Any of the tubular branching vessels that carry blood from the capillaries toward the heart.
hog:0001250
hog:0000014 extraembryonic vitelline veinhog:0000015 extraembryonic umbilical veinhog:0000642 hepatic portal veinhog:0001133 pulmonary veinhog:0001194 posterior vena cavahog:0001195 anterior vena cavahog:0001197 cardinal veinhog:0001216 venous system endothelium
BFO:0000050 part of
hog:0000277
tao:0000082