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 Peak of the Rat Islands. It is located further north than any of the other hills on the island, taking up a large amount of the northern part of the island. The volcano is located away from Atka, from Shemya, and from Attu. Anvil Peak has two summits, which are both volcanic cones. The larger main summit is tall, making it the highest point on the island. This summit is surrounded by ravines, which contain snow at certain times of the year. The peak is part of the old rim of a crater on the volcano, which had been slightly lowered