Final answer:
The third bone of the middle ear is the stapes, which is one of the three auditory ossicles, including the malleus and incus, responsible for transmitting sound vibrations to the inner ear.
Step-by-step explanation:
The term for the third bone of the middle ear is the stapes. The middle ear houses three tiny bones known as the auditory ossicles, which are critical for transmitting sounds from the air as vibrations to the cochlea, a fluid-filled part of the inner ear. These bones are named the malleus (hammer), incus (anvil), and stapes (stirrup), with the stapes being the smallest and resembling a stirrup in shape. Collectively, these are the smallest bones in the human body and are unique to mammals.
These bones have distinct functions in the process of hearing, where the malleus connects to the tympanic membrane, the incus links the malleus to the stapes, and the stapes then transfers the vibrations to the inner ear. Without the malleus and incus, the vibrations caused by sound waves would not be efficiently conveyed to the stapes, and thus, the inner ear. These auditory ossicles not only transmit vibrations but also serve to collect force and amplify sound.