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 for specialized work. The "step" is that area of the anvil between the "horn" and the "face". It is soft and is used for cutting; its purpose is to prevent damaging the steel face of the anvil by conducting such operations there and so as not to damage the cutting edge of the chisel, though many smiths shun this practice as it will damage the anvil over time. The "hardie hole" is a square hole into which specialized forming and cutting tools, called Hardy tools, are placed. It is also used in punching and bending operations. The "pritchel hole" is