Muscle · Head and neck
Depressor labii inferioris: origin, insertion, action and innervation
The depressor labii inferioris runs from the mandible to the lower lip. It pulls the lip down and out; facial nerve (CN VII), marginal mandibular branch.
Quick answer
- Latin name
- Musculus depressor labii inferioris
- Origin
- Oblique line of the mandible, between the symphysis and the mental foramen
- Insertion
- Skin and mucosa of the lower lip, blending with the orbicularis oris and the muscle of the other side
- Action
- Depresses the lower lip and draws it laterally
- Innervation
- Facial nerve (CN VII), marginal mandibular branch
- Blood supply
- Inferior labial artery (from the facial artery) and the mental artery
See it on the 3D body
The depressor labii inferioris lit on the 3D head, as in the head quiz. Turn the body, peel the layers, tap any structure for its name.
The depressor labii inferioris is a small, four-sided muscle of the chin that pulls the lower lip down and slightly sideways, uncovering the lower teeth. It runs from the front of the mandible to the lower lip and is supplied by the marginal mandibular branch of the facial nerve (CN VII).
Where it is
The muscle lies on the front of the chin, on either side of the midline, between the lower lip and the lower edge of the jaw. Older texts called it the quadratus labii inferioris because of its square shape.
Three muscles share this small area, and their positions are worth learning together:
- the mentalis, closest to the midline, at the tip of the chin;
- the depressor labii inferioris, just lateral to it;
- the depressor anguli oris, further out and more superficial, overlapping the lateral part of the depressor labii inferioris.
Below, its fibers continue into the platysma of the neck. The mental nerve and vessels come out of the mental foramen of the mandible underneath it, on their way to the skin of the chin and lower lip.
Origin and insertion
- Origin: the oblique line of the mandible, on the front of the jaw between the symphysis (the midline where the two halves of the mandible fused) and the mental foramen.
- Insertion: the skin and mucosa of the lower lip. Its fibers run up and inward and mix with the orbicularis oris and with the depressor labii inferioris of the other side.
What it does
The depressor labii inferioris depresses the lower lip and draws it laterally. When both sides work, the lower lip rolls down and out and the lower teeth come into view.
You use it in several everyday expressions: a grimace showing the lower teeth, a sulky or doubtful look, or the face people make when they say "eek". The platysma often contracts at the same time, so the skin of the neck tightens.
It is worth comparing with the mentalis, its neighbor. The mentalis does almost the opposite: it raises the skin of the chin and pushes the lower lip up and out, the pout of a child about to cry. Moving the lower lip down is the job of the depressor labii inferioris; pushing it out is the mentalis.
Innervation and blood supply
The muscle is supplied by the marginal mandibular branch of the facial nerve. This branch leaves the lower part of the parotid gland, runs forward along the lower border of the mandible and turns up to supply the muscles of the lower lip and chin. Because this single branch is the main supply, the lower lip on one side can droop unevenly when the branch is injured.
Blood comes from the inferior labial artery, a branch of the facial artery that runs inside the lower lip, and from the mental artery, which leaves the mandible at the mental foramen with the mental nerve.
How to remember it
- Labii inferioris = of the lower lip. The name says which lip it pulls down.
- Square under the lip: think of its old name, quadratus, and picture a small square tile on each side of the chin.
- Middle of three: from the midline outward, mentalis, depressor labii inferioris, depressor anguli oris.
- Show your bottom teeth: pulling the lower lip down to bare the lower teeth is the clearest way to see it work in a mirror.
The muscles of the face page shows the whole group around the mouth, including the buccinator. Then test yourself in the head quiz.
Frequently asked questions
What does the depressor labii inferioris do?
It pulls the lower lip down and slightly sideways, showing the lower teeth.
Which nerve supplies the depressor labii inferioris?
The marginal mandibular branch of the facial nerve (CN VII).
Where is the depressor labii inferioris?
On the front of the chin, between the mentalis and the depressor anguli oris, running from the mandible to the lower lip.
What is the difference between the depressor labii inferioris and the mentalis?
The depressor labii inferioris pulls the lower lip down. The mentalis wrinkles the chin and pushes the lower lip up and out.
