1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 161 



fibers of the visual cortex entering more or less obliquely the lower 

 strata and terminating in the zone of the stripe of Gennari or Vicq 

 d'Azyr, described by Ramon y Cajal, are afferent visual fibers originat- 

 ing in the external geniculate body of the same hemisphere. 



(11) The small segments of the visual cortex supplied by indi- 

 vidual bundles of the visual radiation have sharp limits and definite 

 form. In different portions of the striate area their shape is different : 

 long narrow triangular strips in the fissura calcarina arranged longi- 

 tudinally, but more condensed triangles in the occipital operculum 

 and over the occipital pole. The afferent fiber bundles of each of these 

 small cortical triangles are strictly isolated one from another. Each 

 triangle of the visual cortex gets its own bundle independently from 

 the neighboring triangle. There does not, accordingly, exist an over- 

 lapping of these small zones, a mingling of their respective bundles, 

 or even a "diffuse" termination of individual bundles of the visual 

 radiation in extensive portions of the visual cortex. Neighboring 

 triangles are supplied by neighboring fascicles of the visual radiation. 



(12) The entire afferent visual system from its beginning in the 

 peripheral organ (retina) to its termination in the cerebral cortex 

 (striate area) is composed of individual receptor and conductor units. 

 These structural and functional units are strictly arranged according 

 to the "spatial principle" on the one hand, and according to the 

 "principle of neighborhood" on the other. Each area striata is in 

 some sense a faithful copy of both homonymous halves of both retinae. 

 There exists a full preservation of "spatial relations" in the visual 

 cortex as it exists in the retina, though the absolute shape of the 

 "cortical hemiretina" is somewhat changed in consequence of the 

 slight mutual displacement of neighboring units or segments. 



(13) All visual impulses whatever their special form or quality 

 may be, and regardless of their ultimate destination, so far as they 

 reach the cortex of the forebrain, first go to the striate area, from 

 which they are distributed to other regions of the same and the 

 opposite hemisphere. 



(14) Since there exists a fixed arrangement of functionally differ- 

 ent bundles or segments of the visual radiation (present experiments) 

 as well as of the peripheral portion of the visual system (Ronne, 

 Brouwer-Zeeman), which means a fixed projection of definite retinal 

 quadrants upon definite portions of the visual cortex, symmetrical in 

 both hemispheres, the injuries of the visual system will produce defi- 

 nite symptoms depending on the location and the extent of the injury. 



