The ear has two main functions, that of hearing and of balance.  The ear can be divided into three main portions for the purposes of discussion.  The external ear, the middle ear, and the internal (or inner) ear.  It is the internal ear that is the organ for both hearing and balance.  The external ear and middle ear are an apparatus for sound collecting, and conducting that sound to where it can be interpreted.

    The external ear is a plate made of cartilage, that is a collector of air vibrations, and funnels these vibrations down the ear canal to the tympanic membrane, or eardrum.  The external ear's shape is dependent on the breed of dog; it could be large and drooping, as in a bloodhound; erect and mobile, as in a Border Collie's; or small, thumbnail, as in a Bulldog, or Chinese Shar Pei.

    This is the area behind the eardrum.  The vibrations that have been sent from the external ear are focused and amplified here in the middle ear.  Behind the eardrum (tympanic membrane) is the tympanic cavity.  The tympanic cavity contains the auditory tube, the tympanic nerve, the vestibular window and the cochlea.  There are many other parts as well, but for the sake of simplicity, we will only name these couple.
    There are also three small bones that transmit the air vibrations from the eardrum and tympanic cavity to the inner ear.  The names of these bones are the malleus, the incus, and the stapes.  The stapes is known as the smallest bone in the body, being approximately 2 mm in length.

The Inner Ear

    The inner ear is a labyrinth of fluid filled ducts and sacs, which are in turn, contained within an osseous labyrinth.  This is where the vibrations transmitted to the inner ear via the mallus, incus and stapes are converted into nerve impulses, which when reaching the brain result in hearing.
    The osseous parts of the inner ear are a shell-shaped cochlea.  This cochlea winds around a hollow core, that contains the cochlear nerve.  In dogs, the cochlea makes three and one quarter turns.  The importance of the cochlea can be understood, when one realizes that it contains approximately 10,000 hair cells, which respond to sound waves, and this stimulates the nerve cells to send messages to the brain.  This is one of the ways the ear changes vibrations of the air to electrical signals.
    This then leads to the osseous vestibule, which connects to three semicircular canals, and within all this are groups of small openings which accommodate the nerves of this region.
    There is a membranous labyrinth which is a fluid like substance, that does not completely fill the hollow system within the osseous labyrinth.  It is thought that the equilibrium is controlled here.

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