allantois

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

noun

, Embryology, Zoology.

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

allantois

/ ˌælənˈtəʊɪs; ˌælənˈtəʊɪk; əˈlæntɔɪs /

noun

1. 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

allantois

/ ə-lăn′tō-ĭs /

, Plural allantoides ăl′ən-tō′ĭ-dēz′

1. 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.

Derived Forms

• allantoic, adjective

Word History and Origins

Origin of allantois¹

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

Word History and Origins

Origin of allantois¹

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

Example Sentences

The cavity of the allantois, if developed, vanishes completely.

From Project Gutenberg

This bag is called the allantois, and serves as a sort of lung for the developing chick.

From Project Gutenberg

It draws its oxygen and throws off its wastes through the instrumentality of the allantois, which covers it over.

From Project Gutenberg

The blood vessels of the allantois take in oxygen and give out carbon dioxide through the porous shell.

From Project Gutenberg

The allantois of the chick now gains a new development and an altered function.

From Project Gutenberg