54 "Journal of Comparative Neurology and Psychology. 



different neurones among one another I refer to the treatise of 

 AiCHEL and to the works of Neumayer, Fusari, Mirto, Van 

 Gehuchten and Bellonci, who made their investigations on the 

 structure of the tectum for the most part with Golgi prepara- 

 tions (Bellonci with osmium preparations). 



The outer fiber layer is formed by the termini of the optic 

 nerves. These fibers join the fibers of Herrick's commissure, 

 entering at the antero-lateral part. Immediately under this layer, 

 which contains medio-dorsally also the fibrae tectales N. optici, 

 and connected with it are the fibers of the brachia tecti. These 

 brachia tecti consist of two chief groups of fibers, a smaller one, 

 situated dorso-medially and a larger one, situated laterally; the 

 latter one may be followed under the ventral opticus root as far as 

 the most caudal part of the tectum. The brachia end in the 

 corpus geniculatum laterale. 



I shall now describe the deeper layers of the tectum. I men- 

 tion first the lowest which is very broad, extending over almost the 

 whole tectum (Figs, xlv, xlviii) and rightly described as lamina 

 commissuralis tecti. A part of the most anterior medullated 

 fibers are connected with the ganglion cells of the torus longi- 

 tudinalis, in which I cannot confirm for the cod Auerbach's 

 statement for the trout that this torus does not receive fibers. In 

 fact, P. Ramon y Cajal and Sala and after them Catois have 

 already described similar connections after Golgi preparations. 



The most frontal fibers of this deep layer (Figs, xli, xliv) gather 

 and form some small bundles lying in an oblique plane, and after 

 first going a little forward and then backward form a part of the 

 anterior portion of the commissura posterior, whose fiber relations 

 will be treated later. These fibers of the stratum alburn pro- 

 fundum tecti do not take part in the formation of the lemniscus, 

 but end in groups of cells situated in and laterally from the 

 eminentia medialis of the subventricular gray substance, nucleus 

 lentifornus and ;;. corticalis. 



Before continuing I should treat of the macroscopic structure of 

 this subventricular w^all, the nomenclature of whose different 

 parts is in some confusion. The earlier anatomists described in 

 this region the so-called torus-semicircularis as an important semi- 

 circular elevation of its postero-lateral part (Figs, xlv, li). This 

 name, however, has evidently been abused. Thus, for instance, 

 Mayser, Bellonci, Krause and others call the place where the 



