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Pars marginalis

Other Terms: Pars marginalis musculus orbicularis oris

Muscle parts

Marginal part; Labial part

Latin name

Musculus orbicularis oris

Latin muscle parts

Pars marginalis; Pars labialis

Group

Branchial arch muscle – second arch (Facial muscle)

Etymology

The English name for this muscle is the little circle muscle of the mouth. The word orbicularis comes from the Latin orbis meaning “circle or disk” and ulus which is a diminutive ending meaning “little.” The Latin term oris is from the Latin os meaning “a mouth or opening.”

Origin

Modiolus at the angle of the mouth (both marginal and peripheral parts); maxilla above second incisor; mandible below second incisor.

Insertion

The peripheral part interdigitates with opposite fibers crossing the midline to insert into the skin near the opposite midline from the nasolabial sulcus to the margin of the red lip superiorly and from the mentolabial sulcus to the margin of the red lip inferiorly. The marginal part, likewise, interdigitates and crosses the midline to insert into the red lip dermis just opposite the midline in both superior and inferior lips.

Action

This complex arrangement of muscle fibers performs a variety of actions associated with the lips and adjoining muscles. It functions in modifying the actions of the surrounding muscles that insert into the lips and angles of the mouth. It functions in puckering the lips and assists in compressing the lips together and turning them inward.

Nerve supply

Facial nerve (Cranial nerve VII)

Blood supply

Superior labial and inferior labial branches of the facial artery.

Latin

Pars marginalis musculus orbicularis oris

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