1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 11 



strata of the cortex above the upper stripe of Baillar^er a few tine 

 exogenous afferent fibers were seen also but only in the cortex around 

 the bottom of the sulcus centralis, these being absent in the convexities 

 of both central convolutions. From the above findings it is evident 

 that the coarse, oblique, and horizontal fibers of both the precentral 

 and the postcentral convolutions and of the sulcus centralis, described 

 by the students of the cortical myeloarchitecture in the lower layers 

 (compare Vog-t, 1919), are exogenous afferent thalamo-cortical fibers 

 mostly quite distinct from the actual "radiated fibers" and identical 

 with the exogenous somato-sensory fibers of Ramon y Cajal (who found 

 them, however, in the precentral cortex only, see Ramon y Cajal, 1909- 

 11, vol. II, pp. 576, 584, 640-643, 646, 829) and of Flechsig (1920, pp. 

 16, 17). These exogeneous thalamic fibers form a part of the so-called 

 "basal meshwork" ("Grundfaserfilz" of Vogt) discernible between 

 the "radiated fibers" in the lower cortical layers. These peculiarities 

 of the afferent somato-sensory fibers are comparable to those of the 

 intra-cortical afferent visual fibers of the striate area. Further, it 

 should be mentioned that the supply of the afferent fibers to the somatic 

 sensory cortex is continuous, at least in the cortex around the sulcus 

 centralis, at which spot dense bundles of degenerated fibers enter the 

 cortex. Here, at any rate, there are no small cortical islets, supplied 

 with afferent fibers and separated from each other by narrow zones 

 devoid of such a supply; this negative feature characterizes likewise 

 the striate area. 



6. FUNCTION OF THE SOMATO-SENSORY PROJECTION CORTEX 



The present experiments demonstrate that the somato-sensory cor- 

 tex extends to both sides of the central sulcus occupying the precentral 

 region and a portion of the parietal region, besides the postcentral 

 region of the students of the cortical cytoarchitecture. Since each 

 of the regions mentioned receives afferent impulses by way of its own 

 fibers and since this is probable also with respect to each of the indi- 

 vidual cytoarchitectural areas, it must be assumed that the extensive 

 somato-sensory region is a composite cortical organ consisting of a 

 considerable number of suborgans, each of them with its own specific 

 receptive function (besides various efferent and other functions). The 

 special receptive function of each precentral-postcentral and parietal 

 area must be determined by further investigations. 



