All around the oral opening eleven muscles are laid out: one initially, of annular form, the labial or orbicular one of the lips, which governs its occlusion then a series of ten others which from the various areas of the face, come to fit on its circumference like so many convergent rays. They are, from top to bottom: the common elevator of the wing of the nose and the upper lip; the very elevator of the upper lip; the canine one; the minor zygomatic muscle; the big zygomatic; the buccinator; the risorius; the triangular one of the lips; the square of the chin; the muscle of the bunch of the chin.
This is a flat, thin, digastric muscle, extended from the occiput to the forehead (from which circumstance its name is derived), and placed immediately beneath the cranial integument, to which it closely adheres, at the same time that it rests upon the arch of the skull, over which it slides. It consists of two broad but short fleshy bellies, united by an intervening aponeurosis.
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