Membrane

n.
  1. A thin layer or fold of tissue, usually supported by a fibrous network, serving to cover or line some part or organ, and often secreting or absorbing certain fluids.
    2. Adventitious membrane ,
    a membrane connecting parts not usually connected, or of a different texture from the ordinary connection; as, the membrane of a cicatrix.
    Jacob's membrane .
    See under Retina.
    Mucous membranes (Anat.),
    the membranes lining passages and cavities which communicate with the exterior, as well as ducts and receptacles of secretion, and habitually secreting mucus.
    Schneiderian membrane . (Anat.)
    See Schneiderian.
    Serous membranes (Anat.)
    , the membranes, like the peritoneum and pleura, which line, or lie in, cavities having no obvious outlet, and secrete a serous fluid.