Labial Commissure

Description

Seen in lateral profile from the shoulders up, the oral commissure (labial commissure) marks the junction of the upper and lower lips at the angle of the mouth. At this point, fibers of orbicularis oris interlace with the modiolus, receiving contributions from risorius and buccinator deep to the cheek, and from the elevators and depressors of the commissure (zygomaticus major, levator anguli oris, depressor anguli oris) arranged around it. Two surface callouts over the anterolateral cheek sit just lateral to the commissure, consistent with the superficial course and insertion zone of risorius as it draws the angle of the mouth laterally. Skin texture and lip vermilion are rendered with attention to melanated complexion in an adult Black female. For teaching facial expression mechanics, the commissure is where muscle vectors become clinically legible: zygomaticus major elevates the modiolus during smiling, depressor anguli oris pulls it inferolaterally in frowning, and orbicularis oris seals and purses the lips for speech and oral competence. Small asymmetries here are the day-to-day findings in peripheral facial nerve palsy, where weakness of zygomaticus and risorius produces commissure droop and drooling, and in post-traumatic or post-surgical scarring that tethers the modiolus. It is also a frequent site for angular cheilitis and for cosmetic planning, since filler placement and chemodenervation near the commissure can change smile breadth and the depth of perioral rhytids. A tight landmark. Use this asset in head and neck anatomy, dental and orthodontic teaching on perioral soft tissues, plastic and reconstructive surgery references for commissuroplasty and scar revision, and speech-language pathology materials focused on articulation and oral competence. Anatomical accuracy verified by SciePro's Medical Advisory Board.