• WordNet 3.6
    • n allantois the vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals)
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Webster's Revised Unabridged Dictionary
    • n Allantois (Anat) A membranous appendage of the embryos of mammals, birds, and reptiles, -- in mammals serving to connect the fetus with the parent; the urinary vesicle.
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Century Dictionary and Cyclopedia
    • n allantois A fetal appendage of most vertebrates, developing as a sac or diverticulum from the posterior portion of the intestinal cavity. It is one of the organs of the embryo of all amniotic vertebrates, or those which develop an amnion, but is wanting or is at most rudimentary in amphibians and fishes. In birds and reptiles it is large and performs a respiratory function, and in mammals contributes to form the umbilical cord and placenta. Its exterior primitively consists of mesoblast, its cavity receiving the secretion of the primordial kidneys (Wolffian bodies). So much of the sac as remains pervious within the body of the embryo becomes the urinary bladder, or, in some degree, a urinary passage. The umbilical arteries and veins course along the elongated stalk of the sac, which becomes the umbilical cord, and that part of these allantoic vessels within the body which does not remain pervious becomes the urachus and round ligament of the liver. The expanded extremity of the allantois, in most mammals, unites with the chorion to form the placenta. In those vertebrates, as mammals, in which the umbilical vesicle has but a brief period of activity, the allantois chiefly sustains the functions whereby the fetus is nourished by the blood of the mother, and has its own blood arterialized. In parturition, so much of the allantois as is outside the body of the fetus is cast off, the separation taking place at the navel. See cut under amnion.
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Chambers's Twentieth Century Dictionary
    • n Allantois a-lan′tō-is a membranous sac-like appendage for effecting oxygenation in the embryos of mammals, birds, and reptiles
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Chambers's Twentieth Century Dictionary
Gr. allas, a sausage.


In literature:

A very early condition of Man, with yelk-sac, allantois, and amnion (original).
"Lectures and Essays" by T.H. Huxley
ALLANTOIS, a membrane enveloping the foetus in mammals, birds, and reptiles.
"The Nuttall Encyclopaedia" by Edited by Rev. James Wood
Blood is taken out to the allantois, however, by the arteries of the latter type.
"Text Book of Biology, Part 1: Vertebrata" by H. G. Wells
Endochorium: the layer of the allantois that lines the chorium; the inner layer of the chorium.
"Explanation of Terms Used in Entomology" by John. B. Smith
This bag is called the allantois, and serves as a sort of lung for the developing chick.
"The Meaning of Evolution" by Samuel Christian Schmucker
The allantois also contains a fluid which is known as the allantoid liquid.
"Special Report on Diseases of Cattle" by U.S. Department of Agriculture
Three sets of structures are concerned in human embryonic nourishment, namely, the Allantois, the Villi of the Chorion, and the Placenta.
"Embryology" by Gerald R. Leighton
C. The very young puppy, with attached ends of the yelk-sac and allantois, and invested in the amnion.
"Man's Place in Nature and Other Essays" by Thomas Henry Huxley
After the passing away of the yolk sack, the embryo is nourished and sustained by the "allantois," another peculiar sack which is formed.
"Private Sex Advice to Women" by R. B. Armitage
The function of the allantois is still in a great measure unknown.
"A System of Midwifery" by Edward Rigby