TEETH OF ANIMALS. 259 



jaw; and when fully grown, they will remain sta- 

 tionary and on a level, if subjected to the natural 

 pressure of mastication : but without this they 

 will rise too high, project, and at last fall out. It 

 is on this principle, that if we lose teeth in one 

 jaw, we lose them in both : and there are no means 

 of preventing the loss of these, but by such me- 

 chanical substitutes as shall restore them to their 

 due exereise. And yet nature modifies the law 

 with perfect ease, and, as it were, at will. Let 

 us take an example : 



The front teeth of the horse are called " nip- 

 pers ;" they meet and crop the herbage. As the 

 horse is a vegetable feeder, he must grind with 

 his back teeth, and, during this act, the front teeth 

 must participate in the grinding motion. We 

 shall presently see how they are protected against 

 this attrition. But in the ruminant animals, those 

 which chew the cud, there is a necessity for a more 

 thorough grinding of the food, whilst at the same 

 time the front teeth must preserve their edge. 

 For this purpose, the teeth are wanting in the fore 

 part of the upper jaw, and there is only a cushion, 

 which embraces and holds the grass against the 

 edge of the lower teeth, so that it is cut as with a 

 sickle, by a smart twitching motion of the head. 

 Thus the front teeth undergo no attrition. Now, 

 although there be no teeth in the upper jaw, those 

 below do not rise or become loose, as they cer- 

 tainly would in man, or in any other animal, not 

 of the class of ruminants. This reasoning will be 



