Risorius

Description

Shown in left lateral view of an adult male head and upper neck, the risorius (Santorini) is isolated as a thin, superficial slip running horizontally across the cheek toward the modiolus at the angle of the mouth. Its fibers lie anterior to the parotid-masseteric region and typically course superficial to the masseter, approaching the orbicularis oris laterally where several muscles of facial expression interdigitate. Superior to the risorius, the zygomaticus major and minor track inferomedially from the zygomatic bone, while the buccinator forms a deeper muscular layer of the cheek. Temporalis, orbicularis oculi, and key cervical landmarks such as sternocleidomastoid and upper trapezius provide orientation. Risorius anatomy matters because it sits at the intersection of expression, facial nerve anatomy, and common procedural planes. The muscle is supplied by buccal branches of the facial nerve (CN VII) that traverse the parotid region, so this lateral cheek view helps teach why superficial dissection, rhytidectomy flaps, or trauma in the preauricular and masseteric area can produce selective weakness in smiling, often alongside adjacent zygomaticus dysfunction. Variable presence and morphology are common, and distinguishing risorius from the zygomaticus complex and platysma reduces confusion when mapping facial action units or interpreting asymmetry in Bell palsy recovery. Use this illustration in head and neck gross anatomy labs, facial expression modules for dentistry and speech pathology, and surgical education materials that discuss SMAS-plane dissection, parotidectomy landmarks, or buccal space approaches. It also fits well in atlases and review figures where a single highlighted muscle guides the reader through layered facial musculature at the cheek. Anatomical accuracy verified by SciePro's Medical Advisory Board.