action coding system (FACS) / edited by Paul Ekman & Erika L. Rosenberg.—2nd ed. p. cm.—(Series States of America on acid-free paper who wish to use or understand the Facial Action Coding System (FACS), as Ekman and. Friesen's. AU, Description, Facial muscle, Example image. 1. Inner Brow Raiser. Frontalis, pars medialis. 2. Outer Brow Raiser. Frontalis, pars lateralis. 4. Brow Lowerer.