The anterior cardinal veins (precardinal 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.Human embryo of about fourteen days, with yolk sac. The anterior cardinal veins (precardinal 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. This article incorporates text in the public domain from page 520 of the 20th edition of Gray's Anatomy (1918)