ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 703 



the ascending frontal convolution. The corresponding motor tract 

 develops from the area of large pyramidal cells in the ascending 

 frontal convolution. Thus the sensory and motor areas in the brain 

 are not mixed, except in the fissure of Rolando. 



The experiments of Sherrington and Griinbaum on the chim- 

 panzee are in accord with the results of Flechsig. They found the 

 motor centers to be in the ascending frontal convolution, separate 

 from the sensory centers of touch and muscle-sense in the ascend- 

 ing parietal convolution. Around each primary sense area develops 

 a border zone of association centers. 



Only about one-third of the brain is composed of sensory and 

 motor areas; the question arises, "What is the function of the other 

 two-thirds ?" The fibers going to the latent, inexcitable area of the 

 brain take on myelin much later than those of the excitable area. 

 The fibers in this latent area do not run downward like the projec- 

 , tion fibers, but run in a more or less longitudinal direction, and are 

 known as internuncial or association fibers; they are of both a cen- 

 trifugal and centripetal nature. These internuncial fibers connect 

 the latent cortex with the excitable cortex. According to Flechsig 

 there are three association centers: (1) the frontal, (2) the parieto- 

 occipito-temporal, and (3) the insular. These centers are centers to 

 receive impressions, and are the seat of memory. The internuncial 

 fibers are : (1) the superior longitudinal bundle uniting the Eolandic 

 ind parieto-occipital region; (2) the perpendicular bundle passing 

 'tween the parietal lobule and the temporo-occipital region; (3) 

 the anterior association bundle connecting the frontal and temporal 

 lobes and traversing the bottom of the sylvian fissure; and (4) the 

 inferior association bundle uniting the temporal and occipital lobes, 

 'he frontal association center is in front of the ascending frontal 

 convolution; the insular, or middle, association center is the cortex 

 of the island of Reil; whilst the parieto-occipito-temporal associa- 

 ion center is situated back of the ascending parietal convolution. 



The anterior association center, or frontal, is made up of the 

 iterior half of the first and a great part of the second frontal con- 

 volution. The middle association center or insular is covered by the 

 isula, whilst the posterior or parieto-occipito-temporal is made up 

 )f the prsecuneus, the parietal convolution, the second and third 

 temporal, and the anterior part of all three occipitals. Disease of 

 the anterior association center, as in idiocy and dementia, changes 

 the character; a man of good and orderly habits becomes irritable 

 ind disorderly, and loses his sense of morality; there is a loss of 



