Meckel's diverticulum

n.
  1. A diverticulum formed from the remains of an unobliterated yolk stalk, located on the ileum a short distance above the cecum and sometimes attached to the umbilicus.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.