192 University of California Publications in Anatomy [Vol.. 2 



the visual cortex since, because of the isolation of the visual receptors 

 and conductors, the inte^ation of elementary excitations into "one 

 whole" must be an exclusive cortical process.^^ This would mean that 

 the inte^ation of a ^eat number of independent visual stimulations, 

 as far as "psychic" utilization is concerned, is not performed by any 

 sub-cortical structures (at least in primates and in man). The 

 regular "spatial" arrangement of elementary visual units: of peri- 

 pheral receptors, of fibers of the optic ner\^e and tract, of nerve cells 

 in the external geniculate body, of fibers of the visual radiation, and 

 of the nerve cells of the visual projection cortex into sets of fiber 

 bundles and into regular cell layers, is an indispensable mechanism for 

 the "spatial" reception, "spatial" conduction, and "spatial" trans- 

 mission of any kind of combinations of elementary light stimuli. Yet 

 these can be brought together and fused into a single "total" impres- 

 sion only after entering the cerebral cortex. The regular arrangement 

 of structural elements, of cells, and of fibers composing the afferent 

 visual system, the equable distribution of afferent visual fibers to the 

 entire visual cortex without any visible gaps or interv^als in the supply, 

 in a word, the arrangement of structural elements into ' ' surfaces, ' ' into 

 ' ' laminae, ' ' and into ' ' cables, ' ' and on the other hand the isolation of 

 the elementary conductor units, the preservation of the ' ' neighboring 

 relations" of these units along their entire course up to the visual 

 cortex, renders possible and guarantees the perception of "spatial" 

 or "localizing" signs of light stimuli whatever their combination 

 might be at a certain moment, whatever the "figures" may be. 

 Whether, however, a part or all of the integrating cortical processes 

 are performed in the striate area or in other cortical areas surround- 

 ing the striate area, is not feasible to decide here. The most that can 

 be said is that certain structures of the striate area (see Ramon y Cajal, 

 1909-11, 2, p. 599) suggest that the striate area is itself to some degree 

 involved in this process of integration. Other structural features, 

 however, lead to the conclusion that the area peri-parastriata plays 

 in this process an important and perhaps the main role. This assump- 

 tion is supported by the existence of innumerable fine association 

 fibers springing from the striate area proper and terminating in the 

 neighboring segments of the peri-parastriate area (field 18 and 19 of 

 Brodmann). Yet the preference for certain directions of part of these 

 association fibers, as shown in Experiment XIV, figures 25, 86-94, 



15 We are even more forced to accept such a conclusion, since there are no 

 "intercalated" or other "associative" neurons in the external geniculate body, 

 as Experiment V-D and V-e prove. 



