SOLIPEDA. 



733 



siderable interval ; and a similar interspace 

 also exists, but to a less extent, in the lower 

 jaw. 



The molar teeth of the horse are of a pris- 

 matic form, their grinding surfaces being 

 marked with four crescents of enamel in the 

 lower jaw, and with five in the upper : these 

 crescentic patches in the upper jaw have their 

 concavities turned outwards, but in the lower 

 jaw in the opposite direction. The teeth of 

 the horse are, moreover, distinguishable from 

 those of the ox and some other Ruminants, 

 which they resemble in their general appear- 

 ance, from the circumstance that, in the latter, 

 the crescentic patches of enamel are arranged 

 in pairs, and are placed parallel to each other ; 

 whilst in the horse they are situated alter- 

 nately, the first of the inner margin of the 

 tooth corresponding to the interval between 

 the two of the outer margin. 



Professor Owen * observes, that the cha- 

 racter by which the horse's molars may be 

 best distinguished from the teeth of other 

 Herbivora corresponding with them in size, 

 is the great length of the tooth before it 

 divides into fangs. This division, indeed, 

 does not begin to take place until much of 

 the crown has been worn away ; and thus, 

 except in old horses, a considerable portion 

 of the whole of the molar is implanted in the 

 socket by an undivided base. The deciduous 

 molars have shorter bodies, and sooner begin 

 to develope roots ; but in these, or in an old 

 permanent molar with roots, the pattern of 

 the grinding surface, though it be a little 

 changed by partial obliteration of the enamel 

 folds, yet generally retains as much of its cha- 

 racter as to serve, with the form of the tooth, 

 to distinguish such tooth from the permanent 

 molar of a Ruminant. 



A knowledge of the structure and history 

 of the teeth of the horse becomes addition- 

 ally important, from the circumstance that it 

 is from the condition of the dental apparatus 

 that an estimate may be formed concerning 

 the age of the animal ; and, in order to un- 

 derstand the data thus afforded, it will be 

 necessary to consider the structure of these 

 organs rather more closely. 



The incisors f , when the permanent teeth 

 are first completely developed, are arranged 

 close together, forming the arc of a circle at 

 the extremity of both jaws ; they are slightly 

 curved, with long simple sub-trihedral fangs, 

 tapering to their extremity. The crowns are 

 broad, thick, and short; the contour of the 

 biting surface, before it is much worn, ap- 

 proaching an ellipse. These teeth, if found 

 detached, recent, or fossil, are distinguishable 

 from those of the Ruminants by their greater 

 curvature, and from those of all other animals 

 by a fold of enamel, which penetrates the 

 bodv of the crown from its broad flat summit, 

 like the inverted finger of a glove. When the 

 tooth begins to be worn, the fold forms an 

 island of enamel, inclosing a cavity partly 



* Odontography, p. 574. 



f Owen, Odontbgraphy, p. 572. 



filled with cement, and partly by the dis- 

 coloured substances of the food, and is called 

 " the mark." In aged horses the incisors are 

 worn down below the extent of the fold, and 

 " the mark " disappears. The cavity is usu- 



Fig. 505. 



Lower jaw of a one-year-old Colt; milk incisors, 

 {After Youatt.). 



Fig. 506. 



Two-years' -old ; milk incisors, middle pair much worn- 

 {After Youatt.) 



Fig. 507. 



Three years; the two middle teeth have been shed and 

 renewed ; the canines just appearing above the qums. 

 (After Youatt.} 



