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See also:HORSE (a word See also:common to See also:Teutonic See also:languages in such forms as hors, hros, See also:ros; cf. the Ger. See also:ross)
, a name properly restricted to the domesticated See also:horse (Equus caballus) and its See also:wild or See also:half-wild representatives, but in a zoological sense used as a See also:general See also:term for all the members of the See also:family See also:Equidae
.
See also:SPECIES
The distinctive characteristics of the family, and its position in the zoological See also:system, are given in the articles EQUIDAE and See also:PERISSODACTYLA
.
Here See also:attention is concentrated on the leading features of'the horse as contrasted with the other members of the same family, and subsequently on the anatomical structure of the former See also:animal
.
The See also:evolution of the existing representatives of the family from See also:primitive See also:extinct animals is summarized in the See also:article EQUIDAE
.
Horse, Wild Horse, See also:Pony.—The horse (Equus caballus) is distinguished from the others by the See also:long hairs of the tail being more abundant and growing quite or nearly from the See also:base as well as the end and sides, and also by possessing a small See also:bare callosity on the inner See also:side of the See also:hind See also:leg, just below the "hock" or See also:heel See also:joint, in addition to the one on the inner side of the fore-See also:arm above the carpus or " See also:knee," See also:common to all the genus
.
The mane is also longer and more flowing, and the ears are shorter, the limbs longer, and the See also:head smaller
.
Though existing horses are usually not marked in any definite manner, or only irregularly dappled, or spotted with See also:light surrounded by a darker See also:ring, many examples are met with showing a dark median dorsal streak like that found in all the other members of the genus, and even with dark stripes on the shoulders and legs
.
Two distinct types of horse, in many instances largely modified by interbreeding, appear to exist
.
(I) The See also:northern, or dun type, represented by the dun ponies of See also:Norway (Equus caballus typicus), the closely allied See also:Celtic pony (E. c.celticus) of See also:Iceland, the
See also:Hebrides, &c., and the wild pony of See also:Mongolia (E. c. przewalskii), with which the now extinct tarpan of the See also:Russian See also:steppes appears to have been identical
.
The prevalent See also:colour is yellow-dun, with dark See also:
See also:Europe are descended from the dun type, with more or less admixture of Barb See also:blood
.
(2) The See also:southern, or Barb type, represented by Barbs, See also:Arabs, thoroughbreds, &c
.
(E. c. asiaticus or libycus), in which the typical colour is See also:bay with black " points " and often a white See also:star on the forehead, and the mane and tail are long and full
.
The skull generally shows a slight depression in front of the socket of the eye, which, although now serving as the See also:attachment for the muscle See also:running to the nostril, may represent the See also:face-gland of the extinct Hipparion
.
Many of the dark-coloured horses of Europe have Barb or Arab blood in their See also:veins, this being markedly the See also:case with the Old See also:English black or See also:Shire horse, the skull of which shows a distinct depression in front of the eye-socket
.
This depression is still more marked in the extinct See also:Indian E. sivalensis, which may have been the ancestral See also:form
.
In Europe wild horses were abundant in the prehistoric See also:Neolithic or polished-See also: These asses have moderate ears, the tail rather long, and the back-stripe dark brown and running from head to tail . On the See also:neck and withers this stripe is formed by the mane . There are two species of Asiatic wild ass, with several varieties . The first and largest has two races, the chigetai (Equus hemionus) of Mongolia, and the kiang (E. h. kiang) of See also:Tibet, which is a redder animal . The onager (E. onager), of which there are several races, is smaller, with a broader dorsal stripe, bordered with white; the colour varying from sandy to greyish . This species ranges from See also:Baluchistan and N.W . See also:India to See also:Persia, See also:Syria and See also:Arabia . These asses inhabit See also:desert plains or open table-See also:land; the kiang dwelling at elevations of about 14,000 ft . They are generally found in herds of from twenty to See also:forty, although occasionally in larger See also:numbers . All are See also:fleet, and See also:traverse rough ground with See also:speed . On the lowlands they feed on dry See also:grasses, and in Tibet on small woody See also:plants . In India and Persia they are difficult to approach, although this is not the case in Tibet . Their sandy or See also:chestnut colouring assimilates them to the horse, and separates them widely from the See also:African wild asses, which are See also:grey . The kiang has also larger and more horse-like hoofs, and the tail is haired higher up, thus approximating to Equus caballus przewalskii . Among the striped species, or zebras and quaggas of Africa,the large See also:Grevy's zebra (Equus grevyi) of See also:Somaliland and See also:Abyssinia stands apart from the See also:rest by the number and narrowness of its stripes, which have an altogether See also:peculiar arrangement on the hind-quarters, the small size of the callosities on the fore-legs, the mane extending on to the withers and enormous rounded ears, thickly haired internally . The large size of the ears and the narrow stripes are in some degree at any See also:rate adaptations to a See also:life on scrub-clad plains . Next comes the closely allied species with small pointed ears, of which the true quagga (E. quagga) of South Africa is now extinct . This animal has the dark stripes limited to the head, neck and shoulders, upon a brown ground . In the typical form, now also extinct, of the bonte-quagga, dauw, or Burchell's zebra (E. burchelli), the ground-colour is white, and the stripes See also:cover the See also:body and upper See also:part of the limbs . This was the commonest species in the great plains of South Africa, where it roamed in large herds, often in See also:company with, the quagga and numerous antelopes . The species ranges from the See also:Orange See also:river to the confines of Abyssinia, but its more northern representatives show a See also:gradual increase in the striping of the legs, culminating in the See also:north-See also:east African E. burchelli granti, in which the stripes extend to the hoofs . The markings, too, are alternately black and white, in See also:place of brown and creamy, with intermediate " See also:shadow stripes," as in the southern races . Lastly, there is the true or See also:mountain zebra (E. zebra), typically from the mountain ranges of Cape See also:Colony, where it is now specially protected, but represented by E. zebra penricei in south-See also:west Africa . In its relatively long ears and general build it approaches the African wild asses, from which it chiefly differs by the striping (which is markedly different from that of the quagga-group) and the reversal of the direction of the hairs along the spine . The African wild ass (E. asinus) is the See also:parent of the domesticated breed, and is a long-eared grey animal, with no forelock, and either a See also:shoulder-stripe or dark barrings on the legs . There are two races, of which the Nubian E. a. See also:africanus is the smaller, and has a continuous dorsal stripe and a shoulder-stripe but no bars on the legs . The Somali See also:race (E. a somaliensis), on the other See also:hand, is a larger and greyer animal, with an interrupted dorsal and no shoulder-stripe, but distinct leg-barrings . Hybrids.—There are thus eight modifications of the horse-type at See also:present existing, sufficiently distinct to be reckoned as species by most zoologists, and easily recognizable by their See also:external characters . They are, however, all so closely allied that each will, at least in a See also:state of domestication or captivity, breed with any of the others . Cases of fertile See also:union are recorded between the horse and the quagga, the horse and the bonte-quagga or Burchell's zebra, the horse and the onager and kiang or Asiatic wild asses, the common ass and the zebra, the ass and bontequagga, the ass and the onager, the onager and the zebra, and the onager and the bonte-quagga . The two species which are farthest removed in structure, the horse and the ass, produce, as is well known, hybrids or mules, which in certain qualities useful to man excel both their progenitors, and in some countries and for certain kinds of See also:work are in greater requisition than either . Although occasional more or less doubtful instances have been recorded of See also:female mules breeding with the See also:males of one or other of the pure species, it is more than doubtful if any case has occurred of their breeding inter sc, although the opportunities of doing so must have been great, as mules have been reared in immense numbers for at least several thousands of years . We may therefore consider it settled that the different species of-the group are now in that degree of physiological differentiation which enables them to produce offspring with each other, but does not permit of the progeny continuing the race, at all events unless reinforced by the aid of one of the pure forms . The several members of , the group show See also:mental See also:differences quite as striking as those exhibited by their external form, and more than perhaps might be expected from the similarity of their brains . The See also:patience of the ass, the high spirit of the horse, the obstinacy of the See also:mule, have long been proverbial . It is very remarkable that, out of so many species, two only should have shown any aptitude for domestication, and that these should have been from time immemorial the universal and most useful companions and servants of man, while all the others remain in their native freedom to this See also:day . It is, however, still a question whether this really arises from a different mental constitution causing a natural capacity for entering into relations with man, or whether it may not be owing to their having been brought gradually into this See also:condition by long-continued and persevering efforts when the need of their services was See also:felt . It is possible that one See also:reason why most of the attempts to add new species to the See also:list of our domestic animals in See also:modern times have ended in failure is that it does not See also:answer to do so in cases in which existing species See also:supply all the See also:principal purposes to which the new ones might be put . It can hardly be expected that zebras and bontequaggas fresh from their native mountains and plains can be brought into competition as beasts of See also:burden and See also:draught with horses and asses, whose useful qualities have been augmented by the training of thousands of generations of progenitors . Not infrequently instances occur of domestic horses being produced with a small additional toe with See also:complete hoof, usually on the inside of the principal toe, and, though far more rarely, three or more toes may be present . These malformations are often cited as instances of reversion to the condition of some of the earlier forms of equine animals previously mentioned . In some instances, however, the feet of such polydactyle horses See also:bear little resemblance to those of the extinct Hipparion or .4 nchilherium, but look rather as if due to that tendency to reduplication of parts which occurs so frequently as a monstrous condition, especially among domesticated animals, and which, whatever its origin, certainly cannot in many instances, as the cases of entire limbs superadded, or of six digits in man, be attributed to reversion . See also:ANATOMY The anatomical structure of the horse has been described in detail in several See also:works mentioned in the bibliography at the end of this See also:section, though these have generally been written from the point of view of the veterinarian rather than of the See also:comparative anatomist . The limits of the present article will only admit- of the most salient points being indicated, particularly those in which the horse differs from other See also:Ungulata . Unless otherwise specified, it must be understood that all that is stated here, although mostly derived from observation upon the horse, applies equally well to the other existing members of the group . See also: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 See also:cranial portion . The basal See also:line of the cranium from the See also:lower border of the foramen magnum to the incisor border of See also:tale See also:palate is nearly straight . The See also: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 See also:bone with prominent edges . Behind it, and freely communicating with it beneath the osseous See also:bridge (the See also:post-orbital See also: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 See also:row of cheek-See also:teeth, and having a prominent See also:ridge running forward from below the orbit for the attachment of the nasseter muscle . The lachrymal occupies a considerable space on the See also:flat See also:surface of the cheek in front of the orbit, and below It the ,fugal does the same . The latter sends a See also: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 See also: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 See also:closure of the orbit behind distinguishes the skull of the horse from that of its See also:allies the See also:rhinoceros and See also:tapir, and also from all of the perissodactyles of the See also:Eocene period . In front of the See also: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 narros' 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 arc curved downwards to form the semicircular alveolar border which supports the large incisor teeth . The palate is narrow in the See also:interval between the incisor and molar teeth, in which are situatedthe large anterior See also: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 See also:canal for the passage of the See also: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 See also:medium behind . The glenoid surface for the See also:articulation of the mandible is greatly extended transversely, See also:concave' from side to side, See also:convex from before backwards in front, and hollow behind, and is hounded 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 See also:aids to hold in place the otherwise loose tympano-periotic See also:hone . Behind this the exoccipital gives off a long paroccipital process . ...a% Pa t' is es Fie. i.—Side view of Skull of Horse, with the bone removed so as to expose the whole of the teeth . PMx, Premaxilia. c, The canine tooth . Mx, Maxilla. pm', The situation of the rudi- Na, Nasal bone. mentary first premolar, Ma, Jugal or See also:malar bone. which has been lost in L, Lacrymal bone. the lower, but is present Fr, Frontal bone. in the upper See also:jaw . Sq, Squamosal bone. p"tn2, pm3, and pm', The three Pa, Parietal bone. fully developed pre- ac, Occipital condyle. molar teeth . pp, Paroccipital process. m', m2, and m3, The three true i', i2, and is, The three incisor teeth. molar teeth . 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 See also: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 out-wards and slightly backwards . It is not dilated into a distinct bulla, but ends in front in a pointed See also:rod-like process . It completely embraces the truncated cylindrical tympanohyal, which is of great size, corresponding with the large development of the whole anterior See also:arch of the hyoid . This consists mainly of a long and compressed stylohyal, See also: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 See also:tongue . A similar but - less developed process is found in the rhinoceros and tapir . The lower jaw' is large, especially the region of the See also: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 See also: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 . The vertebral See also:column consists of seven cervical. eighteen dorsal, six lumbar, five sacral. and fifteen to eighteen caudal vertebrae There may be nineteen See also:rib-bearing vertebrae, in which case five only will be reckoned as belonging to the lumbar See also:series . The odontoid process of the See also: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 See also:trunk vertebrae the opisthocoelous See also:character of the eentrum gradually diminishes . The spinous processes of the anterior thoracic region are high and compressed . To these is attached the powerful elastic See also:ligament (ligamentum nuchae, or " paxwax ") which, passing forwards in the See also:middle line of the neck above the neural See also:arches of the cervical vertebrae—to which it is also connected—is attached to the occiput and supports the See also: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 See also:chevron bones beneath . The ribs are eighteen or nineteen in number on each side, flattened, and See also: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 See also:prow of a See also: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 See also:shaft gradually tapers below and is firmly welded to the See also:radius . The latter bone is of nearly equal width throughout . The three bones of the first row of the carpus (scaphoid, lunar and See also: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 See also: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 " See also:cannon bone"; the small lateral metacarpals, which gradually See also:taper towards their lower extremities, and See also:lie in See also:close contact with the large one, are called " splint bones." The single See also: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 See also:phalanx (os pedis, or See also: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 See also: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 " astern," and that between the second and third phalanges the " coffin joint." In the hinder See also: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 See also:mere See also:cod-like rudiment of the upper end . The lower part is absent or completely fused with the See also: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 See also:tarsus, corresponding to the See also:ankle of man, the " hock." The bones and See also:joints of the See also:foot have the same names as in the fore limb . The horse is eminently " digitigrade," See also:standing on the extremity of the single digit of each foot, which is kept habitually in a position approaching to See also: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 See also:simple requirements of flexion and See also:extension of the joints, no such actions as pronation and supination, or opposition of digits, being possible or needed . The muscles therefore which per-form 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 See also: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 the extensor communis digitorum of the arm and extensor long= 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 the extensor minimi digiti of 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 the peroneus brevis of man) the tendon becomes blended with that of the large extensor . A strong ligamentous See also:band behind the metapodium, arising from near the upper extremity of its posterior surface, divides into two at its lower end, and each See also: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 See also:muscular See also:fibres in its substance, show that it is the homologue of the interosseous muscles of other mammals, modified in structure and function, to I6, 4, Third or ungual phalanx (os ligament . pedis, or coffin bone) . 12, See also:Derma or skin of the foot, 5, One of the upper sesamoid covered with See also:hair, and bones, continued into 6, Lower sesamoid or navicular 13, The coronary See also:cushion, bone . 14, The podophyllous or laminar 7, Tendon of anterior extensor membrane, and of the phalanges . 15, The keratogenous membrane 8, Tendon of superficial flexor of the See also:sole . (fl. perforatus) . 16, Plantar cushion . 9, Tendon of deep flexor (fl . 17, Hoof . perforans) . 18, Fatty cushion of fetlock . 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, or flexor perforatus (8) dividing to allow the other to pass through, and then inserted into the middle phalanx . The flexor 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 See also:pulley-See also: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 porticos of man) is united with it . The hoof of the horse corresponds to the See also: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 See also:firm basis of support formed of a non-sensitive substance, which is contintlally renewed by the addition of material from within, as its surface wears away by See also: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-sec 1, Metacarpal bone . - 2, First phalanx (os suffraginis) . 3, Second phalanx (os coronae) . to, Suspensory ligament of fetlock . 11, Inferior or short sesamoid grinding See also:instrument (see fig . 2, in article EQUIDAE) . The See also: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 See also:milk-dentition consists of i. c. a, m. f =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 See also:enamel-foldings . Their eruption commences a few days after See also:birth, and is complete before the end of the first See also: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 See also: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 See also:age of the horse is clearly shown by the condition of dentition, and for some time longer indications can be obtained from the See also:wear of the incisors, though this depends to a certain extent upon the hardness of the food or other circumstances . As a general See also:rule, the depression caused by the infolding of the surface of the incisor (the " See also: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 . See also:Digestive See also: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 the velum palati extends 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 See also:nervous plexus . The membrane lining the jaws is soft and corrugated . An elongated raised glandular See also:mass, 3 in. long and i 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 See also:apex . The dorsal surface generally is soft and smooth . There are two large circumvallate papillae near the base, rather irregular in form, about a See also:quarter of an See also:inch in See also: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 See also: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 See also:ear-See also: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 See also:aperture opposite the middle of the See also:crown of the third premolar tooth . It is not quite so thick as a See also:goose-See also: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 See also: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 See also: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 See also: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 See also:summit of the ridge . The buccal glands are arranged in two papillae or villi, and take the greatest See also:share in the formation of the arranged in a definite See also:pattern, which give it great efficiency as a hoof ; the intermediate part constituting the front and side of the foot (14), corresponding with the See also:wall of the hoof, is covered with parallel, See also:fine See also: |