Forehead aesthetics have a major contribution to the youthful appearance of the face. Restoration of the upper facial aesthetics is important to counteract the changes related to the ageing process. The interaction between the frontalis and its antagonists' muscles contributes to the overall aesthetic balance of the forehead. In this study, we evaluated the gross anatomy of the frontalis and classified the muscle according to the morphological appearance. 26 cadavers of Caucasian and South East Asian origin were dissected. The frontalis muscle was dissected without mobilisation, and the gross anatomy and variations were analysed on the backdrop of gender and ethnicity. Our dissection studies revealed three main variations of the muscle based on the extent of interdigitation between the two bellies in the midline. The average length of the muscle was 10.9 cm in males and 9.1 cm in females. The width of the muscle in females was 4 cm at the origin and 6.5 cm at the insertion and in males 4.4 cm at the origin and 5.8 cm at the insertion. In six specimens, the muscle attached only up to the medial two-thirds of the eyebrows. This was predominantly observed in the Caucasians cadavers and may contribute to the constitutional downward slanting eyebrows in some individuals. This study provides an in-depth analysis and classification of the frontalis muscle. Understanding the morphological variation of the muscle helps to amend clinical application and treatment protocols. Evaluation of the patterns of decussation of the frontalis muscle may assist with non-surgical interventions using botulinum toxin in the treatment of forehead rhytids. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .
Keywords: Eyebrow variation; Frontalis; Muscle classification.