amnion
[am´ne-on] the innermost fetal membrane, which forms a sac filled with
amniotic fluid that surrounds the embryo and later the fetus; as it enlarges it gradually obliterates the chorionic cavity and enfolds the umbilical cord. Called also
bag of waters.

Amnion, chorion, and other embryonic membranes surrounding the embryo of a placental mammal. From Dorland's, 2000.
amnion nodo´sum a nodular condition of the fetal surface of the amnion, usually appearing near the insertion of the cord; it may be associated with multiple congenital abnormalities, especially hypoplastic kidneys and oligohydramnios.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.