What are allantois?

  • (noun): Vascular fetal membrane that develops from the hindgut in embryonic higher vertebrates (reptiles, birds and mammals).


Allantois (/əˈlæntɔɪs/; plural allantoides or allantoises) is a part of a developing animal conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.

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Some articles on allantois:

Allantois - Additional Images
... in midgestation 1 umbilicus, 2 amnion, 3 allantois, 4 Yolk sac, 5 developing marginal hematoma, 6 maternal part of placenta (endometrium) Ultrasound of fetus showing urachus duct from bladder to the ...
Cloaca (embryology)
... first prolonged backward into the body-stalk as the tube of the allantois but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained ... into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward ...
Reptiloform - Evolutionary History - From Aquatic To Terrestrial Eggs
... The first to evolve was probably the allantois, a sack that develops from the gut/yolk-sack ... A very small allantois is found in modern amphibians ... amnion surrounding the fetus proper, and the chorion, encompassing the amnion, allantois, and yolk-sack ...