Why Can We Hear?
We can hear because nature has provided us with a very wonderful organ called the ear and which catches the sound waves that come through the air into the ear and make a part of the ear vibrate.
In man and mammals the ear is generally found on the outside of the body, but the principal part of the ear is located within the skull. What we call ears are only the funnel-shaped extensions on the outside of the head which are not so very important so far as hearing is concerned, because they only help the real ear to hear more easily. The outside of the ear gathers in the sound waves and, because it is much larger than the little hole which takes the sounds in to the real ear, we can detect more sounds by having this funnel-shaped arrangement on the outside.
The inside of the ear contains an eardrum or tympanum which is separated from the outside part of the ear by a membrane. Behind this eardrum is the real hearing part of the ear in a labyrinth containing the nerves of hearing.
Now, when a sound wave strikes the membrane which hangs over the opening before the eardrum, the membrane vibrates and transmits the sound wave through the eardrum into the inner ear which contains the ends of the nerves by which we hear. These nerves, on receiving the sensation, transmit it to the brain which thus records the impression of sounds.
As we descend the scale of animal life from the mammals downward, the ear becomes a more and more simple organ. In the vertebrates which are not mammals, there is no external ear at all, and we find great simplifications of the ear the lower down in the scale we go.