184 University of California Publications in Anatomy \yoL.. 2 



Since there exists a stable, or fixed arrangement of functionally dif- 

 ferent bundles of the visual radiation, symmetrical in both hem- 

 ispheres, and a similar distribution of cortical representations of 

 retinal quadrants, the symptoms produced by various pathological 

 processes or by injuries will largely depend on the size, location, and 

 direction of the injuries. 



Unilateral injuries or pathological processes which are limited to 

 the occipito-parietal and temporal lobes, will produce: 



(1) a complete homonymous hemianopsia of the opposite side with 

 the vertical dividing line passing exactly through the points of fixa- 

 tion if one entire striate area is destroyed (since the striate area 

 represents an extensive curved surface not lying in one plane this 

 explains why portions of the visual fields so often remain unharmed, 

 especially in gunshot injuries producing a channel more or less 

 straight) ; 



(2) an incomplete homonymous hemianopsia of the opposite side 

 with macular vision preserved if one entire striate area lining the 

 fissura calcarina, except its posterior portion and the occipital pole, 

 is destroyed. The latter can be produced not only by tumors, malacic 

 processes, bleedings, etc., but also by injuries if they are followed by 

 subsequent haemorrhage with destruction of both lips of the fissura 

 calcarina and leave the macular fibers of the visual radiation and the 

 pole of the occipital lobe undamaged. On the other hand, it is easy 

 to understand why gunshot injuries will rarely produce such a form 

 of hemianopsia without infringing in some way or another on a por- 

 tion of the macular fibers or of the macular cortex. If the position of 

 the gunshot channel is in the horizontal plane, but perpendicular to 

 the long axis of the hemisphere, this will produce either an inferior 

 quadrantic hemianopsia with the preservation of the macula if the 

 upper horizontal branch of the external sagittal layer alone is 

 destroyed, or a rarer superior quadrantic hemianopsia if the inferior 

 horizontal branch alone is interrupted. But it is likely that either the 

 dorsal or the ventral half of the vertical macular branch of the visual 

 radiation will also be damaged, thus completing the hemianoptic loss 

 up to the points of fixation, in the upper or in the lower visual quad- 

 rants, depending on whether the lower or the upper half of the 

 perpendicular branch of the radiation is interrupted. If the gunshot 

 channel runs in longitudinal direction but near the median line, it 

 will destroy both lips of the fissura calcarina, w^hile not necessarily 

 destroying the macular fibers. More likely than not the macular 



