eustachian tube /yo̅o̅stā″shən/ [Bartolomeo Eustachio, Italian anatomist, 1524–1574; L, tubus] , a tube lined with mucous membrane that joins the nasopharynx and the middle ear cavity. It is normally closed but opens during yawning, chewing, and swallowing to allow equalization of the air pressure in the middle ear with atmospheric pressure.
