hypotympanic

from The Century Dictionary.

• Situated beneath the tympanum: as, the hypotympanic bone.
• noun The so-called tympanic bone, as of birds and reptiles, commonly called the quadrate or os quadratum, which in many vertebrates below mammals forms the suspensorium of the lower jaw. Correlated with epitympanic. See quadrate, n. See cuts at Crotalus and Gallinæ.