Simple (squamous) epithelium lines the terminal bronchioles, air sacs, alveoli of lungs, etc. Simple (cuboidal) epithelium lines small salivary and pancreatic ducts and some portions of ducts of sweat glands, while compound (non-keratinized stratified squamous epithelium is present as the lining of oral cavity tongue, pharynx (lower part), oesophagus. This type of epithelial cells are present on these surfaces which may subject to abrasion but are completely protected from drying, i.e., these are wet surfaces.