The orbicularis oris is a complex facial muscle that encircles the oral opening and forms the bulk of the lips. This muscle controls movements of the mouth and lips, and its main function is to close the mouth by compressing and closing the lips. Although the orbicularis oris may appear to be a single muscle, it consists of two parts: the outer marginal part and the inner labial part.

Orbicularis oris, levator anguli oris, depressor anguli oris and zygomaticus major

It is a multi-layered muscle that originates from the maxilla, mandible, and modiolus (the fibromuscular node at the corner of the mouth), and inserts directly into the skin and mucous membrane of the lips via a thin, superficial musculoaponeurotic system. This muscle also serves as an attachment site for many surrounding facial muscles, such as the buccinator, zygomaticus major, and zygomaticus minor.

In addition to the mentioned functions, the orbicularis oris also protrudes the lips and assists in speech articulation and controlling food intake. The deep fibers of the muscle help retain food within the mouth, while the superficial fibers are more involved in facial expression and precise lip movements during speech.

Together with the buccinator, the orbicularis oris compresses cheeks and lips against the teeth, which is essential for producing speech sounds, as well as during swallowing, mastication, and sucking. This muscle also enables puckering of the lips, earning it the nickname the “kissing muscle.” It also plays an expressive role by helping convey emotions such as sadness, doubt, or determination through lip movements.

Origin: maxilla and mandible, modiolus at the angle of the mouth, and the skin of the mouth. It also receives fibers from adjacent facial muscles.

Insertion: skin and mucous membrane of the lips, blending with fibers of surrounding facial muscles.

Action: closes the mouth by compressing and sealing the lips (marginal part); pushes the lips forward (labial part). This part also compresses the lips against the teeth and assists in speech and food intake control.

Innervation: buccal and marginal mandibular branches of the facial nerve (CN VII).

Arterial blood supply: superior and inferior labial arteries of the facial artery; may also receive contributions from the mental artery and infraorbital artery of the maxillary artery.

Venous drainage: superior and inferior labial veins, which drain into the facial vein.

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Orbicularis oris