The Phylogeny and Ontogeny of Facial Superficial Musculoaponeurotic System.

INTRODUCTION: The superficial musculoaponeurotic system (SMAS), a complex network of fibromuscular tissue, is a fundamental component of facial anatomy, playing a key role in both dynamic function and aesthetic appearance. Although the anatomy of the SMAS has been widely studied, several aspects remain unclear-particularly the presence of its fascial component, the variability in its attachment to deeper tissues, the possibility of distinct SMAS layers, and the association of facial nerve branches with first arch structures. In this study, we propose a hypothesis to explain the anatomical variations in SMAS observed during deep-plane facelift procedures.

METHODS: A comprehensive review of the literature on the phylogeny and ontogeny of the facial SMAS was conducted. While numerous studies address the development of the face and SMAS, many report conflicting findings. For the purpose of this hypothesis, we have relied on the most widely accepted interpretations.

RESULTS: Current understanding suggests that the facial SMAS originates from the primordial panniculus carnosus, a primitive muscular layer present in many lower vertebrates. Our analysis indicates contributions from the platysma myoides, platysma cervicalis, and sphincter colli profundus. The latter two structures undergo regression and are represented in the adult form as fascia. The relationship of the SMAS to deeper tissues appears to depend on whether it lies deep to the platysma cervicalis or the platysma myoides. Additionally, existing literature on the embryology of the facial nerve explains the presence of its branches among first arch structures, as well as their maintained connections with the SMAS.

CONCLUSION: The phylogeny and ontogeny of the facial SMAS represent a complex developmental process that likely accounts for the observed anatomical variations and inconsistencies in its relationship with surrounding fascial planes and facial nerve branches.