Eyebrow Muscle: How it works
It seems that it either takes one muscle (the Occipitofrontalis) OR two (the Frontalis and the Occipitalis) to lift the eyebrow, depending on what source you choose to listen to.
The Occipitofrontalis is a term used by some to describe a muscle of the human body, with two parts: the "occipital" part/belly, and the "Frontal" part/belly.
Other sources consider the Occipitofrontalis to be a structure consisting of two distinct muscles, the Frontalis and the Occipitalis.
The medial margins of the Frontales are joined together for some distance above the root of the nose; but between the Occipitales there is a considerable, though variable, interval, occupied by the galea aponeurotica.
Its medial fibers are continuous with those of the Procerus; its immediate fibers blend with the Corrugator and Orbicularis oculi; and its lateral fibers are also blended with the latter muscle over the zygomatic process of the frontal bone. From these attachments the fibers are directed upward, and join the galea aponeurotica below the coronal suture.
The Frontalis is thin, of a quadrilateral form, and intimately adherent to the superficial fascia. It is broader than the Occipitalis and its fibers are longer and paler in color. It has no bony attachments
The Occipitalis, thin and quadrilateral in form, arises by tendinous fibers from the lateral two-thirds of the superior nuchal line of the occipital bone, and from the mastoid part of the temporal. It ends in the galea aponeurotica.