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

  • n. A membranous sac that develops from the posterior part of the alimentary canal in the embryos of mammals, birds, and reptiles. It is important in the formation of the umbilical cord and placenta in mammals. Also called allantoid.

from Wiktionary, Creative Commons Attribution/Share-Alike License

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

from the GNU version of the Collaborative International Dictionary of English

  • n. 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 The Century Dictionary and Cyclopedia

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

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

  • n. 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, from allantoīdes, from Greek allantoeidēs, sausage-shaped : allas, allant-, sausage + -oeidēs, -oid.



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

    January 9, 2010

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

    August 28, 2008

  • 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