Depressor Anguli Oris Muscle Under the Skin, Anterior View

Description

Centered on the lower face, the depressor anguli oris (triangularis) appears as a paired, superficial muscle arising from the oblique line of the mandible and converging superomedially toward the modiolus at the oral commissure. Its fibers sit inferior and slightly lateral to orbicularis oris, blending with the depressor labii inferioris medially while lying anterior to the mandibular body and mental region. Superiorly, the corners of the mouth relate to the zygomaticus major and risorius, which counterbalance commissure depression during facial expression. Bony landmarks remain visible beneath the semi-transparent soft tissues, including the maxilla, mandible with adult dentition, zygomatic arches, and the margins of the orbits. Lower lip posture depends on this small triangle of fibers. Unilateral weakness of depressor anguli oris, from marginal mandibular branch injury after submandibular surgery or from a lower motor neuron facial nerve palsy, produces an asymmetric smile with reduced commissure depression and drooling at the affected corner. Cosmetic chemodenervation targets the same anatomy: selective botulinum toxin injection into depressor anguli oris can soften a downturned mouth, but diffusion into depressor labii inferioris risks lower lip incompetence and speech distortion. The anterior orientation also clarifies how the modiolus functions as a fibromuscular hub where perioral elevators and depressors interdigitate. Small muscle, big effect. Use this illustration for head and neck anatomy teaching in dental, medical, and speech-language pathology curricula, or to support operative notes and textbooks discussing facial nerve anatomy, lower facial reanimation, and perioral injection technique. It also fits patient-education materials explaining asymmetric facial expression after parotid, mandibular, or submandibular procedures. Anatomical accuracy verified by SciePro's Medical Advisory Board.