1JO AN1MAI FUNCTION 5 ?. 



and spreading on the lower jaw, and by which the latter 

 is chiefly moved, is small and feeble when compared with 

 the corresponding part in the feline race. The articulation 

 of the lower jaw, instead of being such as to allow only of 

 a hinge-like action, is so connected as to play laterally 

 with a grinding motion. 



316. Such are the differences which the Creator Jhas 

 made between the masticating organs of the flesh-eating 

 and the grain-eating races of quadrupeds. 



317. Teeth of the Gnaviers. There is still another 

 family of mammalia, which are remarkably well distin- 

 guished by their teeth, and which remove them very 

 decidedly from either of the above classes. These are the 

 rodentia or gnawing quadrupeds, as the squirrel, rat, bea- 

 ver, and rabbit. 



318. These animals appear to be formed for gnawing 

 the hardest of vegetable bodies, as the shells of nuts, or for 

 living on dry tough materials, as the bark of trees, .and 

 even on the woody fibres. They are generally of diminu- 

 tive size, and reside mostly either in hollow tree's, or in 

 burrows which they dig for themselves. 



319. As an example of the chewing mechanism of this 

 family, the scull and teeth of the rat are presented by 

 Fig. 78. The cutting teeth Fig. 78. 



are two in number in each 

 jaw. They project forward 

 so as merely to admit of be- 

 ing covered by the lips, and' 

 are exceedingly sharp, having 

 at the edge the exact shape of 

 a chisel. The roots are large, 

 curved, and set in solid bone, 

 so that in the dry scull they cannot be extracted without 

 breaking the jaws. The grinding teeth are marked with 

 raised, angular lines, by which they are rendered veiy 

 perfect instruments for the trituration of hard substances. 



320. Masticating Organs in Man, compared u-ith those 

 of the Mammalia. In comparing our own organs of masti- 



What is the difference between the teeth and jaws of carnivorous and 

 herbivorous animals? What peculiarities do the teeth of the gnawers 

 preset*. 



