After food has been thoroughly chewed, moistened, and rolled into a bolus, or ball, it is forced into the pharynx by swallowing action. The pharynx, an open area that begins at the back of the mouth, serves as a passageway for both air and food. As Figure 48-8 shows, a flap of tissue called the epiglottis (EP-uh-GLAHT-is) prevents food from entering the trachea, or windpipe, during swallowing. Instead, the bolus passes into the esophagus, a muscular tube approximately 25 cm long that connects the pharynx with the stomach.

The esophagus has two muscle layers: an inner circular layer that wraps around the esophagus and an outer longitudinal layer that runs the length of the tube. As you can see in Figure 48-9, alternating contractions of these muscle layers push the bolus through the esophagus and into the stomach. This series of rhythmic muscular contractions and relaxations is called peristalsis.

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