Superficial muscular aponeurotic system (or superficial musculoaponeurotic system[1]) (SMAS) is a thin yet tough[2]: 438 unitary tissue plane of the face[3] formed by facial fasciae, subcutis connective tissue, and facial muscles.
[2]: 438 Its composition varies, containing muscle fibres in some areas, and fibrous or fibroaponeurotic tissue in others.
In most areas, a distinct plane can be defined deep to the SMAS (continuous with that formed between the platysma and underlying investing layer of deep cervical fascia).
[3] Superiorly, the SMAS extends to the galea aponeurotica of[citation needed] the scalp,[2]: 438 becoming continuous with temporoparietal fascia[1][1] (at the zygomatic arch[1]) and galea.
[4] The SMAS is clinically important in facial plastic surgery for rhytidectomy (facelift procedure).