1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 205 



half of each macula is projected upon another hemisphere. In other 

 words, each macular cortex represents homonymous halves of both 

 maculae. The sparing of "central" or macular vision in cases of 

 hemianopsia is due to the sheltered position both of the macular cortex 

 and of the macular portion of the visual radiation and to the peculiar 

 arrangement of the "peripheral" and macular bundles in the visual 

 radiation, and also probably to the peculiar blood supply of the cal- 

 carine fissure. 



4. ORGANIZATION AND FUNCTION OF THE VISUAL SYSTEM 

 IN GENERAL 



The entire afferent visual system in primates from its beginning in 

 the retina to its cortical termination is a definite anatomical and 

 functional entity organized "spatially," that is, according to the 

 "principle of localization." In the peripheral portion of the visual 

 system from the retina to the external geniculate body (and also in 

 the superior colliculus of the midbrain) this was shown in an experi- 

 mental way by Brouwer and Zeeman, and by Overbosch. In the cen- 

 tral portion of the visual system, from the external geniculate body 

 to the cortex, the same principle has been demonstrated by experi- 

 mental, clinical, and pathological studies of Wilbrand, Henschen, 

 Minkowski, A. Meyer, Uhthoff, Lenz, Saenger, Wilbrand-Saenger, 

 Axenfeld, Brouwer, Marie-Chatelin, Holmes-Lister, Holmes, Souques- 

 Odier, Best, Putnam, Heuven, and many other investigators, and is 

 confirmed by the present experiments. It seems, therefore, that there 

 is no longer reason for continued adherence to the old view of a three- 

 fold subcortical origin of the visual radiation and no ground whatever 

 to support the hypothesis of a multiple or "diffuse" projection of the 

 retina and especially of the macula upon a wide region of the cerebral 

 cortex. The relation of the afferent visual path to the cortex is quite 

 definite, and there is but one cortical area which receives direct visual 

 impulses from the peripheral receptor organ. Besides this "gross" 

 relation of the afferent visual path to the cerebral cortex which is 

 decidedly localistic, the same strict localistic principle has been found 

 here to hold for the finer, internal organization of the visual radiation 

 and for its minute relation to the visual cortex. This seems to settle 

 the long dispute about whether there is a fix:ed, geometric projection 

 of the retina upon the cortex or whether the retina is projected in an 

 unstable or a "diffuse" manner: the decision favors the first view. 

 In general this means that to each minute morpho-physiological unit 



