If you are needing a sound amplifier, you can use the stapes to vibrate against against the ear capsule, while it is also serving as a jaw support. The stapes is a hearing bone, an auditory ossicle, present in all derived tetrapods. They make up a chain of three hearing bones, located within the middle ear. The stapes retains its old position of butting against a window in the inner ear capsule, but now the malleus connects to a new membrane, the tympanium or ear drum, and the incus is in between. A nice series of Mesozoic synapsids, nicely described in Gould's article 3.
Modern mammals develop the ear bones from cartilage rudiments in a von Baerian style.
Using dissection of a developmental series of pig embryos he was able to follow Meckel's cartilage through the transition to the Malleus. Simply amazing science for its day. Mutation of Hoxa3 in the mouse converts the stapes into the incus. We take up this argument more on Monday. Connections Come back for a self test on Monday.