The risorius (also risorius muscle, latin: musculus risorius) is a muscle of facial expression located laterally to the mouth opening, which pulls the angle of the mouth laterally.
The risorius originates from the masseteric fascia and inserts into the skin of the angle of the mouth.
Upon activation the risorius pulls the angle of the mouth laterally. Contractions of the risorius muscle produce facial expression of pleasure and laughter.
The risorius is innervated by the buccal branch of the facial nerve (CN VII).