allantois

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al·lan·to·is

 (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 digestive tract 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.

[New Latin allāntois, variant of allāntoīdēs, from Greek allāntoeidēs, sausage-shaped : allās, allānt-, sausage (perhaps from Greek dialectal (Magna Graecia) *allāwent-, (sausage) seasoned with garlic, from *allā-, garlic, of Italic origin; akin to Latin ālium, garlic; see allium) + -oeidēs, -oid.]

al′lan·to′ic (ăl′ən-tō′ĭk) adj.

allantois

(ˌælənˈtəʊɪs; əˈlæntɔɪs)
n
(Zoology) 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
[C17: New Latin, irregularly from Greek allantoeidēs sausage-shaped, allantoid]
allantoic adj

al•lan•to•is

(əˈlæn toʊ ɪs, -tɔɪs)

n., pl. al•lan•to•i•des (ˌæl ənˈtoʊ ɪˌdiz)
a nourishing membrane surrounding the embryo, between the amnion and chorion, in birds and reptiles developing as a sac from the hindgut and in mammals as an inner layer of the placenta.
[1640–50; < New Latin < Greek allantoeidḗs (see allantoid).]
al`lan•to′ic, adj.

al·lan·to·is

(ə-lăn′tō-ĭs)
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.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.allantois - the vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals)allantois - the vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals)
mammal, mammalian - any warm-blooded vertebrate having the skin more or less covered with hair; young are born alive except for the small subclass of monotremes and nourished with milk
fetal membrane - any membrane that functions for the protection or nourishment or respiration or excretion of a developing fetus