Two pairs of veins in the embryo that carry blood from the head (anterior cardinal veins) and trunk (posterior cardinal veins); they unite to form the common cardinal vein, which drains into the sinus venosus of the heart.
In an embryo of up to 6 weeks’ gestation, any of the veins (the bilateral anterior and posterior) that are the original venous drainage system leading to the heart. Over the next few weeks, the right anterior cardinal vein gives rise to the major upper body veins (jugulars, brachiocephalics, subclavians, and superior vena cava); the far ends of the posterior cardinal veins give rise to the iliac systems; and the rest of the cardinal venous system is then replaced by the sub-cardinal and supra-cardinal veins.