32 yonvfial of Comparative Neurology and Psychology. 



directly behind the commissura posterior in the most anterior part 

 of the eminentia mediaHs. The two tracts which it joins are the 

 tr. rotundo-lentiformis and the tr. mesencephalo-cerebellaris 

 superior, which will be discussed later. Goldstein called my 

 attention to this cerebellar tract, of w^hich I had recognized before 

 only the most frontal part. He regards the com. horizontalis 

 as a prolongation of this tr. mesencephalo-cerebellaris superior, 

 which, however, I cannot confirm. That in this course between 

 the nucleus rotundus and the nucleus lentiformis mesencephali 

 there are two tracts is not so easily demonstrable in Gadus as in 

 Lophius, for in the latter fish the two bundles are difi^erent in color 

 and are not so close together. 



Having now discussed the relations amongst the fore-brain and 

 the diencephalon, the optic connections and the praeinfundibular 

 commissures, I shall now proceed with the description of the tracts 

 which originate in the diencephalon, beginning with the ganglia 

 habenul?e. 



The ganglia habeniilce form on either side two groups of cells, 

 an anterior group, more lateral, and a posterior group, more 

 medial. Both are relatively better developed in Lophius than in 

 Thynnus, Salmo and Gadus, where I have already described under 

 the fore-brain the connection of the tractiis olfaeto-habennlaris 

 with the antero-lateral ganglion and where I also mentioned that 

 its fibers decussate for the greater part in the commissura habenu- 

 laris. 



In Fig. xlii (Plate II) we see coming from the postero-medial 

 ganglion the so-called fasciculus reiroflexus or Meynert's bundle 

 or tr. habenulo-peduncularis, a thin compact unmedullated tract 

 on both sides, which in Figs, xliii to xlvi passes under the com. 

 posterior. In the more caudal sections it may be followed to the 

 beginning of the mid-brain basis and after decussation to its 

 entrance into the so-called gatighon interpedunculare (Figs, il, 1). 

 The detailed description of this ganglion will be found in the 

 chapter on the mid-brain. 



As the third habenular relation, I have to mention the commis- 

 sura habenularis (com. superior or com. tenuissima), more dis- 

 tinct in Lophius (Fig. xxvii, Plate II) than in Gadus (Fig. xlii). 

 This commissure, the medullated fibers of which originate from 

 the tr. olfacto-hahenularis, contains also fibers connecting the 

 anterior habenular ganglia which are unmedullated. The pos- 



