n :  any of a system of three veins which drain the thoracic wall and much of the abdominal wall and which form a collateral circulation when either the inferior or superior vena cava is obstructed : esp  :  a vein that receives blood from the right half of the thoracic and abdominal walls, ascends along the right side of the vertebral column, and empties into the superior vena cava - compare ACCESSORY HEMIAZYGOS VEIN HEMIAZYGOS VEIN  .
 
 
 
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