i68 JoirRNAL OF Comparative Neurology. 



homologize the pallium with the plexus-bearing projection 

 from the posterior and mesal margin of the mantle. Since 

 the plexus in this case occupies the vertex, instead of pro- 

 jecting from the caudal region, all structures morphologically 

 cephalad to the plexus must be sought still further cephalad 

 or ventrad. Using this clue, and observing that the cerebral 

 cortex folds ventrad over the olfactory structure, we think 

 we find a homologue of the calloso-hippocampal commissure 

 connecting the two halves of the cerebrum cephalad to the 

 openings of the olfactory crura into the common ventricle, 

 and lying just entad to the membranous lamina terminalis 

 (Fig. 2, Plate XIII). The bundle is very small and seems 

 to contain a few fibres from the olfactory regions, as well as 

 others from the cephalic portions of the cerebrum. No in 

 dication of the callosum was seen in Scaphirhynchus. (') 



Regarding the anterior comniissurc there can scarcely be 

 a mistake, as it is a very strong though disperse band of 

 fibres lying in the ventral fused portion of the cerebrum 

 cephalad to the chiasm and cephalo-dorsad to the supra- 

 chiasmic fossa of the third ventricle, and thus well in front 

 of the crura cerebri. This commissure has been generally 

 recognized by later writers, while the callosum seems to 

 have been overlooked. See above for description of the an- 

 terior commissure (C. interlobularis) by Goronowitsch. 



Tracts from the Proscjiccphalon. — We are unable to agree 

 with Goronowitsch in his remarks upon the thalamus and the 

 tracts connecting it with the cerebrum. So far from the 

 pedunculi being absent in ganoids, the gars at least have the 

 tracts as highly developed as could be expected where 

 the gray matter is in so relatively small amount. 



The motor tracts which accumulate along the lateral 

 aspects of the prosencephalon collect, as already described, 

 to form curved tracts dorsad to the basal lobe (homologous 



I Holt, 1. c, mentions what he calls an olfactory commissure in the herring, which 

 may prove to be the same structure as that above described. He does not appear 

 to have thought it possible to homologize it with the callosum. 



