1932] Poliak: Afferent Fiber Systenis, Primate Cerebral Cortex 115 



fairly equally distributed to the whole degenerated zone, the latter 

 bein^ otherwise sharply delimited. 



Farther occipitalward the degenerated bundle slowly ascends and 

 at the same time gradually turns medially. Bending around the 

 callosal bundle (tapetum) and above the dorsal corner of the lateral 

 ventricle it finally reaches the upper lip of the calcarine fissure. Here 

 the degenerated area has the shape of a thin twisted fiber lamina 

 (figs. 55-57). 



The afferent visual fibers, as mentioned above, remain strictly con- 

 fined to the external sagittal layer during their entire course occipital- 

 ward leaving that layer only when approaching the striate cortex. 

 After the most caudal somatic sensory fibers have left the sagittal 

 strata, practically no degenerated fibers whatever deviate toward the 

 cortex until the area striata, marked by a dotted stripe in the cor- 

 responding figures, appears. This point was studied with particular 

 care in Experiment II as well as in the remaining experiments where 

 special attention was paid to sections showing deep fissures closely 

 approaching sagittal layers (for example, figs. 55-57, compare also 

 figs. 13, 40, 41, 71, 72, 75, 76 in Experiments I, III, IV, and V-a). It 

 appears justifiable, therefore, to maintain the dictum that visual fibers 

 do not reach any cortical region which does not belong to the striate 

 area or field 17 of Brodmann. So also, neither in this nor in any of the 

 present experiments, have visual fibers been seen to turn into the 

 corpus callosum in order to reach the opposite hemisphere in this way 

 (figs. 52-54). The evidence was particularly clear in the present 

 experiment, since no callosal fibers whatsoever degenerated. 



Finally the degenerated visual fiber bundle gradually tui-ns medi- 

 ally and enters the striate cortex of the upper lip of the fissura cal- 

 carina (figs. 55-57). The region supplied by that bundle is a well 

 delimited one, con-esponding with a long narrow strip of the striate 

 cortex buried in the calcarine fissure (upper lip). As the present 

 degenerated bundle represents the dorsal "boundary bundle" of the 

 en,tire visual fiber fan, so the portion of the striate area supplied by 

 it represents also a "boundary zone," the most dorso-medial, of the 

 entire visual projection cortex (fig. 2, lower figure). 



A few more details must be mentioned since they are apparently 

 important for an understanding of the finer arrangement and cortical 

 distribution of individual bundles composing the visual radiation. In 

 sections where the most anterior portion of the striate cortex appears 

 lining the bottom of the calcarine fissure, individual degenerated 



