Pulmonary vein drain into the pulmonary circulation in whole or in part, this is known as a total anomalous pulmonary venous connection (or drainage), or partial anomalous pulmonary connection, respectively. Pulmonary vein The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four "main pulmonary veins", two from each lung that drain into the left atrium of the heart. The pulmonary veins are part of the pulmonary circulation. Two main pulmonary veins emerge from each lung hilum, receiving blood from three or four bronchial veins apiece and draining into the
Tail vein Tail vein Tail vein or caudal vein is the largest vein in vertebrate animals' tail. It leads directly into the posterior cardinal vein in the posterior trunk in fishes. Mammal caudal vein (the middle caudal vein) leads to inferior vena cava. Caudal vein is one of the many places from which a laboratory worker can withdraw blood from a mouse specimen. The process does not require the death of the mouse, that is, assuming that not too much more than the established standard of "no more than two blood samples are taken per session and in any one 24-hour period.".