Ventrolateral view, right side

Note that the azygos vein is dorsal to the right lung - therefore, it should not be confused with the caudal vena cava that is found medial to the right lung.  The azygos vein drains the blood from the dorsal (posterior) thoracic wall into the cranial (superior) vena cava.  It also can serve as an alternate path for the return of blood from caudal (inferior) to the diaphragm if the caudal (inferior) vena cava were to be blocked.