122 



THE STRUCTURE OF THE HORSE. 



takes place, the surface, besides the external enamel 

 layer, as in the ordinary simple tooth, shows, in ad- 

 dition (see Fig. 19), a sec- 

 ond, inner ring of the same 

 substance surrounding the 

 pit, which, of course, adds 

 greatly to the efficiency of 

 the tooth as an organ for 

 biting tough, fibrous sub- 

 stances. The bottom and 

 sides of the pit are par- 

 tially lined with cement, 

 but a considerable cavity 

 remains, generally filled, 

 in the living animal, with 

 particles of food, and, be- 

 ing conspicuous from its 



FIG. 19. -Incisor tooth of dark color > & constitutes 



horse, with the crown par- the mar k by which the 

 tially worn, showing the pit 



surrounded by its enamel age of the horse IS judged, 

 layer, outside of which is 



the dentine with its external In Consequence of its 



enamel covering. The en- , ,. 



amel is represented white, Onl 7 extending to a cer- 



p^blaTk! 116 gray ' and the tain de P th ^ the CrOWn > 

 it becomes obliterated as 



the tooth wears away, the section of which then as- 

 sumes the character of that of an ordinary incisor, con- 

 sisting of only a core of dentine, surrounded by an 



