Bifid Zygomaticus Major Muscle With Absent Risorius and Facial Artery Trifurcation

The zygomaticus major muscle (ZM) is pivotal in midfacial expression and smile dynamics and serves as a key anatomic landmark in craniofacial surgery. Although traditionally described as a single, uniform muscle, accumulating evidence reveals significant morphologic variability, including bifid configurations and atypical relationships with neurovascular structures. A meticulous lateral facial dissection was performed on a 74-year-old male cadaver to assess ZM morphology and its spatial associations with surrounding anatomic structures. Special attention was given to perioral musculature, branches of the facial nerve, the parotid duct, and facial vasculature. The ZM demonstrated a bifid configuration, comprising distinct superior and inferior slips converging at the modiolus. The risorius muscle was absent. The parotid duct coursed deep to the ZM inferior slip. At the mandibular lower border, the facial artery showed an atypical trifurcation into submental, ascending facial, and premasseteric branches. Zygomatic and buccal branches of the facial nerve were identified traveling deep to the bifid muscle slips. These observations underscore the coexistence of muscular and vascular abnormalities in the midfacial region. This case illustrates the complex anatomic variability of the ZM and its intimate relationship with critical neurovascular structures. Recognition of such variants is essential for optimizing surgical outcomes in facial reanimation, rhytidectomy, and minimally invasive aesthetic procedures.