PROJECTION OF THE RETINA IN THE BRAIN 13 



tions on the structure of the chiasma in monkeys the con- 

 clusion may be deduced that pressure on its dorsal surface 

 may first cause defects in the inferior quadrants of the field 

 of vision; some of our clinical observations point in this 

 direction. If this is correct we should here have a means of 

 distinguishing between tumours of the hypophysis on the 

 one hand and suprasellar tumours or dilatation of the third 

 ventricle on the other hand. In this line we can also use 

 our results on localization in the optic tracts. We have 

 found that there is certainly a locaHzation of the fibres from 

 the upper and lower parts of the periphery of the retina. 

 The projection is approximately the same in both the 

 crossed and uncrossed tracts. The fibres from the upper 

 quadrants of the periphery lie dorsally, those from the lower 

 ventrally; there is no overlap between these. The macular 

 fibres are situated in the centre and gradually become larger 

 in a lateral direction. The medio ventral position of the 

 macular fibres overlap the fibres from the dorsal and ventral 

 parts of the peripheral retina. This localization remains 

 the same throughout the whole length of the optic tract. 



We shall now discuss the primary optic centres, but first, 

 however, I must say something about the pulvinar. This 

 forms a part of the optic thalamus and lies in the immediate 

 neighbourhood of the geniculate body. It is often regarded 

 as a third primary optic station. In rabbits it has been 

 up to now very difficult to decide which part of the optic 

 thalamus corresponds to the pulvinar of higher animals. 

 After operations on the eye of rabbits, many fibres are seen 

 to turn round the external geniculate body and then pass 

 along the dorsal border and through the most dorsal part 

 of the optic thalamus. We must not infer, however, that 

 these terminate here, as there is reason to beheve that they 

 all only pass through this region of the brain in order to reach 

 the midbrain. In cats a pulvinar can be easily recognized, 

 and after retinal operations a secondary degeneration can 

 be seen in its dorsal border, smaller and less intense than 



