Immediately under the skin of the neck is the platysma muscle, which you can easily see in a mirror when you clench your teeth and tighten your jaw. In youth, this paired muscle meets in the midline below the chin. With age, the right and left sides of the platysma often separate, producing vertical 'cords' in the anterior neck.
The platysma can be divided anteriorly and tightened during neck lift cosmetic surgery to permanently eliminate these 'cords' and improve the neck contour. One tightened in the midline below the chin, lateral traction on the platysma then creates a 'sling' which elevates the soft tissues below the jawline.