Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A thin, tough, membranous sac that encloses the embryo or fetus of a mammal, bird, or reptile. It is filled with a serous fluid in which the embryo or fetus is suspended.

from The Century Dictionary.

  • noun In anatomy and vertebrate zoöl., one of the fetal appendages; the innermost one of the membranes which envelop the embryo of the higher vertebrates, as mammals, birds, and reptiles; the lining membrane of a shut sac, familiarly called the “bag of waters,” in which the fetus is contained.
  • noun In entomology, a membrane which surrounds the larva of many insects, as the millepeds (Iulidæ), for some time after they are batched from the egg. It is regarded by some as the analogue of the amnion of a vertebrate.
  • noun A reflected portion of a membrane, in ascidians, which lines the inner wall of the ovisac, and forms a kind of amniotic investment of the embryo.
  • noun In botany, a name formerly given to the fluid contents of the embryo sac.
  • noun Sometimes erroneously written amnios.
  • noun In echinoderms, the sac in the pluteus larva inclosing the developing echinus.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Anat.) A thin membrane surrounding the embryos of mammals, birds, and reptiles.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun anatomy the innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[Greek amniōn.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin for "membrane around a fetus", from Greek "bowl in which the blood of victims was caught", from ame, (bucket)

Examples

  • In these three classes alone we find the remarkable embryonic membrane, already mentioned, which we called the amnion; a cenogenetic adaptation that we may regard as a result of the sinking of the growing embryo into the yelk-sac.

    The Evolution of Man — Volume 2

  • They described primitive cells found in a part of the placenta called the amnion, which they coaxed into forming a variety of cell types and which look very similar to sought-after embryonic stem cells.

    Medpundit

  • They described primitive cells found in a part of the placenta called the amnion, which they coaxed into forming a variety of cell types and which look very similar to sought-after embryonic stem cells.

    Archive 2005-08-01

  • —The amnion is a membranous sac which surrounds and protects the embryo.

    I. Embryology. 11. Development of the Fetal Membranes and Placenta

  • A great step in evolution was implied in the origin of this ante-natal hood or foetal membrane and another one -- of protective significance -- called the amnion, which forms a water-bag over the delicate embryo.

    The Outline of Science, Vol. 1 (of 4) A Plain Story Simply Told

  • As the watery condition of the blood increases with advancing pregnancy, so dropsy of the amnion is a disease of the last four or five months of gestation.

    Special Report on Diseases of the Horse

  • All the amniotes have a distinctive embryonic membrane known as the amnion

    The Evolution of Man — Volume 1

  • After the egg has been fertilized by the male, the blastoderm, or primitive skin, forms, and subsequently two layers, or embryonal membranes, appear; the outer is called the amnion (Fig. 114, _am_), while the inner visceral membrane (_db_) partially wraps the rude form of the embryo in its folds.

    Our Common Insects A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses

  • They are caused by a tearing of the inner part of the placenta called the amnion, which produces the fiber-like bands that may trap the baby's extremities such as the arms, legs, fingers or toes.

    Emaxhealth

  • They are caused by a tearing of the inner part of the placenta called the amnion, which produces the fiber-like bands that may trap the baby's extremities such as the arms, legs, fingers or toes.

    Emaxhealth

Comments

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  • I found this word in my reading today, from the memoir A Step from Death, by Larry Woiwode a great word in and of itself:

    " . . . I feel my mind is treading water, so deep in moribund amnion I'll drown."

    September 5, 2008