from The American Heritage® Dictionary of the English Language, 4th Edition
- n. 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 is suspended.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. the innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
from the GNU version of the Collaborative International Dictionary of English
- n. A thin membrane surrounding the embryos of mammals, birds, and reptiles.
from The Century Dictionary and Cyclopedia
- n. 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.
- n. 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.
- n. 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.
- n. In botany, a name formerly given to the fluid contents of the embryo sac.
- n. Sometimes erroneously written amnios.
- n. In echinoderms, the sac in the pluteus larva inclosing the developing echinus.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)
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.
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.
The amnion is a membranous sac which surrounds and protects the embryo.
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.
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.
All the amniotes have a distinctive embryonic membrane known as the amnion
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.
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.
The egg has no nutritive cells; the formation of the primitive band, usually the first indication of the germ, is retarded till the second larval stage is attained; and the embryonal membrane is not homologous with the so-called "amnion" of other insects, but may possibly be compared with the skin developed on the upper side of the low, worm-like acarian,
The two outer ones multiply by subdivision and form the embryonal membrane, or "amnion," which is a provisional envelope and does not assist in building up the body of the germ.