Herkick, Morphology of Brain of Bony Fishes. 319 



The basal portion of the cerebrum consists of two lobes 

 which are considered to be the homologues of the axial lobes 

 of the Sauropsida. They are connected below by a mem- 

 brane which may be considered as a continuation of the 

 pallium, and are otherwise quite distinct from each other 

 except in the region of the anterior commissure. Each lobe 

 is oblong, about as high as it is wide, and about one-fourth 

 longer than it is wide and is attached to the diencephalon by 

 by its caudo-ventral angle. The dorsal (ventricular) surface 

 of these lobes is marked with an intricate system of 

 fissures and convolutions, which, however, seem not to be 

 very constant, even in the same species. There are four 

 fissures which are alrpost always obvious externally, though 

 somewhat variable in size and position. They are found in 

 other fishes quite generally and are here named in accordance 

 with the nomenclature of Prof C. L. Herrick as given else- 

 where in this number. The most strongly-marked and con- 

 stant fissure is the rhinalic fissure, or sinus rhinalis, on the 

 ventral surface. This marks the line of union between the 

 pallium and the basal lobe. This line passes from the lateral 

 edge of the olfactory crus at its point of exit caudo-laterad to 

 about the centre of the hemisphere; it then turns at an obtuse 

 angle, passing caudo-mesad to the lateral edge of the optic 

 nerve at its exit. The two rhinalic fissures thus define a 

 broad pentagonal depression in which lies the decussation of 

 the optic nerves, and dorsad of which, in the substance of the 

 basal lobes, lie the olfactory crura, and farther caudad, the 

 fibres of the crura cerebri. It is present in other teleostean 

 brains, though not usually as strongly marked as in the 

 Siluridas, and may be called the rhinalic aspect. On the 

 dorsal surface the most prominent fissure is the frontal fissure, 

 which arises on the fronto-median aspect of the cerebrum 

 from about the middle of the olfactory crus at its exit and 

 passes caudo-laterad in an irregular line almost to the 

 diagonally opposite angle of the basal lobe. Here it meets 

 the occipital fis§vire, which arises on the }atero-caudal aspect 



