1932] Poli-ak: Afferent Fiber Systems, Primate Cerehral Cortex 15 



to the cerebral cortex, as in its internal organization, "diffusely" 

 arrang'ed, and if there are several distinct, independent portions of 

 the visual radiation, and the cortical representation of the retina 

 together with that of the macula is multiple, as claimed by the decen- 

 tralists, one would expect this to be demonstrable by experimental 

 anatomical methods. In this important question only an opinion based 

 on facts controllable and measurable by exact methods can be accepted. 

 The fact that opinions on the visual apparatus still fluctuate and are 

 contradictory, unquestionably a consequence of insufficient anatomical 

 knowledge, is exemplified by the explanation of the preservation of 

 the ' * central ' ' or macular vision in cases of hemianopsia given recently 

 by Wilbrand (192'5, 1926). Although there should be, according to 

 Wilbrand, a fixed or stable projection of the retina upon the cerebral 

 cortex, this in some sense should not be the case in the macular portion 

 of the visual radiation and of the visual cortex (exactly in that portion 

 where the most rigid observance of the "principle of localization" 

 could justly be expected, if that principle exists at all in the visual 

 system; here I call attention to the very minute projection of the 

 individual retinal segments upon the external geniculate body, belong- 

 ing in all probability to the macula, found in the cat by Overbosch, 

 1927). According to Wilbrand, each macula should be projected in 

 its totality upon the cortex of both hemispheres, wherein each of the 

 macular sensitive elements, each cone, would perhaps be represented 

 in both hemispheres. Such a bilateral or double cortical representa- 

 tion of each total macula would explain the preservation of ' ' central ' ' 

 or macular vision in cases of hemianopsia where such a sparing is 

 observed, but would undoubtedly be an obstacle in explaining macular 

 (central, paracentral) scotomata and other cases of hemianopsia where 

 there is no sparing of the "central" vision. A bilateral cortical repre- 

 sentation of each total macula would be somehow reconcilable with 

 the strict localistic viewpoint, although, as will be shown later, for 

 anatomical reasons no bilateral projection of each total macula in the 

 above sense is acceptable. Yet in his attempts to explain the sparing 

 of macular vision Wilbrand constructed an additional hypothesis. He 

 supposes a substitution of the function of the destroyed segments of 

 the macular cortex or of the interrupted macular fibers by other por- 

 tions of the macular cortex remaining normal, since, according to his 

 notion, each macular cortex has to be regarded in some sense as a 

 functional unit, working as a whole. But, as can easily be understood, 

 such a conception of the organization and function of the macular 



