Salivary gland tissue contains two types of secretory cells: serous and mucous. Myoepithelial cells circumferentially envelop secretory acini and intercalated ducts to aid in secretion. The relative distribution of serous and mucous cells varies tremendously between parotid, submandibular, and sublingual glands. Parotid gland secretory units are lined primarily by serous cells and produce a watery secretion. Submandibular gland secretory units have a higher density of mucous cells and produce a secretion of intermediate consistency. Sublingual gland secretory units have the highest density of mucous cells and produce a viscous secretion.