Kappers, Teleostean and Selachian Brain. 15 



at once to treat of the tracts and groups of cells, whose description 

 I shall illustrate with the pictures which Galeus canis gives, which 

 are a great deal clearer and more easy to control than those of 

 Angelus squatina. 



Starting with the olfactory fibers, which have been studied by 

 BoTAZZi, in Mustelus, I can confirm his assertion that these tracts, 

 which in the lobus olfactorius itself lie directly adjacent to the 

 ventricle, spread out in the fore-brain, both dorsad and ventrad. 

 The greater part of them, however, go in a more dorsal direction. 

 They end on the same side in that part of the brain which is 

 situated in the direct continuation of the olfactory lobes — area 

 olfactoria posterior. A decussation of these fiber tracts, however 

 general in other animals, is scarcely important in the selachians. 

 The highly developed decussatio inter-hemispherica seems to 

 contain no direct olfactory fibers, in which I quite agree with 

 BoTAZZi, Romano, Houser and Catois, and the commissura 

 anterior is in Galeus comparatively poorly developed, and gets its 

 fibers from other secondary regions. I ev£n doubt whether in 

 Galeus it contains any direct ventral olfactory tracts, which in 

 Mustelus also, accordmg to Botazzi, are only few. 



The region where the olfactory fibers end forms a large part of 

 the fore-bram situated dorso-laterally, characterized by rather 

 large cells (Fig. xvii, Plate I), which are continued farther forward 

 (nucleus olfactorius dorsalis) than the insertion of the lobi olfac- 

 torii, thus formmg an elongated layer in the whole anterior half 

 of the prosencephalon (see Plate X). 



From this extensive region a tract arises broadly and runs to 

 the dorsal median line, where it finally decussates with the corre- 

 sponding tract of the opposite side, and then terminates in two 

 places. The smaller part remains after the decussation medial 

 to the ventricle, where it terminates in a group of small disperse 

 cells (Fig. xviii) by which the ventricle is here compressed to a 

 fissure (cf. Fig. xvii with the following figures). I consider this 

 region equivalent to the regio uncinata described by Botazzi in 

 Mustelus, with which it agrees in situation and which he also 

 observed to be connected at least partially with the above-men- 

 tioned decussation. 



However, as I have said, by far the smaller part of these fibers 

 terminate in this region. The greater part, after the decussation, 

 incline over the roof of the lateral ventricle and end much farther 



