Corpus: Risorius muscle

The risorius muscle is a superficial muscle located in the region of the mouth and cheek that pulls the corners of the mouth to the side. It is part of the facial expression (mimic) musculature.

The risorius muscle originates from the skin of the cheek and the fascia overlying the masseter muscle. Its fibers run medially toward the modiolus at the corner of the mouth, where they insert.

The risorius muscle is innervated by the zygomatic and buccal branches of the facial nerve (cranial nerve VII).

The primary function of the risorius muscle is to pull the corners of the mouth laterally and slightly backward, widening the mouth. While often referred to as a "smile muscle," this term is not entirely accurate, as the risorius does not elevate the corners of the mouth. However, it does play a role in expressions associated with laughter, working together with the zygomaticus major muscle. The risorius muscle is closely fused with the underlying skin, causing the skin to follow its movements.