Depressor Labii Inferioris

The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle that helps lower the bottom lip.Position of depressor labii inferioris muscle (red).Mandible. Outer surface. Side view. The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle that helps lower the bottom lip. This muscle arises from the oblique line of the mandible, and inserts on the skin of the lower lip, blending in with the orbicularis oris muscle.At its origin, depressor labii is continuous with the fibers of the platysma muscle. Much yellow fat is intermingled with the fibers of this muscle. The depressor labii inferioris is innervated by the mandibular division of the facial nerve.