1932] Poliak: Afferent Fiber Systems, Priniate Cerehral Cortex 189 



5. ORGANIZATION AND FUNCTION OF THE VISUAL SYSTEM 

 IN GENERAL 



From the present investigations some further conclusions must 

 be drawn, conclusions which bear on the general principle according 

 to which the entire central visual apparatus is organized. In none of 

 the five experiments (Experiments I, II, III, IV, and V-a) was the 

 entire visual radiation caused to degenerate. By the experimental 

 lesions made, a variable portion of the radiation was interrupted. In 

 accordance with this in each of the five experiments not the entire 

 visual cortex, but a part only, was found to receive degenerated fibers. 

 The remaining visual cortex was found to be entirely free. Moreover, 

 the visual cortex was found to be equally well supplied with afferent 

 fibers. This fact favors the conception that each given small segment 

 of the striate area is supplied by its own independent small bundle, 

 and only by it. (This is supported also by Experiment V-b and V-c.) 

 There does not exist, accordingly, a "diffuse" spreading of individual 

 bundles of the visual radiation over a large segment of the visual 

 cortex or even over the whole area striata. A ' ' wide ' ' cortical repre- 

 sentation of the macula also does not exist. The size of the delimited 

 cortical segments, different in each experiment, is in fair proportion 

 with the size of the degenerated fiber segments. Where a single small 

 fiber segment was interrupted, the supplied cortical segment is small. 

 When tw^o fiber segments were interrupted and in addition other 

 fibers in neighboring segments degenerated, the cortex affected had a 

 larger extent. Besides, two degenerated bundles were followed sep- 

 arately during their course up to the cortex ; they become only seem- 

 ingly mixed where they change their course, terminating, however, in 

 different segments of the visual cortex. If the same segment was 

 interrupted in different experiments, the supplied cortical segment 

 proved to be the same. When the seat of the injury was slightly 

 changed, a somewhat differently shaped cortical segment, although 

 similar, was found to be supplied. Attention must also be called to 

 the regular limits of supplied cortical segments (Experiments II, III, 

 IV, and V-a) . Most often these limits approach a straight line, though 

 this has been denied. Such straight limits are due to the sharpness 

 of the lesion in the external sagittal stratum of the parieto-occipital 

 lobe, produced by a sharp instrument. Yet undoubtedly a sharp 

 lesion would not suffice to produce such sharp limits if there did not 

 exist a strictly regular, parallel arrangement of fibers of the visual 



