CorpusHuman Anatomy
Special SensesBone

Incus

Incus

Also known as: anvil

The middle auditory ossicle ("anvil"), linking the malleus to the stapes; its long process ends in the lenticular process, which articulates with the head of the stapes.

Show on body map Ear — Coronal Section

Overview

Length≈7 mm
Mass≈25–32 mg

The incus (≈7 mm) resembles a premolar tooth with two roots. Its body lies in the epitympanic recess and articulates with the head of the malleus. The short process (crus) projects backwards and is anchored by the posterior ligament of the incus in the fossa incudis near the aditus. The long process (crus) descends parallel and posterior to the handle of the malleus and bends medially at its tip into the small lenticular process, which articulates with the head of the stapes at the incudostapedial joint (a ball-and-socket synovial joint).

The long process has a precarious blood supply (end-arterial mucosal vessels), so it is the part of the ossicular chain most often eroded in chronic otitis media and cholesteatoma, causing discontinuity and a large conductive hearing loss.

Location

Middle ossicle; body in the epitympanic recess, long process hanging down behind the malleus handle (seen through the posterosuperior quadrant of the drum).

Parts & subdivisions

  1. Body
    Articulates with the malleus head.
  2. Short process
    Anchored near the aditus to the mastoid antrum.
  3. Long process
    Descends behind the malleus handle; commonly eroded in chronic ear disease.
  4. Lenticular process
    Rounded tip articulating with the stapes head.

Anatomy

Arterial supply

Branches of the anterior tympanic, posterior tympanic and superior tympanic arteries; the long process is a vascular watershed.

Articulations

Incudomallear joint (saddle synovial) with the malleus; incudostapedial joint (ball-and-socket synovial) with the stapes.

Ligaments

Posterior and superior ligaments of the incus.

Development

First pharyngeal arch (Meckel cartilage).

Function

  • Transmit vibration from the malleus to the stapes
  • Form the shorter arm of the ossicular lever

Clinical significance

Incudostapedial discontinuity

Erosion of the long/lenticular process or traumatic dislocation of the incus (head injury) produces conductive loss up to ≈50–60 dB; repaired with ossiculoplasty.

Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.