BRAIN OF ONE OF THE SALAMANDERS lOI 



The principal paper presenting this view is by Osborne.^ He considers 

 that there is no doubt that this is a true callosum, and bases his judgment 

 upon a study of Necturus and Proteus. In these forms he found the 

 dorsal bundle completely separated from the ventral and a fold of the 

 plexus passing between them. Herrick,^ moreover, recognized the cells 

 here, a clearly dej&ned, continuous film of epithelium separating them. 

 He considers these two points of great value in determining the true 

 relations of the bundle. The chief objection to its being called a callo- 

 sum had hitherto been, that while the callosum forms the roof of the 

 ventricle, this bundle forms the floor. The conditions observed by 

 Osborne and Herrick are considered to mark the bundle as morpho- 

 logically belonging to the roof of the ventricle and not to the lamina 

 terminalis. 



Other observers consider the conditions observed in these cases not 

 normal, Kingsbury ('95) finds in larval forms of Necturus, that the 

 two bundles are separated by several layers of cells, none of which are 

 epithelial, and in twelve adult brains, he finds no separation by cells 

 at the median line. This agrees with the observations of Fish ('95) 

 and Mrs. Gage ('93) on Necturus and other forms. Fish does not 

 agree that the tract is dorsal. Nevertheless he considers that it is a 

 true callosum, and that a phylogenetic study clearly shows its homology. 

 He holds that though the tract is of ventral origin, a continuous growth of 

 the hemispheres would cause it to migrate upward and forward in the 

 lamina terminalis until it would come to occupy a position that would 

 approximate that of the callosum in higher vertebrates. To show the 

 actual migration of the bundle, he presents a series of drawings from 

 median sagittal sections from Desmognathus, Cryptohranchus frog, 

 turtle, and bird. If we consider only the relations at the median line, 

 he seems to make his point. But, as Kingsbury ('95) points out, he 

 ignores the question of the distribution of the fibers as regards the inter- 

 ventricular foramen. The mammalian callosum is in jront of the fora- 

 men and above the ventricle. The so-called callosum of Amphibia 

 is behind the foramen and below the ventricle. '*It is evident that how- 

 ever far cephalad and dorsad the terma [lamina terminalis] might be 



» KmcsBURY, 'ps, p. 154. ' Hid., p. 153. 



