The |platysma| muscle is a broad, thin sheet of muscle that originates in the pectoral and |deltoid| (chest and shoulder) muscles and runs upward over the collar bone and inward along each side of the neck. This muscle works to draw the lower |lips| and corner of the |mouth| sideways and down partially opening the |mouth|. It is used when expressing surprise. It also increases the diameter of the neck as seen during intense breathing from fast running.
