1932] Poliak: Afferent Fiber Systems, Primate Cerelral Cortex 183 



valid. If every maeular cone were in connection with each striate 

 area, according: to the principle of identical cortical representation of 

 homonymous points, this would, it seems, annihilate any stereoscopic 

 effect of binocular vision. Also, the individual differences in the size 

 and shape of the macular portion of the visual fields preserved in 

 cases of hemianopsia can easily be explained without resorting' to an 

 additional hypothesis of a varying degree of double macular represen- 

 tation in various persons, since it is natural that the destroyed portion 

 of the perimacular cortex or of the perimacular portion of the radia- 

 tion will vary according to the individual case." 



Our conclusion is : no evidence and no necessity exist for accepting 

 a bilateral cortical representation of each total macula in the sense of 

 Wilbrand, Lenz, et al}~ The preservation of macular vision must be 

 explained by the (1) separate course and protected position of the 

 macular portion of the visual radiation and a well protected loca- 

 tion of the human macular cortex, and (2) by the close position of 

 those portions of the striate area which represent extramacular 

 portions of the visual fields, in both lips and in the bottom of the 

 fissura calcarina, which arrangement renders separate injury to these 

 latter regions possible (besides the multiple blood supply of the pole 

 of the occipital lobe). 



4. FUNCTION AND DISTURBANCES OF THE VISUAL EADIATION AND 

 OF THE VISUAL PROJECTION CORTEX 



Since projection of various quadrants of the hemiretinae upon 

 definite portions of the visual cortex and the arrangement of definite 

 bundles of the visual radiation are as described at the beginning of 

 this chapter, it is easy to understand that various symptoms follow 

 variously situated cortical or subcortical injuries to the visual system. 



11 Further, not only does the hypothesis of a bilateral representation of each 

 total macula inadequately explain the escape of macular vision in cases of ordi- 

 nary vertical homonymous hemianopsia, but it explains the macular escape when 

 the superior or the inferior quadrants are abolished bilaterally less well. In fact, 

 to apply the principle of a bilateral macular representation as an explanation of 

 superior or inferior incomplet-e hemianopsia it would be necessary to construe an 

 additional hypothesis: tliat of a projection of each total macula upon the upper 

 and as well upon the lower half of each macular cortex. 



isFoerster's (1929) ease in which after unilateral removal of the occipital 

 lobe and section of the splenium of the coi-pus callosum, a complete hemianopsia 

 without sparing of macular vision followed, can hardly be ascribed to the inter- 

 ruption of hypothetical decussating macular fibers. A contrary conclusion would 

 be unavoidable had the corpus callosum not been damaged and had the macular 

 vision remained unimpaired (providing that one occipital lobe had been completely 

 removed). 



