226 



plexus choneoideus 



tr hypoth.oiPmed 



nucl.posthaö. os.nucl. 

 internnediu5 

 r. olf! thai, p, dor5^>^^'^fe*jl 



nucl. entopedunculans 





^y^> 



-^A^-v- /^ ': 





5-yps. 



v" -^ ,• i ' •"'^Vi P-POSt. 





n opt 





comm. trans 



nuclpraerot 

 tn. pnaeth.cin 



tr. pnaeopthab 

 plat 



lobus pyriPormis 





nucl. praenot. 



comm. trans. 



^ Tibpae ansulatae 



Fig. 6. Synbranchus marmoratus. 



entirely surrounded by other parts of the cerebrum, though the 

 dorsallj situated septum reaches rather further caudally. 



Of the fore-brain tracts the tractus olfactorius claims our atten- 

 tion first. 



The lateral olfactory tract (tractus olfactorius lateralis) is found 

 ill its usual position near the fissura endorhinalis. It sends its fibres 

 into the lateral olfactory regions, the area olfactoria lateralis of 

 Kappers and Theunissen (5). In the level of the sulcus ypsiliformis 

 this olfactory tract has entirely disappeai-ed. It is my opinion there- 

 fore that in Synbranchidae only that part of the lateral olfactory 

 region which lies in front of the sulcus ypsiliformis is provided 

 with olfactory fibres from the tractus olfactorius lateralis. According 

 to Sheldon in the Cyprinidae the nucleus piriformis and the nucleus 

 taeniae also receive fibres from the lateral olfactory tract. 



In the tractus olfactorius medialis I can distinguish three bundles. 

 One, non-meduUated, connects the septum with the bulb and is 

 probably the same as Sheldon describes as tractus olfactorius ascen- 

 dens (running frontally). 



