i8 95 . THE TEETH OF THE HORSE. 257 



ably similar in character, the molars being practically indistinguish- 

 able from the premolars. 



There are two infundibula, one anterior and one posterior, 

 running vertically through the whole length of the crown of the cheek 

 teeth ; but in the lower jaw the infundibula are, until filled with 

 cement, cleft for their whole length down the internal face of the tooth. 

 In the upper teeth, five main divisions of the pulp-cavity can be 

 distinguished, four of these being disposed symmetrically with regard 

 to the two infundibula, while the fifth is an outgrowth from the antero- 

 internal division and belongs to the accessory internal pillar of the 

 tooth. In the lower teeth there are two main divisions of the pulp- 

 cavity, and three (or four) minor divisions belonging to the two 

 duplicated columns on the internal or lingual surface of the teeth. 

 Since the pattern of the worn tooth is determined by the disposition 

 of the dentine and enamel about the cement-filled infundibula and 

 the divisions of the pulp-cavity occupied by secondary dentine, the 

 tables of the teeth are very elaborate ; and, by the inequality in the 

 wear of the three constituents, enamel, dentine, and cement, a very 

 efficient grinding surface is preserved. On the table of one of the 

 upper teeth, three closed sinuous bands of enamel stand out in relief 

 by virtue of their superior hardness. One ridge, large and irregular 

 in form, and called the " peripheral enamel," encloses all five divisions 

 of the pulp-cavity (which, on the table, are always closed by 

 secondary dentine) ; and two, smaller and of crescentic shape, line 

 the cement-filled infundibula, and are known as the " central enamel" 

 of the tooth (Fig. A.). The dentine of the tooth is disposed inside the 

 larger enamel zone and around the enamel crescents, whereas the 

 cement only occurs in the infundibula and on the periphery of the 

 outer enamel band. In the lower teeth, since the infundibula are open 

 on their internal edge, the central and peripheral ridges of enamel on 

 the tables are continuous (Fig. F.), and the cement filling the infundi- 

 bula is continuous with the peripheral cement. The enamel band is 

 thus even more tortuous than in the upper teeth, but, as in the latter, 

 the dentine is everywhere separated from the cement by enamel. As 

 in the case of the incisor teeth, the infundibula are at first open at 

 the root end of the tooth (Fig. C), and only close when the tooth 

 cuts the gum, the cavities being by that time nearly filled with the 

 later developed cement. 



There is hardly any difference in pattern or size between the last 

 premolar and the first molar in a middle-aged animal ; but in 

 advanced life the disparity in the ages of these teeth, visible between 

 four and five years, becomes once more apparent, the molar wearing 

 down more than the premolar, and, consequently, becoming less 

 deeply rooted in the jaw. This applies, however, chiefly to the upper 

 jaw, since the teeth wear more evenly in the lower jaw. 



The pattern of the deciduous molars is nearly the same as that of 

 the premolars, but is slightly simpler. The crowns of these teeth do 



