30 ELEPHANTS. 



Wall- caseC.) ; it is not certain whether or not there were any tusks 

 ease4.>. j fl ^ ne U pp er jaw. The teeth are of a much simpler character 

 '" than those found in the Mastodon-elephant line. In the upper 

 jaw of the adult there are two premolars, both simpler than 

 the molars ; of these latter the anterior one consists of three 

 transverse crests, the other two of two crests only,, a notable 

 peculiarity, since in the other Proboscidea it is the hindermost 

 molar which is the most complex. The posterior milk-molar 

 also has three crests. In the lower jaw in addition to the 

 down-turned tusks there are two prernolars and three molars. 

 As in the upper jaw, the premolars are simpler than the molars : 

 the anterior molar has three crests, the second and third two 

 only, though in the last there may be a trace of a third. In 

 the young there are three milk-teeth, the hinder one having 

 three crests, like the anterior true molar. All the molars and 

 premolars remain in use throughout the animal's life, a condition 

 already lost in the earliest Tetrabelodous, as has been already 

 described. It has been suggested that Dinotherium was a 

 more aquatic animal, but there is nothing in the structure of 

 the limbs to give any support to this idea, though the lowness 

 of the crowns of the teeth probably indicates that it lived on 

 soft herbaceous vegetation, such as may have grown in swampy 

 places. 



In Tetrabelodon longirostris the main characteristics of the 

 modern elephants are already established, and the later changes 

 of importance include, (1) the still further reduction of the 

 mandibular symphysis and the loss of the lower incisors, and 

 (2) the great increase in the size and complication of the 

 cheek-teeth. It will be convenient to consider these changes 

 separately. 



In the shortening of the chin the next stage is found in 

 Pliocene forms like Mastodon atticus from the Lower Pliocene 

 of Pikermi. In this the symphysis,*though much shortened, 

 is still more or less spout-like,, and in very young indivi- 

 duals the incisors may be present, though they are soon shed ; 

 the absence of these teeth in the adult is the chief character 

 distinguishing the genus Mastodon (fig. 18) from Tetrabelodon. 

 One of the best known species belonging to this stage of 



