Risorius Muscle Beneath The Skin

Description

Running superficially across the lateral cheek, the risorius (often labeled Santorini’s muscle) appears as a thin, subcutaneous fascicle extending from the parotidomasseteric fascia overlying the masseter toward the modiolus at the angle of the mouth. Anterior to it, orbicularis oris encircles the oral aperture, while zygomaticus major and minor descend from the zygomatic bone to converge near the same perioral fibromuscular hub. Superiorly, orbicularis oculi forms the palpebral and orbital rings around the eye, and frontalis spans the forehead; inferior and posterolateral landmarks include the sternocleidomastoid on the neck and the auricle in anatomic position. A delicate muscle with outsized teaching value. Risorius retracts the oral commissure laterally, modulating the smile and shaping facial expression during speech. Its variable origin and occasional absence matter in facial reanimation planning and in interpreting asymmetric smiles after injury, where marginal mandibular and buccal branches of the facial nerve (CN VII) can be involved. The close relationship to the parotid region also makes this anatomy relevant when discussing parotidectomy approaches and safe planes that protect the facial nerve while working across the masseteric fascia. Use this artwork in head and neck anatomy courses to contrast the muscles of facial expression with the deeper muscles of mastication (masseter and buccinator) and to teach the modiolus as a functional intersection for perioral muscles. It also fits surgical atlases and patient-facing education on facial nerve palsy, chemodenervation patterns, and reconstructive planning around the oral commissure. Anatomical accuracy verified by SciePro's Medical Advisory Board.