154 Journal of Comparative Neurology., 



fered in appearance from the cells of the surrounding cinerea, 

 nor was the more dorsal layer differentiated from the rest as a 

 layer of endymal cells. Mrs. Gage found this condition of a 

 separation by cinerea to persist quite late in Dieniyctyhts, and it 

 was present even in some young adults. It is possible that the 

 same may be true in Nectiints, which would account for the re- 

 sults of Herrick and Fish, if the individuals examined by them 

 were young. The brain upon which Osborn's figures and con- 

 clusions were based must have been abnormal in the relation of 

 these two commissures. 



The presence of cells separating the two commissures is 

 seen from the larval conditions to be insignificant, but the recog- 

 nition of these cells as endymal, as has been done by Herrick 

 would be vital. In the distribution of the fibers of the dorsal 

 bundle in Ncctunis, the observations of Osborn and Herrick'are 

 in the main here confirmed. Whether or not this commissure 

 can be regarded as the representative of the mammalian callosum 

 as first prominently advocated by Osborn seems doubtful. In 

 view of the differences which exist in the interpretation of this 

 bundle in Amphibia, and the importance of the question, a brief 

 review here of the history may be warranted. 



Although a callosum had been ascribed to Amphibia pre- 

 viously, Reissner (1864) was the first to accurately figure in 

 Biifo the bundle in question, which he regarded as a callosum. 

 Following him, Stieda ('70) rejected the homology of callosum 

 and regarded it as the pars olfactoria of the precommissure. 

 This latter view was then generally accepted by the investigators 

 who followed him, — Goette, Bellonci ('82 and '83), Rabl-Riick- 

 hard ('83) and Osborn in his papers of 1883-4, until the appear- 

 ance in 1886 of Osborn's paper on the origin of the callosum, 

 in which occurs the statement of the peculiar relation of the 

 dorsal bundle in Ncctunis to the precommissure, before men- 

 tioned, and also the following statement of the relations of this 

 bundle: — " An important character is that the cerebral commis- 

 sures in the Amphibia lie behind the foramina of Monro." 

 Again : — "The upper bundle [his callosum] ascends in the me- 

 dian hemisphaeral walls, forming the posterior boundary of the 



