1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 61 



those where no degenerated afferent somato-sensory fibers whatever 

 were found in the present experiments. 



The absolute number of the afferent fibers of the entire somatic 

 sensory region of the hemisphere must be estimated as quite con- 

 siderable, exceeding that of the visual fibers of the striate area and 

 being considerably above that of the auditory projection cortex. (This, 

 it must be admitted, might only appear to be so since the somato- 

 sensory fibers have, on the whole, a stronger caliber than the visual, 

 producing a more intensive degeneration.) The relative number of 

 the intracortical afferent fibers of the precentral half of the somatic 

 sensory region (areas 4 and 6) if compared with the postcentral- 

 parietal half of the same region (areas 1, 2, 3, 5, and 7) is likely to 

 be equal, although the fibers are more condensed in the narrow post- 

 central strip of cortex around the bottom of the central sulcus, that 

 is, in area 3. 



Thus, according to the results obtained in the present experiments, 

 there exists a wide region of the hemisphere which receives fibers of 

 thalamic origin and extends about equally, orally and caudally, from 

 the sulcus centralis as well as over the internal face of the hemisphere 

 where it reaches the sulcus cingiili. Most richly supplied with the 

 thalamo-cortical fibers is a narrow zone corresponding with the entire 

 length of the sulcus centralis from the dorsal margin of the hemi- 

 sphere down to the Sylvian fissure. This zone is entirely buried within 

 the central sulcus, occupying both walls of that sulcus, although partly 

 only. Accordingly, this zone around the bottom of the sulcus centralis 

 must be regarded as the ' ' nuclear or focal zone ' ' of the entire somatic 

 sensory region. Whether this zone belongs partly only, or, perhaps 

 entirely to the postcentral granular region, has not been possible to 

 decide conclusively, by studying the Marchi's series alone, although 

 considering the facts obtained by students of the cortical cytoarchi- 

 tecture and myeloarchitecture in primates and in man (Brodmann, 

 Vogt, Mauss, Naiiagas, Economo-Koskinas) one would be inclined to 

 believe that it corresponds wholly to the granular postcentral region, 

 and is identical with its most anterior portion where the inner granu- 

 lar layer is best developed (area 3 of Brodmann in the monkey and in 

 man, areas PA and PB of Economo) . This also stands in good accord 

 with Vogt's finding the number of very coarse oblique and horizontal 

 fibers in low^er cortical layers to be greatest in the posterior lip of the 

 central sulcus (Vogt's areas 67 and 69; see also Koussy, Mauss, and 

 Flechsig, 1920). A second zone, less well supplied than the first 



