Surgical anatomy of the mimic muscle system and the facial nerve: importance for reconstructive and aesthetic surgery.

Mimic muscles are arranged in four layers regarding their origins, and these four layers should be considered when muscle tissue is added or lifted. All mimic muscles are built up by parallel fibers. Mean values of length, width, and thickness of the three lip elevators have been determined. These data might be of importance when dealing with this muscle system, which appears rather different from all other muscles in the human. The individual muscles receive their innervating facial nerve branches from their deeper surface when they belong to the superficial (first, second, or third) layer and from outside when they lie in the deepest (fourth) layer. Nerve branches communicate at least four times before innervating their respective muscles.