KINE TOGENESIS. 



347 



increased directly as the increase in the length of the 

 . incisors, especially those of the lower jaw. 



The first effect of this posterior pressure will have 

 been to slide the condyle of the mandible posteriorly 



over thq postglenoid surface, if any were present, as is 

 probable, in the bunotherian ancestor of the rodent. 

 Continued repetition of the movement would probably 

 push the process backwards so as to render it ineffec- 

 tive as a line of resistance, and ultimately to flatten it 



