The membraneous lining on which the ultimate ends of the nerves are spread is virtually a sensitive beach, and the little otoconia, showers of pebbles and sand, which are raised and let fall by each succeeding wavelet of sound. This wonderful mechanism constitutes the inner ear.
The ear, as a whole, consists of three parts: the outer ear, which is a trumpet-shaped passageway called the pinna serving to collect the sound waves and pass them on through the auditory canal to a small membrane called the eardrum; the ossicles, a series of three little bones, the hammer, the anvil, and the stirrup, they are called; and the inner ear just described.
FIG. 121.—The ossicles.
The foot of the stirrup is connected with an oval membrane, which closes a hole in the inner ear.
Sounds passing through the auditory canal cause the drum to vibrate and send tremors through the bones to the liquid in the little sacs. The tumbling of the "pebbles" against the filaments of the auditory nerve sends the intelligence to the brain.
The impression which the mind receives through the organ of hearing is called sound.
All bodies which produce sounds are in a state of vibration, and they communicate their vibrations to the surrounding air and thus set it into waves, just as a stick waved back and forth in a pool of water creates ripples.
Sound implies vibration, and whenever a sound is heard some substance, a solid, a liquid, or a gas is in vibration and the surrounding air is in unison with it.
