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Re: Reptilians Get Cheeky



David Marjanovic (David.Marjanovic@gmx.at) wrote:

<Hmm... my cheeks at least don't contract dorsoventrally. There
are muscles in the cheeks that pull the lips around, but I
haven't found any that move my jaws...>

  The circumoral muscles do indeed affect the jaws position, but
only at the level of the symphysis (chin); the m. buccinatoris
in humans serves (as pinnate muscles do) a brace and also
contract elastically. They themselves do not contract on their
own. Their main function is to stretch, and pulls in the action
of the jaw as the space between the buccal and the jaw
articulation increases. The disarticulation of one side of the
jaw as the other occludes precisely acheives this pulling
effect. The dorsal and ventral fiber sheets align with each
other, and elasticity pulls them back, and out, forcing food
through the jaws. Incidentally, the muscle M. risorius does the
mouth opening fuction in direct relativity to this process, as
do the zygomatic group. These pull the lips in various
directions backward. Actual jaw-moving muscles can be located in
the temple (M. temporalis), below the jaw (M. pterygoideus), and
behind the jaw at the angle of the os mandibulare (M.
stylohyoideus). These should be readily felt. Others articulate
within the jaw, but unless you want to risk damaging your
fingers, I wouldn't suggest trying to locate these as they work.
The Mm. mylohyoideus and digastricus are below the jaw, but
don't immediately serve jaw action (more throat action).

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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