CorpusHuman Anatomy
MuscularMuscle

Orbicularis oris

Musculus orbicularis oris

Also known as: oral sphincter, kissing muscle

The complex sphincter of the mouth, forming most of the lips. It closes, purses and protrudes the lips.

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Overview

Orbicularis oris is not a simple ring. It is made partly of intrinsic fibres within the lips and partly of fibres from the converging dilator muscles, especially buccinator, whose fibres cross at the modiolus. A few fibres attach to the maxilla and mandible near the midline (incisive slips). The marginal part produces the red margin (vermilion) of the lip, and the peripheral part extends toward the nose and chin.

Its actions are finely graded: closing the lips (oral competence), compressing them against the teeth, pursing and protruding them (kissing, whistling, sucking through a straw), and shaping the lips for speech (labial consonants p, b, m). It works with buccinator to keep food and saliva in the mouth.

Location

Within the upper and lower lips, encircling the oral fissure.

Parts & subdivisions

  1. Marginal part
    Lies under the vermilion border.
  2. Peripheral part
    Extends to the nasal base and the mentolabial sulcus. Contains decussating fibres from buccinator and the other dilators.

Anatomy

Origin

Maxilla and mandible near the midline (incisive slips), the deep surface of the skin, and the modiolus (fibres from buccinator and other perioral muscles).

Insertion

Mucous membrane and skin of the lips.

Action

Closes the oral fissure, compresses the lips against the teeth, and purses and protrudes the lips.

Innervation

Facial nerve (CN VII), buccal and marginal mandibular branches.

Nerve roots

Cranial nerve VII; no spinal roots

Arterial supply

Superior and inferior labial arteries (facial artery); mental and infraorbital arteries.

Function

  • Closes and protrudes the lips
  • Shapes the lips for speech and whistling
  • Keeps food and saliva in the mouth (oral competence)

Clinical significance

Drooling and dysarthria in facial palsy

Weakness of orbicularis oris causes food and saliva to escape at the corner of the mouth and slurs labial consonants. Patients cannot whistle or puff out their cheeks.

Cleft lip repair

Reconstructing the continuity of orbicularis oris across the cleft is essential for normal lip function and appearance.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.