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Medical Definition of Allantoic diverticulum
1. An endoderm-lined outpouching of the hindgut (in humans, the yolk sac of a very young embryo) representing the primordium of the allantois; in most amniotes, it grows into the extraembryonic celom; in humans, the distal part of the allantoic lumen is rudimentary, not extending beyond the body stalk. Synonym: allantoenteric diverticulum. (05 Mar 2000)