platysma cutaneous ligaments,
58
and the zygomatic major and minor
muscles via their bony attachments. Bony attachments are at the zy-
gomatic arch
48,55
and the mandible,
58
as well as at the inferior or-
bital rim via the orbitomalar ligament,
50
which in turn sends fibers
anteriorly to the skin to form the nasojugal fold.
The SMAS is subject to age-related changes, which are in large
part responsible for mid-face ptosis. Lucarelli et al.
49
demonstrated
age-related attenuation of the orbitomalar, masseteric cutaneous, and
zygomatic ligaments, which support the SMAS and associated malar
and buccal fat pads. Cutaneous projections of the orbitomalar liga-
ment help form the nasojugal and malar skinfolds; increased traction
on the ligament by a descended SMAS may be partly responsible for
the accentuation of the nasojugal and malar skin folds that appear
with age.
50
Involutional descent of the malar fat pad, which attaches
to the superficial surface of the SMAS, results in increased promi-
nence of the nasojugal fold.
59–61
A recent outcomes study by Hamra
62
indicated that the malar fat pad may continue to descend more rap-
idly than the SMAS following facelift surgery.
Musculature
The muscles of facial expression are flat muscles that have high vari-
ability from one individual to another. Freilinger et al.
63
reported in
1987 the three-dimensional arrangement of these muscles in the mid-
face and lower face, dividing the muscles into four layers. The first
and most superficial layer includes the orbicularis oculi, zygomaticus
minor, and depressor anguli oris. The second layer includes the zy-
gomaticus major, levator labii superioris nasae et alaque, platysma,
risorius, and depressor labii inferioris. Progressing deeper, the third
layer includes the orbicularis oris and levator labii superioris. The
fourth and deepest layer includes the mentalis, levator anguli oris,
and buccinator. The facial nerve branches travel between the third
and fourth layers, innervating the first three layers from below and
the fourth layer from above. Subsequent study has shown the zygo-
maticus major, zygomaticus minor, and levator labii superioris all to
be invested in the SMAS,
51
illustrating an evolving understanding of
the muscular anatomy of the mid-face.
The muscles of mastication include the masseter and temporalis,
with two associated muscles: the buccinator and orbicularis oris. The
orbicularis oris acts as a sphincter at the mouth, and the buccinator
provides medially directed tension on the cheeks, keeping food in the
center of the mouth. The masseter originates at the zygomatic arch
16 Cosmetic Facial Anatomy