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any unpaired part, as the azygos vein.
azygos vein a vein beginning in the abdomen as a continuation of the ascending lumbar vein; it and its tributaries serve as vessels for the return of blood from the thorax to the superior vena cava. The azygos vein also serves as a connecting link, through the ascending lumbar vein, between the venae cavae returning blood from above and below the heart. See anatomic Table of Veins in the Appendices.
Etymology: Gk, a + zygon, not yoke
occurring as a single entity or part, such as any unpaired anatomical structure; not part of a pair. Also azygos. -azygos [az′əgos′] , n.
azygousOccurring singly rather than in pairs. From the Greek azugos , unyoked.