The general name given to the membrane which lines many of the hollow organs of the body. These membranes vary widely in structure in different sites, but all have the common character of being lubricated by MUCUS – derived in some cases from isolated cells on the surface of the membrane, but more generally from definite glands placed beneath the membrane, and opening here and there through it by ducts. The air passages, the gastrointestinal tract and the ducts of glands which open into it, and also the urinary passages, are all lined by mucous membrane.