Medical Definition of subcostal vein
: either of two veins:a: one that arises on the right side of the anterior abdominal wall, follows a course along the lower margin of the twelfth rib, and joins in the formation of the azygos vein—called also right subcostal veinb: one on the left side of the body that usually empties into the hemiazygos vein—called also left subcostal vein
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