With the shadows that I've come up with most of my ideas come from animals found in the wild. The Moray Eel being one of them. They have what is known as a Pharyngeal Jaw. Basically a smaller set of jaws found in the back of the mouth. The Xenomorph's jaws are based off of the Eel.
My Draorien's Jaws are the same way the smaller jaws are more like another head but there are five of them that snake out of the main jaws like an Eel.
Drawing (c) Me