The mentalis muscle or musculus mentalis is a conical shaped bundle of muscle fibers that are part of the lower group of oral muscles. The other two are: the depressor anguli oris, and the depressor labii inferioris. The mentalis muscle is the deepest of the two.
It lies at the side of the lower lip frenulum and originates from the incisive fossa of the mandible, just inferior to the incisor teeth. Its muscular fibers run downward and medially to insert in the skin of the chin. The inferior labial branch of the facial artery and the mental branch of the maxillary artery are responsible for its blood supply. And it is innervated by the mandibular branch of the facial nerve (VII).
The mentalis muscle raises the lower lip and wrinkles the skin of the chin. The elevation of the base of the lower lip results in protrusion. This allows the lip to drink from a cup and to express doubt or disdain through pouting.
Geniospasm is a very rare benign genetic disorder of the mentalis muscle. It develops during childhood and causes involuntary trembling of the chin and lower lip. The movement is always present, but can be aggravated by emotion, stress or concentration.
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