Functional factors in Ihe morphology of the forebrain of fishes i6i 



descending fibers of the tractus pallii. These connections are all similar 

 in principie with those of Acipenser. 



Acanthias possesses an additional connection between the área dorsa- 

 lis and the hypothalamus which marks a distinct advance, viz., the 

 columna fornicis (fig. 15, <^- ^■)- The tractus pallii enters the área dorsalis 

 from the lateral side and is described by Johnston (191 1, p. 18) as reaching 

 ♦;the whole extent of the roof», that is, of the área dorsalis. The fornix, 

 on the other hand, connects with the medial part of the área only, descends 

 through the área olfactoria medialis near the median plañe, and ends in 



tr ol.-- 



íi.ol.m 



aoi.l 



cotn.ant 



14 



Fig. 14. — The forebrain of Acanthias seen from the left side, illustrating the 



subdivisions of the telencephalon and the distribution of the tractus olfactorius. 



The olfactory bulb has been removed. Redrawn from Johnston ( 191 i, fig. 68). 



the Corpus mamillare. The presence of these lateral and medial hypotha- 

 lamic connections of the área dorsalis may mark the first step toward the 

 differentiation of this región into primordia of the lobus pyriformis (late- 

 rally) and hippocampus (medially) as these are found in the Amphibia, 

 though these homologies are questionable (see the discussion beyond). 



3. The área olfactoria lateralis is not so greatly enlarged as are the 

 medial and dorsal áreas. It occupies the región surrounding the attach- 

 ment of the crus olfactorius and ventrally of this (fig. I4). It is connected 

 by fiber tracts with the área dorsalis, área somática, hypothalamus and 

 habenula. 



4. The tiiberculum oljactorium (área superficialis basalis, Johnston) is 

 a ventral olfactory área which is not differentiated in Acipenser. It 

 appears to have been elaborated from both the medial and lateral subdi- 



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