The smallest bone in the body is the stapes. It is the 3rd bone of the 3 ossicles in the large middle ear. So what is the purpose of the smallest bone in the ear? This is because it is used in the transmission of sound vibrations to the inner ear from the outer ear. It is also the lightest bone in the body. Ever wondered why it is called stapes? The name came from its shape which resembles the stirrup.