A mucous membrane or mucosa (plural, mucosae or mucosas; Latin tunica mucosa) is a biological membrane that lines various cavities in the body and surrounds internal organs. It is of endodermal origin and consists of a layer (or layers) of epithelial cells overlying a layer of loose connective tissue. It is continuous with the skin at various body openings such as the eyes, ears, nose and mouth, the urethral opening and the anus. Some mucous membranes secrete mucus, a thick protective fluid. The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.