serous membrane, one of the many thin sheets of tissue that line closed cavities of the body, such as the pleura lining the thoracic cavity, the peritoneum lining the abdominal cavity, and the pericardium lining the sac that encloses the heart. Between the visceral layer of serous membrane covering various organs and the parietal layer lining the cavity containing these organs is a potential space moistened by serous fluid. The fluid reduces the friction of the structures covered by the serous membrane, such as the lungs, which move against the thoracic walls in respiration. Compare mucous membrane, skin, synovial membrane.
