24 ELEPHANTS. 



skull are much more elephant-like than in Palteomastodon. 

 Thus the nostrils have shifted still further back, and the great 

 development of air-cells in the bones at the back of the skull 

 has led to the disappearance of the ridge along the middle 

 of the roof, which is now flat. Further, the upper tusks, 

 which were quite small and flattened in Palaomastodon, are 

 now large and round, and differ from those of a modern 

 elephant only in curving downward instead of upward, and in 

 having a band of enamel along the outer side relatively much 



Fig. 13. 



jimi 



sym. 



rn.2 



Lower milk-dentition of (A) Palcsomastodon, (B) Tetrabelodon anyustidens. 

 Showing some of the milk-teeth in situ, with the germs of replacing 

 premolars. The germs of the 2nd molars are shown at the back of the 

 jaw. About I nat. size. 



i., incisor; m. 1-2, permanent molars ; mm. 3-4, third and fourth 

 milk-molars ; mm., socket of second milk-molar ; pin. 3-4, premolars ; 

 sym., symphysis of mandible. 



narrower than in Palcsomastodon, in which nearly the whole 

 outer face of the tooth is enamel-clad. As the tusks increase in 

 size, the dentine of which they are composed acquires a peculiar 

 structure, which is shown in transverse sections of the tusks (see 



