Kingsbury, Bi'ain of Ncdnnis. 153 



" In Menobranchus [Necturus] however, he [Osborn] 

 makes the significant discovery that the upper bundle is com- 

 pletely separated from the lower and crosses the ventricle inde- 

 pendently, so that a fold of the vascular plexus of the pia \sic\^, 

 which in this genus is greatly developed, passes through the in- 

 terspace. This statement of Osborn we had overlooked, but 

 upon theoretical grounds suspected that the dorsal commissure 

 would prove to belong to the roof and not to the floor of the 

 ventricle. We, therefore, had introduced the accompanying 

 drawing (Plate IX, Fig. 5) before noticing that Osborn's Fig. 

 14 is substantially identical. We have never found the dorsal 

 commissure so completely separated as represented by the latter, 

 but always in juxtaposition with the floor; it was therefore a 

 matter of congratulation to find a clearly defined continuous 

 film of epithelium separating it from the subjacent pre-commis- 

 sure. The series being continuous and faultless and doubly 

 stained with hematoxylin and fuchsin to differentiate epithelial 

 from nervous elements the evidence is conclusive. Knowing, 

 as we now do, that the plexus is but a diverticle of the roof we 

 recognize of necessity that the commissure is morphologically 

 dorsal." Thirdly, Fish (21) in connection with the homology 

 of this commissure in Amphibia with the callosum of mammals, 

 from the examination of a larval and adult Necturus, reports "a 

 non-separation of these commissures except by a simple cellular 

 layer." The results of my own observations differ entirely 

 from those of the investigators mentioned above. Twelve adult 

 brains were examined in this connection, and in no one of them 

 was there a separation at the meson, by cells, endymal or 

 otherwise, much less by an extension of the cavity and a fold 

 of plexus. The dorsal bundle rested immediately upon the 

 ventral, the precommissure. The dorsal bundle turns dorsad to 

 the mesal wall of the hemicerebrum while the ventral passes 

 directly laterad so that on each side of the meson cinerea be- 

 comes interpolated between them. In five larval forms exam- 

 ined the condition was precisely that found by Mrs. Gage in 

 larval Dieinyctylus ; in these the separation of the two commis- 

 sures is by three or four layers of cells which in no way dif- 



