410 



Prof. E. A. Scliafer. 



[Mar. 1, 



slight downward or upward inclination accompanying or immediately 

 following the lateral movement. 



The upward inclination of the eyes is often accompanied by eleva- 

 tion of the upper lids, and the downward inclination by depression of 

 these lids. 



Simultaneous excitation of corresponding points on the two hemi- 

 spheres by the same stimulus usually produces a struggle between the 

 muscles producing the lateral movement, the eyes quivering, but not 

 being directed more to one side than the other. On one occasion, 

 however, when corresponding points of the mesial surfaces were 

 simultaneously stimulated slight convergence of the optic axes was 

 obtained. 



If, as is highly probable, the movements of the eyes, which occur 

 on excitation of the occipital lobe and adjacent parts, are the result of 

 the production of subjective visual sensations, these effects of excita- 

 tion of the several parts of that lobe and the adjoining portions of the 

 brain would appear to indicate — 1. A connexion of the whole visual 

 area of each hemisphere with the corresponding lateral half of each 

 retina. (This has already been ascertained to be the case from the 

 result of removing the whole of the area on one side, bilateral homo- 

 nymous hemianopsia being thereby produced.) 



2. A connexion of the superior zone with the superior part of the 

 corresponding lateral half of each retina. 



3. A connexion of the inferior zone with the inferior part of the 

 corresponding lateral half of each retina. 



4. A connexion of the intermediate zone with the middle part of 

 the corresponding lateral half of each retina. 



If we imagine the visual areas of the two cerebral hemispheres to 

 be united in the middle line we may conceive each retina as projected 

 in its normal position over the united area. It will then at once 

 appear that the upper and lower parts of both retinas will fall upon 

 the corresponding parts of the united area, that the outer part of the 

 left retina and the inner part of the right will fall upon the outer 

 portion of the left side of the united area, and vice versa, and that a 

 vertical line bisecting each retina will fall along the line of union of 

 the two cerebral visual areas. The parts concerned with direct or 

 central vision will therefore correspond with a part of the mesial 

 surface. And each pair of " identical points " of the retinas will 

 correspond with one and the same spot of the cerebral surface.* 



* A more detailed account of this investigation will appear in the April number 

 of ' Brain.' 



