The ear is divided into three portions—
The external ear is concerned with focussing sounds and collecting them and consists of the pinna which stands out from the side of the head, the meatus or opening into the external auditory canal. This canal naturally secrets the bitter ear wax (cerumen) and at its farthest end it is stopped by a thin membrane, the eardrum. On the other side of the drum is the middle ear in which lie three bones interlocked with each other for transmitting the vibrations set up by sounds in the eardrum. It is this middle ear, from which arises a narrow tube (eustachian tube) opening into the interior of the mouth. Beyond the middle ear situated inside the temporal bone is the internal ear. This internal ear is made up of a cochlea (conch-shell-like body) and three semi-circular canals placed at right angles to each other. These semicircular canals are full of fluid and it is the level of fluid in them that enables us to maintain equilibrium of our body. The cochlea contains the final terminals of the nerve of hearing (auditory nerve) spread out like the keys of harmonium. Sound collected by the external ear vibrates the drum; the vibrations of the drum are transmitted by the bones of the middle ear to the fluid in the cochlea. This vibration of the fluid is picked up by the keys (organs of Corti) and transmitted to the brain as sound impulses.