Kappers, Teleostean and Selachian Bram. 47 



medullated tract (Fig. liv) running for the greater part separately 

 from the fibers mentioned above and ending decussated in the 

 medial ganp-lia. It is more difficult to state the function of this 

 tract, which, indeed, is evident from the literature which contains 

 only a few^ data on this point given by Edinger and Haller. 

 In his studies on the 'tween-brain Edinger mentioned this bundle 

 as a decussated tract, which next to the fasciculus retroflexus (still 

 to be described) is the strongest tract which originates from the 

 ganglia. He also describes its decussation as caudad to the gang- 

 lia habenulae but could not be certain about its ventral end, which, 

 according to him, perhaps lies in the 'tween-bram. In order not 

 to prejudicate it, he calls this tY2iCtt\\Qtr. descendens gangl. habenu- 

 Ice, which name I shall retain. Evidently Haller observed 

 the same bundle, of which he, however, says that it partly ends as 

 "Hauben-Zwischenhirn Bahn" in the most anterior region of the 

 thalamus and partly passes over into the opticus, which habenular 

 opticus root has also been mentioned by Viault and Dumeril. 

 Indeed, it seems to me most probable that this tractus descendens 

 joins the opticus fibers, though not as an opticus root to the eye, 

 but first descends for some distance and then rises again back- 

 ward. In this case it might be a crossed part of the "tr. gang- 

 lionis habenulae ad mesencephalon," mentioned by Edinger. 

 More investigations, especially experimental ones, would perhaps 

 explain many questions in this connection. 



The bundle now to be described has been seen in all fishes by all 

 investigators and in appearance and situation is one of the most 

 constant, viz., the fasciculus retroflexus, also called the bundle of 

 Meynert. This bundle which arises entirely without decussa- 

 tion from the postero-median ganglion and runs under the com. 

 habenularis may be followed in all sections adjacent to the ventric- 

 ulus tertius and the aquaeductus Sylvii into the mesencephalon. 

 It is remarkable that in Galeus canis the left tract contains no 

 myelin at all, while the right one is medullated. The latter evi- 

 dently does more work than the former (experimental investiga- 

 tions of Ambronn and Held concerning the formation of myelin), 

 which is in conformity with the fact that the left ganglion is less 

 developed than the right. The latter point has also been stated 

 for the cyclostomes (Ahlborn, Johnston) as well as for the 

 ganoids (Goronowitsch, Johnston), but has never been ob- 

 served in the teleosts either by my predecessors or by myself. 



