Frontalis muscle

At a glance

English

Frontalis muscle

Latin (TA2)

Musculus frontalis

System

Muscle

Region

Head

Side

Paired, left and right

About the frontalis muscle

The frontalis is the front belly of the occipitofrontalis, the muscle of the scalp, and current anatomical terminology treats it as part of that muscle rather than as a separate one. It is a thin, four-sided sheet covering the forehead under the skin, firmly bound to the overlying superficial fascia. Compared with the occipital belly at the back of the head it is wider, with longer and paler fibres. In humans it serves only for facial expression.

Unusually, it has no attachment to bone. Its lower fibres are tied into the skin and other muscles of the brow: the medial ones run into the procerus over the root of the nose, the intermediate ones blend with the corrugator supercilii and orbicularis oculi and so reach the eyebrow skin, and the lateral ones merge with orbicularis oculi above the outer orbital angle, where the frontal bone meets the zygomatic. From this line the fibres rise towards the crown and end in the epicranial aponeurosis, the tough sheet joining front and back bellies, a little in front of the coronal suture. The left and right frontalis bellies meet in the midline for a short distance above the nose, while the two occipital bellies stay separated by a gap filled with aponeurosis.

Its main action is to lift the eyebrows, opposing the orbital part of orbicularis oculi, and in doing so it throws the skin of the forehead into horizontal creases. It comes into play in surprise and attention, when looking upwards, and when straining to see something faint or far away. With the occipital belly anchoring the aponeurosis behind, it can also draw the scalp forwards.

It is supplied by the temporal branches of the facial nerve, and its blood comes from the supratrochlear and supraorbital vessels, with the superficial temporal artery. Because its upper part is supplied from both sides of the brain, a stroke usually spares the forehead, whereas damage to the facial nerve itself paralyses it, a useful bedside distinction. It is often treated with botulinum toxin for horizontal forehead lines.

Attachments, action and supply

Origin

Skin and muscles of the eyebrow and root of the nose (procerus, corrugator supercilii, orbicularis oculi); no bony attachment.

Insertion

Epicranial aponeurosis, in front of the coronal suture.

Action

Raises the eyebrows and wrinkles the forehead; draws the scalp forwards.

Nerve supply

Temporal branches of the facial nerve (cranial nerve VII).

Blood supply

Supratrochlear and supraorbital arteries, with the frontal branch of the superficial temporal artery.