Orbicularis oris

The muscle of the lips

Face · sphincter round the mouth

The ring of muscle that lies in the upper and lower lips and surrounds the mouth. It is not a simple circular sphincter but a weave of its own fibres with those of the other facial muscles that insert into the lips, so that the lips can pucker, purse, seal against a spoon or shape the sounds of speech. It is supplied by the facial nerve.

How to spot them

▸A ring of fibres in the lips, with a deep part of its own and a superficial part made of fibres from other muscles
▸Fibres of buccinator, risorius and the elevators and depressors of the lips blend into it at the modiolus, the knot at the corner of the mouth
▸Supplied by the buccal and marginal mandibular branches of the facial nerve
▸Incompetence leads to drooling and difficulty whistling or drinking from a straw

What to know

The ring of muscle in the lips that closes and purses the mouth

Orbicularis oris — the sphincter of the lips.

Popularly nicknamed for the pursing action used in a kiss, or in whistling and blowing out candles

Orbicularis oris — the kissing muscle.

The knot of fibres at the corner of the mouth where several muscles meet and blend into it

Orbicularis oris — the modiolus, the meeting point of the facial muscles at the angle of the mouth.

Fibres of the muscle that forms the cheek wall cross over into the lips to join it, so that it acts as more than a simple ring

Orbicularis oris — buccinator fibres decussate into it.

In a child with a cleft lip the ring is interrupted, and surgical repair reconnects its two halves

Orbicularis oris — muscle repair is an essential step in closing a cleft lip.

Trumpet and horn players build strength in it to control the shape of their lips

Orbicularis oris — the embouchure.

A facial palsy affecting the lower branches leaves food and saliva escaping from the corner of the mouth

Orbicularis oris — the buccal and mandibular branches of the facial nerve.

Key ideas

The muscle has a deep part, from its own fibres, and a marginal part that forms the red border of the lips; the outer layers are supplied from the other facial muscles, so the lips can move in ways a simple ring could not.
Its tone against the buccinator and the cheeks keeps food in the mouth while chewing and seals the lips for sucking and swallowing in infants.

Quick-fire facts

•Origin: the maxilla and mandible near the midline (via the incisive fossae) and the modiolus, with fibres from other muscles of the lips and cheeks
•Insertion: the skin and mucous membrane of the lips
•Action: closes and purses the lips, narrowing the oral opening
•Nerve supply: buccal branches (and the marginal mandibular branch) of the facial nerve
•Blood supply: the superior and inferior labial branches of the facial artery
•The modiolus is a fibromuscular node about 1 cm lateral to the corner of the mouth
•A pure sphincter of the mouth does not exist; its fibres are largely those of the muscles that blend with it
•The muscle is important for speech sounds such as p, b and m, and for whistling and blowing
•It is tested clinically by asking the patient to purse the lips or blow out the cheeks against resistance

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Sources

TeachMeAnatomy — Orbicularis oris