Cardinal veins

The superior cardinal veins (or precardinal veins) come from the cranial part of the embryonic body, and the inferior cardinal veins (or postcardinal veins) come from the caudal part. On each side, they join together to form the common cardinal veins and then end in the right and left sinus horn. As the venous supply to the heart shifts towards the right, the left horn of the sinus degenerates. Only its proximal part remains, as the coronary sinus. The left and right precardinal veins form anastomoses, giving rise to the left brachiocephalic vein. With increasing size of the brain, three venous plexuses (anterior, middle, and posterior plexus) are formed on each side. These flow through the corresponding primary head vein into the respective precardinal vein (later internal jugular vein). Blood flows via the brachiocephalic vein from the left side into the right precardinal vein, which becomes the superior vena cava.