EVOLUTION OF ELEPHANTS 



367 



jaw — became more prominent, they progressively inter- 

 fered more and more with the animals' feeding, rendering 

 it necessary to depend increasingly upon the prehensile 

 power of the trunk. Thus in the lapse of generations and 

 through the successive form-modifications, as the tusks grow 

 longer and more ponderous, so does the trunk lengthen and 



Mammoth etched on the rock of the "Grotte des Combarelles," dept, 

 Dordogne, France, the outUnes being coloured with oxide of manganese. 

 — From R. S. Lull, "Evolution of the Elephant." 



gain in vigour. An anatomical change dependent upon the 

 excessive growth of the tusks is a lengthening of the jaw- 

 bone, very noticeable in the Trilophodons and still present 

 in the immediate predecessors of the Dibelodons, where the 

 tusks of the lower jaw, with few exceptions, have already 

 ceased to assume a tusk form. The teeth of the earliest 

 ancestors of the mastodon were exceedingly simple in form, 

 having but two transverse ridges; in later forms the number 



