154 



C. Judson Herrick 



ed by fibers of the tractus olfactorius and discharges fibers into the 

 hypothalamus by the medial forebrain bundle. There are probably also 

 ascending fibers from the hypothalamus to this área, though these have 

 not been described. Both área medialis and nucleus preopticus send 

 fibers into the habenula, as in Acipenser. 



nab 



com hdD. 



"-1. Shp. 

 ' C. S. 



"~-^ *'■■, áol.rri. 

 com.dnt.-x^ 



---__^ fr. som. p. 



"fr; pal. 



ñ uc. po. 



f. med. t. 



com. pi. 



com pn 



Fig. 8. — Median view of the left half oí the forebraia of Ichthyomyzon conco- 

 lor, X 37. The courses of some of the fiber tracts as described by Johnston and 

 Tretjakoff in related species of petromvzonts are diagrammatically indicated. 

 The ventricular surface of the right half of this specimen has l)een figured by Her- 

 rick and Obenchain (191 3, figs. 3 and 4). In the left half the habenula and corpus 

 mamillare are smaller than on the right side and (probably incidental to these 

 differences) the sculpturing of the ventricular surface is in some respects simpler. 

 Since these differences are not significant to the present discussion, they are not 



considered here. 



Ihe área olfactoria dorsalis fjohnston's epistriatum, 1902, and pri- 

 mordium hippocampi, 1912J extends along the entire length ofthe telen- 

 cephalon médium and posteriorly is broadly joined to the habenula and 

 a contiguous part of the diencephalon termed the lobus subhabenularis. 

 The área dorsalis receives fibers from the olfactory bulb, correlation 

 fibers from the área medialis, and ascending fibers from the hypothalamus 

 in the tractus pallii. It discharges broadly into the habenula, meagerly 



