Chapter XVIII 



GENERAL CONSIDERATIONS OP THE RELATION OF THE 

 AFFERENT PATHS TO THE CEREBRAL CORTEX 



It may be of interest to consider the general results of the present 

 investigation of the three main afferent paths of the cerebral cortex 

 and their terminal areas as recorded in the foregoing pages. Clearly 

 the gross relation of all three paths investigated, somatic sensory, 

 auditor^', and visual, to the forebrain cortex is definite and constant. 

 Eaeh path is a discrete anatomical and functional entity, distinct, 

 though not entirely separated (anatomically), from other fiber sys- 

 tems ; each has its own relationship to a circumscribed cortical locality 

 and its own specific function. Of the three cortical areas wherein 

 these afferent paths terminate (the projection areas or "gateways," 

 the "primary sensory spheres" of Flechsig) and through which the 

 peripheral impulses reach the cortex, the area striata (visual) is 

 sharply delimited structurally, the somatic sensory and auditory areas 

 somewhat less so. These three projection areas appear separated from 

 one another partly by narrow, partly by fairly broad, intercalated 

 cortical zones seemingly void of an afferent fiber supply (fig. 24). 

 Between the somatic sensory and the acoustic projection areas there 

 is a more intimate relationship, both these fields being close together. 

 This fact is, of course, in accord with the view that the auditory (that 

 is, cochlear) system is phylogenetically a derivative of the original 

 common cutaneous system. Between the somatic sensory region and 

 the striate area the intermediate cortex, corresponding in the brain of 

 the monkey with Brodmann's fields, 18 and 19, and perhaps wath a 

 part of field 7, is a relatively narrow zone which appears to receive 

 no afferent fibers; this zone is much more extensive between the 

 auditory and the visual projection areas, comprising areas 18, 19, 20, 

 21 and a large portion of area 22 (compare fig. 24 with fig. 7). It is 

 significant that even in the lower primates considerable portions of 

 the cerebral cortex seem to lack afferent fibers. In this respect the 

 present investigation does not support the belief, shared by many 

 modem neurologists, that all regions of the cerebral cortex (regard- 

 less of whether or not they are projectional in the ordinary sense, 



