246 THE DEVELOPMENT OF THE CHICK 
I'ia. 148. — Median sagittal section of an embryo of eight days. 
a. A., Aortic arch. All., Allantois. An., Anus. A. o. m., Om- 
phalomesenteric artery. B. F., Bursa Fabricii. b. P., Basilar plate. 
C. A., Anterior commissure. ec. C., Central canal. Ch. op., Optie 
chiasma. C. p., posterior Commissure. Cl, Cloaea. Cr., Crop. 
d. Ao., Dorsal aorta. D. Hyp., Duet of the hypophysis. Ep., Epi- 
physis. Fis. Eus., Fissura Eustachii. Hem., Surface of hemisphere 
barely touched by section. Hyp., Hypophysis. L. t., Lamina ter- 
minalis. mn. A. 8, neural arch of the eighth vertebra. Nas., Nasal 
