Corrugator supercilii

The corrugator supercilii (also known as the muscle of Koyter) is a pair of small, narrow, pyramidal-shaped facial muscles located above the medial aspects of the orbits at the level of the eyebrows. They lie between the frontalis, depressor supercilii, and orbicularis oculi, contributing to eyebrow movements.

The corrugator supercilii muscles arise from the medial ends of the superciliary arches of the frontal bones, where they are found deep to the frontalis and orbicularis oculi muscles. From the origin sites, the muscles pass laterally. Above the orbital rim, they become more superficial. And finally, they insert into the skin over the middle part of the eyebrows, above the supraorbital margins. In some individuals, these muscles may extend to the lateral third of the eyebrows.

The corrugator supercilii works together with other muscles of the glabellar region, including the procerus, depressor supercilii, and orbicularis oculi muscle. Together, they help maintain the position and shape of the eyebrows.

The corrugator supercilii muscle itself pulls the eyebrow medially and also depresses its medial aspect, causing vertical wrinkling of the skin over the glabella. This movement helps protect the eyes (e.g., from bright sunlight or rain) and also contributes to frowning. As the corrugator supercilii draws the eyebrow downward, it acts as a depressor muscle.

Because this muscle is responsible for frowning and squinting, it plays a key role in the formation of vertical wrinkles in the glabellar region. Frown lines between the eyebrows are typically the first facial wrinkles treated with Botox by cosmetic surgeons, and this muscle is one of the most common areas for injection.

Origin: medial end of the superciliary arch (a landmark of the frontal bone).

Insertion: skin over the middle part of the eyebrow; it also merges with the fibers of the frontalis muscle.

Action: draws the eyebrow downward and medially, producing vertical wrinkles in the skin between the eyebrows (over the glabella); this muscle contributes to the facial expression of anger or perplexion.

Innervation: temporal branches of the facial nerve (CN VII); innervation to this muscle sometimes also comes from the zygomatic and buccal branches of the facial nerve (CN VII).

Arterial blood supply: frontal branch of the superficial temporal artery (branch of the external carotid artery), and the supraorbital and supratrochlear arteries of the ophthalmic artery (branch of the internal carotid artery).

Venous drainage: superior ophthalmic vein (it drains into the cavernous sinus).