facial muscle, one of numerous muscles of the face that seldom remains distinct over its entire length because of a tendency to merge with a neighboring muscle at its termination or its attachment. The five groups of facial muscles are the muscles of the scalp, the extrinsic muscles of the ear, the muscles of the nose, the muscles of the eyelid, and the muscles of the mouth. The platysma is one of the facial group but is classified among the muscles of the neck. Also called muscle of expression.
