Artistic Anatomy Part 5: Mouth Muscles III

The "lower" muscles of the mouth:

Risorius

L. risus—laughter

origin: fascia over the cheek
insertion: skin at corner of mouth
action: pulls corner of mouth laterally causing dimples

Triangularis (Depressor anguli oris)

Of triangular shape

origin: lower margin of the mandible

insertion: skin at corner of mouth

action: pulls corner of mouth down; pulls upper lip down

Quadratus labii inferioris (Depressor labii inferioris)

L. quadratus—square-shaped + labii—of lip

origin: lower margin of mandible
insertion: skin of the lower lip
action: pulls lower lip down and out

Mentalis (Levator labii inferioris)

L. mentum—chin

origin: mental protuberance
insertion: skin at chin
action: raises skin of chin and wrinkles it; protrudes lower lip

Next in the series:

eyes, nose and mouth planes, frontal view.