1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 169 



the spiral course neither the upper nor the lower horizontal branch 

 can be seen in its entire length in a single section or even in a few 

 closely neighboring sections.^ 



Accordingly, we must look on the dorsal horizontal branch of the 

 visual radiation as transmitting impulses from the superior extra- 

 macular quadrants of the homonymous halves of both retinae to the 

 upper lip of the fissura calcarine (figs. 22, 23). 



The next portion of the visual radiation, forming the intermediate 

 perpendicular branch of the external sagittal layer, has been traced 

 in the present experiments up to the pole of the occipital lobe and to 

 the occipital operculum (Experiment I and especially V-a, and partly 

 Experiment IV). Although this portion of the radiation has not been 

 interrupted at its origin, it is fairly safe to regard it as not originating 

 from the internal but from the next laterally situated large interme- 

 diate segment of the external geniculate body, which segment, accord- 

 ing to K<)nne (1914) and Brouwer-Zeeman (1926), receives macular 

 fibers from the retinae. It is this and the lateral segment of the exter- 

 nal geniculate body as well as their bundles of the radiation which 

 remained undamaged in Experiments II and III where the perpen- 

 dicular and the lower horizontal branch of the external sagittal layer 

 remained normal. The question which could be asked here is whether 

 the perpendicular branch of the external sagittal layer does not 

 also originate from the lateral segment of the external geniculate 

 body. Knowing, however, on the one hand, from R<)nne's and especially 

 from Brouwer's studies, the orderly sequence in the arrangement of 

 the segments of the external geniculate body, with the macular segment 

 being placed between both "peripheral" segments, and on the other 

 hand, the parallel arrangement of the bundles of the ^dsual radiation, 

 the only possible origin of the perpendicular branch of the visual 

 radiation in the existing order or sequence of the segments is the 

 intermediate macular segment of the external geniculate body. This 

 is also supported by Experiment V-d. Therefore: (1) from the fact 

 that the intermediate segment of the external geniculate body is the 

 macular projectional segment (Ronne, Brouwer-Zeeman), (2) from 

 observations that in pathological cases where the macular' or the 

 "central" vision is disturbed the pole of the occipital lobe was 

 damaged (Henschen, Holmes et al.), (3) from the fact that the inter- 



3 That in the human brain the fibers of the upper horizontal branch reach also 

 directly the upper lip of the calcarine fissure is demonstrated by the case of 

 Balado-AdrogTie-Franke, and by my anatomical-pathological cases not yet published. 



