Her HICK, Morphology of NcriH^us System. li^i^ 



appear upon the dorsal portion of the encephalon wall, 

 which have the structure of the basal ganglia. This struc- 

 ture extends soon to embrace the entire lateral walls of the 

 prosencephalon. These ganglia consist of a very compact, 

 finely- granular stroma, with peculiarly arranged ganglion 

 cells, and of a system of exceedingly fine, non-medullated 

 fibres. Beneath the epithelium, in the dorsal region of the 

 ganglia, is a layer of small cells whose fibres extend ventrad 

 and radially. Such cells are not found in the ventral por- 

 tions, but instead irregularly scattered small cells. In the 

 midst of the ganglion are large cells with large round nuclei 

 and pale body. The processes are here also radially disposed 

 to the ventricular surface, producing in cross-sections a very 

 characteristic habitus. The transition in structure in passing 

 into the olfactory lobes is gradual. 



"In transections corresponding to about the middle of 

 the prosencephalon the basal ganglia are connected by a 

 thick commissure — the commissura interlobularis. I preserve 

 the older name for reasons suggested by Osborn. The mass 

 of the commissure is composed of finely-granular substance, 

 with scattered small nuclei. It is only in its dorsal portion 

 that fibres may be seen crossing. It proved impossible to 

 determine their further course. Besides these, there are a 

 few thicker bundles of non-medullated fibres from the olfac- 

 tory lobes which cross with those of the opposite side, and, 

 passing caudad, apparently coinbine with the systems leading 

 to the lobus infundibuli. The latter observation is neverthe- 

 less somewhat doubtful. 



" Ventro-mesad to the optic tracts there is a well-devel- 

 oped system containing apparently fibres from the anterior 

 (interlobular) commissure. The greater part is derived from 

 the central substance of the basal ganglia. Associated with 

 these are a number of fibres from a cluster of small nerve 

 cells lying cephalad to the chiasm. Sagittal sections show 

 that the lateral portions of the above-mentioned systems of 

 fibres pass to the caudal part of the lobi inferiores. The 



