9-6 E\OLUTIO\AL MODIFICATIONS 



pons N'arolii is a more protuberant structure. The cerebral peduncles attain 

 greater definition and size, while structural differentiation in the base of the 

 brain stem reaches its full development in man. The increasing size of the 

 pyramid, of the pons and of the cerebral peduncle seems to indicate the final 

 development of new motor capabilities made possible by manual specializa- 

 tion. Man and all his works are epitomized by these structures of the brain. 

 ^^ ithout them there would be neither reason nor opp>ortunity to discuss the 

 achievements of mankind. Too great importance, therefore, cannot be laid 

 upon this specialization, which has progressed through certain preparatory- 

 stages of quadrumanal differentiation, and finally attained its definitive 

 manual development. 



But lest over-much emphasis be attributed to the hand de ipso, it 

 must be borne in mind that no such development could have occurred had 

 not an almost equally important specialization affected the lower extremity. 

 The structural standard of the human upper extremity insists upon certain 

 proportions in the length of the arm, forearm and hand in relation to the 

 rest of the body. It also prescribes definite intrabrachial relations of the 

 arm to the forearm, the forearm to the hand, and the hand to the fingers. 

 This human standard seems essential to the most perfectly differentiated 

 upper extremity. "\'et it is a fact that many of the low er apes come nearer to 

 this standard than do the anthropoids standing nearest to man. This is 

 notably the case in the orang, in the chimpanzee and in the gorilla. In them 

 the upper extremity is out of all proportion with the human standard. In 

 the three great anthropoids, the arm, forearm and even the hand are too 

 long for the most fiexible adaptability. The limitations of adaptive range of 

 motion imposed by this excessive length ha\e been noted in recounting the 

 behavioral activites of the higher anthropoids. The fact that the fingers 

 almost touch the ground when the animals stand in the erect position shows 

 in what respect these members are limited in the accomplishment of skilled 



