EVOLUTION OF THE ELEPHANT — LULL. 657 



a strong tendency to form yet another crest. There were 26 teeth 

 altogether. The neck is still fairly long, though the hinder neck 

 vertebra? are beginning to shorten. 



Palcpomastodon is confined to the Upper Eocene, and has thus far 

 been found only in the Fayum region. 



CLASSIFICATION OF THE LATER PROBOSCIDEA. 



We know as yet no Oligocene proboscidians, the next forms being 

 found in the lower Miocene of northern Africa and Europe, so that 

 a considerable break occurs in the continuity of our series. It is 

 evident that the line was still African in distribution, for apparently 

 the exodus from Egypt did not occur before Miocene times. 



The mastodons have been divided in two ways, one depending upon 

 the number of ridges borne upon the grinders, while the other classi- 

 fication is based upon the number and character of the tusks. The 

 latter seems the more logical from a developmental viewpoint. The 

 first of these genera is T etrahelodon^ with four enamel-banded tusks. 

 The second is Dihelodon., having but two tusks which still retain the 

 band of enamel. The last genus is Mammut^ with enameless upper 

 tusks in the adult, though one or two may also be present in the 

 adolescent lower jaw. The latter are sometimes retained throughout 



life. 



Tetrdbelodon. 



The third recorded stage in the evolution of the elephants is repre- 

 sented by the Miocene Tetrabelodon angustidens^ of which a splendid 

 specimen from Gers, France, 

 is preserved in the museum 

 of the Jardin des Plantes at 

 Paris. It was an animal of 

 considerable size, nearly as 

 large as the Indian elephant, 

 but differing markedly from 

 the latter in the peculiar 

 character of the lower jaw, 

 which was enormously long 

 at the symphysis and con- 

 tained a pair of relatively short tusks. This form represents the 

 culmination of the jaw elongation, for in its successors the sym- 

 physis is rapidly shortened and the inferior tusks finally disap- 

 pear. The upper tusks in TetraheJodon were longer than those of 

 the lower jaw, but did not extend much beyond the latter. The tusks 

 had an enamel band upon the outer and lower face and were slightly 

 curved downward. The nasal orifice had receded farther to the rear, 

 indicating a still greater development of the trunk than in Palceo- 



FiG. 14. — Skull of TetraheJodon anfjustidens. 



