What type of membrane lines the cavities that do not open to the outside?

A serous membrane is the correct type of membrane that lines the cavities of the body which do not open to the outside. These membranes are crucial because they produce a lubricating fluid that reduces friction between the organs and the cavity walls. They are primarily found in body cavities such as the pleura (surrounding the lungs), pericardium (surrounding the heart), and peritoneum (lining the abdominal cavity).

In contrast, a mucous membrane lines cavities that do open to the outside, like the respiratory and digestive tracts, and is involved in secretion and absorption. A synovial membrane is found in joint cavities and produces synovial fluid to lubricate joints, but it is not associated with body cavities that do not open to the outside. The cutaneous membrane, or skin, covers the outer surface of the body and also does not pertain to the lining of internal cavities. Each of these types serves specific functions and locations within the body, making the understanding of serous membranes particularly important for recognizing their role in internal cavity protection and organ function.