The mouth is a versatile area of the human anatomy, responsible for articulation in speech, and tasting, chewing, and swallowing food. The mouth cavity is located just below the nasal cavity and is formed by the palatine bones and the palatine processes of the maxilla on top and by the mandible on bottom. At the opening of the mouth cavity are the lips - muscular structures which are covered with thin, membranous skin.
The lips occlude the mouth opening during chewing to keep food and liquid within, help manipulate food during chewing, facilitate articulation in speech, and even give a friendly kiss. Within the mouth cavity, the teeth extend down from their maxillary sockets and up from their mandibular sockets to form the dental arcade. The muscles and skin of the cheeks cover the outer sides of the mouth cavity, while the muscular structures of the tongue and sublingual mucosal lining and muscles.
When food is brought into the mouth, the lips close (except in some unruly children) while the salivary glands produce saliva. The saliva lubricates the mouth and moistens the food. The inner surface of the lips, the tongue, and the cheeks manipulate the food so that it is brought between the teeth as the teeth clamp down on the food. In a combined action of these motions, with a semicircular, grinding motion of the teeth, the food is chewed into a paste with the saliva.
Enzymes within the saliva begin to break down the food and the tongue moves a portion of this food paste to the back of the mouth cavity by pressing it up and back along the hard palate. The soft palate, meanwhile, raises to seal off the nasal cavity. The ball of food paste, called a bolus, is passed into the pharynx. The epiglottis lowers to cover the airway so that the food does not enter the larynx. From the pharynx, wavelike contractions, called peristaltic waves, push the bolus down into and through the esophagus and into the stomach, where it is further digested.