Functional factors in th(' mf)ri)lK)loc;v of the fort-hrain of fishes 



>f'5 



evidence of inversión like that of elasmobranchs i. The área olfactoria 

 lies wholly in the telencephalon médium. It is not crowded forward cióse 

 to the attachment of the bulbus olfactorius as in elasmobranchs, but as in 

 Acipenser it is enlarged throughout the length of the telencephalon mé- 

 dium. This suggests an application of Kappers' principie of neurobiotaxis, 

 the elasmobranch condition being determined by the enormous deve- 

 lopment of the olfactory tracts with relatively smaller ascending non- 



a oi. d. 



com.hab. 



hab. 



V tr. 



-F 



-a.ol. m. 



~C om ant 



en 



nuc. po. 



7 



¥i'¿. 17. — Medial view of the left half of the forebrain of S(]uahis acanthias. 

 Drawn from a dissection. The ventricular sulci were differently arranged 011 the 

 opposite side of this specimen, and a different pattern was shown on each side of 

 a second specimen similarly bisected. Xo one of these four half brains agrees 

 exactlv with the Squalus acanthias from the American Atlantic coast or the Acan- 

 thias vulgaris from the Naples Station figured by Johnston (iqii, figs. 71 and 72). 

 It is impossible to determine what is the typical pattern of the diencephalic sulci 

 without studv of additional specimens in correlationwith internal structure. 



olfactory diencephalic connections, while in Teleostomi the olfactory 

 tracts are smaller and the diencephalic connections are relatively more 

 important and they extend farther forward. The centers of correlation 

 between the descending olfactory tracts and the ascending diencephalic 

 tracts tend to accumulate cióse to the olfactory bulbs in the former case 

 and to differentiate in closer association with the diencephalic centers in 

 the latter case. 



' In the Synbranchidae (van der Horst, 19 17) there is a secondary fusión of 

 the media! olfactory áreas in the median plañe within the ventriculus commune. 

 and there is a similar fusión in Gadus merlangus (Holmgren, 19201. This appa- 

 rently is a local thickening and (loes not involve an inversión similar to that ot 

 (lasniobranchs. 



