arises from the merger of the right ascending lumbar vein with the right subcostal vein and often a communication with the inferior vena cava; ascends through the aortic hiatus of the diaphragm or its right crus; it runs along the right side of the thoracic vertebral bodies in the posterior mediastinum, and terminates by arching anteriorly over the root of the right lung to enter the posterior aspect of the superior vena cava. Syn: vena azygos [NA], azygos(2), vena azygos major.