Depressor Labii Inferioris
Facial Expression · Head & Neck
The depressor labii inferioris is a muscle of facial expression that lowers the lower lip. It arises from the oblique line of the mandible, between the symphysis and the mental foramen, and passes upward and medially to insert into the skin and muscle of the lower lip, where it blends with the orbicularis oris and with its fellow of the opposite side. On contraction it depresses the lower lip and draws it slightly laterally, an action used in expressions of irony or doubt and in exposing the lower teeth. It is supplied by the facial nerve (CN VII) through its marginal mandibular branch. This branch runs superficially near the lower border of the mandible and is at risk during surgery in the submandibular region.
Origin, Insertion, Action & Nerve
Origin
Oblique line of the mandible, between the symphysis and the mental foramen
Insertion
Skin and muscle of the lower lip, blending with orbicularis oris and the opposite muscle
Action
Depresses the lower lip and draws it laterally
Nerve
Marginal mandibular branch of facial nerve (CN VII)
Attachments explained
The Depressor Labii Inferioris is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Oblique line of the mandible, between the symphysis and the mental foramen
Insertion
Skin and muscle of the lower lip, blending with orbicularis oris and the opposite muscle
Action & function
When the Depressor Labii Inferioris contracts, it produces the following movement: Depresses the lower lip and draws it laterally.
As part of the Facial Expression group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Depressor Labii Inferioris receives its nerve supply from the Marginal mandibular branch of facial nerve (CN VII).
Because a muscle can only contract when its nerve is intact, injury to the Marginal mandibular branch of facial nerve can weaken or paralyse the Depressor Labii Inferioris, impairing the movements it normally produces (depresses the lower lip and draws it laterally). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Depressor Labii Inferioris (the OIANS method)
Learn the depressor labii inferioris by its straightforward name: it depresses the lower lip. Because it arises from the front of the mandible between the symphysis and the mental foramen and runs up into the lip, its contraction pulls the lower lip downward and outward; blending with orbicularis oris explains why it also helps evert the lip. Contrast it with the deeper mentalis, which raises rather than lowers the lower lip.
Tie its nerve to a clinical hook: like the depressor anguli oris, it is supplied by the marginal mandibular branch of the facial nerve (CN VII), which lies superficially near the lower jaw and is vulnerable in surgery, causing an uneven lower lip when injured. Studying the two lower-lip and mouth-corner depressors together keeps this shared, testable innervation firmly in mind.
Frequently asked questions
Where is the Depressor Labii Inferioris located?
The Depressor Labii Inferioris is a muscle of the Facial Expression group, located in the Head & Neck.
What is the origin of the Depressor Labii Inferioris?
Oblique line of the mandible, between the symphysis and the mental foramen
What is the insertion of the Depressor Labii Inferioris?
Skin and muscle of the lower lip, blending with orbicularis oris and the opposite muscle
What movements does the Depressor Labii Inferioris produce?
Depresses the lower lip and draws it laterally
What nerve supplies the Depressor Labii Inferioris?
Marginal mandibular branch of facial nerve (CN VII)
Is the Depressor Labii Inferioris free to study in OIANS?
The Depressor Labii Inferioris is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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