307
CHAPTER NINE
Muscular System
cause side-to-side grinding motions of the mandible; and pull
the mandible forward, causing it to protrude. The muscles of
mastication are shown in F gure 9.25 and reference plate 66
and are listed in
table 9.4
. They include the following:
Masseter
Medial pterygoid
Temporalis
Lateral pterygoid
The
masseter
(mas-se
ter) is a thick, fl
attened muscle
that can be felt just in front of the ear when the teeth are
clenched. Its F bers extend downward from the zygomatic
The
platysma
(plah-tiz
mah) is a thin, sheetlike muscle
whose F bers extend from the chest upward over the neck to
the face. It pulls the angle of the mouth downward, as in pout-
ing. The platysma also helps lower the mandible.
Muscles of Mastication
±our pairs of muscles attached to the mandible produce
chewing movements. Three pairs of these muscles close the
lower jaw, as in biting; the fourth pair can lower the jaw;
Epicranial aponeurosis
Frontalis
Occipitalis
Epicranius
Masseter
Sternocleidomastoid
Temporalis
Orbicularis oculi
Zygomaticus major
Zygomaticus minor
Buccinator
Orbicularis oris
Platysma
Buccinator
Medial pterygoid
Lateral pterygoid
Temporalis
(a)
(c)
(b)
FIGURE 9.25
Muscles of the head and face. (
a
) Muscles of facial expression and mastication; isolated views of (
b
) the temporalis and buccinator
muscles and (
c
) the lateral and medial pterygoid muscles.
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