The outermost part, the skin-covered _auricle_, contains no bone, being
simply a mass of cartilage covered by skin. It acts as a sound catcher
and improves the hearing by directing sound-waves into the opening or
external _meatus_. This meatus or passage-way runs directly inward for
an inch and a half. The inner half of the passage-way runs through solid
bone, ending abruptly at the membrane or sounding-board of the ear.
[Illustration: =THE JOURNEY OF SOUND WAVES TO THE BRAIN=
This diagram shows the marvelous structure of the ear, and how sound
reaches the brain. There is marked similarity between the ear and a
telephone receiver by which we are able to receive messages from the
outside world. Hearing is simply the result of sound-waves striking the
drum of the ear which set in vibration the bones of the middle ear, and
they in turn vibrate the drum of the inner ear. This sets in motion a
fluid, and the wave motions are conveyed along the spiral staircase to
the wires, or nerves of hearing, and from there to the telephone
exchange, or brain.]