106 Journal of Comparative Neurology 



tremity where it is attached. A blood vessel is found in the 

 pia near its point of attachment. Following the sections ven- 

 trad we find that the blood vessel divides as the crista enlarges 

 and the pia also splits giving it a forked appearance in frontal 

 sections (Fig. 35). As this branching of the vessel and split- 

 ting of the pia occurs, the central portion of the wall between 

 the two laminae of the pia begins to thicken and as we proceed 

 ventrad we find it projecting into the interior of the structure as 

 a ridge cone shaped in transection. This ridge is of 

 neuroglia and its limiting endyma has the normal appearance of 

 that membrane, while at either side, opposite the attachment of 

 the pia the cells have the long shape with processes toward the 

 pia (Fig. 35). The base of the walls as 'shown in the figure is of 

 the normal neuroglia structure. Herrick (44, plate XV, Fig. 5) 

 figures a structure in this region in the brain of Menopoma and 

 applies to it the term callosum. Whether it contains fibers 

 or not I could ascertain. 



The presence of this structure in so many forms of verte- 

 brates argues some morphological importance for it. Work is 

 now in progress in the laboratories of Cornell University which it 

 is hoped will be able to throw the light of comparative study 

 upon this small but persistent structure. 



Callosum. — Since the announcement by Osborn of the 

 presence of the callosum and a probable fornix in Reptilia, the 

 subject has been carefully investigated by different workers and 

 the almost unanimous opinion is that both of these structures 

 are present. Of recent writers Meyer alone seems to doubt the 

 homology. It is generally accepted, that the commissural fibers 

 lying in the terma ventrad of the porta and connecting the mes- 

 al portions of the cerebral cortex, represent the callosum of 

 the higher vertebrates. The relation of the callosum and 

 precommissure varies considerably in Reptilia. In Clielydra, as 

 pointed out by Herrick (44), these bundles are brought into 

 juxtaposition and cross the meson as a single bundle. This 

 bundle extends laterad a short distance and then divides, the 

 ventral portion extending latero-cephalad as the true precom- 

 missure (Fig. 36). With the methods used I was unable to 



