SENSE AREAS AND ASSOCIATION AREAS. 229 



with more complex connections, and they serve to mediate, pos- 

 sibly, the higher psychical activities. Flechsig, in his report, 

 designates these areas from an anatomical point of view as terminal 

 or central zones. As the result of his histological 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 thirty-six areas are subdivided as follows: 

 L Primary areas. 



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

 eight in number, and provided with projection fibers 

 sensory and motor. 



I&. Primary areas without projection fibers (3, 9, 10, 11, IS, 13) 

 and apparently without association fibers. Functions un- 

 certain. 

 II. Association areas. 



II^ Intermediate or border areas, 14, 16-33, provided with 



short association fibers. 



II 6 * 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 or laminae, 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 differentiation in structure implies a subdivision of physio- 

 logical activity, and to this extent this recent histological 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 local- 

 izations described in the preceding pages. Thus the cortex in the 

 postcentral convolution (body-sense area) has a structure dis- 

 tinctly 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), and a marked dimi- 

 nution in the width of the granular layer of cells. In the occipital 

 lobes the region round the calcarine fissure has a structure differ- 

 ent from that of the contiguous cortex, and a similar difference is 

 claimed for the auditory region. Campbell believes that the ex- 

 treme end of the frontal lobe (prefrontal region) has a compara- 



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

 Cambridge, 1905; See also Brodmann, "Journal f. Psychol. u. NeuroL," 

 1902, 7. 



