The depressor labii inferioris is a small, triangular muscle located in the lower lip and chin region of the face. It extends from the mandible (lower jaw) to the skin of the lower lip and is responsible for pulling the lower lip downward and to the side. This muscle also helps to widen the oral opening and protrude the lower lip, allowing for speech and facial expressions such as frowning or pouting. The depressor labii inferioris muscle is innervated by the mandibular branch of the facial nerve (cranial nerve VII). It works with other facial muscles to produce a range of facial expressions. Dysfunction or weakness of the depressor labii inferioris muscle can lead to difficulties with speech, eating, and facial expressions, such as smiling or puckering the lips.