Muscle · Head

Risorius

Musculus risorius

A narrow band of muscle running horizontally across the cheek from the tough fascia over the parotid gland and the chewing muscle forward to the corner of the mouth. It pulls the mouth corner straight sideways, widening the mouth into a grin without lifting it — which is what distinguishes a stretched smile from a warm one. It is the most variable of all the facial muscles: it may be broad, narrow, doubled or entirely absent, and unlike its neighbours it reaches bone at neither end — fascia at one, skin and the fibrous knot of the mouth corner at the other. Where its fibres cross the cheek unevenly it is one of the structures credited with producing a dimple.