\Eu*sta"chi*an\, a. [From Eustachi, a learned Italian
physician who died in Rome, 1574.] (Anat.)
(a) Discovered by Eustachius.
(b) Pertaining to the Eustachian tube; as, Eustachian
    catheter.
{Eustachian catheter}, a tubular instrument to be introduced
   into the Eustachian tube so as to allow of inflation of
   the middle ear through the nose or mouth.
{Eustrachian tube} (Anat.), a passage from the tympanum of
   the ear to the pharynx. See {Ear}.
{Eustachian valve} (Anat.), a crescent-shaped fold of the
   lining membrane of the heart at the entrance of the vena
   cava inferior. It directs the blood towards the left
   auricle in the fetus, but is rudimentary and functionless
   in the adult.