12 STUDIES ON THE CENTRAL NERVOUS SYSTEM 



On looking over our observations of secondary degenera- 

 tions in the optic nerve we find there is, to a certain degree, 

 a locahzation of the peripheral quadrants of the retina. 

 The fibres from the upper half of the retina are situated 

 above those from the lower; further, the temporal fibres lie 

 lateral and the nasal medial. The difficult point is the 

 localization of the macular fibres. It is certain that the 

 number of those fibres is large. Near the eye they are 

 situated laterally in the optic nerve, but towards the chiasma 

 the degenerated area has a tendency to pass more centrally 

 into the nerve. We believe that the macular fibres separate 

 those from the temporal upper and lower quadrants of the 

 peripheral retina from one another. There is not a very 

 exact localization of the macular fibres in the optic nerve, 

 for it is certain that several of them are found between 

 fibres from the various quadrants of the retina. 



We shall now pass to the relations in the chiasma. Our 

 experiments have shown that the fibres from the upper part 

 of the retina generally cross dorsally in the chiasm.a and 

 those from the lower half ventrally. The macular fibres 

 cross chiefly in the middle of the chiasma. In the middle 

 and in the most proximal sections of the chiasma it is per- 

 fectly evident that the macular fibres have a tendency to 

 move towards its dorso-lateral part. In this way the posi- 

 tion occupied by the macular fibres in the optic tracts, 

 as we shall presently see, has already been determined in the 

 chiasma. 



Our observations in regarding to the position of the 

 various parts of the retina in the chiasma of the monkey 

 correspond to what Henschen and Wilbrand found in man. 

 From their and our own observations we can understand 

 why it is that tumours of the hypophysis so often cause an 

 early defect in the superior temporal quadrants of the field 

 of vision, since the tumour presses first on the ventral border 

 of the chiasma and consequently damages the function of 

 the ventral quadrants of the retina. From our investiga^ 



