mouth

mouth entrance to the digestive and respiratory tracts. The mouth, or oral cavity, is ordinarily a simple opening in lower animals; in vertebrates it is a more complex structure. In humans, the mouth is defined in front and at the sides by the lips, jawbone, teeth , and gums; in the rear it merges with the throat. The roof of the mouth is composed of the hard and soft palates and the floor of the mouth is formed by the tongue , a muscular structure that contains the organs of taste (taste buds). The lips, palates, tongue, and teeth are the major components in speech formation, using the "raw sound" formed in the larynx . The process of digestion begins in the mouth; the chewing and grinding action of the teeth reduces the food to a readily digestible substance. The enzymatic process of converting starch to sugar is initiated by salivary amylase (ptyalin) excreted by the three salivary glands located at the angle of the jawbone and under the tongue. Saliva produced in these glands moistens food, preparing it for processing in the digestive system .

mouth The opening of the alimentary canal, which in most animals is used for the ingestion of food. It leads to the buccal cavity (mouth cavity).

mouth be all mouth (and no trousers) tend to talk boastfully without any intention of acting on one's words.
a mouth to feed a person, typically a child, who has to be looked after and fed.
out of the mouths of babes— proverbial saying, late 19th century, meaning that young children may at times speak with disconcerting wisdom; it may be used of anyone who is seen as young and inexperienced. The saying ultimately derives from two biblical passages, Psalms 8:2, ‘Out of the mouth of babes and sucklings hath thou ordained strength’, and Matthew 21:16, ‘have ye never read, Out of the mouths of babes and sucklings thou hast perfected praise.’

See also turn to ashes in one's mouth, a bone in her mouth, born with a silver spoon in one's mouth, put one's foot in one's mouth, one's heart in one's mouth, from the horse's mouth, the lion's mouth, put one's money where one's mouth is, have a plum in one's mouth, straight from the horse's mouth.