The mentalis muscles (TA: musculus mentalis) are paired muscles, one on each side of the mouth, important as elevators of the chin and lower lip; the muscles are one of the facial muscles.

The mentalis muscle is a slight cone-shaped muscle which originates from the incisive fossa of the mandible. These superior fibers of mentalis are intertwined with inferior fibers of the orbicularis oris muscle. The more lateral superior fibers of the mentalis are also mixed in with fibers of the incisivus labii inferioris muscle ⁵.

The incisive fossa is a small depression in the body of the mandible lying just below the lateral and central incisor teeth on each side. The fibers then pass anteroinferiorly, deep to the oral mucosa of the vestibule of the mouth, on either side of the midline labial frenulum ^1-3,5.

Insertion

The mentalis muscle fibers insert into the skin of the chin ^1-3,5. These fibers are best further considered as medial and lateral groups ⁵:

medial fibers from each side pass forwards and cross their counterpart fibers from the other side before inserting into the contralateral aspect of the skin of the chin
lateral fibers run downwards with a medial orientation in most (in a small percentage of individuals they bend laterally), intertwining with fibers of the depressor labii inferioris muscle before inserting into skin of the chin ipsilaterally

Action

raises skin of the mental region (chin) effecting wrinkling +/- dimpling, and may be important for the expression of doubt
elevation and protrusion of the lower lip
superior mentalis muscle fibers, merge with the orbicularis oris muscle, forming a contiguous muscular structure, and acts to strengthen orbicularis oris as it moves the lower lip ⁵

Radiographic features

The mentalis muscle may be seen on high resolution ultrasound of the chin as a consistently identifiable hypoechoic structure in the mental region ⁴.

History and etymology

Mentalis is from the word 'mentum' which is Latin for chin ⁶.

References

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Mentalis muscle

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