8 STUDIES ON THE CENTRAL NERVOUS SYSTEM 



to the animal making an unexpected movement. This 

 necessitated a second prick. These operations are easily 

 made, provided, of course, one has not to do it oneself. 



After eighteen days the animal was killed. The size and 

 exact position of the lesion was controlled by post-mortem 

 examination. In all lesions of the macula in monkeys and 

 in several of the peripheral retina, a microscopical examina- 

 tion in serial sections was made. In this way we got a 

 good oversight of the conditions in the periphery. 



The nervous system was treated by the Marchi method. 

 A complete series was cut through the chiasma, the optic 

 tracts and the primary optic stations. In several cases the 

 peripheral nerve was also examined by this method. Our 

 investigations were started in the Central Institute for 

 Brain Research (Director Dr. C. U. Ariens Kappers) and 

 have been continued in the neurological and ophthal- 

 mological laboratories of the University of Amsterdam. 



In rabbits a localization of the various parts of the retina 

 up to a certain degree is already seen in the optic nerve. 

 The fibres coming from the ganglion cells of the dorsal 

 half of the retina are situated more dorsally in the optic 

 nerve than those of the ventral part. The fibres issuing 

 in the nasal part of the retina proceed medially from 

 those of the temporal part. This locaHzation is, how- 

 ever, not an absolute one in the optic nerve. One can 

 find fibres of various quadrants mixed together. It is 

 very difficult to show a special localization in the chiasma of 

 the rabbits. This is easier in the optic tract. We have 

 found that the upper quadrants of the retina send their 

 fibres through the ventro-medial part of the optic tract and 

 the lower quadrants through the dorso-lateral part. The 

 turning of these quadrants takes place chiefly in the chiasma. 

 Hence we may deduce that in the chiasma of the rabbit 

 there is not only a partial crossing from the left side to the 

 right and the reverse but also a crossing from dorsal to 

 ventral and vice versa. 



