The Phylogeny and Ontogeny of Facial SMAS.

The superficial musculoaponeurotic system, a complex and intricate network of fibromuscular tissue, is a fundamental element of the facial anatomy, integral to the dynamic function and aesthetic appearance of the human face. Even though the anatomy of SMAS is widely studied, no explanations are given for the presence of fascial part of SMAS of the face and why there is variations in its attachment to deeper tissue, is there two layers of SMAS and why are the branches of the facial nerve seen with first arch structures. We are proposing a hypothesis to explain the anatomical variations seen in the SMAS anatomy of the face noticed during a deep plane face lift.

Method: A comprehensive review of the available literature on the phylogeny and ontogeny of the facial SMAS was conducted. Many scientific papers are available on the phylogeny and ontogeny of the face and facial SMAS. Many contradictory findings have been published as well. We have accepted the commonest acceptable views to make our hypothesis.

Result: The current understanding of the facial SMAS is that it arises from the primordial panniculus carnosus, a primitive muscle layer found in many lower vertebrates. We found contributions from platysma myoides, platysma cervicalis and sphincter colli profundus. Of these, the latter two atrophied and is represented by fascia. The relation of SMAS to deeper tissue varies, depending on whether it is deeper to platysma cervicale or platysma myoides. Available literature on the embryology of facial nerve explains why the facial nerve branches are found among 1st arch structures and the soft tissue connections maintained by branches of facial nerve with SMAS.

Conclusions: The phylogeny and ontogeny of facial SMAS is a complex process and is responsible for the observed anatomical variations and inconsistencies in its relations to surrounding fascial planes and facial nerve branches.