azygos vein

Unpaired abdominal & thoracic vein arising from the junction of the right ascending lumbar vein with the right subcostal vein in the abdomen & often a communication with the inferior vena cava. It ascends through the aortic hiatus of the diaphragm or its right crus & runs along the right side of the thoracic vertebral bodies in the posterior mediastinum. It terminates after arching anteriorly over the root of the right lung, emptying into the posterior aspect of the superior vena cava.

References

Stedman's Medical Dictionary 26th ed, Williams & Wilkins, Baltimore, 1995