Three muscles are associated with the orbital opening, and they are the orbicularis oculi, corrugator supercilii, and depressor supercilii.

Orbicularis oculi

The orbicularis oculi is a circular shaped muscle around the opening of the eye. Among other functions, the orbicularis oculi muscle is involved in closing the eyelids.

This muscle consists of three parts: 

• Orbital part - encircles the orbital opening;
• Palpebral part - situated in the upper and lower eyelids;
• Lacrimal (deep palpebral) part - lies the most profoundly.

Corrugator supercilii

The corrugator supercilii is a small, narrow facial muscle located at the medial end of the eyebrow between the frontalis and orbicularis oculi muscles.

This muscle originates from the medial part of the superciliary arch, penetrates the frontalis and orbicularis oculi muscles and inserts into the skin over the middle of the eyebrow.

The corrugator supercilii pulls the skin of the eyebrow downward and medially. It also produces vertical wrinkles of the forehead.

Depressor supercilii

The depressor supercilii is another paired facial muscle that belongs to the orbital group. It is found at the medial and superior aspects of the orbit, stretching between the orbit and the eyebrow. Some authors state that the depressor supercilii is a part of the orbicularis oculi muscle rather than a distinct muscle. 

The origin site of this muscle is found at the lateral aspect of the nasal bridge and medial part of the orbital rim. It depresses the eyebrow. Along with the procerus, the depressor supercilii wrinkles the skin across the glabella.