1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 177 



It is also noteworthy that both in the human and the monkey brain 

 the calearine fissure usually remains in its anterior portion (that 

 closer to the corpus callosum) , a simple undivided furrow. The change 

 in this respect occurs fairly suddenly near the occipital pole where 

 regnlarly, in the monkey brain, the fissura calcarina divides into two 

 branches, an ascending and a descending branch. (Compare figures 

 in this treatise showing the inner face of the hemisphere.) This 

 can be explained only in the sense of a rapid increase in the size of 

 the striate area in its posterior portion. It is the posterior portion 

 of the striate area which in the phylogenetic scale, with the perfection 

 of ''central" or macular vision and with the more perfect structural 

 development of the macula lutea,, undergoes the greatest expansion, 

 while the oral portion of the striate area participates in these changes 

 only moderately. 



Clinical experiences with small scotomata aifecting "central" or 

 macular vision can only be understood by accepting a thin and yet a 

 broad macular segment of the visual radiation, which the vertical 

 branch of the radiation actually is, and an extensive cortical repre- 

 sentation of the macula. (The necessity of accepting a wide macular 

 projection area was recognized by most investigators studjdng the 

 visual apparatus, though this led to the erroneous acceptance of a 

 multilocular or a "diffuse" projection upon an extensive region of 

 the cerebral cortex; see for example Monakow.) If the macular fibers 

 were collected into a tiny, compact fascicle as imagined by some inves- 

 tigators, and the macular cortex were a small region in any way com- 

 parable proportionally to the small size of the macula lutea as com- 

 pared with the remaining portion of the retina, macular vision would 

 be usually completely abolished even by subcortical or cortical lesions 

 of a moderate extent. Since, as we saw, the perpendicular macular 

 branch represents a considerable portion of the entire visual radiation 

 and the macular cortex also is a wide region, only extensive injuries 

 will result in complete annihilation of macular vision. Small subcor- 

 tical lesions, on the contrary, because of the peculiar distribution of 

 macular fibers in a fairly thin though broad lamina, will be able to 

 interrupt only a small segment of that lamina; and in the same way 

 small cortical injuries will destroy only a small portion of the macular 

 cortex, in both cases producing only small sharply delimited ' ' central ' ' 

 scotomata. Multiple lesions of the macular vertical branch interrupt- 

 ing a great number of individual fibers and finest fascicles will result 

 in no circumscribed loss of the visual fields determinable by present 



