Risorius muscle

Last revised by Dr Daniel J Bell on 22 Sep 2021

The risorius muscle (TA: musculus risorius) is one of the muscles of the mouth, a subset of the facial muscles. It is often absent and has been described as an accessory muscle.

  • origin: fascia overlying the parotid, masseter and/or platysma muscles
  • insertion: angle of the mouth
  • innervation: facial nerve (VII)
  • action: pulls back the angle of the mouth

The risorius muscle arises from the superficial fascia as a bundle of muscle fibers which pass anteriorly to insert into the angle of the mouth. The bundle is widest at its origin, narrowing towards its insertion.

  • angle of the mouth 4
  • pulls back the angle of the mouth 2

The risorius muscle is commonly absent. Occasionally the risorius muscle is duplicated or markedly larger than normal. The fibers of risorius may be merged into the platysma muscle 2 or fused with the transversus nuchae muscle 5.

Giovanni Domenico Santorini (1681-1737), described the risorius muscle, hence its historical name, muscle of Santorini 6. The German born, naturalised Dutch, anatomist Bernhard Siegfried Albinus (1697-1770), wrote a detailed treatise on the risorius muscle, such that it was also called the muscle of Albinus in the past 7.

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