allantois

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

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.

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. 2018

Examples from the Web for allantois

Historical Examples of allantois

So the allantois of the reptile has become the placenta of the mammal.
The Meaning of Evolution
Samuel Christian Schmucker
The function of the allantois is still in a great measure unknown.
A System of Midwifery
Edward Rigby
The cavity of the allantois, if developed, vanishes completely.
The Works of Francis Maitland Balfour, Volume III (of 4)
Francis Maitland Balfour
It thus comes about that the further splitting of the mesoblast merely enlarges the cavity in which the allantois lies.
The Works of Francis Maitland Balfour, Volume III (of 4)
Francis Maitland Balfour
As the allantois increases in size and importance, the allantoic vessels are correspondingly developed.
The Works of Francis Maitland Balfour, Volume III (of 4)
Francis Maitland Balfour

British Dictionary definitions for allantois

allantois

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

allantois in Medicine

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.

allantois in Science

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.