Risorius

Risorius
Muscles of the head, face, and neck.
Latin	musculus risorius
Gray's	subject #108 385
Origin	parotid fascia
Insertion	modiolus
Artery	facial artery
Nerve	Buccal branch of the facial nerve
Actions	draw back angle of mouth

The risorius arises in the fascia over the parotid gland and, passing horizontally forward, superficial to the platysma, inserts onto the skin at the angle of the mouth. It is a narrow bundle of fibers, broadest at its origin, but varies much in its size and form.

Action

The risorius retracts the angle of the mouth to produce a smile, albeit an insincere-looking one that does not involve the skin around the eyes. Compare with a real smile, which raises the lips with the action of zygomaticus major and zygomaticus minor muscles and causes "crow's feet" around the eyes using the orbicularis oculi muscles.

Innervation

Like all muscles of facial expression, the risorius is innervated by the facial nerve (CN VII). The specific nerve being the buccal branch.

Human unique

It has been suggested that the risorius is only found in humans: "Among the hominoids dissected for the present study, only modern humans had a well-defined, separate, risorius" and in chimpanzees potentially similar fibers "did not form a distinct, well defined muscle risorius such as that found in most humans".^[1]

References

External links

• LUC ris
• -1160773552 at GPnotebook
• Risorius+muscle at eMedicine Dictionary
• PTCentral

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

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