Pier- 

 cases 

 41, 42. 



Table- 

 cases 

 23, 24. 



-44 ELEPHANTS. 



This form of ivory is not found in either the upper or lower tusks 

 of Moeritherium and Palceomastodon or in the lower tusks of 

 Dinotherium, and appears for the first time in the large tipper 

 tusks of Tetrabelodon angustidens. In some of the American 

 Tetrabelodouts in which the lower tusks are very large, this 

 structure is also found in them. 



In the lower teeth also of Tetrabelodon angustidens (fig. 16 A) 



Fig. 13. 



A 



m.7 



mm.* pin 3. 



flI7l4 



Lower milk-dentition of (A) Pal(so?nastodon, (B) Tetrabelodon angustidens. 

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

 milk-molars ; m.m., socket of second milk-molar ; pm. 3-4, premolars ; 

 sym., symphysis of mandible. 



great changes have taken place. The milk-molars are still 

 replaced by premolars, but these are quickly dropped out 

 (fig. 13 B). This is chiefly the result of the great increase in 

 size of the true molars, particularly of the third, which is not 

 accompanied by a corresponding increase in the length of the 

 tooth-bearing portion of the jaws, so that there is not room for 



