The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle. It helps to lower the bottom lip.

Structure

The depressor labii inferioris muscle arises from the lateral surface of the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. This is below the

mental foramen The mental foramen is one of two foramina (openings) located on the anterior surface of the mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels. Structure The ...

, and the origin may be around 3 cm wide. It inserts on the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

of the

lower lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

, blending in with the

orbicularis oris muscle In human anatomy, the orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. It is a sphincter, or circular muscle, but it is actually composed of four independent quadrants that interlace and give only an appearance ...

around 2 cm wide. At its origin, depressor labii is continuous with the fibers of the platysma muscle. Some yellow fat is intermingled with the fibers.

Nerve supply

The depressor labii inferioris muscle is supplied by the marginal mandibular branch of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste ...

Function

The depressor labii inferioris muscle helps to depress and everts the

. It is the most important of the muscles of the lower lip for this function. It is an antagonist of the

. It is needed to expose the mandibular (lower)

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, ...

during smiling.

Clinical significance

Resection

The depressor labii inferioris muscle may be resected (cut and removed) using

surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...

to correct an asymmetry of the lower lip when smiling. This asymmetry can be caused by paralysis of the marginal mandibular branch of the

on one side, so the healthy side may be cut to create symmetry.

Local anaesthesia Local anesthesia is any technique to induce the absence of sensation in a specific part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It ...

may be used, such as by blocking the mental nerve. This operation tends to be successful.

History

The depressor labii inferioris muscle has also (mainly historically) been called the quadratus labii inferioris muscle.

Additional images

File:Depressor_labii_inferioris_muscle_animation small.gif, Position of depressor labii inferioris muscle (red). File:Gray176.png, Mandible. Outer surface. Side view.

References

{{Authority control Muscles of the head and neck