IIOKSI; 



791 



dorsal, six lumbar, five sacral, and fifteen or mop- 

 <'iuiiliil vertebra-. MiMit of the vertebra- are more 

 or less hollowed behind, this character being more 

 nun ked in the fore than in the hinder part of the 

 Hpine. The dorsal processes of the vertebra; in the 

 t'on-|i.ut of the chest are very high, and to them 

 i> attached the great elastic ligament (///////////// 

 inirlue) which relievcM the muscles of the heavy 

 \vi_,'ht of the head and neck. The sternum con- 

 si>u uf six segment**, the anterior one lieing shaped 

 Minn-tiling like the prow of a l>oat. There are no 

 collar l>oii.'-, these Wing in fact absent from all 

 hoofed mammals (Ungulata). The shoulder-blade 

 i- long and narrow, and tears a prominent rounded 

 tubercle, representing the coracoid bone. The 

 hu inertia is short and stout ; of the two bones of 

 'the forearm the ulna is well developed behind, 

 win-re it forms the great process (olecranon), pro- 

 jecting backwards from the elbow-joint, but it 

 tapers gradually away below, and is firmly fused 

 with tin; radius. The wrist ('knee' of common 

 .speech ) consists of six bones, disposed in two rows 

 of three each ; in the second row the middle bone 

 (os magnum) is very large, and supports the cannon- 

 bone, whilst the two- laterals are small, and each 

 supports a splint-bone. The fore-foot of the horse 

 consists of only one fully-developed digit, corre- 

 sponding to the middle finger of tne human hand. 

 The metacarnal bone of this finger is known as 

 the ' cannon -none,' and approximated to its upper 

 end are the thin tapering rudiments of the second 

 And fourth metacarpals, commonly known as 

 'splint-bones;' the cannon-bone is succeeded by 

 three phalanges, known respectively as the ' large 

 pastern,' 4 small pastern,' and 'conin-bone.' Be- 

 hind the foot are three small bones (sesamoids), 

 two behind the joint letween the cannon-bone and 

 large pastern ( commonly called the ' fetlock ' ), and 

 a, single one placed transversely behind the joint 

 between the small pastern and the coffin-bone, 

 commonly called the 'navicular.' In the hinder 

 limb the thigh-bone has a prominent flattened 

 process on its outer side, about one-third down ; 

 this is known as the ' third trochanter,' and is 

 characteristic of all odd-toed ungulates. What is 

 really the knee is known as the 'stifle joint.' 

 The fibula is rudimentary. The tarsus consists of 

 seven bones. The os calcis has a well-marked 

 flattened heel-process, commonly known as the 

 'hock.' The bones of the hind-foot resemble very 

 closely those of the fore-foot, and have the same 

 names. A very strong ligament passes down the 

 hinder surface of the foot, and the two smaller 

 esamoid bones above mentioned are imbedded in 

 it. It is commonly known as the ' suspensory 

 ligament of the fetlock;' occasionally muscular 

 ill ires are found in its substance, and this fact, 

 taken in conjunction with its position and attach- 

 ments, shows that it is the representative of the 

 interosseous muscles of the human hand. The 

 navicular Imne lies in the tendon of the deep flexor 

 muscle of the foot. 



The hoof is the representative of the claws or 

 nails of other animals. The last segment of the 

 toe is widened out to form a foundation for it, and 

 this is increased by cartilaginous side-pieces and 

 A fibrous and fatty sole-piece. The integument is, 

 of course, continuous with the skin of the limb, 

 "but it is extremely vascular, and its surface is 

 developed into papilla^ or lainin;e, which secrete the 

 horny matter of the hoof. The chief share in this 

 process is taken by the ' coronary cushion,' or 

 thickened ring round the upper part of the foot, 

 and by the cushion in the sole. The result of this 

 is that the hard external tissue of the hoof is 

 renewed from within as fast as it wears away on 

 the outside. The lower surface which conies Into 

 contact with the ground is hollow, and its centre 



in occupied by the 'frog,' a triangular eminence 

 with iU ape\ <lin-ctcd forwards, and coiihbtin^- of 

 pavement epithelial cells arrange*! concentrically, 

 oilier horny HtmctureM are the Mi-culled 'che-t 

 nut-.' hard' oval warts situated on the inner 

 surface of all four legs in the horse (A*, mlml/ux), 

 and of both fore-legs in the other ineinliers of the 

 genus. 



The teeth of the horse when the series is com- 

 plete are forty-four in niimW : three incisors, one 

 canine, four premolars, and three molars on cither 

 side of each jaw. The incisors form a semicircle : 

 they have a pit in the apex nartiallv filled up with 

 bony matter, and this it IH which produces the well- 

 known appearance of concentric rings as the tooth 

 wears away, and their disapj>earance when the 

 wearing has carried the surface of the tooth lievond 

 the bottom of the pit. The canines are either 

 rudimentary or absent in the females. Hetween 

 them and the grinding-teeth is a wide gap (dia- 

 stema) in which the bit is placed. The first pre- 

 molars are either quite rudimentary or absent ; 

 when present they are usually lost liefore maturity, 

 so that the gnnding-teeth in actual use only 

 amount to six in number. They have very long 

 crowns, which are gradually pushed up as the 

 surface wears away ; this peculiarity in structure 

 is only seen in the teeth of the more recent horses, 

 and is probably to be associated with the removal of 

 the animal from swamps to drier plains, and hence 

 from soft moist vegetation to foou more difficult of 

 mastication. The enamel of the teeth forms a 

 curved folded plate, the pattern being derivable 

 from that seen in other Perissodactyles ; and it is 

 this which produces the characteristic pattern seen 

 in the surface of the horse's molars. The temporary 

 or milk teeth are twenty-four in number three 

 incisors and three milk-molars on either side of 

 each jaw. At birth the first and second molars 

 are present ; at one week old the central incisors 

 appear ; at six weeks the two next incisors ; at 

 three months these incisors are level, and a third 

 molar has come into view ; at six months oblitera- 

 tion is apparent in the central incisors ; at eight 

 months tne lateral incisors have erupted, making 

 the full number of six in each jaw ; at one year 

 the fourth molar is visible ; at eighteen months' the 

 mark is very faint in the central incisors ; at two 

 years old there are five molars ; at three years the 

 permanent central incisors replace the temiMirary 

 ones ; at three and a half and four and a half years 

 respectively, the same happens with the second and 

 the lateral incisors, and at the latter date the 

 canines appear in the male ; at five years the 

 mark is nearly, and at six years quite effaced in 

 the central incisors ; at seven years the like has 

 happened to the next incisors; and at eight 

 years the mark has disap|>eared from all the 

 teeth, and the canines have become blunted. 

 Hence by the presence of the different teeth ami 

 their condition as regards wear, it is possible to 

 tell the age of a horse with considerable accuracy 

 up to six or eight years of age, but after that no 

 reliable conclusions can be drawn from 



organs. 



The lips are flexible ; the palate long and narrow, 

 and transversely ridged ; tne soft palate has no 

 uvula, and, except during the actual process of 

 swallowing, embraces the epiglottis, so that respira- 

 tion is carried on entirely through the nostrils. 

 Three pairs of salivary glands are present, the 

 parotid leing by far the largest. The stomach is 

 simple and a good deal curved upon itself : at the 

 oesophageal opening is a kind of muscular valve to 

 which is commonly attributed the diHictilty which a 

 horse experiences in vomiting. The small* intestine 

 is eighty or more feet in length, and terminates in 

 a large circum with sacenlatetl walls. The liver is 



