The Collaborative International Dictionary of English v.0.48:

Eustachian \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.
       [1913 Webster]

   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.
      [1913 Webster]