158 Journal of Comparative Neurology. 



commissure, that of a callosum, involves the general problems 

 just mentioned. The recognition of this as a callosum, it is 

 thought is open to serious objections. It would not be expected 

 that a commissure which in Mammalia is very largely, at least, 

 a cortex commissure, would be present in so well developed a 

 condition in forms in which no true cortex exists. This sug- 

 gests, of course, the question of how far ectocinereal areas 

 may be represented by non-migrated entocinerea. The re- 

 gions to which these fibers are distributed have been regarded 

 as an incipient cortex, it is true, but they are also considered as 

 representing the hippocamp, and the question of the homody- 

 namy of callosum and fornicommissure arises. Far more ser- 

 ious than objections such as the above seems the morphologic 

 one suggested by the relation of this bundle to the portas. 

 The fibers collect from the mesal wall, pass ventrad, caudad of 

 the porta and cross in the terma. In no way does it appear 

 possible to homologize such a bundle with one whose fibers 

 arise in the dorsal or mesal walls of the hemicerebrums and 

 cross in the terma cepJialad of the portas. This peculiar rela- 

 tion in Amphibia is commented on by Osborn as was noted. 

 He evidently saw in it nothing to invalidate the homology of 

 the tract to the callosum. The objection however seems to the 

 writer to be a vital one. 



Fish ('95) contends at some length and forcibly for the ho- 

 mology of the dorsal commissure with the callosum of mam- 

 mals, or callosum-fornix as he believes, and presents as forming 

 a series illustrating the transition from the condition in urodeles 

 to that of reptiles and birds, mesal views of the region of the 

 terma in Desviognathus, CryptobrancJms, frog, turtle, and bird. 

 I cannot consider these forms as entirely comparable in this re- 

 spect ; the relations at the meson seem to me to be misleading. 

 The difficulty lies riot in the relations here but in the distribu- 

 tion of the fibers as regards the portas. In Amphibia (frog 

 included) the fibers pass dorsad to the mesal walls caudad of the 

 portas as already stated, while in reptiles they pass ccpJialad of 

 of the portas. It is evident that however far cephalad and dor- 

 sad the terma might be bent, the relations in Amphibia could 



