219 



Thus seen from the ventral side, the fissura- endorhinalis is 

 shaped like two half arcs, which form an obtuse angle with each 

 other. The anterior of these bounds the tnbercnluni laterale, the 

 posterior the tuberculum posterius. 



Not only latero-ventrallj, but also candallj the tuberculum 

 posterius is strongly developed like the median portion of the fore- 

 brain. The caudal portion in these fishes thus covers a greater part 

 of the thalamus. One consequence of this is that the posterior fold 

 of the velum transversum points forwards instead of backwards 

 (fig. 2). Whereas the dorsal sack (pulvinar epiphyseos) usually lies 

 on the roof ependyma of the fore-brain, here we see just the reverse; 

 the richly folded dorsal sack is covered by the ependyma of the 

 fore-brain which bends backwards over it. 



Sulcus iimitans teiencephaii 

 striatum 



comm. ant 



nervus opticus 

 Fig. 2. Monopterus albus. Wax model of the fore-brain Median side. 



A short distance behind the luiddle of the hemispheres, in a lather 

 frontal position consequently the sulcus ypsiliformis of Golstein (1) 

 begins at the place where the fissura endorhinalis forms the afore- 

 mentioned obtuse angle (fig. 1). The sulcus, very deep at this place, 

 proceeds at first perpendicularly upwards, but later on bends in a 

 somewhat caudal direction. As in Cyprinus, according to Sheldon's 

 description, the groove then divides. The two grooves then formed 

 run along the whole dorso-lateral side of the hemispheres. Tiiey 

 constitute the boundary between the lateral part of the fore-brain, 

 the palaeopallium (tuberculum laterale and tuberculum posterius), 



15* 



