n6 Journal of Comparative Neurology 



Fig. 2g. Section of the same farther ventrad. Shows the membrane of 

 dorsal sac stretching across between the diacoelian walls. It still contains a few 

 cells from the paraphysis. 



Fig. jo. A sagittal section near the meson through the brain of an embryo. 

 Shows the relations of the structures in the roof of the diaccele from the mesal 

 aspect. It also shows the formation of the plexus of the aula from the mem- 

 brane cephalad of the paraphysis. 



Fig. 31. Transection of the diencephal through the posterior part of the 

 diencephal, slightly diagramatic. Shows the relations of the caudal division of 

 the supracommissure and the various nidi of that region. 



Fig. 32. Sagittal section through the hypophysis of an embryo Chelydra. 

 Shows the structure of the hypophysis, and its relations to the infundibulum, 

 pia and dura. 



Fig. 33. View of the regions of the aula and porta from the caudal aspect 

 in the brain of Chelone tnidas. Made by transecting the brain through the cau- 

 dal part of the portse. Shows the position of the crista and the callosum. 



Fig. 34. Frontal section through the stem of the crista. Shows its struc- 

 ture and relations to the pia and hemi-cerebrums. 



Fig. 35. Frontal section through the main body of the crista. Shows its 

 general structure, the peculiar splitting of the pia with the intrusion of the nerv- 

 ous substance between the laminae of the pia. 



Fig. 36. Diagram of the relations of some of the principal commissural 

 and decussating tracts and the large nidi of the brain, seen from the mesal as- 

 pect as if the brain were transparent. Only position of tracts is shown, relative 

 size being disregarded. 



