THE NERVOUS SYSTEM 



correspondence in time between the development of the tracts and the mani- 

 festation of functions known to involve the tracts in question. The great 

 somesthetic area and its tracts are first to develop ; then tracts to the occipital or 

 visual center, to the auditory and other sensory centers, and, finally, to these 

 great areas whose functions remain obscure. 



Basing his deductions on the facts of development, on the isolated cases of 

 lesion and disease, and on the careful comparative studies of the brains of cer- 

 tain men of unusual intellectual powers, whose personal characteristics and 



FIG. 417. The Association Fibers in the Centrum Ovale. A, Between adjacent convolutions; 

 B, between frontal and occipital lobes; C, between frontal and temporal lobes, the cingulum; D, 

 between temporal and frontal lobes lesion of this tract causes paraphasia; E, between occipital 

 and temporal lobes lesion of this tract causes word -blindness; C.N, caudate nucleus; O.T, 

 ptic thalamus. 



intellectual genius are known, Flechsig has advanced the hypothesis that the 

 areas of the cortex not concerned directly with motor or sensory functions are 

 association areas. 



The Association Centers of Flechsig. The great association centers 

 are the frontal, parietal, and temporal, figure 415. These regions of the cor- 

 tex are apparently not directly connected with tracts of the brain stem and 

 cord, but they are richly connected with the areas that do have connection with 

 the cord. Short association fibers connect neighboring convolutions within 

 the centers, fibers which are chiefly the axones of the polymorphous cells of the 

 fourth layer of the cortex. Long association fibers run from one center to 

 another, such as the cingulum, superior and inferior longitudinal fasciculi, 

 etc. The longer connectives run from association to association centers, 

 and from association to sensory and motor centers. Flechsig believes that 

 the sensory centers are not connected directly with each other, but only in- 

 directly through the association areas. 



Cases of injury and of disease of the human brain in the association areas 

 are not numerous, but such as there are tend to confirm Flechsig's hypothesis 

 that the function of these areas is that of the higher psychic activity. 



