* The term is also often applied to the thin, expanded parts, of various texture, both in animals and vegetables.

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.