HISTORY OF THE PROBOSdIDEA 441 



elephant's jaw. As the grinding teeth increased in height, 

 there was a concomitant increase in the vertical depth of the 

 jaws for their lodgment. 



It was an obvious advantage in the mechanical problem 

 of supporting the enormous weight of head, tusks and trunk 

 to shorten the neck and thus bring the weight nearer to the 

 point of support at the withers, the lengthening proboscis 

 rendering it unnecessary for the mouth to reach the ground 

 in feeding or drinking. The other parts of the skeleton under- 

 went comparatively little change, the degree of modification 

 being greatest between ^Mceritherium and ^Palceomastodon. 

 Throughout the series the bones of the fore-arm and lower 

 leg remained separate, and the feet very short and five-toed. 

 In size also the great stature and massiveness were attained 

 early. After the great migration of the Proboscidea to the 

 northern continents, we find considerable differences of size 

 between the various phyla, though all were very large, and 

 even as early as the lower Miocene of France, there were 

 species which rivalled the modern elephants in bulk. It was 

 this rapid attainment of great size and weight which appears 

 to have been the determining factor in the conservatism of the 

 skeleton. After the skeleton had become fully adjusted to 

 the mechanical necessities imposed by immense weight, and 

 that adjustment, as we have seen, was effected at a com- 

 paratively early period in the history of the order, then no 

 further modification of importance would seem to have been 

 called for. No doubt the habits and mode of life of these 

 massive, sedate and slow-moving animals underwent but little 

 change from the lower Oligocene onward. There is reason to 

 think that fMoeritherium was semi-aquatic and a haunter of 

 marshes and streams, but, if so, the change to a life on dry 

 ground was complete in the lower Oligocene, for the structure 

 of ^Palceomastodon gives no reason for supposing that it was 

 anything but a dweller on solid land and a denizen of forests. 



Although this book does not undertake to deal with the 



