Depressor Anguli Oris Muscle, Anterior View

Description

Arising from the oblique line of the mandible and coursing superomedially, the depressor anguli oris (triangularis) reaches the modiolus at the corner of the mouth, where it interlaces with orbicularis oris and the adjacent elevators. From an anterior facial view, its paired bellies frame the inferior-lateral perioral region, lying lateral to depressor labii inferioris and inferior to zygomaticus major as it runs toward the oral commissure. Superficially, the skin of the lower cheek and chin overlies the muscle; deep to it sit the mandibular body and the emerging mental region. Symmetry matters. Clinically, this muscle is a key contributor to downward pull of the oral commissure and lower-lip eversion, so weakness or hypertonicity changes resting mouth posture and the pattern of expression. Facial nerve dysfunction involving the marginal mandibular branch can denervate the depressor anguli oris, producing an asymmetric smile and an apparent droop that is often compared side to side during cranial nerve VII testing. The same anatomy guides botulinum toxin injection planning for downturned mouth corners, where diffusion into depressor labii inferioris can worsen lower-lip competence. Use this anterior reference when teaching perioral musculature in head and neck anatomy, facial expression labs, or dental and orthodontic curricula that address the modiolus and lower facial balance. It also fits surgical and aesthetic medicine materials discussing lower face rejuvenation, marginal mandibular nerve risk in submandibular approaches, and targeted chemodenervation around the oral commissure. Anatomical accuracy verified by SciePro's Medical Advisory Board.