What is risorius muscle?

The risorius muscle is a thin, narrow muscle located in the face. It is one of the muscles of facial expression and is responsible for pulling the corners of the mouth sideways. The risorius muscle works with other muscles in the face to produce expressions such as smiling and grimacing.

The risorius muscle originates from the fascia overlying the masseter muscle (a muscle of mastication) and inserts into the skin of the corner of the mouth. It is innervated by the facial nerve (cranial nerve VII).

The primary function of the risorius muscle is to retract the corner of the mouth horizontally, producing a smile. In some individuals, the risorius muscle may be underdeveloped or absent, leading to a lack of movement in the corners of the mouth.

Overall, the risorius muscle plays an important role in facial expression and contributes to the wide variety of emotions and expressions that humans can convey through their faces.