The Incus has received its name from its supposed resemblance to an anvil, but it is more like a premolar tooth, with two roots, which differ in length, and are widely separated from each other. It consists of a body and two crura.
The body (corpus incudis) is somewhat cubical but compressed transversely. On its anterior surface is a deeply concavo-convex facet, which articulates with the head of the malleus.
The two crura diverge from one another nearly at right angles :
- The short crus (crus breve; short process), somewhat conical in shape, projects almost horizontally backward, and is attached to the fossa incudis, in the lower and back part of the epitympanic recess.
- The long crus (crus longum; long process) descends nearly vertically behind and parallel to the manubrium of the malleus, and, bending medialward, ends in a rounded projection, the lenticular process, which is tipped with cartilage, and articulates with the head of the stapes