This picture is a cross section of the ear. It shows the auditory canal, which is about an inch deep. The end of the canal is blocked by a thick membrane, the eardrum. The middle ear is a small chamber just behind the eardrum. There is a tunnel from the middle ear down to the mouth. This is the Eustachian tube.
In the middle ear we see the tiny hammer, anvil, and stirrup which form an arching chain between the eardrum and oval window on the other side of the middle ear. The round window is just below the oval window. Both windows are openings to the inner ear that are covered with thin membrane.
The inner ear is half filled with the snail shaped cochlea, and otherwise consists of three hooplike tubes.
The next drawing will show the cochlea unwound, and reveal it to be a tapered tube with the basilar membrane dividing it lengthwise. The narrow end of the cochlea is closed, but the wide end is open to the oval window above the basilar membrane and the round window below it. The basilar membrane does not quite reach the narrow end of the cochlea, so the regions above and below it are connected.