1. The outermost of the three small bones (malleus, incus, and stapes) in the ear of mammals, that transmits the vibrations of the tympanum to the incus or anvil.
2. The largest of the three auditory ossicles, resembling a club rather than a hammer; it is regarded as having a head, below which is the neck, and from this diverge the handle or manubrium, and the slender, anterior process; from the base of the manubrium the short lateral process arises.

The manubrium and lateral process are firmly attached to the tympanic membrane, and the head articulates with a saddle-shaped surface on the body of the incus (a small bone, shaped like an anvil, found in the middle ear of mammals between the malleus and the stapes bones). Also called a "hammer".