SEPTUM, HIPPOCAMPUS, PALLIAL COMMISSURES 379 



2 show that an oblique ridge runs upward and forward from 

 the lamina supraneuroporica into the medial wall of the hemi- 

 sphere. In the brain of the adult turtle (fig. 9) this ridge is 

 occupied by the hippocampal commissure. The recessus neuro- 

 poricus is evident in the adult upon the inner surface of the 

 transverse ridge which is occupied by the anterior and the hippo- 

 campal commissures (fig. 9). In Chelydra serpentina the two 

 commissures form a ridge projecting farther into the ventricle 

 and the neuroporic recess is nearly obliterated. 



Elliot Smith's ('03) figures and clear description of Hydro- 

 saurus show that a deep recess (his recessus inferior) exists 

 between the anterior and hippocampal commissures in this Mon- 

 itor. Professor Smith points out that this recess corresponds to 

 the recessus triangularis of Sehwalbe in mammalian brains. 



In his work on the pineal region of Sphenodon, Dendy ('10) 

 shows in text-figure 1 a median section which agrees very well 

 with my latest stage of Chelydra serpentina. In agreement with 

 Burckhardt's earlier work he applies the name lamina supraneu- 

 roporica to the tela chorioidea, while to the thick lamina to 

 which the tela is attached he gives the name cerebral hemisphere. 

 Although of course the hemisphere can not really be seen in a 

 median section, the application of this name by Dendy serves 

 to show that the structure which the writer has called lamina 

 supraneuroporica is a nervous bridge connecting the two hemi- 

 spheres in Sphenodon as in the turtles. 



The same conformation in the region of the anterior and hip- 

 pocampal commissures in a late embryo of Anguis fragilis is 

 shown in v. Kupffer's figure 248 in his article in Hertwig's 

 Handbuch. 



From his own observations on turtles and from the comparison 

 of the results of other workers, the writer is convinced that the 

 neuroporic recess in reptiles is located immediately above the 

 anterior commissure and that the hippocampal commissure 

 crosses the middle line in a lamina supraneuroporica which serves 

 as a massive bridge between the medial walls of the two hemi- 

 spheres. In these relations the reptiles agree strictly with the 

 selachians. 



