Io6 UNIVERSITY OF COLORADO STUDIES 



prosencephalic tract. The two bundles soon become indistinguishable 

 as separate tracts. Probably a part of this tract turns backward, but 

 this could not be very definitely determined. This part is commonly 

 present in Amphibia. Medullated fibers enter the commissure from 

 the basal prosencephalic tract from before and from behind. They 

 may possibly be decussating fibers. 



''Corpus callosum.^^ — The tract designated by this name has been 

 fully described elsewhere. The term corpus callosum is probably not 

 a proper one for this structure, as it more likely represents a hippo- 

 campal commissure. However, it is simpler, and less likely to lead to 

 confusion, to use the old term till we have sufficient knowledge of the 

 structure to apply a fitting new one. In Pldhedon the fibers of this 

 tract are chiefly non-meduUated. 



Supracommissure. — In the region of the habenulae, in sagittal sections, 

 three separate bundles can be distinguished crossing the median hne 

 (Fig. lo). The most anterior of the three occupies a position at the 

 very forward part of the habenulae. It is by far the smallest of the 

 bundles. It could not be traced for any considerable distance. It is 

 probably composed of commissural fibers between the habenulae of 

 the two sides. It may possibly represent the commissura habenularis 

 (Edinger, '99, p. 126 et seq.). In accounts of other Urodelan brains, 

 so far as I have been able to learn, only two bundles arc described at 

 the median line. The other two bundles correspond to the supracom- 

 missure as described for other Urodcla. These two bundles on either 

 side of the median line, soon unite, at least apparently, into one bundle. 

 Probably, however, the two parts really remain distinct. The bundle 

 passes in a ventral direction on either side, and soon, from its posterior 

 part fibers begin to be given off backward; finally a quite distinct 

 bundle passes backward into the diencephalon. The remainder of the 

 bundle, probably representing the middle part at the median Hne passes 

 forward and outward into the hemispheres. \^ 



Meynerfs bundle. — The bundle generally described under this name 

 in Amphibia is the tractus habenulo-peduncularis described by Edinger. 

 ('99, pp. 131, 132 and 306). In Plethedon, as in other Urodela, it is a 

 compact bundle of non-medullated fibers. It arises from the habenulae, 



