SENSE AREAS AND ASSOCIATION AREAS. 215 



be considered as association areas with more complex connections, 

 and they serve to mediate therefore the higher psychical activities. 

 Flechsig, in his recent report, designates these areas from an anatom- 

 ical point as terminal or central zones. As the result of his his- 

 tological work, as far as it has progressed, he distinguishes 

 thirty-six areas in the cortex in which the myelinization of the 

 fibers occurs separately, and in which, therefore, by inference, 

 different physiological activities are mediated. These 36 areas 

 are subdivided as follows: * 



I. Primary areas. 



la. Primary projection areas (1, 2, 4, 5, 6, 7, 8 (15} t seven or 

 eight in number, and provided with projection fibers 

 sensory and motor. 



16. Primary areas without projection fibers (3, 9, 10, 11, 12, 13) 

 and apparently without association fibers. Functions un- 

 certain. 

 II. Association areas. 



IP* Intermediate or border areas, 14, 16-33, provided with 



short association fibers. 



II & * Terminal or central areas, 34, 35, 36, provided with long 

 association fibers. 



Histological Differentiation in Cortical Structure. While 

 the general structure of the cortex is everywhere similar, detailed 

 examination has shown differences in the shape of the cells, the 

 thickness and number of the strata, the calibre of the fibers, etc., 

 which are said to be constant for any given region. By this means 

 it is possible to divide the cerebral cortex into a number of areas 

 whose structures are sufficiently distinct to be recognized with some 

 certainty. Reasoning from analogy we should infer that a differen- 

 tiation in structure implies a subdivision of physiological activity, 

 and to this extent this recent hist o logical work supports the view 

 of a localized distribution of function in the cortex. Campbell,* 

 in a very thorough investigation of this kind, has succeeded in 

 separating some fifteen or sixteen different areas, and the results 

 obtained by him support in a general way the localizations described 

 in the preceding pages. Thus the cortex in the postcentral con- 

 volution (body-sense area) has a structure distinctly different 

 from that of the precentral convolution (motor area), the latter 

 being characterized among other things by the presence of giant 

 pyramidal cells (Betz cells). In the occipital lobes the region 

 round the calcarine fissure (visuosensory) has a structure different 

 from that of the contiguous cortex (visuopsychic) , and a similar 

 difference is claimed for the auditory region. Campbell calls 

 attention to the fact that the extreme end of the frontal lobe 

 (prefrontal region) has a comparatively undeveloped structure. 



* Campbell, " Histological Studies on Localisation of Cerebral Functions," 

 Cambridge, 1905. 



