18 STUDIES ON THE CENTRAL NERVOUS SYSTEM 



monkeys there is a localization of the different parts of the 

 retina in the cortex of the corpus quadrigeminum anticum. 

 Our material is, however, too limited to give a detailed 

 scheme, as has been done in rabbits. 



A distinction should be made between lesions in the 

 macula and lesions in other parts of the retina. Hence 

 we speak of macula lesions and of peripheral lesions. Our 

 experiments show that the upper quadrants of the retina lie 

 medial in the external geniculate body and the lower 

 quadrants lateral. In the medial part the crossing and non- 

 crossing fibres lie close to one another. Hence the upper 

 nasal part of the left retina and the upper temporal quadrant 

 of the right retina are here localized. The same is the case 

 with the lateral parts of this ganglion, where the right 

 lower quadrants of both retinae meet one another. The 

 fibres from these two parts do not overlap. The difference 

 between the specimens with lesions in the upper and in the 

 lower halves of the retina is already apparent in the optic 

 tracts in the neighbourhood of the ganglion; after an 

 operation on the upper quadrants the degenerated fibres 

 are situated medially and remain there, while after a lesion 

 in the lower half of the retina the fibres tend to pass to the 

 lateral side. 



It has not been possible to give a more detailed localiza- 

 tion of various parts of the different quadrants. On the 

 contrary, we were struck by the fact that the secondary 

 degenerations due to differently situated lesions in the same 

 quadrants resemble each other very much. This is also the 

 case in rabbits and in cats. From a study of our sections of 

 the external geniculate body it is easy to determine whether 

 the operation has been made in the upper temporal or upper 

 nasal, in the lower temporal or lower nasal quadrant, but 

 with the exception of the part of the retina belonging to the 

 monocular field of vision one cannot, in this way, decide 

 whether the lesion was made in the neighbourhood of the 

 macula or more peripherally. 



