orbicularis oris muscle

Fibres that encircle the opening of the oral cavity make up orbicularis oris, a superficial muscle of the face. Its attachments are unusually varied for a facial muscle, taking in the maxilla, the mandible, the skin, and the modiolus, the fibrous node at the angle of the mouth where several facial muscles converge. It participates in oral and pharyngeal behaviours, and like the other muscles of facial expression it is innervated by the facial nerve, cranial nerve VII. The encircling arrangement of its fibres, rather than a simple origin-to-insertion course, is what allows the muscle to act as a sphincter around the mouth. It is classified among the facial muscles.