1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 167 



perhaps multilobular cortical projection of the retina seems apparently 

 not to have lost all its adherents even in modem times. Because of 

 the lack of convincing anatomical arguments old decentralistic objec- 

 tions are every now and then brought forward against attempts to 

 explain rationally the visual mechanisms and their function. 



2. INTERNAL ORGANIZATION OF THE VISUAL RADIATION. 



PROJECTION OF THE RETINA UPON THE 



VISUAL RADIATION 



After having shown in a definite way, as it appears, that there 

 exists only one, single subcortical visual nucleus, the external genicu- 

 late body, which gives rise to one, single, definite central visual path 

 terminating in one, single, sharply delimited cortical region, the 

 striate area; further details must be discussed, that is, the origin, the 

 course, and the termination of particular bundles or segments of the 

 visual radiation, and their particular functional significance. In this 

 way we may expect to determine the exact projection of the retina 

 upon the visual projection cortex. 



Here we must again turn to the investigations of Ronne and par- 

 ticularly to the experiments of Brouwer and his co-workers since they 

 served as a starting point and as an indispensable preliminary founda- 

 tion for the present investigations. The results of these studies can be 

 summarized as follows : both superior quadrants of the extramacular 

 homonymous retinae are projected upon the internal segment of the 

 external geniculate body, the inferior quadrants upon the external 

 segment, the macula upon the intermediate segment of that body. 



In the present experiments it was found that bundles which form 

 the dorsal portion of the visual radiation originate from the internal 

 segment of the external geniculate body (Experiments II and III; 

 this is also clear from Experiment V-b). By forming the dorsal 

 horizontal branch of the external sagittal layer, they enter the upper 

 lip of the fissura calcarina, approximately as far as the bottom of that 

 fissure (figs. 55-57, 69-74). This portion of the \asual radiation, as 

 said before, neighboring at its origin the dorso-caudal somato-sensory 

 (thalamo-cortical) fibers (figs. 52-55, 67-69, 71) which ascend toward 

 the upper parietal region, also ascends at first in a fairly perpendicular 

 though somewhat caudally inclined course before turning occipital- 

 ward (figs. 52-54). At the same time these dorsal bundles gradually 

 describe a spiral turn around and above the posterior horn of the 



