Salivary glands secrete saliva, which has the effect of moistening the mouth, facilitating swallowing and speaking, enhancing digestion, and keeping the mouth clean. Salivary glands, are glands that secrete saliva in the mouth of humans or vertebrates. The oral cavity has two kinds of salivary glands, large and small. Small salivary glands are scattered in the oral mucosa, including lip, cheek, palate and tongue glands; large salivary glands include parotid, submandibular and sublingual glands. Saliva secreted by the salivary glands is a kind of digestive fluid, most of which is water, but also contains mucin and amylase. Saliva can not only moisten the mouth, soften the food, easy to swallow; saliva in the amylase enzyme can promote the starch decomposition into maltose, enhance digestion; saliva can also remove food debris and foreign objects in the mouth, to keep the mouth often clean. In addition, saliva also contains lysozyme, with bactericidal effect.