MUCOUS MEMBRANE. The mucous membranes line passages and cavities which communicate with the exterior of the body, where they become continuous with the skin. They constitute the lining of the alimentary canal or tract, which begins at the mouth and ends at the anus, a distance of about 27 feet, and is the passage through which the food for nutrition of the body is introduced, digested and taken up for the preservation and health of the body. They also form the lining of the nose, the throat, the middle ear, the various sinuses communicating with these cavities, the eyes, and of the respiratory apparatus, which comprises the lungs, the windpipe or trachea, and the larynx. The kidneys, the ureter, the bladder, the testes and the urethra in the male, and the Fallopian tubes, womb, vagina and vulva of the female are all lined with mucous membrane, together with the membrane of the ducts of glands which open upon it. In the female it becomes continuous with the peritoneum at the fimbrice of the Fal lopian tubes. The surface of the mucous membranes of the body is subjected to the con tact of various matters, such as the food, the air, and the different glandular secretions and excretions. They are protected from undue
irritation by a viscid liquid called mucus (q.v.), which constantly bathes their surface, and are also well supplied with blood-vessels and nerves. The mucous membranes are not of a single origin, but may he derived from ectsderm, as is the case with the lining of the mouth, entoderm, as with the greater part of the digestive tract, or mesothelium, as in the urogenital ducts. A mucous membrane consists of an epithelium, or layer of lining cells; a con nective-tissue basement-membrane, which may be hyaline and apparently homogeneous; and a further connective-tissue support or tunico pro prio. It usually is invaginated into glands, and may be evaginated into villae, as in the case of the stomach and intestine. For the diseases of the mucous membrane. see the respective or gans or systems concerned.