Head and neck muscles (chewing, facial, and throat muscles)

Risorius

Musculus risorius

Origin

Parotideomasseteric fascia (fascia over the masseter muscle, near the ear)

Insertion

Skin of the corner of the mouth

Function

Pulls the corner of the mouth straight laterally ('grinning', a social smile without Duchenne features)

Innervation

Buccal branch of the facial nerve (CN VII)

Movement & chain

Pulls the corner of the mouth straight laterally; a superficial mimetic movement without a joint chain.

Palpation

Palpable as a superficial muscular slip overlying the parotid-masseteric fascia.

Clinical

Highly variable in development between individuals (sometimes absent); of little clinical significance, though relevant to smile-pattern analysis.

Segmental innervation

CN VII, motor.

In clinical practice

Retracts mouth angle laterally; relaxation and soft tissue stretching for hypertonic facial synkinesias.

Region in the model

Head and neck muscles (chewing, facial, and throat muscles)