allantois

[ uh-lan-toh-is, -tois ]

/ əˈlæn toʊ ɪs, -tɔɪs /

noun Embryology, Zoology.

a vascular, extraembryonic membrane of birds, reptiles, and certain mammals that develops as a sac or diverticulum from the ventral wall of the hindgut.

Nearby words

Origin of allantois

1640–50; < New Latin < Greek allantoeidḗs, wrongly taken for plural and given a singular, on the model of words like hērōís (singular), hērōídes (plural)

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for allantois

A very early condition of Man, with yelk-sac, allantois, and amnion (original).
Lectures and Essays|T.H. Huxley
The blood vessels of the allantois take in oxygen and give out carbon dioxide through the porous shell.
The Meaning of Evolution|Samuel Christian Schmucker
Then, later, the placenta replaces the allantois, and the latter passes away as did its predecessor.
Private Sex Advice to Women|R. B. Armitage
The ureters (fig. 407, 3) open higher up than the other ducts into the stalk of the allantois which dilates to form the bladder .
The Works of Francis Maitland Balfour, Volume III (of 4)|Francis Maitland Balfour

The allantois was quite free and not attached to the subzonal membrane.
The Works of Francis Maitland Balfour, Volume III (of 4)|Francis Maitland Balfour

British Dictionary definitions for allantois

allantois

/ (ˌælənˈtəʊɪs, əˈlæntɔɪs) /

noun

a membranous sac growing out of the ventral surface of the hind gut of embryonic reptiles, birds, and mammals. It combines with the chorion to form the mammalian placenta

Derived Formsallantoic (ˌælənˈtəʊɪk), adjective

Word Origin for allantois

C17: New Latin, irregularly from Greek allantoeidēs sausage-shaped, allantoid

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for allantois

allantois

[ ə-lăn′tō-ĭs ]

n. pl. al•lan•to•i•des (ăl′ən-tō′ĭ-dēz′)

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

Related formsal′lan•to′ic (ăl′ən-tō′ĭk) adj.

Science definitions for allantois

allantois

[ ə-lăn′tō-ĭs ]

Plural allantoides (ăl′ən-tō′ĭ-dēz′)

A membranous sac that grows out of the lower end of the alimentary canal in embryos of reptiles, birds, and mammals. In mammals, the blood vessels of the allantois develop into the blood vessels of the umbilical cord.