1932] Poliak: Afferent FiJ)er Systems, Primate Cerebral Cortex 179 



1929, et al.). Each macula, according' to this hypothesis, would be 

 projected upon both hemispheres in such a way as to bring each small 

 segment of each total macula or even each of the macular cones in 

 connection with the visual cortex of both hemispheres. Thus, if one 

 of the visual cortical centres or its aiferent fibers were destroyed, 

 nevertheless, both total maculae would still remain in connection with 

 the hemisphere remaining undamaged. This hypothesis would explain 

 why macular vision is so often preserv^ed.' But, briefly, this would 

 not explain why in other cases of hemianopsia there is no sparing of 

 macular vision, nor, why a unilateral partial destruction of the visual 

 cortex or of its radiation produces absolute, permanent, and very 

 sharply delimited central scotomata (compare, for example Holmes, 

 1919; Wilbrand, 1926). That the hypothetical decussating macular 

 fibers from the ipsilateral homonymous hemimaculae (with respect to 

 the seat of the lesion in the occipital lobe) cannot use the optic chiasm 

 to reach the opposite hemisphere is proved by the fact that macular 

 vision is not spared in cases where the optic tract is completely inter- 

 rupted. In such cases macular vision shows the affection of a hemian- 

 optic character most frequently with the vertical line passing exactly 

 through the points of fixation. A partial crossing of the macular por- 

 tion of the visual radiation through the corpus callosum was, there- 

 fore, supposed. Some investigators even claimed to have seen the 

 decussating bundle of the macular fibers, a "fasciculus corporis cal- 

 losi cruciatus," converging toward the corpus callosum (Niessl von 

 Mayendorf, R. A. Pfeifer) . Thus, if the lesion interrupting the visual 

 radiation were situated far enough from the point of decussation or 

 if the visual cortex on one side were injured, the impulses from both 

 total maculae would, nevertheless, reach the undamaged hemisphere 

 by way of the corpus callosum. But this hypothesis is also weak since 

 it does not give a satisfactory explanation for the "central" scotomata 

 of cortical origin. 



As has been said in the foregoing parag^raphs, no decussating 

 fibers of the visual radiation were seen in any ^f the present experi- 



'^ The supposition, that in all cases of hemianopsia where there is no sparing 

 of the macular vision macular cortical regions in both occipital lobes have been 

 damaged (Lenz), is too artificial to be probable (although in rare eases such a 

 bilateral damage may occur). Also that would not explain why in such hemianop- 

 sias the macular vision is preserved on the functioning sides in spite of the bilat- 

 eral damage to the macular cortex. Finally, the explanation of the preserv-ed 

 macular vision, usually found in cases of hemianopsia, in the sense of the preserved 

 "remnant" of the visual fields ("Gesichtsfeldrest") is no explanation at all. 



