54 University of California PuUications in Anatomy l^^^^- 2 



or those originating from the lenticular nucleus. Nevertheless, it is 

 certain that at least the greater majority of the fibers supplying this 

 new receptive region, and especially the large calibered ones tending 

 toward the posterior extremity of the Sylvian fissure (fibers marked 

 with X in figs. 52-54) , belong to an aiferent fiber system originating 

 either in the internal geniculate body or somewhere in the ventro- 

 lateral nucleus of the thalamus or even in the hypothalamus. (In 

 Experiment I where the ventro-lateral nucleus was damaged to a small 

 extent only, these fibers remained mostly normal, while in Experiment 

 III, a few of them degenerated.) That cortical area, accordingly, also, 

 belongs to the receptive regions of the hemisphere. 



The above mentioned posterior Sylvian receptive region is almost 

 entirely hidden within the Sylvian sulcus, appearing on the free face 

 of the hemisphere only in the most caudal portion of the supramarginal 

 convolution (x in fig. 54). This region is in reality continuous along 

 the posterior part of the Sylvian fossa and along the entire posterior 

 extremity of the Sylvian fissure. It occupies the lower portion of 

 Brodmann's area 7 and the upper portion of area 22, suggesting 

 another division of that part of the parietal and temporal regions than 

 that made by cytoarchitectural studies. The "nucleus" of this poste- 

 rior Sylvian receptive region might correspond very well with Brod- 

 mann's dorso-caudal portion of the insular region hidden in the 

 Sylvian fossa which possesses a well formed inner granular layer (see 

 Brodmann, 1909, p. 156), and is otherwise distinguished in the 

 monkey's brain by an intra-cortical fiber layer not unlike the inner 

 stripe of Baillarger. The region in question extends, however, farther 

 caudally and does not possess sharp limits comparable to those of the 

 striate area. Only by new detailed investigation can it be decided 

 whether this posterior Sylvian region in the monkey is an homologue 

 of the parietal areas covering the angular convolution in the human 

 brain (Brodmann's area 40, and perhaps also, his areas 39 and 22; 

 area PF and perhaps PG of Economo-Koskinas), which have a distinct 

 function ; or whether, as appears probable, this region is nothing other 

 than the caudal or posterior extension of a much wider auditory area 

 than is usually accepted, corresponding in the human brain to the 

 entire granular cortex which occupies, according to the delimitation 

 of Economo-Koskinas, the posterior Sylvian fossa, the greater part of 

 the superior temporal convolution, the angular and the supramarginal 

 convolution. (See also Chapter X and XI, 2.) 



