Innermost of the extraembryonic membranes enveloping the embryo in utero and containing the amniotic fluid; it consists of an internal embryonic layer with its ectodermal component, and an external somatic mesodermal component; in the later stages of pregnancy the amnion expands to come in contact with and partially fuse to the inner wall of the chorionic vesicle; derived from the trophoblast cells. Syn: amniotic sac.


[G. the membrane around the fetus, fr. amnios, lamb]

amnion nodosum