The "lower" muscles of the mouth:
Risorius
Risorius
L. risus—laughter
origin: fascia over the cheek
insertion: skin at corner of mouth
action: pulls corner of mouth laterally causing dimples
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
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
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.