4.6.2 Lower facial muscles
The three muscles that join the orbicularis from below are quite hard to tell apart. They're depressor anguli oris, depressor labii inferioris, and mentalis.
The last two run into one another, and are embedded in this mass of fat and fibrous tissue which forms the prominence of the chin. These three muscles arise from here on the mandible. Between them they pull the lower lip downward, and pucker the chin.
The last muscle we'll add to the picture, the platysma, lies partly in the face but mainly in the neck. Here's the neck as we saw it in the last tape, without the platysma. Here are the sternocleidomastoid muscle, the infrahyoid muscles, and the digastric muscle.
Now we'll add the platysma to the picture. All this is platysma. It lies within the subcutaneous fascia of the neck. Its lowest fibers extend below the clavicle, onto the chest. Platysma has a free posterior border here, and a free anterior border here near the midline.
Most of the fibers of platysma insert here along the border of the mandible, but its more posterior fibers cross the mandible, and insert into the orbicularis oris complex. The platysma muscle pulls the corner of the mouth downwards and backwards, producing these ridges beneath the skin.