aes 
Os ws ane ‘ 
2 > ~ 
S SS = 
Fig. 135. — Circulation in the embryo and yolk-sac after 74 hours’ incuba- 
tion. Stage of about 27s from below. Injected. (After Popoff.) 
1, Marginal vein. 2r, 21, Right and left anterior vitelline veins sur- 
rounding the mesoderm-free area. 3, Anterior intestinal portal. 4, In- 
termediate veins connecting with the venous network centrally. 5, Right 
dorsal aorta. 6, Posterior vitelline vein in process of formation. 7, Vitel- 
line arteries. 
Note that the right anterior vitelline vein (2 r) is much atrophied. 
