Vein retroperitoneal and runs to the right and roughly parallel to the abdominal aorta along the spine. Large veins feed into these two veins, and smaller veins into these. Together this forms the venous system. Whilst the main veins hold a relatively constant position, the position of veins person to person can display quite a lot of variation. The pulmonary veins carry relatively oxygenated blood from the lungs to the heart. The superior and inferior venae cavae carry relatively deoxygenated blood from the upper and lower systemic circulations, respectively. The portal venous system is a series of veins or venules that
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.".