior end rests against the anterior surface of the transverse process of the atlas, from which it extends forwards and downwards, slightly curved, to beneath the ramus of the jaw. The duct which runs along its upper and internal border passes forwards in the usual course, lying in the inner side of the sublingual gland, to open on the outer surface of a distinct papilla, situated on the floor of the mouth, half an inch from the middle line, and midway between the lower incisor teeth and the attachment of the fraenum linguae. The sublingual is represented by a mass of glands lying just beneath the mucous membrane of the floor of the mouth on the side of the tongue, causing a distinct ridge, extending from the fraenum backwards, the numerous ducts opening separately along the summit of the ridge. The buccal glands are arranged in tworows parallel with the molar teeth. The upper ones are the largest, and are continuous anteriorly with the labial glands, the ducts of which open on the mucous membrane of the upper lip.
The stomach of the horse is simple in its external form, with a largely developed rightcul de sac, and is a good deal curved on itself, so that the cardiac and pyloric orifices are brought near together. Theantrum pyloricumis small and not very distinctly marked. The interior is divided by the character of the lining membrane into two distinct portions, right and left. Over the latter the dense white smooth epithelial lining of the œsophagus is continued, terminating abruptly by a raised crenulated border. Over the right part the mucous membrane has a greyish-red colour and a velvety appearance, and contains numerous peptic glands, which are wanting in the cardiac portion. The œsophageal orifice is small, and guarded by a strong crescentic or horseshoe-like band of muscular fibres, supposed to be the cause of the difficulty of vomiting in the horse. The small intestine is of great length (80 to 90 ft.), its mucous membrane being covered with numerous fine villi. The caecum is of conical form, about 2 ft. long and nearly a foot in diameter; its walls are sacculated, especially near the base, having four longitudinal muscular bands; and its capacity is about twice that of the stomach. It lies with its base near the lower part of the abdomen, and its apex directed towards the thorax. The colon is about one-third the length of the small intestine, and very capacious in the greater part of its course. As usual it may be divided into an ascending, transverse, and descending portion; but the middle or transverse portion is folded into a great loop, which descends as low as the pubis; so that the colon forms altogether four folds, generally parallel to the long axis of the body. The descending colon is much narrower than the rest, and not sacculated, and, being considerably longer than the distance it has to traverse, is thrown into numerous folds.
The liver is tolerably symmetrical in general arrangement, being divided nearly equally into segments by a well-marked umbilical fissure. Each segment is again divided by lateral fissures, which do not extend quite to the posterior border of the organ; of the central lobes thus cut off, the right is rather the larger, and has two fissures in its free border dividing it into lobules. The extent of these varies, however, in different individuals. The two lateral lobes are subtriangular in form. The Spigelian lobe is represented by a flat surface between the postal fissure and the posterior border, not distinctly marked off from the left lateral by a fissure of the ductus venosus, as this vessel is buried deep in the hepatic substance, but the caudate lobe is distinct and tongue-shaped, its free apex reaching nearly to the border of the right lateral lobe. There is no gall-bladder, and the biliary duct enters the duodenum about 6 in. from the pylorus. The pancreas has two lobes or branches, a long one passing to the left and reaching the spleen, and a shorter right lobe. The principal duct enters the duedenum with the bile-duct, and there is often a second small duct opening separately.
Circulatory and Respiratory Organs.—The heart has the form of a rather elongated and pointed cone. There is one anterior vena cava, formed by the union of the two jugular and two axillary veins. The aorta gives off a large branch (the anterior aorta) very near its origin, from which arise—first, the left axillary, and afterwards the right axillary and the two carotid arteries.
Under ordinary circumstances the horse breathes entirely by the nasal passages, the communication between the larynx and the mouth being closed by the velum palati. The nostrils are placed laterally, near the termination of the muzzle, and are large and dilatable, being bordered by cartilages upon which several muscles act. Immediately within the opening of the nostril, the respiratory canal sends off on its upper and outer side a blind pouch (“false nostril”) of conical form, and curved, 2 to 3 in. in depth, lying in the notch formed between the nasal and premaxillary bones. It is lined by mucous membrane continuous with that of the nasal passage; its use is not apparent. It is longer in the ass than in the horse. Here may be mentioned the guttural pouches, large air-sacs from the Eustachian tubes, and lying behind the upper part of the pharynx, the function of which is also not understood. The larynx has the lateral sacculi well developed, though entirely concealed within the alae of the thyroid cartilage. The trachea divides into two bronchi.
Nervous System.—The brain differs little, except in details of arrangement of convolutions, from that of other ungulates. The hemispheres are rather elongated and subcylindrical, the olfactory lobes are large and project freely in front of the hemispheres, and the greater part of the cerebellum is uncovered. The eye is provided with a nictitating membrane or third eyelid, at the base of which open the ducts of the Harderian gland.
Reproductive System.—The testes are situated in a distinct sessile or slightly pedunculated scrotum, into which they descend from the sixth to the tenth month after birth. The accessory generative glands are the two vesiculae seminales, with the median third vesicle, oruterus masculinus, lying between them, the single bilobed prostate, and a pair of globular Cowper’s glands. The penis is very large, cylindrical, with a truncated, expanded, flattened termination. When in a state of repose it is retracted, by a muscle arising from the sacrum, within the prepuce, a cutaneous fold attached below the symphysis pubis.
The uterus is bicornuate. The vagina is often partially divided by a membraneous septum or hymen. The teats are two, inguinally placed. The surface of the chorion is covered evenly with minute villi, constituting a diffuse non-deciduate placenta. The period of gestation is eleven months.
Authorities.—R. I. Pocock, “The Species and Subspecies of Zebras,”Ann. Mag. Nat. Hist.ser. 6, vol. xx., 1897, and “A New Arrangement of the Existing Species of Equidae,”Op. cit.ser. 7, vol. x., 1902; R. Lydekker, “Notes on the specimens of Wild Asses in English Collections,”Novitates Zoologicae, vol. xi., 1904; B. Salensky, “On Equus przewalskii,”Mém. Acad. St Pétersburg, 1902; M. S. Arloing, “Organisation du pied chez le cheval,”Ann. Sci. Nat., 1867, viii. 55-81; H. Burmeister,Los caballos fosiles de la Pampa Argentina(Buenos Aires, 1875); Chauveau and Arloing,Traité d’anatomie comparée des animaux domestiques(Paris, 1871), and English edition by G. Fleming (1873); A. Ecker, “Das Europäische Wildpferd und dessen Beziehungen zum domesticirten Pferd,”Globus, Bd. xxxiv. (Brunswick, 1878); Major Forsyth, “Beiträge zur Geschichte der fossilen Pferde besonders Italiens,”Abh. Schw. Pal. Ges.iv. 1-16, pt. iv.; George, “Études zool. sur les Hémiones et quelques autres espèces chevalines,”Ann. Sci. Nat., 1869, xii. 5; E. F. Gurlt,Anatomische Abbildungen der Haussäugethiere(1824), andHand. der vergleich. Anat. der Haussäugethiere(2 vols., 1822); Huet, “Croisement des diverses espèces du genre cheval,”Nouv. Archives du Muséum, 2nd ser., tom. ii. p. 46, 1879; Leisering,Atlas der Anatomie des Pferdes(Leipzig, 1861); O. C. Marsh, “Notice of New Equine Mammals from the Tertiary Formation,”Am. Journ. of Science and Arts, vol. vii., March 1874;Id., “Fossil Horses in America,”Amer. Naturalist, vol. viii., May 1874;Id., “Polydactyle Horses,”Am. Journ. Sci. and Arts, vol. xvii., June 1879; Franz Müller,Lehrbuch der Anatomie des Pferdes(Vienna, 1853); R. Owen, “Equine Remains in Cavern of Bruniquel,”Phil. Trans.vol. clix., 1870, p. 535; W. Percivall,The Anatomy of the Horse(1832); G. Stubbs,Anatomy of the Horse(1766); W. H. Flower,The Horse(London, 1891); Ridgeway,Origin of the Thoroughbred Horse(1905).
(W. H. F; R. L.*)
History
From the evidence of philology it appears that the horse was already known to the Aryans before the period of their dispersion.1
The first mention of the British horse occurs in the well-known passages in Caesar (B.G.iv. 24. 33, v. 15. 16; cf. Pomp. Mela iii. 6), in which he mentions the native “essedarii” and the skill with which they handled their war chariots. We are left quite in the dark as to the character of the animal thus employed; but there would appear to be much probability in the surmise of W. Youatt, who conjectures the horse to have been, “then as ever, the creature of the country in which he lived. With shortfare, and exposed to the rigour of the seasons, he was probably the little hardy thing we yet see him; but in the marshes of the Nen and the Witham, and on the borders of the Tees and the Clyde, there would be as much proportionate development of frame and strength as we find at the present day.” After the occupation of the country by the Romans, it appears that the horses of their cavalry were crossed with the native mares, and thus there was infused into the breed new blood, consisting probably of strains from every quarter from which Roman remounts were procured. As to the effect of this cross we are not, however, in a position to judge. We are also quite uncertain as to the extent to which the Jutes and Saxons may in their turn have again introduced a new breed of horses into England; and even to the close of the Anglo-Saxon period of English history allusions to the horse are still very infrequent. Thehorsthegnwe know, however, was from an early period a high court official; and from such a law as that of Athelstan prohibiting the exportation of horses except as presents, it may be inferred that the English breed was not only much valued at home but also in great request abroad.2
The period of the Norman Conquest marks an important stage in the history of the British horse. William the Conqueror’s own horse was of the Spanish breed, and others of the same kind were introduced by the barons on their estates. But the Norman horses included many varieties, and there is no doubt that to the Conquest the inhabitants of Britain were indebted for a decided improvement in the native horse, as well as for the introduction of several varieties previously unknown. According to Giraldus Cambrensis, Roger de Bellesme, a follower of William I., afterwards created earl of Shrewsbury, imported some stallions from Spain into England; their produce was celebrated by Drayton the poet. It is curious to notice that agriculture seems to be the last use to which the horse has been put. The earliest suggestion that horses were used in agriculture is derived from a piece of the Bayeux tapestry, where a horse is represented as drawing a harrow. This, however, must have been an exceptional case, for we know that oxen were used until a comparatively late time, and that in Wales a law existed forbidding horses to be used for ploughing.
In 1121 two Eastern horses are said to have been imported,—one of them remaining in England, and the other being sent as a present by King Alexander I. to the church of St Andrews, in Scotland. It has been alleged that these horses were Barbs from Morocco, but a still more likely theory is that they existed only in name, and never reached either England or Scotland. The crusades were probably the means of introducing fresh strains of blood into England, and of giving opportunity for fresh crossings. The Spanish jennet was brought over about 1182. King John gave great encouragement to horse-breeding: one of his earliest efforts was to import a hundred Flemish stallions, and, having thus paved the way for improving the breed of agricultural horses, he set about acquiring a valuable stud for his own use.
Edward III. was likewise an admirer of the horse; he procured fifty Spanish horses, probably jennets. At this time there was evidently a tendency to breed a somewhat lighter and speedier horse; but, while the introduction of a more active animal would soon have led to the displacement of the ponderous but powerful cavalry horse then in use, the substituted variety would have been unable to carry the weight of armour with which horse and rider were alike protected; and so in the end the old breed was kept up for a time. With the object of preserving to England whatever advantages might accrue from her care and skill in breeding an improved stamp of horses, Edward III. forbade their exportation; they consequently improved so rapidly in value that Richard II. compelled dealers to limit their prices to a fixed maximum. In the ninth year of his reign, Edward received from the king of Navarre a present of two running horses, supposed to have been valuable. The wars of 1346 checked the improvement of horses, and undid much of what had been previously accomplished, for we read that the cavalry taken into France by Edward III. were but indifferently mounted, and that in consequence he had to purchase large numbers of foreign horses from Hainault and elsewhere for remounts. The reign of Richard III. does not seem to have been remarkable for the furtherance of horse-breeding; but it was then that post-horses and stages were introduced.
Our information on the whole subject is but scanty down to the reign of Henry VII., who continued the enactment against the exportation of stallions, but relaxed it in the case of mares above two years old. His object was to retain the best horses in the country, and to keep the price of them down by limiting the demand and encouraging the supply. In his reign gelding is believed to have had its origin, on account of numerous herds of horses belonging to different proprietors grazing together, especially in time of harvest. Henry VIII. was particularly careful that horse-breeding should be conducted on right principles, and his enactments, if somewhat arbitrary, were singularly to the point. In the thirty-second year of this reign, the “bill for the breed of horses” was passed, the preamble of which runs thus:—“Forasmuch as the generation and breed of good and strong horses within this realm extendeth not only to a great help and defence of the same, but also is a great commodity and profit to the inhabitants thereof, which is now much decayed and diminished, by reason that, in forests, chases, moors and waste grounds within this realm, little stoned horses and nags of small stature and of little value be not only suffered to pasture thereupon, but also to cover mares feeding there, whereof cometh in manner no profit or commodity.” Section 2 of the act provides that no entire horse being above the age of two years, and not being of the height of 15 “handfulls,” shall be put to graze on any common or waste land in certain counties; any one was to be at liberty to seize a horse of unlawful height, and those whose duty it was to measure horses, but who refused to do so, were to be fined 40s. By section 6 all forests, chases, commons, &c., were to be “driven” within fifteen days of Michaelmas day, and all horses, mares and colts not giving promise of growing into serviceable animals, or of producing them, were to be killed. The aim of the act was to prevent breeding from animals not calculated to produce the class of horse suited to the needs of the country. By another act (27 Henry VIII. chapter 6), after stating that the “breed of good strong horses” was likely to diminish, it was ordered that the owners of all parks and enclosed grounds of the extent of one mile should keep two mares 13 hands high for breeding purposes, or, if the extent of the ground was 4 m., four mares. The statute was not to extend to the counties of Westmorland, Cumberland, Northumberland or the bishopric of Durham. Henry took great pains to improve the royal stud: according to Sir Thomas Chaloner—a writer in the reign of Elizabeth—he imported horses from Turkey, Naples and Spain.
Queen Elizabeth is reputed to have been an accomplished horsewoman, and to have indulged in riding late in life. In the first year of her reign she revived an act passed by Henry VIII. making it felony “to sell, exchange or deliver within Scotland, or to the use of any Scottishman, any horse”; this, however, was very naturally repealed by James I. Carriages were soon after introduced, and the use of them speedily became so fashionable that a bill was brought in “to restrain the excessive and superfluous use of coaches.” Prior to the introduction of carriages horseback was the means of locomotion, and Queen Elizabeth rode in state to St Paul’s on a pillion; but even after carriages were used, horseback was held to be more dignified, for James I. and his judges rode on horseback to Westminster Hall. One advantage of the introduction of carriages was that it created a demand for a lighter and quicker sort of horse, instead of the ponderous animal which, despite all attempts to banish him, was still the horse of England—the age of chivalry having been the first epoch of the British horse.
Gunpowder, too, was invented; and now that the weightof the cavalry soldier was diminished by the substitution of lighter armour, a quicker and better bred horse was thought desirable for military service. The introduction of carriages and the invention of gunpowder thus opened out a new industry in breeding; and a decided change was gradually creeping on by the time that James I. came to the throne (1603), which commences the second epoch. James was a thorough sportsman, and his taste for racing, in which he freely indulged, caused him to think but little of the speed of even the best English horses. With the laudable motive, therefore, of effecting improvement in horses, he gave the then large sum of 500 guineas for an Arab stallion which had been procured from Constantinople by a Mr Markham, since known as the “Markham Arabian.” This is the first authentic account we have of the importation of Arab blood, and theStud-Booksays he was the first of that breed ever seen in England. The people having to do with horses at that time were as conservative in their notions as most of the grooms are now, and the “Markham Arabian” was not at all approved of. The duke of Newcastle, in his treatise on horsemanship, said that he had seen the above Arabian, and described him as a small bay horse and not of very excellent shape. In this instance, however, prejudice (and it is difficult to believe that it was anything else) was right, for King James’s first venture does not appear to have been a success either as a race-horse or as a sire, and thus Arabian blood was brought into disrepute. The king, however, resolved to give Eastern blood another trial, and bought a horse known as Place’s White Turk from a Mr Place, who subsequently held some office in connexion with the stable under Cromwell. Charles I. followed in the footsteps of James, and lent such patronage to the breeding of a better kind of horse that a memorial was presented to him, asking that some measures might be taken to prevent the old stamp of horse “fit for the defence of the country” from dying out.
We now come to a very important period in the history of the British horse, for Charles II. warmly espoused the introduction of Eastern blood into England. He sent his master of the horse abroad to purchase a number of foreign horses and mares for breeding, and the mares brought over by him (as also many of their produce) were called “royal mares”; they form a conspicuous feature in the annals of breeding. TheStud-Bookshows of what breed the royal mares really were: one of them, the dam of Dodsworth (who, though foaled in England, was a natural Barb), was a Barb mare; she was sold by the stud-master, after Charles II.’s death, for forty guineas, at twenty years old, when in foal by the Helmsley Turk.
James II. was a good horseman, and had circumstances been more propitious he might have left his mark in the sporting annals of the country. In his reign, according to theStud-Book, the Stradling or Lister Turk was brought into England by the duke of Berwick from the siege of Buda.
The reign of William III. is noteworthy as the era in which, among other importations, there appeared the first of three Eastern horses to which the modern thoroughbred race-horse traces back as the founders of his lineage. This was the Byerly Turk, of whom nothing more is known than that—to use the words of the first volume of theStud-Book—he was Captain Byerly’s charger in Ireland in King William’s wars. The second of the three horses above alluded to was the Darley Arabian, who was a genuine Arab, and was imported from Aleppo by a brother of Mr Darley of Aldby Park, Yorkshire, about the end of the reign of William III. or the beginning of that of Anne. The third horse of the famous trio, the Godolphin Arabian or Barb, brought to England about five-and-twenty years after the Darley Arabian, will be more particularly referred to further on. All the horses now on the turf or at the stud trace their ancestry in the direct male line to one or other of these three—the Byerly Turk, the Darley Arabian, and the Godolphin Arabian or Barb. In the female line their pedigrees can be traced to other sources, but for all practical purposes it suffices to regard one or other of these three animals as theultima Thuleof racing pedigree. Of course there is a large interfusion of the blood of each of the trio through the dams of horses of the present day; indeed, it is impossible to find an English race-horse which does not combine the blood of all three.
The Race-horse.—The third and last epoch of the British horse, viz. that of the thoroughbred racer, may be taken to date from the beginning of the 18th century. By thoroughbred is meant a horse or mare whose pedigree is registered in theStud-Bookkept by Messrs Weatherby, the official agents of the Jockey Club—originally termed the keepers of the match-book—as well as publishers of theRacing Calendar. The first attempt to evolve order out of the chaos which had long reigned supreme was made in 1791, for we find in the preface of the first volume of the Stud-Book, published in 1808, that “with a view to correct the then increasing evil of false and inaccurate pedigrees, the author was in the year 1791 prevailed upon to publish anIntroduction to a General Stud-Book, consisting of a small collection of pedigrees which he had extracted from racing calendars and sale papers and arranged on a new plan.” It will be seen that the compiler of the volume on which so much depends had to go back fully a century, with little else to guide him but odds and ends in the way of publications and tradition. Mistakes under such circumstances are pardonable. TheStud-Bookthen (vol. i.), which is the oldest authority we have, contains the names and in most cases the pedigrees, obscure though they may be, of a very large number of horses and mares of note from the earliest accounts, but with two exceptions no dates prior to the 18th century are specified in it. These exceptions are the Byerly Turk, who was “Captain Byerly’s charger in Ireland in King William’s wars (1689, &c.),” and a horse called Counsellor, bred by Mr Egerton in 1694, by Lord D’Arcy’s Counsellor by Lord Lonsdale’s Counsellor by the Shaftesbury Turk out of sister to Spanker—all the dams in Counsellor’s pedigree tracing back to Eastern mares. There is not the least doubt that many of the animals named in theStud-Bookwere foaled much earlier than the above dates, but we have no particulars as to time; and after all it is not of much consequence.
TheStud-Bookgoes on to say of the Byerly Turk that he did not cover many bred mares, but was the sire of the duke of Devonshire’s Basto, Halloway’s Jigg, and others. Jigg, or Jig, is a very important factor, as will be seen hereafter. TheStud-Book, although silent as to the date of his birth, says he was a common country stallion in Lincolnshire until Partner was six years old—and we know from the same authority that Partner was foaled in 1718; we may therefore conclude that Jigg was a later foal than Basto, who, according to Whyte’sHistory of the Turf, was a brown horse foaled in 1703.
The reign of Queen Anne, however (1702-1714), is that which will ever be inseparably connected with the thoroughbred race-horse on account of the fame during that period of the Darley Arabian, a bay stallion, from whom our very best horses are descended. According to theStud-Book, “Darley’s Arabian was brought over by a brother of Mr Darley of Yorkshire, who, being an agent in merchandise abroad, became member of a hunting club, by which means he acquired interest to procure this horse.” TheStud-Bookis silent, and other authorities differ, as to the date of the importation of this celebrated Arab, some saying he came over in the year 1700, others that he arrived somewhat later; but we know from theStud-Bookthat Manica (foaled in 1707), Aleppo (1711), Almanzor (1713), and Flying Childers (1715) were got by him, as also was Bartlett’s Childers, a younger brother of Flying Childers. It is generally believed that he was imported in Anne’s reign, but the exact date is immaterial, for, assuming that he was brought over as early as 1700 from Aleppo, he could scarcely have had a foal living before 1701, the first year of the 18th century. The Darley Arabian did much to remove the prejudice against Eastern blood which had been instilled into the public mind by the duke of Newcastle’s denunciation of the Markham Arabian. Prince George of Denmark, consort of Queen Anne, was himself a large horse-owner; and it was in a great measure owing to his intervention that so many valuable stallions were imported during her reign.
At this period we find, among a mass of horses and mares in theStud-Bookwithout any dates against their names, many animals of note with the earliest chronology extant, from Grey Ramsden (1704) and Bay Bolton (1705) down to a mare who exercised a most important influence on the English blood-horse. This was Roxana (1718) by the Bald Galloway, her dam sister to Chanter by the Akaster Turk, from a daughter of Leedes’s Arabian and a mare by Spanker. Roxana threw in 1732 the bay colt Lath by the Godolphin Arabian, the sorrel colt Roundhead by Childers in 1733, and the bay colt Cade by the Godolphin Arabian in 1734, in which year she died within a fortnight after foaling, the produce—Cade—being reared on cow’s milk. The Godolphin Barb or Arabian, as he was commonly called, was a brown bay about 15 hands in stature, with an unnaturally high crest, and with some white on his off hind heel. He is said to have been imported into England from France by Mr Coke, where, as the editor of theStud-Bookwas informed by a French gentlemen, he was so little thought of that he had actually drawn a cart in the streets of Paris. Mr Coke gave him to a Mr. Williams, who in his turn presented him to the earl of Godolphin. Although called an Arabian, there is little doubt he was a Barb pure and simple. In 1731, being then the property of Mr. Coke, he was teazer to Hobgoblin, and on the latter refusing his services to Roxana, the mare was put to the Godolphin, and the produce was Lath (1732), the first of his get, and the most celebrated race-horse of his day after Flying Childers. He was also the sire of Cade, own brother to Lath, and of Regulus the maternal grandsire of Eclipse. He died at Gogmagog in Cambridgeshire, in the possession of Lord Godolphin, in 1753, being then, as is supposed, in his twenty-ninth year. He is believed to have been foaled in Barbary about 1724, and to have been imported during the reign of George II.
In regard to the mares generally, we have a record of the royal mares already alluded to, and likewise of three Turk mares brought over from the siege of Vienna in 1684, as well as of other importations; but it is unquestionable that there was a very large number of native mares in England, improved probably from time to time by racing, however much they may have been crossed at various periods with foreign horses, and that from this original stock were to some extent derived the size and stride which characterized the English race-horse, while his powers of endurance and elegant shape were no doubt inherited from the Eastern horses, most of which were of a low stature, 14 hands or thereabouts. It is only necessary to trace carefully back the pedigree of most of the famous horses of early times to discover faults on the side of the dam—that is to say, the expression “dam’s pedigree unknown,” which evidently means of original or native blood. Whatever therefore may be owing to Eastern blood, of which from the middle of the 17th to the beginning of the 18th century a complete wave swept over the British Isles, some credit is unquestionably due to the native mares (which Blaine says were mostly Cleveland bays) upon which the Arabian, Barb, or Turk blood was grafted, and which laid the foundation of the modern thoroughbred. Other nations may have furnished the blood, but England has made the race-horse.
Without prosecuting this subject further, it may be enough here to follow out the lines of the Darley Arabian, the Byerly Turk, and the Godolphin Arabian or Barb, the main ancestors of the British thoroughbred of the 18th and 19th centuries, through several famous race-horses, each and all brilliant winners,—Flying Childers, Eclipse, Herod and Matchem,—to whom it is considered sufficient to look as the great progenitors of the race-horse of to-day.