An anatomical study of the insertion of the zygomaticus major muscle in humans focused on the muscle arrangement at the corner of the mouth

BACKGROUND: The aim of this study was to clarify the arrangement of the zygomaticus major muscle by means of topographic examination, and to evaluate the anatomical variations in the insertion of the zygomaticus major at the perioral region. METHODS: After a detailed dissection in the modiolar region, the insertion area of the zygomaticus major was observed in 70 embalmed cadavers. RESULTS: At the perioral region of the dissected specimens, the anatomical aspects of the muscular arrangement and attachment of the zygomaticus major muscle were classified into four categories. In type I, the superficial muscle band of the zygomaticus major is blended and interlaced with the levator anguli oris, whereas the fibers of the deep muscle band blend into the buccinator, passing deeper to the levator anguli oris; this was the situation most commonly encountered (54.3 percent). It was found that the insertion of the zygomaticus major was divided into superficial and deep bands (types I and IV) [42 cases (60 percent)] and into three layers of superficial, middle, and deep fibers (type II) [17 cases (24.3 percent)]. The others were cases where the zygomaticus major was inserted deep into the levator anguli oris as a single muscle band (type III) [11 cases (15.7 percent)]. CONCLUSION: The arrangement and insertion patterns of the zygomaticus major in this study are expected to provide critical information for surgical planning for the procedure of facial reanimation surgery.