SUBTLE EXPRESSIONS. “Functioning of the modiolus is complex, as its position may change many times in a minute to allow the orbicularis oris muscle to take any position and do any movement as if it was inserted on bone. With its complex physiology, the modiolus is of critical importance in the subtle expressions of the lips and must be preserved or reconstructed when performing repair of full-thickness tissue defects of lips.”
http://europepmc.org/abstract/med/10783511