200 Vertebrate Embryology 



large veins on each side of the body (Fig. 66, 

 y, C) ; these are the anterior and posterior 

 cardinal veins ; the anterior cardinals, as the 

 name would suggest, bringing the blood back 



I.CAE. 



FIG. 65. DIAGRAM OF THE ARTERIAL CIRCULA- 

 TION ON THE THIRD DAY. (After Foster and Bal- 

 four.) 



1, 2, 3, the first three pairs of aortic arches. A, the vessel 

 formed by the junction of the three pairs of arches. A.O., 

 dorsal aorta, formed by the junction of the two branches, A , 

 it quickly divides into two branches, which pass down one on 

 each side of the notochord. Of. A ., vitelline artery. E.CA ., 

 I.CA,, external and internal carotid arteries 



to the heart from head region, and the pos- 

 terior cardinals bringing it back from the 

 posterior end of the body. The anterior and 

 posterior cardinal veins of each side unite to 

 form a common vein that empties, at right 

 angles, into the sinus venosus (Figs. 66, dc, 



