During development of the veins, the first indication of a parietal system consists in the appearance of two short transverse veins, the ducts of Cuvier (or common cardinal veins), which open, one on either side, into the sinus venosus

Sinus venosus

The sinus venosus is a large quadrangular cavity which precedes the atrium on the venous side of the chordate heart. In humans, it exists distinctly only in the embryonic heart, where it is found between the two venae cavae...

. Each of these ducts receives an ascending and descending vein. The ascending veins return the blood from the parietes of the trunk and from the Wolffian bodies, and are called cardinal veins

Cardinal veins

The precardinal veins or anterior cardinal veins contribute to the formation of the internal jugular veins and together with the common cardinal vein form the superior vena cava. In an anastomosis by anterior cardinal veins, the left brachiocephalic vein is produced.-External links:*...

.