Herrick, Brain of Certain Reptiles. 89 



emphasize to the utmost the functional homologies believed to 

 exist. 



Back of the callosum the roof of the aula is a thin tela 

 which is plexiform and gives rise at its lateral portions to the 

 preplexus, which enters the lateral ventricles a short distance. 

 Lying some distance caudad is the hippocampal commisure. 

 This does not differ in any morphological respect from the cor- 

 responding body in mammals. The statement that it is pecu- 

 liar in being situate beneath a plexus, i. e. that it perforates the 

 ventricle instead of lying in the dorsal wall has been very care- 

 fully investigated in many families of reptiles and in birds. It 

 is an error, or rather a misinterpretation. Above the commis- 

 sure of Fig. 5, a part of the plexus may be seen but it is a irt- 

 roflexed diverticle of the plexiform roof in front of it. In a 

 section immediately following, the commissure lies plainly in 

 the roof without connection with the plexus. Fig. 6. reveals 

 the interesting fact that the fornix fibres and those of the com- 

 missure pass to the caudal cortex, i. e. to the exact locus which 

 in the March number was identified with the hippocampus. 



We differ from Edinger only in that he seems to include 

 the whole mesal and dorsal region with our occipital lobe as hip- 

 pocampus. This question, however, we discuss in full else- 

 where. 



TJie callosum. Dr. Meyer ' regards the indentification of 

 the callosum in lower vertebrates as unwarranted. He says : 

 " In ungulates it is easy to see how the callosum stretches be- 

 tween the outer acuate gyre and the septum pellucidum or for- 

 nix fibres of the two sides in the form of a secondary bridge — a 

 completely discrete organ. This locus corresponds to the 

 groove which forms the mesal limit of the mantle — and such a 

 structure is [in reptiles] entirely lacking." To this it must be 

 said that embryology shows that the callosum develops within 

 the lamina and never normally lies free upon the surface. The 

 indusium, which is carefully described by Mr. Fish in this num- 

 ber, is the remnant of the supracallosal cortex which has be- 



M. c. p. 77 and Ii8. 



