The frontalis is a sheet-like muscle running vertically down the forehead. There are two distinct halves, which join just above the nasal bones. The fixed end of the frontalis is right at the widow's peak, where it attaches to the thick fiber of the scalp. The free end attaches along a horizontal line at the level of the eyebrows. Some people have conscious control over just one half of the muscle, allowing them to raise one eyebrow. When we're distressed, only innermost fibers of muscle contract (A). This raises inner end of eyebrow and only happens in combination with action of corrugator.
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