358 NERVOUS SYSTEM OF VERTEBRATES. 



surface in the apes to a position almost wholly on the mesial surface 

 of the hemisphere in man, and also in the position of the auditory 

 area in the temporal lobe. Finally the anterior association field 

 has developed from the front border of the somaesthetic area and 

 is relatively small in the apes and probably absent in the lower 

 mammals. The development of this field seems to be directly 

 proportional to the grade of self- consciousness and in the several 

 races of men, to the grade of civilization. So, the full appreciation 

 of the self has probably been the last and highest factor in the 

 development of individual and social conduct. 



The development of the several areas demands an increase in 

 cortical surface. This is secured by surface foldings which form 

 the gyri and sulci. Such foldings took place (i) within the sensory 

 areas themselves, serving to increase their surface; (2) at the border 

 of the sensory areas and so forming the boundaries between sens- 

 ory and association areas; and (3) within the association fields 

 themselves. The deeper and more constant furrows belong to 

 the first and second groups, since the furrows in the association 

 fields appear much later than the others. After the fundamental 

 furrows were formed they were mechanically prolonged, branched 

 and bent until it is difficult to compare the furrow patterns of the 

 brains of different mammals. 



One other consideration concerning the association centers 

 should be touched upon in closing this book, namely their sig- 

 nificance for education and morals. The object of human knowl- 

 edge is the world in its multitudinous forms and man's mani- 

 fold relationships in it. The knowledge already acquired when 

 taken in comparison with the simplicity of the child's brain and 

 knowledge has become enormously complex. It is so complex 

 that when it is systematized and divided and subdivided many 

 times, the average man can grasp only one small subdivision. 

 How many of these shall the child entering school today learn to 

 understand, with how many can he become reasonably familiar, 

 in how many will he be able to add to human knowledge? This 

 will depend chiefly upon the number of related facts which come 

 to his notice during the plastic period of his brain. If he is early 

 brought into contact with the world of matter and of life under 



