Cardinal Veins

CARDINAL VENAE (cardinal veins), the main venous trunks that collect blood from the periphery of the body in lower vertebrates, as well as in the early stages of embryonic life in higher vertebrates, including humans. The cardinal veins are paired, running along the length of the body symmetrically with respect to the midline, and are divided into anterior or upper cardinal veins, otherwise known as the jugular veins (v. cardinales anteriores, s. jugulares), and lower or posterior cardinal veins (v. cardinales posteriores) (see figure). The anterior and posterior veins of each side converge and flow into the transversely running Cuvierian duct (ductus Cuvieri), which empties into the venous sinus of the heart. The anterior cardinal veins collect blood from the head, the posterior from the body walls via segmental veins, as well as venous blood from the portal system of the kidneys. Such a schematic arrangement is present in fishes and in the initial stages of development of the venous system in all other vertebrates. Beginning with amphibians, the cardinal veins gradually lose their significance and become part of the superior vena cava.

This is related to the emergence of the inferior vena cava, which in amphibians takes over the venous blood of the kidneys, leaving only the segmental veins to the posterior cardinal veins (in tailless amphibians the posterior cardinal veins even disappear completely). In reptiles, they are insignificant vessels emptying into the superior vena quais (vertebral veins, v. vertebrales); in mammals and humans, they become asymmetrical: the right empties into the superior vena cava and is known as the azygos vein (v. azygos); the left connects by a transverse anastomosis with the azygos vein, loses its connection with the superior vena cava system, and forms the hemiazygos vein (v. hemiazygos). The anterior cardinal veins, or jugular veins, together with the developed subclavian veins, become branches of the superior vena quais; in mammals, after the disappearance of the left superior vena cava, the left jugular vein empties into the brachiocephalic vein. Such is approximately the course of development of the cardinal veins in human ontogeny (see Circulatory system, development).