Musculature of the pars marginalis of the upper orbicularis oris muscle.

The aim of this study is to elucidate the muscular structure of the pars marginalis of the upper orbicularis oris muscle. Full-thickness upper lips of 11 Korean adult cadavers were used. Four sagittal sections were made and stained with trichrome. Throughout the vermilion zone of the upper lip, the pars marginalis is substantially anterior to the adjacent bundles of the pars peripheralis. The breadth was 1.3 to 2.5 mm above the vermillion border (2.5 +/- 0.8 mm on the midline of philtrum, 1.3 +/- 0.6 mm on the peak point of Cupid's bow, 1.6 +/- 0.5 mm at midlateral side, and 1.6 +/- 0.4 mm at mouth corner). The lowest limit of the pars marginalis was located 2.5 to 3.1 mm below the vermillion border (3.1 +/- 0.4 mm on the midline of philtrum, 3.0 +/- 0.7 mm on the peak point of Cupid's bow, 3.0 +/- 0.7 mm at midlateral side, and 2.5 +/- 0.7 mm at mouth corner). The thickness of the pars marginalis varied between 1.1 and 2.0 mm (2.0 +/- 0.5 mm on midline of philtrum, 1.8 +/- 0.5 mm on the peak point of Cupid's bow, 1.9 +/- 0.5 mm at midlateral side, and 1.1 +/- 0.3 mm at mouth corner). An anatomic knowledge is conducive to precise repairs of the upper lip, particularly in cheiloplasty of congenital cleft lips.