Either of two veins in the mammalian embryo and various adult lower vertebrate forms located in the thoracic and abdominal regions dorsolateral to and on either side of the descending aorta and giving rise to the azygos and hemiazygos veins and a part of the inferior vena cava[MW]. These veins drain the body wall via the segmental intercostal veins, thus taking over the function of the posterior cardinals[ISBN] [ https://www.worldcat.org/search?q=bn%3A0443065837 http://www.merriam-webster.com/medical/supracardinal%20vein ]