TEETH OF THE FOKCUriXE. 



2(57 



Before quitting the carnivorous order, the peculiar 

 development of the upper canines of the morse or walrus 

 deserve to be noticed. The staple food of this large mo- 

 dified seal is shell-fish, crustaceans, and sea- weed, which 

 are pounded to a pulp by its small obtuse molar teeth. 

 The canines (Fig. 70), c, exist only in the upper jaw, 

 where they are imbedded in deep and large prominent 

 sockets, whence they sweep down^ slightly incurved, 

 forming large and long tusks, which serve as weapons of 

 attack and defence, and as instruments in aid of climbing 

 the floes and huip^imocks of ice, amongst which the walrus 

 passes its existence. 



In the order of mammalia, called gnawers or rodents, 

 some of which, e. g. the rat, are mixed feeders, but most 

 of them herbivorous, the canine teeth are wanting in 

 both jaws, and the incisors, reduced to two in number, 

 are the seat of that excessive and uninterrupted growth, 

 which makes them allied to tusks. 



These incisors (Fig. 71), ^, are curved, the upper pair 



Fig. 71. 



SKULL AND TEETH OF A PORCUPINE. 



describing a larger part of a smaller circle, the lower 

 ones a smaller part of a larger circle, the latter being the 



