Eustachian tube(redirected from eustachian)
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auditory tube, in terrestrial vertebrates, the canal that unites the pharynx with the cavity of the middle ear; named for B. Eustachio, who first described it in 1563.
The eustachian tube serves to equalize the air pressure in the middle ear with that of the surrounding environment. It originates from the rudiment of the gill slit. In crocodiles it forms a complex system of anastomosing canals. It is absent in snakes because of the reduction of the middle ear.
In man, the eustachian tube is a tubular formation that unites the nasopharynx with the tympanic cavity of the middle ear. Air enters the tympanic cavity through the eustachian tube from the nasopharynx. When the eustachian tube is inflamed, the entry of air into the tympanic cavity often ceases or is limited, producing a sensation of noise and congestion in the ear; hearing is somewhat decreased.