platysma /plətiz″mə/ [Gk, platys, broad] , one of a pair of platelike, wide muscles at the side of the neck. It arises from the fascia covering the superior parts of the pectoralis major and the deltoideus, crosses the clavicle, and rises obliquely and medially along the side of the neck. The platysma covers the external jugular vein as the vein descends from the angle of the mandible to the clavicle. The platysma is innervated by the cervical branch of the facial nerve and serves to draw down the lower lip and the corner of the mouth. When the platysma fully contracts, the skin over the clavicle is drawn toward the mandible, increasing the diameter of the neck.
