Herrick, Brain of Certain Reptiles. 91 



sure. Its fibres pass to the ventricular aspect of the Hmbic cor- 

 tex, as in other reptiles. 



The course of the commissures of the mesal cortex can be 

 well traced in Cistndo. The hippocampal fibres pursue the us- 

 ual course but they are accompanied by cortex for nearly all 

 their extent and the fimbria thus becomes small and incomplete. 

 The fibres pass to the mesal side of the callosal tract without de- 

 cussation and there turn abruptly ventrad and caudad. Such 

 commissural fibres as there are are clesely associated with the 

 callosum immediately dorsad of the precommissure. The callo- 

 sum itself, after crossing in a large compact bundle extends for 

 some distance on either side in the "septum" directly cephalo- 

 dorsad and afterwards divides into scattered fascicles which pass 

 to the ventricular aspect of the intraventricular wall of the pal- 

 lium. In perpendicular sections it can be seen that these fibres 

 include the whole extent of the fronto-median lobe and continue 

 upon the dorsal surface at least as far as this lobe extends. 



It might be questioned how far we are authorized to go, in 

 following these commissures in their fluctuations with the fa- 

 miliar names 'of mammalian anatomy, but, for our part, we 

 think our nomenclature should express our morphological point 

 of view as far as consistent with clearness. 



The explanation of the modifications here exhibited is 

 found in the relatively great distension of the ventricles in tur- 

 tles, which elevates the median wall disproportionately. The 

 terma drops very abruptly and the course of all the commissures 

 of the median wall below the arcuate fissure is lengthened. Thus 

 the perpendicular length of the fronto-median cortex in a snake 

 might form less than one third of the entire height of the cere- 

 brum, while in a corresponding region of the turtle the fronto- 

 median cortex is two thirds the entire height. 



In Amphibia we are inclined to differ from Osborn in his 

 identification of the callosum. He does not identify the fornix 

 and hippocampal commissure, but classes all fibres connecting 

 the mantle and crossing dorsad of the precommissure as callo- 

 sum. The position and course of these fibres makes the identi- 

 fication of these fibres unsatisfactory for, as he indicates, the po- 



