What is the Incus
Incus, also known as the anvil, is one of the middle ear bones, besides the malleus and stapes. In Latin, ‘incus’ means ‘anvil’, which gives the bone its other name due to its resemblance in shape.
Where is the Incus Located
|How many are there in the human body||2 (1 in each ear)|
|Articulates with||Malleus and stapes|
It transmits vibrations from the outer to the inner ear via malleus and stapes. When sound waves hit the eardrum, it sets a vibration, which travels through all three bones, malleus, incus, and stapes, reaching the inner ear.
The incus has a body, two crura (singular: crus), short and long, that diverge nearly at right angles, and a lenticular process.
1. Body: It is somewhat cubical but compressed transversely. The body also features a deep concavo-convex facet on its anterior surface, which articulates with the head of the malleus.
2. Short crus: Also called short limb or process, it is somewhat conical in shape, projecting almost horizontally backward. The posterior ligament of the incus attaches here.
3. Long crus: Alternatively known as long limb or process, it descends inferiorly from the body and runs parallel to the malleus.
4. Lenticular process: The lower end of the long crus bends at a right angle to form this hooked-shaped part. It articulates with the head of the stapes.
The two ligaments that suspend the incus in place are:
- Superior ligament of incus – Attaches the body of the incus to the roof of the tympanic cavity.
- Posterior ligament of incus – Attaches the short limb of the incus to the posterior wall (mastoid) of the tympanic cavity.
i. Incudomalleolar joint: It is a synovial joint between the body of the incus and the head of the malleus.
ii. Incudostapedial joint: It is another synovial joint formed between the lenticular process of the long limb of the incus and the head of the stapes.