9 6 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



the skull, which clearly has for its object such a con- 

 centration of the parts as will produce the greatest ef- 

 fectiveness of the biting function. This is accom- 



plished by reducing the number of the segments, so as 

 to bring the resistance of the teeth nearer to the power, 

 that is, the masseter and related muscles, and their 

 base of attachment, the brain-case. This 



is seen in 



