Inferior Maxillary Region Facial Muscles (Mandibular region)

Mentalis Facial Muscles

The Mentalis muscles are also known as Levator labii inferioris muscles.

They originate at the incisive fossa external to the mandibular symphysis (cleft of the chin, for those who have one).

The fibres run downward to be inserted in the skin of the chin.

Their action is to raise and protrude the lower lip and simultaneously wrinkle the skin over the chin. These muscles are the primary articulators of labio-dentals.

Depressor Labii Inferioris Facial Muscles

The Depressor labii inferioris is sometimes called Quadratus menti.

Each is a small, quadrilateral muscle which originates at the external oblique line of the mandible between the symphysis and the mental foramen.

The fibres run upward and inward to be inserted into the orbicularis oris and into the fibres of its companion from the other side.

It is continuous with the Platysma at its origin and contains a fair amount of yellow fat in its fibers.

Their action is to draw the lower lip directly downward and a little outward.

Depressor Anguli Oris Facial Muscles

The Depressor anguli oris is sometimes called the Triangularis menti.

Each is triangular in shape and originates by the broad base at the external oblique line of the mandible.

The fibres extend upward to be inserted into the angle of the mouth.

It is continuous with the Platysma at the origin and with the Orbicularis oris and Risorius at insertion.

Some fibres are directly continuous with those of the Levator anguli oris.

Their action is to depress the angle of the mouth and act as antagonist to the Levator anguli oris and Zygomaticus major.

Acting together with these muscles, they will draw the angle of the mouth directly backward, as in the articulation of a unrounded high , front vocoid.