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 known as the face. It is generally made of hardened steel and should be flat and smooth with rounded edges for most work. Any marks on the face will be transferred to the work. Also, sharp edges tend to cut into the metal being worked and may cause cracks to form in the workpiece. The face is hardened and tempered to resist the blows of the smith's hammer, so the anvil face does not deform under repeated use. A hard anvil face also reduces the amount of force lost in each hammer blow. Hammers, tools, and work pieces of hardened