210 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



with reference to the time of acquisition of the myelin sheaths. 

 Thus he finds that the fibers to the sense areas acquire their myelin, 

 and therefore according to his view become fully functional before 

 those distributed to the association areas. Moreover, in the em- 

 bryo, at least, these latter areas are not supplied with projection 

 fibers, that is, they are not connected directly with the under- 

 lying parts of the nervous systems. Their connections are with 

 the various sense centers and motor centers of the cortex. 



The association areas may be regarded therefore as the regions 

 in which the different sense impressions are synthesized into complex 

 perceptions or concepts. The foundations of all knowledge are 

 to be found in the sensations aroused through the various sense 

 organs; through these avenues alone can our consciousness come 

 into relation with the external or the internal (somatic) world, 

 and the union of these sense impressions into organized knowledge 

 is, according to Flechsig, the general function of the association 

 areas. This function of the association areas is indicated by the 

 anatomical fact that they are connected wdth the various sense 

 centers by tracts of association fibers, suggesting thus a mechanism 

 by which the sense qualities from these separate sense centers may 

 be combined in consciousness to form a mental image of a complex 

 nature. The sequence of phenomena in the external world is or- 

 derly, and, corresponding to this fact, the reflection of these phenom- 

 ena in the sequence and combinations of sensations is also orderly. 

 In the association areas our memory records of past experiences 

 and their connections are laid down in some, as yet unknown, 

 material change in the network of nerve cells and fibers. Here, 

 as elsewhere in the nervous system, it may be supposed that the 

 efficiency of the nervous machine^- is conditioned partly by the 

 completeness and character of training, but largely also by the 

 inborn character of the machinery itself. The very marked differ- 

 ences among intelligent and cultivated persons for instance, in 

 the matter of musical memory and the power of appreciating and 

 reproducing musical harmonies cannot be attributed to differences 

 in training alone. The gifted person in this respect is one who is 

 born with a certain portion of his brain more highly organized than 

 that of most of his fellow-men. This general conception that the 

 special capacities of talented individuals rest chiefly upon inborn 

 differences in structure or organization of the brain may be re- 

 garded as one outcome of the modern doctrine of localization of 

 functions in this organ. In the beginning of the nineteenth century 

 it seems to have been the general view that those who had a high 

 degree of mental capacity might direct their activity with equal 

 success in any direction according to the training received. A man 

 who could walk fifty miles to the north, it was said, could just as 



