Which is not one of the three tiny bones in the middle ear?

cochlea

hammer

anvil

stirrup

the answer is the cochlea, its not part of the middle ear

hammer, anvil, and stirrup are the three tiny bones found in the middle ear

they are also known as malleus, incus, and stapes.

The average ear (Auris media) is the middle part of the ear and consists of the tympanic membrane, the Eustachio tube and the oval and round windows. In the tympanic cavity are contained the oscillations of the middle ear. Timpan has the role of transforming the sounds collected by the external ear into vibrations, which are sent to the three oscillators (hammer, anvil and stair). In turn, they send the vibrations to the inner ear.

So the cochlea is not part of the average ear