a tube leading from the tympanic cavity to the nasopharynx; it consists of an osseous (posterolateral) portion at the tympanic end, and a fibrocartilaginous (anteromedial) portion at the pharyngeal end; where the two portions join, in the region of the sphenopetrosal fissure, is the narrowest portion of the tube (isthmus); the auditory tube enables equalization of pressure within the tympanic cavity with ambient air pressure, referred to commonly as popping of the ears. Syn: tuba auditiva [NA], tuba auditoria [NA], eustachian tube, guttural duct, otopharyngeal tube, otosalpinx, pharyngotympanic tube, salpinx(2), tuba acustica, tuba eustachiana, tuba eustachii.