Hekkick, MorpJiology oj Brain of Bony PisJics. 229 



The glomerules are chiefly massed ectad. The nervous ele- 

 ment are small and inconspicuous. 



The cerebrum overlaps the olfactory dorsally, and the 

 lateral ventricle descends to the level of the olfactory 

 mesally, but is separated from the crus by a small spur of 

 the cerebrum. Gradually the olfactory lobe narrow^s into the 

 crus, and is embraced by the cerebrum laterad as well as 

 mesad. The cerebrum is completely enveloped by the pal- 

 lium and ventricle except near the attachment of the crus 

 and thence some distance laterad to beyond the rhinalis 

 fissure or sinus of the ventral surface. There is a dense col- 

 lection of fusiform cells mesad of the crus on either side of 

 the ventricle. The latter represents a forw^ard protrusion 

 of the third ventricle rather than the aula. The centre of the 

 crus is occupied by a tract, while others gather about the 

 rhinalis sinus. The first mentioned tract can be easily traced 

 as far caudad as to the anterior (or interlobular) commissure, 

 where it turns mesad, decussates with its fellow and con- 

 tinues in nearly the same relative position toward the thala- 

 mus upon the opposite side. Other fibres derived from the 

 crus follow the rhinalis sinus and constitute a distinct radix 

 lateralis which can be traced to a point opposite to the com- 

 missure, where they seem to enter the hippocampal lobe, to 

 be described beyond, although part may pass directly mes^d 

 to the commissure. 



In Hyodon (the moon-eye) the olfactory lobes are un- 

 usually large and lie some distance from the cerebrum, while 

 the lateral ventricles extend well out upon the dorsal surface 

 of the crura cephalad of the cerebrum. The crura are accord- 

 ingly flattened, and enter the meso-cephalic angle of the 

 cerebral lobes in two partially distinct radices. The radix 

 lateralis is smaller, and spreads out about the sinus rhinalis 

 in the form of a series of small bundles. The radix mesalis 

 is a large bundle, which retains its position in the ventro- 

 mesal angle of the cerebrum as far caudad as the anterior 

 commissure. 



