Kappers, Teleostean and Selachian Brain. 41 



lobaris, the commissura supra-infundibularis or post-infundib- 

 ularis, the tr. lobo-cerebellaris and finally the tr. lobo-peduncu- 

 laris. From this it results that the back part of the lobi, which, 

 moreover, is connected with the dorsal regions by fibers of the tr. 

 mesencephalo-lobaris anterior et posterior, is the most important 

 part of the lobi. It must, however, be stated that it is very diffi- 

 cult to place an exact limit between these two parts, especially 

 because the tr. lobo-cerebellaris seems to get its fibers from 

 both. 



I must mention still that a basal optic tract such as has been 

 mentioned by Goldstein could not be found in the basal thala- 

 mus regions or in the so-called ganglia ectomammillaria either in 

 Lophius, Gadus, Thynnus or Salmo, nor a commissura post- 

 chiasmatica which should connect such basal regions. However, 

 it is possible that there are variations in this point in different 

 fishes. Nor did I find a second cerebellar connection between the 

 nucleus rotundus (nucleus ventralis of that author), or the medul- 

 lary tract which C. L. Herrick describes for the nucleus rotundus 

 (his nucleus ruber). 



2. The "Tween-brain of the Selachians. 



The 'tween-brain of the selachians in its general features shows 

 the same structure as that of the teleosts, but is distinguished from 

 the former, among other things, by a much less compact arrange- 

 ment of its tracts and nuclei, which makes the investigation very 

 difficult, as Edinger rightly observes. While in the bony fishes 

 I could follow the diff^erent tracts — and there were many of them — 

 very definitely and with good results, and find out their origins 

 and terminations, the number ot fibers of the 'tween-brain of the 

 selachians, even of the full-grown animals, is so considerable that 

 many systems go quite close to and even through each other. 

 Moreover the groups of cells are so difl^usely scattered that it is 

 very difficult to distinguish many nuclei here. 



Accordingly, it is no wonder that the number of investigators 

 who have been successful m the examination of this material is 

 much smaller than in the teleosts. The most important results 

 (after the older authors of the period before Weigert) have been 

 obtained by Edinger, and afterward by Houser, Haller and 

 Catois. Especially the first named has clarified this region. 



