The Tympanic Ossicles

The Tympanic Ossicles

Description : The three tympanic ossicles: the malleus, the incus and the stapes are the smallest bones in the body.

The stapes (stirrup), the smallest and most medially placed ossicle, is composed of a head, neck, diverging crura (arch) and a footplate. The head articulates with the incus and the footplate sits in the oval window niche of the bony inner ear.

These three bones which are referred to as the “ossicluar chain” span the middle ear and connect the tympanic membrane to the oval window of the bony labyrinth of the inner ear.

The Ossicles
The stapes, incus and malleus are displayed from left to right upon a Canadian 1 cent coin. The black line underneath the date is 5 mm in length.

The malleus (hammer), the outermost ossicle, is 9 mm in length and consists of three parts: a rounded head situated in the attic and hidden from otoscopic view, a neck, and a handle embedded in the upper half of the tympanic membrane which has a short process protruding from its lateral aspect.

The incus (anvil), the middle ossicle, is tooth-like in appearance and consists of a body and two diverging processes.

The body of the incus lies in the attic, where it articulates with the head of the malleus. The short process of the incus extends backwards into the fossa incudis and is attached to it by a ligament.

The long process of the incus, which may be seen through the posterosuperior quadrant of a thin tympanic membrane, descends medially and terminates in a knob, the lentiform process, which articulates with the head of the stapes.

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