PROTHEOSODON CONIFERUS 43 



"pillar" already developed opposite the posterior end of 

 the back crescent. In fact, the tooth is molariform, except 

 as to the tiny extra cusp found on the molars. Premolar 

 4 is more completely molariform consisting of the same 

 parts as the preceding tooth. 



The molars may be distinguished by the presence of a 

 tiny median cusp on the rear of the tooth, behind the cres- 

 cent, which, when the tooth is worn, makes a median spur 

 to the rear. In both the premolars and molars, the teeth 

 are characterized by their plumpness, and the isolation 

 and lowness of the cusps. 



Fig. 16. Right mandible 1/2 natural size. 



The two halves of the lower jaw are completely fused at 

 the symphysis. The horizontal ramus is thick, but low 

 dorso-ventrally, giving the appearance of a slender jaw. 

 The posterior angle is prolonged backward and bent in- 

 ward. The fossa for the masseter muscle, while large, is 

 but faintly outlined. The ascending ramus hardly rises 

 above the level of the teeth, except as the slender coronoid 

 projects to a good height above the articular condyle 

 and curves backward over it. 



