Depressor Anguli Oris

Description

Arising from the anterolateral mandible along the oblique line, the depressor anguli oris forms a triangular sheet that runs superiorly and medially to the modiolus at the angle of the mouth. Superficial to it lie the risorius and platysma fibers near the lower cheek and jawline, while deeper planes relate to the depressor labii inferioris and the orbicularis oris at the oral commissure. Posterior to the muscle, the masseter occupies the ramus of the mandible, with the zygomatic arch and dentition providing fixed bony landmarks in lateral profile. Bony context includes the mandible, maxilla, and adjacent cranial bones, with the cervical vertebrae visible inferiorly. Functionally, this muscle pulls the oral commissure inferolaterally, a key contributor to frowning and to asymmetric mouth corner position at rest. Denervation in facial nerve (CN VII) lesions, most often involving the marginal mandibular branch, produces lower lip and commissure asymmetry that becomes obvious during smiling and speech. The mandibular origin and its relationship to the modiolus also make it relevant in perioral reconstructive planning and in targeted chemodenervation for selected dystonias or unwanted downward pull at the mouth corner. Small muscle, big tell. Use this lateral head and neck view to teach muscles of facial expression in gross anatomy, dental anatomy, and maxillofacial surgery modules, where students need to orient the triangularis (depressor anguli oris) against the mandible, masseter, and dental arches. It also fits well in clinical texts and patient education materials discussing facial nerve branch injuries, lower-face asymmetry, and perioral injection anatomy. Anatomical accuracy verified by SciePro's Medical Advisory Board.