44 Journal of Comparative Neurology. 



zones of fibres parallel to the latero-basal aspects of the colliculi. 

 There then arises a distinction between a larger, ectal, lemniscus 

 portion and a smaller, ental portion which seems to pass, after 

 decussating, into the cerebellar peduncles. The lemniscus por- 

 tion passes to the region of the pons and gives off other- fibres 

 to the cerebellar decussation, while the remainder accumulates 

 on the latero-ventral aspects of the medulla. 



Undoubtedly something more than a brief statement is 

 necessary to be convincing of the correctness of statements so at 

 variance with the descriptions of earlier writers. It will not be 

 possible at present to publish the numerous figures necessary to 

 elucidate these points so that a more detailed discussion is held 

 in reserve, in the hope of making wider comparisons. The 

 statement of Fritsch that the caudal root of the optic tract rises 

 in the collicukis has not been verified. Nothing is easier in 

 some of our series from large-eyed species, where the horizontal 

 section is inclined somewhat ventro-cephalad, than to follow 

 fibres, almost in a single section, from the root to the caudal 

 portion of the tectum. It is perfectly certain that no considerable 

 portion of these optic nerve fibres enter the stratum zonale of 

 the coUiculus. On the other hand the fibres of the ventral com-' 

 missure can be followed to the stratum zonale, though, as above 

 said, those of the commissure proper seern to go on into the 

 tectum. Our study supports Bellonci's statement that there is 

 no connection of the optic nerve fibres with the .geniculatum, 

 though we think the posterior brachia, i. e. the descending fibres 

 from the tectum related to the ventral commissure, are interrupt- 

 ed in what may be a homologue of the geniculatum internum. 



In a series of very thin transverse sections of Luciopcrca, in 

 which species the commissures are very much displaced in a lon- 

 gitudinal direction, we followed the ventralis very carfully, and 

 feel sure that there is no passage of the larger optic fibres toward 

 the collicukis. There seems also to be a decussation of a branch 

 of the transverse commissure in this species. In that case the 

 homology between the ventral and transverse commissures would 

 be complete. 



VII. — The tectum opticiim is rendered difficult chiefly by the 

 fact that the fibres pass through it from the numerous tracts in 

 oblique directions and are rarely parallel so the spherical surface 



