[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Depressor labii inferioris [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Depressor labii inferioris The depressor labii inferioris is a small muscle from the lower jaw to the lower lip; it pulls the lower lip down. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=depressor_labii_inferioris&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A small muscle from the jaw to the lower lip. ## What it does Pulls the lower lip down. ## Key points - The muscle tested by asking the person to show the lower teeth; it fails when the marginal mandibular branch of the [facial nerve](https://durgical.com/en/anatomy/facial-nerve/) is cut - Lies deep and medial to the depressor anguli oris; the mental nerve emerges from the mental foramen beneath them - Cervical branch injury can mimic its paralysis through loss of the platysma ## Key facts **Origin** Oblique line of the mandible **Insertion** Lower lip **Action** Pulls the lower lip down **Nerve** Facial nerve (CN VII): marginal mandibular branch **Blood supply** [Facial artery](https://durgical.com/en/anatomy/facial-artery/) branches ## Relations **Superficial** [Depressor anguli oris](https://durgical.com/en/anatomy/depressor-anguli-oris/) laterally and the [skin](https://durgical.com/en/anatomy/skin/) of the chin; fibres of the [platysma](https://durgical.com/en/anatomy/platysma/) blend into it **Deep** [Mandible](https://durgical.com/en/anatomy/mandible/) and the [mental foramen](https://durgical.com/en/anatomy/mental-foramen/) with the mental nerve and vessels; the lower lip mucosa above **Medial** The opposite muscle and the [mentalis](https://durgical.com/en/anatomy/mentalis-muscle/), which lies deeper in the midline **Above** [Orbicularis oris](https://durgical.com/en/anatomy/orbicularis-oris-muscle/) in the lower lip ## How to find it Asked to show the lower teeth, a small sheet of muscle draws the lower lip down and out on each side of the chin. ## Examination - Showing the lower teeth: on the weak side the lower lip stays up and the smile is asymmetric - Lip eversion test: if the person can still evert the lower lip (mentalis intact) but cannot draw it down, a cervical branch or platysma problem is more likely than a marginal mandibular one ## On imaging Rarely imaged on its own: on CT or MRI it is only a faint layer in the chin soft tissue, lateral to the mentalis, over the mental foramen. When the lower lip droops on one side, imaging looks at the facial nerve instead: ultrasound or MRI of the parotid and of the angle of the mandible for a mass along the marginal mandibular branch. ## Clinical notes - The marginal mandibular branch runs deep to the platysma near the lower border of the mandible and can dip below it, so neck incisions for the [submandibular gland](https://durgical.com/en/anatomy/submandibular-gland/) are placed a couple of fingerbreadths below the jaw - Selective weakening of the healthy side's depressor (surgery or toxin injection) is used to balance a lopsided smile after facial palsy ## Development Second pharyngeal arch muscle, supplied by the facial nerve. ## Test yourself Think of the answer, then tap the question to see it. ## How is the depressor labii inferioris tested, and which nerve branch does it check? By asking the person to show the lower teeth; it fails when the marginal mandibular branch of the facial nerve is cut. ## How does the lip eversion test separate a cervical branch from a marginal mandibular branch injury? If the person can evert the lower lip (mentalis intact) but cannot draw it down, a cervical branch or platysma problem is more likely. ## Which nerve emerges beneath the depressor labii inferioris? The mental nerve, from the mental foramen beneath the depressor labii inferioris and depressor anguli oris. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/depressor-labii-inferioris/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** depressor labii inferioris TA2 2083 **Official Spanish (DeCS)** Músculo depresor del labio inferior **English (TA2)** Depressor labii inferioris **Also called** depressor labii inferioris muscle · quadratus labii inferioris muscle · muscle of Aeby · musculus quadratus labii inferioris · musculus labii mandibularis ## Related - [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) Sources: Terminologia Anatomica (TA2); [Anatomy, Head and Neck: Facial Muscles](https://www.ncbi.nlm.nih.gov/books/NBK493209/); [Anatomy, Head and Neck, Lips](https://www.ncbi.nlm.nih.gov/books/NBK507900/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/depressor-labii-inferioris/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/depressor-labii-inferioris/