tunica adventitia

[ăd′vĕn-tĭshē-ə]
n.
  1. The outermost fibrous coat of a vessel or of an organ that is derived from the surrounding connective tissue.membrana adventitia
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.