three small membranous tubes of the vestibular labyrinth within the bony semicircular canals of the bony labyrinth that form loops of about two thirds of a circle. The three semicircular ducts: anterior semicircular duct [TA] (ductus semicircularis anterior [TA]), lateral semicircular duct [TA] (ductus semicircularis lateralis [TA]), and posterior semicircular duct [TA] (ductus semicircularis posterior [TA])—lie in planes at right angles to each other and open into the vestibule by five openings of which one is common to the anterior and lateral ducts. Each duct has an ampulla at one end within which filaments of the vestibular nerve terminate.
Synonym(s): ductus semicircularesTA
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