44 'Journal of Comparative Neurology and Psychology. 



part goes farther caudad through the mid-brain. Yet in his 

 "Vorlesungen" he mentions only the thalamic and hypothalamic 

 termination. Haller also mentions only hypothalamic termini, 

 while Catois, whose opinion is that it is not impossible that some 

 fibers may end in the basis mesencephali, nevertheless also con- 

 siders the hypothalamus to be the end of the greater part, in which 

 HousER also saw its termini. 



Comparing now the fore-brain tracts of the selachians with 

 those of the teleosts, we find that two connections are quite the 

 same, viz., the tr. olfacto-habenularis and the tr. strio-thalamicus. 

 Besides these the teleosts have two tr. olfacto-lobares, medial and 

 lateral, of which the first ends uncrossed in the same level of the 

 hypothalamus as the tr. strio-thalamicus, while the second crosses 

 and ends in the most inferior parts of the inferior lobes. These 

 two tracts are very much like the median bundle constituent of 

 the tr. strio-thalamicus of selachians and the tr. pallii, which 

 crosses and ends in the more inferior parts of the lobes. More- 

 over, in both types of fishes these two sets of tracts originate in 

 secondary olfactory regions. 



From all this it is probable that these two sets of tracts are to be 

 regarded as homologous, and this is another proof of the homology 

 of some parts which in the selachians lie in the pallium and in the 

 teleosts in the lobi anteriores, as has already been made probable 

 by the fact that a great many of the secondary olfactory fibers, 

 which, in the teleosts, all end in the lobi anteriores, in the sela- 

 chians end in the most dorsal regions. And, further, while the 

 bilateral connection between these secondary olfactory centers is 

 represented in the teleosts by a part of the com. anterior (which is, 

 therefore, so much larger in these fishes than in the selachians), 

 in the selachians these connections are situated in the dorsal region 

 of the pallium. So we find that all the facts, as brought out by 

 others and by myself, lead us to believe that in the lobi anteriores 

 of the bony fishes there are parts which in the selachians are repre- 

 sented in the pallium, a fact of very great importance. 



A second question is whether we may extend these homologies 

 any further by stating that the secondary olfactory centers in 

 teleosts related to the tractus olfacto-lobares are in other respects 

 also the complete homologues of the pallial centers of the sela- 

 chians described in the second part of the first chapter from which 

 the tr. medianus and the tr. pallii originate. Regarding this 



