The risorius is a variable muscle — it may be absent, single, or multiple on each side. Its lateral pull on the lip corner produces a retracted, grimacing smile rather than the upward curve of zygomaticus major.
| Origin | Parotid fascia and skin over the masseter |
|---|---|
| Insertion | Modiolus and skin at the lip corner |
| Nerve Supply | Facial nerve — buccal branch (VII) |
| Blood Supply | Facial artery |
| Actions | Draws the lip corner laterally — produces a broad grimace-smile; Variable and often inconsistent between individuals |
|---|
Risorius variability is clinically important in smile reanimation surgery — reconstructive surgeons must account for the patient's native smile pattern (zygomaticus-dominant vs risorius-dominant) when planning the vector of the reanimating muscle transfer.
Visible as a horizontal lip corner retraction during a forced smile or grimace.
Preoperative smile analysis identifying a risorius-dominant horizontal smile pattern, directing the gracilis muscle transfer to a more lateral vector to replicate the native smile.
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