RIDGES OF MASTODON'S TEETH 



characters than the true elephants, we find that 

 their cheek-teeth have very few transverse 

 ridges — from two to five (fig. 78) — and that the 

 jaw is relatively longer, so that there is room, 



Fig. 78. — Lower jaw of the American Mastodon, with two 

 molars on each side, completely cut, showing respectively 

 three and four transverse ridges only. Note also the 

 elongated form of the jaw. 



not only for two complete crowns of molars to 

 be in position on each side at the same time, but 

 even for three. Thus we approach nearer to the 

 central or " typical " condition of the mammals' 

 teeth which, as we have seen in the pig (fig. 50) 



113 I 



