422 NILS HOLMGREN 
The principal characters of the subpallial parts are also the 
same in selachians, holcephalians, and dipnoans. Thus, these 
characters necessarily may be present also in the fish-types with 
everted forebrain, as these fishes belong to the same phylum. 
In the following I will try to show that the everted forebrain 
also in details is built up like the inverted. I begin my descrip- 
tion with Polypterus. 
Polypterus bichir 
The peculiar forebrain of this fish has not yet been described 
in detail. I therefore will try to make a fuller account of this 
forebrain. 
The telencephalon in Polypterus is evaginated and everted. 
The evagination is represented chiefly by the ventricles of the 
bulbi olfactorii (fig. 35). These open into the medial ventricle 
just at the caudal end of the bulbi (fig. 36), where the foramen 
monroi thus should be situated. As will be pointed out later, 
the opening of the bulbar ventricles into the medial ventricle 
does not perfectly correspond to the foramen monroi in inverted 
brains. 
The eversion of the forebrain is a very peculiar one (figs. 36 to 38). 
The dorsal part of the lateral wall of the forebrain or the pallium, 
as it will be named here, is of uniform thickness throughout its 
whole extent. This pallial lamella has a very great height, but 
a little above its middle it is bent double to the lateral side, in 
such a way that its morphological dorsal border points in a 
ventral direction. Through this eversion the epithelial roof of 
the forebrain is highly expanded to form a broad tela covering 
the whole forebrain as in teleosts. Under this everted pallial 
area lies the very strongly developed subpallial forebrain. ‘The 
tela is medially strongly infolded, so as to form a longitudinal 
chorioidal fold (figs. 37, 38). 
The pallium. Above I have called the everted portion of the 
forebrain vesicle the pallium. This requires a further explanation. 
I have before defined the pallium as being a brain part lying 
dorsal to the zonae limitantes and practically also dorsal to the 
sulcilimitantes. As has been pointed out by Johnston, the bulbar 
