1. either of two broad muscles located on either side of the neck and innervated by the facial nerve; extends from lower jaw to clavicle and is involved in moving the mouth and jaw;
WordNet (r) 3.0 (2006):
platysma
n 1: either of two broad muscles located on either side of the
neck and innervated by the facial nerve; extends from lower
jaw to clavicle and is involved in moving the mouth and jaw