180 University of California Publications in Anatomy [^ol. 2 



ments.^ This radiation above the external geniculate body and as 

 far as the cerebral cortex is strictly unilateral. Accordingly, a bilat- 

 eral cortical representation of each total macula cannot be accepted, 

 as justly pointed out by Harris, Holmes-Lister, Igersheimer, Holmes, 

 Souques-Odier, Brouwer, Uhthoff, Best, Kleist, et al. The sparing of 

 the macular vision in many cases of hemianopsia cannot, therefore, be 

 explained by the hypothesis of a bilateral cortical representation of the 

 total maculae. Its cause must lie in the peculiar position of the 

 macular portion of the visual radiation and the macular cortex. 



On several occasions it has been emphasized that the macular por- 

 tion of the visual radiation cannot b€ a tiny, compact fiber "bundle." 

 The macular fibers in fact represent a considerable portion of the 

 radiation, namely its perpendicular branch. On the other hand, the 

 macular cortex, being situated in the occipital pole, and in the monkey 

 in the occipital operculum, occupies a position separating it from the 

 remaining striate cortex which represents the extramacular retina. 

 The position of the macular cortex in fact rather exposes it to various 

 injuries, and undoubtedly this is the case in some respects. Yet in 

 the human brain it is exactly that portion of the visual cortex which 

 is partly hidden in the deep posterior portion of the fissura calcarina 

 where the latter usually splits into two branches. It also ought to be 

 considered that the extramacular striate cortex occupying both lips 

 of the fissura calcarina, these latter adjoining each other, together with 

 both horizontal branches of the visual radiation, forms a topographical 

 and patho-physiological unit which can be injured independently of 

 the macular cortex (for example case Nordenson, see Henschen, 1919 

 or R. A. Pfeifer, 1930). Another important feature is the separation 

 of the calcarine fissure, a frequent seat of pathological processes (see 

 Best), from the perpendicular macular branch of the external sagittal 

 layer by the posterior horn of the lateral ventrical, by the tapetum, 

 and by the internal sagittal layer. It is obvious that if a pathological 

 process destroys the anterior portion of the calcarine fissure, but 

 leaves the occipital pole undamaged, and does not penetrate through 

 the ventricle or exert a pressure upon the macular radiation beneath, 



8 Neither Wenderowic, Putnam, nor Fleehsig (1927) were able to ascertain the 

 existence of such fibers. It is also import-ant to mention that Brouwer and his 

 collaborators in the recent experiments with monkeys in which the striata area of 

 one side was destroyed, were unable to discover any changes in the cells of the 

 contralateral external geniculate body, which would certainly be found if a part 

 of the visual radiation decussates. (According to a personal communication from 

 Professor Brouwer; see also Brouwer-Heuven-Biemond and Heuven, p. 52.) With 

 this our Experiment V-D and V-e stands in a perfect accord. 



