EVOLUTION OF THE PROBOSCIDEA. 105 



in use at the same time, and late in life the posterior molars alone remain. The 

 individual teeth are extremely complex in structure, each consisting of a number of 

 transverse plates united in a common investment of cement ; the plates are extremely 

 hypselodont and increase in number from before backwards ; thus in the Indian 

 elephant the first milk-molar has four plates, while in the last true molar there may 

 he as many as twenty-four. In the lower jaw the number and character of the teeth 

 and their mode of replacement are the same. 



The essential peculiarities of the elephant's dentition, therefore, are : — 



( 1 ) The absence of vertical successors to the milk-molars. 



(2) The gradual forward movement of the series. 



(3) The increase in the size and complexity of the teeth from before backwards. 



(4) The lophodont and hypselodont character of the teeth 



Drcsjvn fe-ncLb. size. 



Fig. 5. — Mandible of Mastodon americanw, Cuvier. Pleistocene. N. America. 



Tctrabelodon angustidens, Cuvier sp. 



The Skull (figs. (3 and 7). — Unfortunately I have only been able to examine a much 

 crushed skull of this species, but with the assistance of photographs of specimens in 

 the Musee d'Histoire Naturelle at Paris, kindly supplied by Professors Gaudry 

 and Marcellin Boule, it has been possible to make out the main points. 



The occipital region is only a little less elevated and expanded than in Elephas ; 

 this is what might be expected, since in this animal, in addition to large tusks and the 

 proboscis, there was also the weight of the greatly elongated mandible to be supported. 

 It seems, however, that the development of cells in the cranial bones is somewhat less 

 than in the recent type, and the skull is rather longer in proportion to its height, so 

 vol. cxc vi. — b. \> 



