THE DEVELOPMENT OF THE VASCULAR SYSTEM 



221 



FIG. 199. Surface view of area vasculosa of a rabbit embryo of 1 1 days, van Beneden and Julin. 

 The vessel around the border is the sinus terminalis; the two large vessels above the embryo are 



the vitelline (omphalomesenteric) veins ; the two large vessels converging below the 



embryo are the vitelline (omphalomesenteric) arteries. 



Chorionic villi 



FIG. 200. Human embryo of 3.2 mm. His. The arrows indicate the direction 



of the blood current. 



