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[Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/)

# Risorius

The risorius is a thin strip of facial muscle from the cheek to the corner of the mouth; it pulls the mouth corner sideways.

Official name: Risorius muscle

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## What it is

A thin strip from the cheek to the mouth corner.

## What it does

Pulls the mouth corner sideways.

## Key points

- The most variable facial muscle: thin, sometimes absent or doubled
- Lies superficially over the masseter and parotid fascia, so it is close under the skin of the cheek
- Supplied by the buccal branches of the [facial nerve](https://durgical.com/en/anatomy/facial-nerve/)

## Key facts

**Origin**
Parotid/masseteric fascia

**Insertion**
Angle of the mouth

**Action**
Pulls the mouth corner sideways

**Nerve**
Facial nerve (CN VII): buccal branches

**Blood supply**
Facial artery branches

## Relations

**Superficial**
[Skin](https://durgical.com/en/anatomy/skin/) and subcutaneous fat of the cheek

**Deep**
Masseteric and parotid fascia, the [masseter](https://durgical.com/en/anatomy/superficial-part-of-masseter/), and further forward the [buccinator](https://durgical.com/en/anatomy/bucinator/); the [facial artery](https://durgical.com/en/anatomy/facial-artery/) and vein pass deep to it

**Medial**
Modiolus at the angle of the mouth

**Below**
[Platysma](https://durgical.com/en/anatomy/platysma/), whose upper fibres often merge with it

## How to find it

Asked to pull the mouth corners straight sideways (a tight, closed-lip grin), a thin horizontal band tightens across the cheek toward the mouth corner.

## Examination

- Grinning with the lips closed: the mouth corner does not pull back on the weak side (buccal branch of the facial nerve)

## On imaging

Usually not identified on imaging: it is thin, variable and often blends with the platysma and the parotid fascia. Ultrasound or MRI of the cheek may show it as a fine superficial band over the masseter. Imaging of this area is aimed at the [parotid gland](https://durgical.com/en/anatomy/parotid-gland/) and masseter beneath it; for a weak smile, MRI follows the course of the facial nerve.

## Clinical notes

- Risus sardonicus, the fixed grin of tetanus, is named after it, though it reflects spasm of many facial muscles
- Botulinum toxin injection into the masseter can spread to it and the [zygomaticus major](https://durgical.com/en/anatomy/zygomaticus-major-muscle/), giving an uneven smile

## Anatomical variants

- Absent, poorly developed or doubled in many people; it may arise from the platysma rather than the fascia

## Development

Second pharyngeal arch muscle; the incomplete splitting of this arch's muscle sheet helps explain why it is so variable and may blend with the platysma.

## Memory aid

Risorius, from the Latin risus (laughter): it pulls the mouth corner sideways, as in a grin.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the action and nerve supply of the risorius?

It pulls the mouth corner sideways; supplied by the buccal branches of the facial nerve.

## Which tetanus sign is named after the risorius?

Risus sardonicus, the fixed grin of tetanus, although it reflects spasm of many facial muscles.

## Why is the risorius often hard to identify?

It is the most variable facial muscle: thin, sometimes absent or doubled, and may arise from the platysma.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
musculus risorius TA2 2078

**Official Spanish (DeCS)**
Músculo risorio

**English (TA2)**
Risorius muscle

**Also called**
muscle of Albinus · Santorini's muscle

## Related

- [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Head and Neck, Risorius Muscle](https://www.ncbi.nlm.nih.gov/books/NBK540999/); Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/risorius-muscle/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/risorius-muscle/