Middle ear to sounds of higher frequency, because these are better taken up by the inner ear (which also responds to higher frequencies than those of non-mammals). The malleus, or "hammer", evolved from the articular bone of the lower jaw, and the incus, or "anvil", from the quadrate. In other vertebrates, these bones form the primary jaw joint, but the expansion of the dentary bone in mammals led to the evolution of an entirely new jaw joint, freeing up the old joint to become part of the ear. For a period of time, both jaw joints existed together, one medially and one
Anvil steel should never directly strike the anvil face with full force, as they may damage it; this can result in chipping or deforming of the anvil face. The horn of the anvil is a conical projection used to form various round shapes and is generally unhardened steel or iron. The horn is used mostly in bending operations. It also is used by some smiths as an aid in "drawing down" stock (making it longer and thinner). Some anvils, mainly European, are made with two horns, one square and one round. Also, some anvils are made with side horns or clips