Hi
Q.Azygos V. Vein connecting I.V.C. with S.V.C., so it forms collateral venous circulation in case of S.V.C. or I.V.C obstruction. It drains most of thoracic wall. *Origin: Variable, most commonly from I.V.C. back opposite L2. *Course & termination: Enters thorax through diaphragm aortic opening & ascends in post. mediastinum till disc between T4/T5, then in sup. mediastinum where it arches forwards just above Rt. lung root ending in middle of S.V.C. back, opposite Rt. 2nd costal cartilage.