Johnston, Forehram Vesicle m Vertebrates. 



487 



c. Roof of the Diencephalon. — In the roof of the interhrain the 

 development of the vehim transversum, dorsal sac, epiphysis and 

 paraphysis has been well described (Minot, Sterzi) so that I have 



Fig. 22. Sqiialus ac, stage M, two sagittal sections near the median plane. 

 X 25. In addition to the features shown in earlier figures, the optic chiasma, 

 anterior, posterior and habenular commissures are seen. 



nothing new to add. I wish only to note that a careful considera- 

 tion of Dr. Neal's sections and of the models made from them leads 

 me to believe that the segmental position of the optic vesicle is 



