Which muscle encircles the eye socket and is responsible for closing the eyelid?

The muscle that encircles the eye socket and is responsible for closing the eyelid is the orbicularis oculi. This muscle plays a crucial role in facial expressions and functions by contracting to close the eyelids, which is essential for protecting the eyes, aiding in blinking, and facilitating the movement of tears across the surface of the eye.

The orbicularis oculi is a circular muscle that wraps around the eye and can be divided into two parts: the palpebral portion, which closes the eyelids gently during blinking, and the orbital portion, which closes the eyelids tightly. The coordinated action of this muscle is vital for maintaining eye health and comfort.

Other muscles mentioned in the choices have different functions and are located in different areas of the face. The quadratus labii inferioris is involved in movements of the lower lip, the auricularis inferior is associated with the movement of the ear, and the procerus is responsible for wrinkle formation between the eyebrows. Each muscle has a specific role that does not include the closure of the eyelid, highlighting the unique function of the orbicularis oculi in this context.