1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 51 



to the following: circumstances : In each, of the experiments, the shape 

 and the position of the somato-sensory area, varies, considerably in 

 front of the sulcus centralis, and somewhat less behind that furrow. 

 This is caused by various sizes and locations of the intrahemispheric 

 injuries, as is easily seen from a comparison of the accompanying 

 illustrations. Yet the Experiments I, II, and III have in common the 

 degeneration of caudal or posterior "fans" of the thalamo-cortical 

 radiation which have been interrupted in all three experiments in 

 almost an identical way. Moreover, in Experiments I and III the 

 pulvinar and the posterior segment of the lateral nucleus of the 

 thalamus were practically separated from the hemisphere. This indi- 

 cates that in these experiments all or nearly all caudal ' ' fans ' ' of the 

 thalamo-cortical radiation must have been caused to degenerate. For 

 that reason it is probable that the posterior boundaries of the presently 

 delimited somatic sensory region come near to its actual limits. 



The same is also probable in respect to the extent of the somatic 

 sensory cortex toward the cingular sulcus and toward the Sylvian 

 fissure. In both Experiments I and II, the most dorsal as well as 

 the most ventral bundles of the thalamo-cortical radiation were 

 interrupted. 



The oral or anterior boundary of the "minimal somatic sensory 

 region" found here, on the contrary, probably falls short of its actual 

 limits. That the sulcus centralis can in no way be accepted as the 

 oral limit, which might seem plausible from Experiment III, is evi- 

 dent from a comparison with Experiments I, II, and V-a. In all of 

 these experiments where the thalamic and capsular lesion reaches more 

 frontal ward, the limits of the respective sensory region also came to 

 lie more orallj^ Indeed, if our experience were limited to Experiment 

 III alone, this would probably lead to the erroneous conclusion that 

 the somatic sensory region occupies the postcentral region only, an 

 error actually committed by some previous investigators. It, therefore, 

 must he regarded as fairly safe to accept the anterior boundary of the 

 somatic sensor j^ region found here as a "minimal" one (fig. 6). It is, 

 however, not possible to decide whether the somatic sensory region 

 does not, in fact, reach beyond the oral boundary determined in the 

 present investigations, and, perhaps, embrace parts of the frontal 

 cortex (regio frontalis) anterior to these limits. It is necessary to 

 bear such a possibility in mind in view of the fact that in neither of 

 the present experiments was the most rostral portion of the lateral 

 nucleus of the thalamus destroyed (compare figures in front of both 



