The orbicularis oris (also orbicularis oris muscle, latin: musculus orbicularis oris) is a facial muscle that is located in the thickness of the lip around the oral opening. The main function of the orbicularis oris is closing of the mouth.
The orbicularis oris has two main parts: the marginal part consisting of longitudinal fibers and the labial part of the orbicularis oris composed of circular fibers.
The longitudinal fibers of the marginal part of the orbicularis oris run below the skin around the mouth opening, originating and inserting within the tissue of the lips.
The marginal part of the orbicularis oris closes the oral opening.
The circular fibers composing the labial part of the orbicularis oris run between the angles of the mouth, having the origin and insertion site within the skin of the corners of the mouth.
The labial part of the orbicularis oris pushes the lips forward.
Both parts of the orbicularis oris are innervated by the buccal branch of the facial nerve (CN VII).
The orbicularis oris is supplied with arterial blood mainly by the superior and inferior labial branches of the facial artery, the mental and infraorbital branches of the maxillary artery and the transverse facial branch of the superficial temporal artery.