#1-2. Upper Face: Forehead & Glabella

Corrugator Supercilii Muscle

Among muscles that pull the eyebrows down, the corrugator supercilii muscle lies the deepest under the skin. The muscle is sometimes divided into the transverse head and oblique head, however, such categorization has little clinical significance. This muscle originates from the bone 2.9mm lateral to the midline and 9.8mm superior to the nasion. It rises superficially as it courses to the right and upward to insert into skin.

Although the course of the muscle and insertion vary between individuals, have the patient furrow the eyebrows to create glabella lines and find skin dimpling to closely observe the area of muscle insertion. Areas lying lateral to this dimpling is the actual site of skin insertion and the muscle stretches more laterally than we expect. This muscle is the thickest between the medial canthal line and mid-pupil line measuring about 2~3mm (Image 2).

Image 2. Corrugator supercilii muscle & Procerus muscle.

Procerus Muscle

The corrugator supercilii muscle creates vertical lines in the glabella, whereas the procerus muscle forms horizontal lines. The procerus muscle originates from the nasal SMAS near the nasal bone and reaches the skin of the eyebrow. This muscle stretches upto the supraorbital rim and down to the medial canthal line or nasion level (Image 2).

The frontalis muscle, corrugator supercilii muscle and procerus muscle discussed above have particular clinical importance as they are the main targets of botulinum neurotoxin injection of the forehead. The frontalis muscle is the single muscle in charge of lifting the eyebrow and excessive injection of botulinum neurotoxin can cause eyebrow ptosis. Currently, the preferred injection method is lower dose injection of botulinum neurotoxin followed by additional injection if necessary. Injection into the corrugator supercilii muscle and procerus muscle, two relatively smaller muscles, require correct knowledge of the level and location of the muscle.