omphalosite

[ŏmfə-lə-sīt′, ŏm-fălə-]
n.
  1. The underdeveloped member of unequal monochorionic twins that derives its blood supply from the placenta of the autosite and is not capable of independent existence or separation from the placenta.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

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