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RESEARCH.

ORBICULARIS ORIS.
 

                    The Orbicularis Oris sits inside the lips themselves.  When we talk, it shapes the lip edges to form the phonemes.  It is made up of specialized layers that shape the mouth.  Mainly it is used when forming expressions such as anger and grief.  The orbicularis oris's chief action is to tighten the lips.  In this instance it is very similar to the action employed by the Orbicularis Oculi.  The orbicularis oris runs, just under the skin, in a oval shape around the mouth.  The muscle stretches from the base of the nose, to the corners of the mouth, to the crease on the chin under the lower lip.  The orbicularis oris appears to be suspended from the side of the head.  Primarily attached by small knots of muscle.  The knots help to define the corners of the mouth.
                    When the lips are tense in sadness or anger, the lips narrow, but the mouth does not shorten.  Muscles deep underneath the skin tighten.  The corner of the mouth is fixed in place by some of the muscles attached to it, the result is it stays in place while the rest of the mouth shrinks.  The lips narrow by curling in on themselves.

Fig . 19 - The Orbicularis Oris Muscle Fibers.                        Fig . 20 - The Orbicularis Oris in action.