I believe it is the orbicularis oris muscle. It is the muscle that controls movements of the mouth and lips. It encircles the mouth, originating in the maxilla and mandible bones. The muscle insets directly into the lips. It is a sphincter muscle that encircles the mouth. It lies between the skin and the mucous membranes of the lips, extending upward to the nose and down to the region between the lower lip and chin.
