ELEPHANTS. 



557 



true elephants. In the third, fourth, and fifth molar teeth of the stegodont 

 elephants, the number of transverse ridges is usually more than six, but in the 

 mastodons it is generally either four (as shown in the figure below) or three, although 

 occasionally there may be as many as five. Moreover/the sixth or last molar gener- 

 ally has only four or five such ridges, in place of from nine to eleven found in the 

 stegodont elephants. In all these respects the mastodons exhibit a less specialised 

 type of structure than that existing in the elephants, and thereby approximate to 

 ordinary Ungulates. This simpler dental structure is further evidenced by the 



TWO SPECIMENS OF MOLAR TEETH OF INDIAN MASTODONS (nat size). 



Both teeth are unworn ; and while the upper belongs to M. cautleyi, the lower 

 belongs to M. perimensis. 



circumstance that portions of three molar teeth may be in use at the same time, 

 whereas in elephants only two such teeth are ever present contemporaneously on 

 one side of the jaw. Then, again, nearly all the mastodons had premolar teeth 

 vertically replacing their milk-molars, in the same manner as in other Ungulates. 



Another peculiarity of some, although by no means all mastodons, is the 

 presence of a pair of larger or smaller tusks in the lower as well as in the upper 

 jaw ; the extremity of the lower jaw in such species being prolonged into a spout- 

 like projection. 



