360 Journal of Comparative Neurology. 



drites have to make a turn through as much as 90° to reach the 

 inner molecular layer. The position of the cell is usually such, 

 however, as to allow the axone to pass without much turning 

 almost directly to the optic nerve. The optic nerve thus pre- 

 sents a very different appearance in regard to its origin from 

 that in the normal eye. The axones from the ganglion cells at 

 the inner surface of the retina unite to form the beginning of 

 the optic nerve. This passes directly through the retina. In 

 the course through the retina these axones, or fibers, are joined 

 by others from cells more deeply situated. The optic nerve 

 thus gradually increases in the number of its fibers until the 

 complete number is attained at the lamina cribrosa (Fig. 23), 



The ganglion cells have an average size of .0123 mm. by 

 ,0153 mm. They possess a large nucleus and a distinct 

 nucleolus (Fig. 31, n and ;//). The nucleus and nucleolus stain 

 deeply, but the cytoplasm stains only faintly. Besides these 

 typical ganglion cells, one occasionally finds cells having no 

 processes and corresponding closely to this type found in the 

 young at birth. It is possible that these may be homologous 

 with similar shaped cells in the optic nerve. 



The retina of the adult thus presents some very rudimen- 

 tary conditions. The rod and cone layer, the outer nuclear and 

 outer molecular layers approach very closely to the normal con- 

 dition. The inner nuclear layer, not having the cell processes 

 so well developed, presents a more rudimentary condition. 

 The inner molecular layer, ganglion cell and nerve fiber layers 

 differ in many respects from the normal mammalian type. The 

 arrangement of the ganglion cells, the course of the nerve fibers 

 and the mode of origin of the optic nerve are of especial 

 interest. 



The outermost layers of the retina are the most regular and 

 normal in appearance. This regularity decreases as one ap- 

 proaches the inner surface of the retina and becomes most pro- 

 nounced in the ganglion cell and nerve fiber layers. 



Though the retina is abnormal and rudimentary in many 

 respects, I think it would still be able to function, though very 

 imperfectly, if other conditions were favorable. The character 



