THE EAR: HEARING AND BALANCE 15. Using the key choices, select the terms that apply to the following descriptions. Place the correct letter in the answer blanks. Key Choices: M. Tympanic membrane, Anvil (incus), External acoustic meatus, Pinna, N. Vestibule, Pharyngotympanic tube, Hammer (malleus), Round window, Semicircular canals, Cochlea, Oval window, Stirrup (stapes), Endolymph, Perilymph. 3. Structures composing the outer bony or osseous labyrinth. Structures composing the inner ear. Collectively called the ossicles. Not involved with hearing. Ear structures.