noun
: a structure that derives from the fertilized ovum but does not form a part of the embryo, including true membranes (as the amnion and chorion) and other structures (as the placenta and umbilical cord) not usually considered membranes
noun
: a structure that derives from the fertilized ovum but does not form a part of the embryo, including true membranes (as the amnion and chorion) and other structures (as the placenta and umbilical cord) not usually considered membranes
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012