TETRABELODON. 



25 



the premolars and molars to remain in position at the same 

 time. The consequence of this is, that as the posterior molars 

 are cut they move forward to take up their position in the jaw> 

 thrusting out the teeth in front of them so that in the adult 

 only the two large back molars remain on each side in both 

 jaws, and in old individuals perhaps only the last is left. This 

 mode of replacement is shown in fig. 13 B. In this species, 

 while the first and second molars still have only three ridges^ 

 as in Palaomastodon, the last may have five or six, and, as 

 already mentioned, all are proportionately very large. 



Fig. 14. 



Pier- 



41, 42. 



Table- 

 cases 

 23, 24. 



Restoration of Teirabelodon angustidens. 



In the mandible (fig. 12) the anterior portion is extremely long 

 and projects much further beyond the skull than it does in Palao- 

 mastodon and indeed it is in this species that we have the 

 greatest degree of lengthening of the lower jaw. The two lower 



