Platysma

Origin: Inferior clavicle and fascia of chest

Insertion: Mandible

Nerve: Cervical branch of the facial nerve (CN VII)

Action: Draws the corners of the mouth inferiorly and widens it (as in expressions of sadness and fright). Also draws the skin of theneck superiorly when teeth are clenched

Antagonist: Masseter,Temporalis

Description:
The Platysma is a broad sheet arising from the fascia covering the upper parts of the Pectoralis major and Deltoideus; its fibers cross the clavicle, and proceed obliquely upward and medialward along the side of the neck. The anterior fibers interlace, below and behind the symphysis menti, with the fibers of the muscle of the opposite side; the posterior fibers cross the mandible, some being inserted into the bone below the oblique line, others into the skin and subcutaneous tissue of the lower part of the face, many of these fibers blending with the muscles about the angle and lower part of the mouth. Sometimes fibers can be traced to the Zygomaticus, or to the margin of the Orbicularis oculi. Beneath the Platysma, the external jugular vein descends from the angle of the mandible to the clavicle.