Definition of "platysma"

(anatomy) A broad sheet of muscle that is situated on each side of the neck immediately under the superficial fascia belonging to the group of facial muscles, extends from the collar bone to the angle of the jaw and overlaps the sternocleidomastoid; it is innervated by the facial nerve, draws the lower lip and the corner of the mouth to the side and down, and when moved forcefully expands the neck and draws its skin upward.  examples