1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 171 



Accordingly, it is the ventral horizontal branch of the visual radia- 

 tion which transmits impulses from the inferior extramacular quad- 

 rants of the homonymous halves of both retinae upon the lower lip of 

 the fissura cal carina (figs. 22, 23). 



Furthermore, it has been noted in the present experiments that 

 the most dorsal and at the same time the most anterior bundles of the 

 visual radiation, after they complete the spiral turn inward, become 

 the most medial and supply a narrow strip of the striate cortex 

 stretching along the inner boundary of that cortex in the upper lip 

 of the fissura calcarina. If the same arrangement in the lower lip is 

 accepted, as it must be, it becomes evident that the most dorsal and 

 the most ventral bundles of the entire visual radiation suppl,y a nar- 

 row striate zone of the fissura. calcarina which actually forms a crescent 

 with one of its horns in the upper lip and the other in the lower lip. 

 This crescent turns both its horns occipitalward and its middle convex 

 portion oralward toward the splenium of the corpus callosum, descend- 

 ing here into the bottom of the fissura calcarina, where both horns of 

 the crescent are linked together (fig. 23). 



These most ventral and most dorsal bundles of the visual radiation 

 must, accordingly, transmit impulses from the most "peripheral" 

 portion of the retina to a narrow "boundary zone" of the striate 

 cortex, lining both the lips and the anterior portion of the bottom of 

 the fissura calcarina. 



The question of the finer projection of the individual macular 

 quadrants upon small portions of the intermediate segment of the 

 external geniculate body has not as yet been completely solved. Con- 

 sidering, however, the evidence for very sharp localization in this seg- 

 ment of the mentioned nucleus, which has come from the work of Over- 

 bosch (see also Brouwer-Zeeman, 1926), and which is well illustrated 

 by our Experiment V-c, it is more than plausible that we have a 

 definite localization of macular quadrants in definite portions of the 

 intermediate segment of the external geniculate body. It appears 

 logical to suppose the location of the projection of the upper homony- 

 mous macular quadrants to be close tO' the internal segment of the 

 external geniculate body (where upper "peripheral" quadrants 

 are projected), and to suppose the location of the lower homony- 

 mous macular quadrants to be close to the external segment (where 

 lower "peripheral" quadrants are projected). Since the per- 

 pendicular branch of the external sagittal layer belongs to the 

 macular portion of the visual radiation, a similar arrangement must 



