Which muscle is responsible for closing the eyelid and compressing the lacrimal sac?

The orbicularis oculi muscle is responsible for closing the eyelid and plays a significant role in the function of the lacrimal sac. This muscle forms a circular band around the eyes and is essential for blinking, which not only protects the eye from foreign objects but also helps to moisten and lubricate the surface of the eye.

When the orbicularis oculi contracts, it facilitates the closing of the eyelids, which assists in creating a vacuum effect that aids in the proper drainage of tears from the lacrimal sac into the nasal cavity. This action is crucial for maintaining ocular health and comfort.

Understanding the function of the orbicularis oculi in both eyelid movement and tear drainage is essential for those studying anatomy and physiology related to the eyes. Other muscles listed do not serve these functions: the orbicularis oris is involved in movements of the mouth, the frontalis assists with raising the eyebrows, and the zygomatic muscle is primarily involved in smiling and elevating the corners of the mouth.