Structure and function of the ear in cats


Most animals suffer from diseases of the ear and the cat is no exception. Careful diagnosis of the exact problem will ensure the most beneficial treatment. To understand some of the problems it is first necessary to know something of the fundamental anatomy of the ear.

Structure (anatomy) of the ear

The ear is divided into three parts – external, middle and inner ear.

External ear 

This comprises all parts of the ear, visible and invisible, from the tip of the ear flap to the ear drum (tympanic membrane). The ear flap (pinna) is erect in the cat, unlike many dogs, and it comprises a cartilaginous plate which is slightly concave on the inner surface. This cartilage is covered by skin bearing shortish hairs on the outer surface and on the inner by fine skin which is closely adherent to the underlying cartilage with hair only towards the edges.

The vertical ear canal should normally have very few hairs, be slightly pink to almost white in colour, have no obvious accumulation of wax. Ear wax in cats (cerumen) is usually dark brown in colour and should not be mistaken for dried blood.

The delicate tympanic membrane (ear drum) at the end of the ear canal is well protected – the vertical ear canal turns through 90 degrees at its base into the horizontal ear canal, and the tympanic membrane is then at the end of the horizontal ear canal (which is approximately 1cm long).

As the tympanic membrane is tucked away ‘around a corner’, it is unlikely to be reached and damaged during careful gentle cleaning of the ear. However, you should never put anything into the ear unless specifically recommended by your vet, and you should only ever clean the parts of the ear that you can easily see.

The lining of the external ear canal is an extension of the skin around the ear but also contains some wax-producing (ceruminous) glands. These may produce increased or excessive amounts of wax in certain ear diseases as a protective mechanism.

Middle Ear 

The middle ear cannot be seen at all, but is contained in a bony pocket at the base of the skull (the tympanic bulla) and contains three tiny bones (osciccles) that transmit sound waves from the tympanic membrane (ear drum) to the inner ear. The three bones are termed the incus (anvil), stapes (stirrup) and malleus (hammer).

Internal ear 

The internal ear is enclosed and protected by a special hard bone within the base of the skull called the ‘petrous temporal bone’. The inner ear contains the delicate organ of hearing (called the organ of Corti) where sound waves transmitted through the tympanic membrane and bones of the middle ear are converted to nerve pulses that are recognised by the brain. Additionally, the inner ear contains three tiny semi-circular fluid-filled canals set at angles to each other that are responsible for the sense of balance – movement of fluid is detected by tiny hairs that line the canals and this enables the brain to determine balance and orientation.