The orbicularis oris is a complex circular muscle that surrounds the mouth and is responsible for controlling movements of the lips, mouth, and facial expressions. It comprises several interlacing muscular fibers that form a ring around the mouth, allowing for precise movements of the lips during speech, eating, and facial expressions. The orbicularis oris muscle is innervated by the facial nerve (cranial nerve VII) and plays a key role in facial expressions such as smiling, puckering, and pouting. It also helps to keep the lips closed and prevent drooling. Dysfunction or weakness of the orbicularis oris muscle can lead to difficulties with speech, eating, and facial expressions.