MASTICATION. 77 



project above the soft dentine. The tables of the back 

 teeth slope downwards and outwards, that is to say, their inner 

 edges are higher than their outer edges. The action of the 

 back teeth is that of a mill, in which the sharp surfaces of the 



Fig. 2. Transverse Section of Skull of Horse, immediately in front 

 of his back teeth. 



lower back teeth on each side of the mouth are worked laterally 

 against those of the upper jaw, and thus the food which is 

 brought between them by the tongue and cheeks, is 

 ground. As the lower jaw is narrower than the upper jaw 

 (Fig. 2), a horse can chew with his back teeth only on 

 one side of his mouth (Fig. 3) at a time, which he often 

 continues to do for even as long as an hour, without changing 

 to the other side. A horse is unable to use his front teeth 

 and his back teeth at the same time ; for when he works his 

 lower jaw laterally, the front teeth of the lower jaw become 

 separated from those of the upper jaw (Figs. 4 and 5). 



