Structures involved in the action of swallowing. A bolus, a soft mass of chewed food, is visible in the esophagus and the epiglottis is bent to cover the windpipe to allow the passage of the bolus. Swallowing, or deglutition, is a complicated process involving over twenty-two muscle groups and the coordination of the tongue, soft palate, pharynx, and esophagus. The first stage is a voluntary action in which the tongue presses against the roof of the mouth and contracts to pass the food to the oropharynx. The second stage, an involuntary action, involves the uplifting of the larynx to allow the epiglottis to cover the trachea while peristaltic contractions move food down the pharynx and esophagus.