KINETOGENESIS. 341 



torial molars in those types. In the Amblypoda, the 

 lower molars even shear backwards on the upper ones. 

 It seems then that this growth of the canines is not in 

 all instances sufficient to cause a proterotome masti- 

 cation. I suspect that the more usual cause is to be 

 found in the voluntary effort of the primitive flesh- 

 eater, to masticate flesh by the manipulation of his 

 lower jaw and the body to be divided. The presence 

 of the inferior canine forbids a posterior shearing move- 

 ment of the molars, so that the anterior shear is the 

 only one possible to most of the Creodonta. The ab- 



Fig. 103. Cynodictis geismarianus Cope ; skull one-half natural size : a, 

 right side; b, left side from below. 



sence of preglenoid crest in primitive Creodonta will 

 permit a manipulation such as we observe in various 

 ungulates to-day. The formation of a habit of a pro- 

 terotome mastication would result, and the structural 

 results would succeed as above pointed out. 



The excess of the forwards pressure of the inferior 

 teeth against the superior over any backwards pres- 

 sure, has left the posterior internal cusp of the triangle 

 of the inferior molar (metaconid) without contact or 

 consequent functional use. It has, consequently, grad- 

 ually disappeared, having become small in the highest 



