THE BEAVER AS A SPECIES 211 



peculiar feature of the head are the teeth, which 

 are most wonderfully developed to meet the 

 animal's method of living. Their total number is 

 twenty, ten in each jaw. These consist of eight 

 molars or grinding teeth and two incisors for cut- 

 ting. These latter are the chisel-like teeth with 

 which the beaver is able to cut down the great 

 forest trees. In their construction they are of 

 especial interest. The outside or front is a thin 

 layer of very hard orange-coloured enamel attached 



Skeleton of Beaver. 



to a thick backing of dentine, which, being soft, 

 wears away by the action of cutting and leaves the 

 shell-like edge of enamel always sharp. The lower 

 teeth are of great length, approximately four inches 

 along the outer curve, of which a minimum of 

 about one quarter extends beyond the jaw-bone. 

 The incisors of the upper jaw are both shorter and 

 more abruptly curved. The distance between 

 these and the molars is about one-and-a-half times 

 the space occupied by the groups of molars. 

 These are curious rootless teeth composed of 



p 2 



