THE TEETH OF MAMMALS 155 



so that the grinding teeth are spread out and de- 

 veloped laterally to resist the transverse move- 

 ment so necessary to the grinding of refractory 

 vegetable fiber. The lophodont type of molars 

 has, of course, been gradually developed from the 



Fig. 63. — Teeth of Cow (Bos taurus) . 



simple Tbunodont or tubercular type, by increasing 

 the number of tubercles and ridges and their erec- 

 tion into sharp crests and ridges. The lateral ex- 

 cursion of the jaw is more extensive in some 

 forms, — as the ox, deer, etc., — and in these the 

 molars present a lateral extension of the grinding 



