EVOLUTION OF THE PROBOSCIDEA. 



107 



by the upper surface of the pair of procumbent lower incisors which are in close 

 contact with one another, at least through the greater part of their length. The 

 horizontal ramus behind the symphysis is not so deep in proportion to its length as in 

 Eleplias. The angle is rounded and the hinder border of the ascending ramus slopes 

 backwards and terminates above in a transversely elongated articulation, convex in all 

 directions. The anterior border of the ascending ramus rises on the outer surface of 

 the jaw in front of the hinder end of the alveolar border, so that in a side view the last 

 molar is more or less concealed by it, but owing to the forward movement of the tooth 



Figs. 8 and 9. — Mandible of Tetrabelodon angustidens, ClTVTER sp. Lower and Middle Miocene. Europe. 



series the relative position of the teeth and the ascending ramus changes. There is a 

 small coronoid process which does not rise so high as the articulation. 



1 2 3 



The Teeth. — The dental formula is I. -, Pm. -, M. -. 



1 2 3 



Upper Teeth. — The upper incisors (figs. 6 and 7) form a pair of large tusks differing 

 from those of Eleplias in the following points : — (l) They are straight and decurved, 

 often to a considerable extent ; (2) they are usually more or less oval in section, the 

 long axis of the oval being antero-posterior ; (3) there is a band of enamel on their 

 outer face, extending from root to tip. 



p 2 



