122 



THE STKUCTUEE 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, 01ll y extending to a Cer- 



P^t e black iUe ^^ and the tain de P th ^ the Cr0Wn > 



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 



