The mucous membranes (or mucosae; singular mucosa) are skin-like
linings of mostly endodermal origin. They are covered in
epithelium, which are involved in absorption and secretion. They
line cavities that are exposed to the external environment and
internal organs. They are at several places contiguous with
skin: at the nostrils, the mouth, the lips, the eyelids, the
ears, the genital area, and the anus. Unlike skin which has hair
growing out of it, mucous membranes are hairless. The sticky,
thick fluid secreted by the mucous membranes and glands is
called "mucus". The term mucous membrane refers to where they
are found in the body and not every mucous membrane secretes
mucus.