VI .1 



THE VASCULAR AREA, 



Fio. 36. 

 AA. 



Ill 



S.CaV. 



Diagram op the Circulation of the Yolk-Sack at the end 

 OP THE Third Day of Incubation. 



B. heart. A A. the second, third and fourth aortic arches ; the 

 first has become obliterated in its median portion, but is 

 continued at its proximal end as the external carotid, and at 

 its distal end as the internal carotid. AO. dorsal aorta. 

 L. Of. A. left vitelline artery. B. Of. A. right viteUine 

 artery. ;S'. T. sinus terminahs. L. Of. left vitelline vein. 

 R. Of. right vitelline vein. S. V. sinus venosus. D. G. 

 ductus Cuvieri. 8. Ca. V. superior cardinal or jugular vein. 

 V. Ca. inferior cardinal vein. The veins are marked in 



