inferior vena cava, the large vein that returns deoxygenated blood to the heart from parts of the body below the diaphragm. It is formed by the junction of the two common iliac veins to the right of the fifth lumbar vertebra and ascends along the vertebral column, pierces the diaphragm, and opens into the right atrium of the heart. As it passes through the diaphragm, it receives a covering of serous pericardium. The inferior vena cava contains a semilunar valve that is rudimentary in the adult but very large and important in the fetus. The vessel receives blood from the two common iliacs, the lumbar veins, and the testicular veins. Compare superior vena cava.
