Two muscles are associated with the orbital opening - orbicularis oculi and corrugator 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 of the eyelid.

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.

Upon contraction, the corrugator supercilii pulls the skin of the eyebrow downward and medially and produces vertical wrinkles of the forehead.