I've got a question that's designed for those with a background in physiology, biology, or neurology.
Here's a little Internet background for those who ain't:
Genioglossus is the fan-shaped extrinsic tongue muscle that forms the majority of the body of the tongue. Its arises from the mental spine of the mandible and its insertions are the hyoid bone and the bottom of the tongue. Innervated by the hypoglossal nerve, the genioglossus depresses and protrudes the tongue. The name derives from the Greek roots: "Geneion" for chin and "glossa" for tongue.
Here's what I'm thinking:
The size of the aperture determines the pitch, right? If that's so then the tongue could do flip flops and it wouldn't effect pitch what so ever. However, if moving the tongue up and toward the front teeth causes or allows the mandible to raise (even just a little) maybe this helps to make the aperture "smaller." The question: Does moving the tongue to play in the upper register result in the mandible moving up causing the lips to be closer together making the aperture smaller?