1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 181 



both macular fibers and macular cortex will escape injury. In such 

 a case the entire extramacular portion of the homonymous halves of 

 the visual fields including the temporal crescent can he eliminated, 

 producing a "peripheral" or incomplete homonymous hemianopsia 

 with macular vision preserved. In this case, the "central" vision 

 of the hemianoptic side will remain in every respect perfectly pre- 

 sers'ed since the association connections between the striate cortex 

 covering the occipital pole, and the area peri-parastriata will not be 

 damaged (see figs. 25, 86-94 of Experiment XIV). In the case of 

 a tumor, however, originating from the internal surface of the 

 hemisphere close to the splenium of the corpus callosum, it is likely 

 that the initial hemianopsia with intact "central" vision will in the 

 course of the illness develop into a complete hemianopsia when the 

 pressure is sufficient to interrupt the deeply situated macular fibers. 

 The appearance of hemianoptic symptoms with macular vision 

 intact can, therefore, be expected most frequently in those pathological 

 processes involving the cortex of the fissura calcarina, where the pres- 

 sure is slight or entirely absent (encephalomalacic and thrombotic 

 processes, see Best) . With both lips of the calcarine fissure lying close 

 together and with both horizontal branches of the radiation being 

 closer to the inner face of the hemisphere, if the destruction is exten- 

 sive enough, both upper and lower homonymous quadrants of the 

 visual fields will be affected without the impairment of the central 

 vision.^ But, as it is easy to understand, this must not necessarily 

 occur if only one of the lips of the fissure is destroyed. Here, too, 

 "central" vision will remain unimpaired in case if neither the retro- 

 calcarina nor the perpendicular branch of the visual radiation (which 

 is fairly distant from the lateral cortex) are affected by the patholog- 

 ical process; but the upper or the lower macular quadrants will be 

 included in the blind portions of the visual fields if the lower or upper 

 halves of the macular cortex or if the lower or upper half of the 

 vertical branch have also been damaged. It can also be understood, 

 and such cases have been reported, that a pathological process can 

 destroy both lips of the fissure and in addition the cortex on the 

 convex face of the occipital lobe (areas 18 and 19 of Brodmann), and 



9 Since both lips of the calcarine fissure are supplied by one single artery 

 (arteria fissurae calcarinae), any damage to it or any pressure upon it will 

 usually impair both lips in a symmetric way. This makes it possible to under- 

 stand why most of the preserved macular portions of the visual fields exhibit 

 regular boundaries and have in various cases a different size depending on the 

 extent of the injury. 



