Middle ear bones. Coloured X-ray of the three bones of the middle ear responsible for conduction of sound waves. They are the smallest bones in the human body. At upper right is the malleus (hammer, 8mm long) which strikes the incus (anvil, 9mm long) at centre; the incus is joined to the stapes (stirrup, 3mm long) at bottom, which conducts sound towards the inner ear. Sound waves enter the ear through the external auditory meatus and cause the eardrum to vibrate. The three bones of the middle ear transmit vibrations towards the fluid- filled cochlear of the inner ear where vibrations are converted into nerve impulses. Magnification: x10 at 8x12 inch, x3 at 6x7cm size.