172 



C. Judson Herrick 



composition of these tracts is exceedingly variable in different species 

 and it is probable that they cannot be directly compared with the tracts 

 so named in Amphibia. In Amia there is a tractus olfactorius dorsalis 

 which. enters the rostral end of the área olfactoria dorsalis (fig. 20), a 

 tractus lateralis which enters the dorsal and lateral áreas, and a tractus 

 medialis which enters the medial and lateral áreas. In the carp (^Sheldon) 

 the tractus olfactorius reaches all parts of the telencephalon (including 

 the nucleus preopticus) except the área somática (nucleus entopeduncula- 



aoi.d 



a oi s. 



aol d.dl 



tr. st.th. 



24 



Fig. 24. — Diagrammatic transverse section through the telencephalon of the 

 carp. Cyprinus carpió, at the level of the commissura anterior. Outline frora 



Sheldon (191 2, fig. 56). 



ris). In Osmerus (Holmgren, 192O) the same relations prevalí and trac- 

 tus olfactorius fibers also reach the hypothalamus and habenula. 



Fibers from the área olfactoria, nucleus preopticus, and área somática 

 enter the stria medullaris to termínate in the habenula. 



There are numerous descending and ascending fibers connecting all 

 parts of the área olfactoria with the hypothalamus. The details of their 

 arrangement vary widely in different species of fishes and these tracts 

 have received many different ñames (tractus olfacto-hypothalamicus, trac- 

 tus strio-thalamicus, tractus pallii, etc.). In principie these fibers agree 

 with the simpler patterns of Acipenser and Acanthias. 



The área olfactoria medialis, nucleus preopticus and hypothalamus 

 are connected by numerous tracts which in the aggregate compose the 



I 



