Kappers, Teleostean and Srlnchiaii Bram. 29 



tion itself gives. However, I will not neglect giving a short survey 

 of the course of the different systems of the praeinfundibular part 

 of the thalamus, beginning with the nervus opticus. 



After the total decussation of the nervi optici (which takes 

 place in Gadus about three-quarters of a centimeter before the 

 lobi anteriores, but in Lophius, Thynnus, Salmo and most bony 

 fishes under the caudal part of the fore-brain and the anterior 

 part of the 'tween-brain) they send a small bundle mesad imme- 

 diately under the fissure-like ventricle and over the commissura 

 transversa. For a short distance these medial bundles maintain 

 this relation and then (without decussating again) join the com- 

 missure of Herrick and so enter the most superficial layer of the 

 tectum opticum, possibly having in the meantime given off 

 collaterals to the ganglion geniculatum, in which, however, no 

 fibers end directly. The chief group of the optic fibers runs 

 laterally and upward from the thalamus and divides just in front 

 of the corpus geniculatum into two paths. 



I must mention here a very small group of strongly medullated 

 fibers which persist diffusely scattered among the degenerated 

 opticus fibers. Where the opticus first touches the hypothalamus 

 it forms a small but compact bundle (Fig. xi) which then comes to 

 lie entirely on the inner aspect of the tractus opticus (Fig. xxxv) 

 and afterward can with difficulty be distinguished from that part 

 of the upper loop of the commissura transversa, which is likewise 

 heavily medullated and lies along the inner border of the opticus. 

 While, however, this commissura transversa bundle very soon 

 becomes closely joined with the other com. transversa bundles 

 (Fig. xxxvi) the outer part of the fibers (Figs, xxxviii, xxxix, xl) 

 turns upward where it ends in the medial wall of the tectum almost 

 in the same place as the brachium mediale, running mesad of the 

 corpus geniculatum. It is evident that these are the -fhrce tectales 

 n. optici, which Krause has also described as the innermost fibers 

 of the optic nerve and which, having their trophic center in the 

 tectum itself, are not degenerated here. 



A part of the centripetal opticus fibers seems to be connected 

 directly or indirectly by means of collaterals with the anterior part 

 of the corpus geniculatum laterale. The great enlargement of this 

 nucleus farther caudad, however, must be attributed to its con- 

 nection with the two brachia, of which the medial is much smaller 

 than the lateral which divides again into dorsal and ventral 



