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. 
