Azygous vein drains into

course and termination of azygos vein - The azygos vein enters the thorax by passing through the aoic opening of the diaphragm, The azygos vein then ascends up to fouh thoracic veebra where it arches forwards over the root of the right lung and ends by joining the posterior aspect of the superior vena cava just before it pierces the pericardium Ref : B D Chaurasia's Human Anatomy, seventh edition, volume 1 , pg. no. 233