from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A membranous sac that develops from the posterior part of the digestive tract in the embryos of mammals, birds, and reptiles. It is important in the formation of the umbilical cord and placenta in mammals.

from The Century Dictionary.

  • noun A fetal appendage of most vertebrates, developing as a sac or diverticulum from the posterior portion of the intestinal cavity.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Anat.) A membranous appendage of the embryos of mammals, birds, and reptiles, -- in mammals serving to connect the fetus with the parent; the urinary vesicle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun anatomy A sac, having a number of functions, that develops in the alimentary canal of the embryos of mammals, birds and reptiles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun the vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals)


from The American Heritage® Dictionary of the English Language, 4th Edition

[New Latin allāntois, from allāntoīdes, from Greek allāntoeidēs, sausage-shaped : allās, allānt-, sausage + -oeidēs, -oid.]



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  • Reesetee, did you know this name? I didn't. (I thought it was just "membrane" or something... duh...)

    It also sounds much prettier than it probably is.

    August 28, 2008

  • No, I didn't--or if I did, I've forgotten. But I think I have just the list for it.... :-)

    August 28, 2008

  • JM refused another allantois roll as he is really trying to give up.

    January 9, 2010