Final answer:
The orbicularis oculi is the muscle responsible for closing the eye and is part of the muscles of facial expression.
Step-by-step explanation:
The orbicularis oculi is the part of the muscles of facial expression that you are asking about. This muscle is responsible for closing the eye and is one of the circular muscles, or sphincters, found in the facial area. The orbicularis oris controls movements around the mouth, and though similar in name, it is different in function from the orbicularis oculi. It should not be confused with the extraocular muscles, which control the movement of the eyeball within the orbit but are not involved in facial expression.