a vessel through which blood passes from various organs or parts back to the heart, in the systemic circulation carrying blood that has given up most of its oxygen. Veins, like arteries, have three coats: an inner coat (tunica intima
), middle coat (tunica media
), and outer coat (tunica externa
); however, in veins these are less thick and collapse when the vessel is cut. Many veins, especially superficial ones, have valves formed of reduplication of their lining membrane. See Appendix 2-6 and see also Plates.
afferent v's veins that carry blood to an organ.
allantoic v's paired vessels that accompany the allantois, growing out from the primitive hindgut and entering the body stalk of the early embryo.
cardinal v's embryonic vessels that include the pre- and postcardinal veins and the ducts of Cuvier (common cardinal veins).
emissary vein one passing through a foramen of the skull and draining blood from a cerebral sinus into a vessel outside the skull. See anatomic Table of Veins in the Appendices.
postcardinal v's paired vessels in the early embryo that return blood from regions caudal to the heart.
precardinal v's paired venous trunks in the embryo cranial to the heart.
pulp v's vessels draining the venous sinuses of the spleen.
subcardinal v's paired vessels in the embryo, replacing the postcardinal veins and persisting to some degree as definitive vessels.
sublobular v's tributaries of the hepatic veins that receive the central veins of hepatic lobules.
supracardinal v's paired vessels in the embryo developing later than the subcardinal veins and persisting chiefly as the lower segment of the inferior vena cava.
thebesian v's smallest cardiac veins; see anatomic Table of Veins in the Appendices.
trabecular v's vessels coursing in splenic trabeculae, formed by tributary pulp veins.
vitelline v's veins that return the blood from the yolk sac to the primitive heart of the early embryo.