1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 197 



In the study of the org^anization of the visual system in the pres- 

 ent work as well as in that of most other investig'ators, only the 

 medullated fibers have been considered. Finer structural relations as 

 they can be revealed by silver impreg-nation of neuronal branches and 

 offshoots were necessarily disregarded. The medullary fibers of the 

 visual radiation were seen assembled into parallel bundles and ter- 

 minating in small, circumscribed segments of the visual cortex. The 

 foregoing conclusions were therefore inevitable. Yet the study of the 

 visual structures by means of silver impregnation may explain the 

 finest relations of visual neurones to one another, and to the other 

 cell elements of the cerebral cortex. It may be that such investiga- 

 tions will reveal only a relative "isolation" of conductor units of the 

 visual system and a partial overlapping of the terminal branches of 

 individual fibers in the external geniculate body and in the visual 

 cortex, in a mode similar to that found in the auditory system 

 (see my paper, 1927). The degree of such possible overlapping of 

 teledendra might be different in different portions of the external 

 geniculate body, in the macular, and in the extra-macular cortex. 

 Even if this turns out to be the case, it would not mean a ' ' diffuse ' ' 

 arrangement of the visual system, but special ' ' neighboring relations ' ' 

 of contiguous visual neurons with preservation of the "principle of 

 localization. ' ' 



6. EEMARKS ON THE CO^rPAEATIVE ANATOMY OF THE VISUAL 

 PROJECTION CORTEX 



Minkowski (1911, 1913, 1914), in his experiments with dogs and 

 cats established the projection of the upper retinal quadrants upon 

 the anterior half of the striate area and that of the lower retinal 

 quadrants upon the posterior and at the same time lower half of the 

 area striata. The lower quadrants of the fields of vision are, accord- 

 ingly, represented in lower mammals in the oral, the upper quadrants 

 in the caudal half of the striate ai'ea. In previous experiments with 

 cats (1927), I was able to determine the supply of the ventro-caudal 

 half of the striate area by the ventral half of the visual radiation. 



would be synthesis. That synthesizing mechanism, the structural basis of the 

 unifying "Gestalt "-processes, must, however, not be imagined as non-neuronal, 

 quasi-immaterial, since the existence of special neurons arranged ' ' diffusely ' ' 

 within the striate (and also peri-parastriate) cortex is not only possible but even 

 probable, as the studies of Ramon y Oajal show. Such special structures perfectly 

 satisfy ail postulates of the Gestalt-psychology without recurring to the immaterial 

 "continuum." Further, a search for the mentioned special structures of the visual 

 and other cortical regions does not appear premature, but rather needed now to 

 give a firm morphological foundation to the new psychological demands. (Com- 

 pare Ramon y Cajal 1911 and 1923.) 



