<prompt> Azygos vein -Formed by arch of aortaOpens into inferior vena cavaArches the groove of the left lungAscends through the aortic opening in the diaphragm  <response>: Azygos vein is formed bySubcostal veinsAscending lumbar veinsLumbar Azygos veinsIt crosses the diaphragm on the right side, by piercing the right crus or the aortic opening.At the level of T4 vertebra, it arches over the hilum of right lung.It opens into the superior vena cava. 