Corpus: Depressor labii inferioris muscle
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from Latin: deprimere - to press down; labium - lip; inferior - lower(r)
Synonym: Musculus quadratus menti
1. Definition
The depressor labii inferioris muscle is part of the deeper layer of the facial muscles that control facial expressions around the mouth. Its primary function is to pull the lower lip downward.
2. Course
The depressor labii inferioris muscle originates from the lower edge of the mandible, specifically at the oblique line between the symphysis and the mental foramen. It continues the fiber direction of the platysma muscle. The muscle fibers run steeply upward and inward towards the lower lip, where they insert into the skin. Some fibers also blend with those of the orbicularis oris muscle.
3. Innervation
This muscle is innervated by the marginal mandibular branch of the facial nerve (cranial nerve VII).
4. Function
The depressor labii inferioris muscle pulls the lower lip downward, helping to express emotions such as sadness or disappointment. The muscle is fused with the skin, causing the skin to move with the muscle. Together with the depressor anguli oris muscle, it contributes to the expression commonly referred to as a "pout."