Anterior Perspective of the Depressor Anguli Oris Muscle

Description

Running from the oblique line of the mandible up to the modiolus, the depressor anguli oris forms a triangular sheet in the inferolateral perioral region, with its broad base inferior and its narrow apex inserting at the corner of the mouth and blending with fibers of orbicularis oris. Medial to it, depressor labii inferioris rises toward the lower lip, while more laterally the risorius and zygomaticus major converge toward the same commissure. Superiorly, orbicularis oris encircles the oral fissure, and posterior to the cheek lie the masseter over the mandibular ramus and the temporalis on the temporal fossa. Beneath the mandibular body, the anterior bellies of the digastric are singled out in red, flanking the midline and sitting superficial to the mylohyoid in the submental region. Clear landmarks. Functionally, depressor anguli oris pulls the labial commissure inferiorly and laterally during frowning and grimacing, and this anterior perspective makes its relationship to the modiolus and the perioral sphincter easy to teach. Weakness of this muscle in marginal mandibular branch injury of the facial nerve (CN VII), after parotidectomy, submandibular surgery, or facelift dissection, produces an asymmetric smile and inability to depress the mouth corner on the affected side. The same anatomy guides botulinum toxin injection planning for downturned oral commissures and helps explain why over-treatment can flatten lower lip animation. Maxillofacial anatomy courses and facial expression modules in head and neck blocks will benefit from this plate when pairing surface expression with named muscular vectors around the lower lip. Plastic surgery, ENT, and dental publications can also use it to illustrate safe planes near the mandibular border and to orient readers to the digastric region under the jaw. Anatomical accuracy verified by SciePro's Medical Advisory Board.