The ossicles are classically supposed to mechanically convert the vibrations of the eardrum into amplified pressure waves in the fluid of the cochlea (or inner ear), with a lever arm factor of 1.3.

There is a steadily increasing body of evidence that shows that the lever arm ratio is actually variable, depending on frequency.

The auditory ossicles can also reduce sound pressure (the inner ear is very sensitive to overstimulation), by uncoupling each other through particular muscles.

Of surgical importance are two branches of the facial nerve that also pass through the middle ear space.

The chorda tympani is the branch of the facial nerve that carries taste from the ipsilateral half (same side) of the tongue.

The middle ear's impedance matching mechanism increases the efficiency of sound transmission.

[5] The vibratory portion of the tympanic membrane (eardrum) is many times the surface area of the footplate of the stapes (the third ossicular bone which attaches to the oval window); furthermore, the shape of the articulated ossicular chain is a complex lever, the long arm being the long process of the malleus, the fulcrum being the body of the incus, and the short arm being the lenticular process of the incus.

The collected pressure of sound vibration that strikes the tympanic membrane is therefore concentrated down to this much smaller area of the footplate, increasing the force but reducing the velocity and displacement, and thereby coupling the acoustic energy.

The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with mucus, but they may be opened by lowering and protruding the jaw; this is why yawning or chewing helps relieve the pressure felt in the ears when on board an aircraft.

Eustachian tube obstruction may result in fluid build up in the middle ear, which causes a conductive hearing loss.

Recent findings indicate that the middle ear mucosa could be subjected to human papillomavirus infection.

[6] The middle ear of tetrapods is analogous with the spiracle of fishes, an opening from the pharynx to the side of the head in front of the main gill slits.

[7] In reptiles, birds, and early fossil tetrapods, there is a single auditory ossicle, the columella which is homologous with the stapes, or "stirrup" of mammals.

This is connected indirectly with the eardrum via a mostly cartilaginous extracolumella and medially to the inner-ear spaces via a widened footplate in the fenestra ovalis.

In these cases, the stapes either is also missing or, in the absence of an eardrum, connects to the quadrate bone in the skull, although, it is presumed, it still has some ability to transmit vibrations to the inner ear.

This is a flat, plate-like bone, overlying the fenestra ovalis, and connecting it either to the stapes or, via a special muscle, to the scapula.

[7] Mammals are unique in having evolved a three-ossicle middle-ear independently of the various single-ossicle middle ears of other land vertebrates, all during the Triassic period of geological history.

The malleus, or "hammer", evolved from the articular bone of the lower jaw, and the incus, or "anvil", from the quadrate.

The evolutionary process leading to a three-ossicle middle ear was thus an "accidental" byproduct of the simultaneous evolution of the new, secondary jaw joint.

[7] Recently found fossils such as Morganucodon show intermediary steps of middle ear evolution.