188 University of California PuUicaiions in Anatomij l^'o^- 2 



small areas of the visual cortex supplied by individual bundles of the 

 visual radiation also have, as we observed, a different shape according 

 to the region. Whereas the dorsal bundles (and also, as we must 

 assume, the ventral) supply long narrow triangular strips of the 

 fissura calcarina, the macular bundles supply cortical segments of a 

 more condensed triangular form. There is good reason to suppose 

 that all macular bundles supply such small triangles, with each of 

 these triangles pointing its sharp wedge toward a central point corre- 

 sponding with the points of fixation. (As we explained previously, 

 the latter points have to be localized at the posterolateral, or in the 

 monkey at the lateral anterior limit of the striate area covering the 

 occipital operculum.) Thus when a single macular bundle or segment 

 of fibers is interrupted, small congruent homonymous triangular 

 scotomata will result pointing their sharp wedges toward the points of 

 fixation. This seems to be the only plausible explanation of the trian- 

 gular shape of "central" scotomata which is usually found. But this 

 also means that this form of scotomata hardly, if ever, will result in 

 consequence of an injury to the macular cortex, but will result usually 

 from a well delimited partial interruption of the macular portion of 

 the visual radiation, since a purely cortical injury will hardly ever 

 have the shape of a triangle corresponding exactly with the triangles 

 supplied by individual bundles.^* If the extramacular cortex sur- 

 rounded in circular or half circular fashion the entire macular cortex, 

 similar to the retinal conditions, the appearance of a circular (recte 

 semicircular) scotoma, the so-called ' ' ring scotoma, " or of a circular 

 reduction of homonymous fields of vision, would be difficult to explain 

 by single rectilinear cortical injury or by other similar pathological 

 processes. But since the "peripheral" or extramacular cortex is sit- 

 uated mainly in the anterior portion of the fissura calcarina, that 

 region can be easily damaged by a single and comparatively small 

 injury. So also the pole of the occipital lobe can be destroyed sep- 

 arately producing "central" homonymous hemianopsia, or "central" 

 scotomata. 



14 Thi3 arrajigement would also explain triangular "rests" of the visual fields 

 in cases where the visual radiation is interrupted with the exception, however, of 

 one single bundle (for example IThthoflf, 1915, case 5; consult Lenz, 1924, fig. 15). 



