224 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



fibers, but which are connected by short association fibers with 

 one or more of the primary projection zones, 14, 16 to 33, in Figs. 

 100 and 101. Later still the great association areas — 34, 35, 36, 

 Figs. 100 and 101^ — acquire their myefinated fibers. These latter 

 centers, as indicated above, may be considered as association areas 

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

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

 designated these areas from an anatomical point of view as ter- 

 minal or central zones. As the result of his histological work he 

 distinguished thirty-six areas in the cortex in which the myelin- 

 ization of the fibers occurs separately, and in which, therefore, by 

 inference different physiological activities are mediated. These 

 thirty-six areas are subdivided as follows: 

 I. Primary areas. 



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

 eight in number, and provided with projection fibers — ■ 

 sensory and motor. 

 lb. Primary areas without projection fibers {3, 9, 10, 11, 12, 13) 

 and apparently without association fibere. Functions un- 

 certain. 

 II. Association areas. 



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



short association fibers. 

 11^- 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 precechng 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- 



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

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

 1902, 7. 



