Fundamentals of Anatomy and Physiology

212 Chapter 9

Frontalis

Orbicularis

oculi

Masseter

Buccinator

Platysma^

Orbicularis oris

Platysma (cut)

Sternocleidomastoid

(^) ®
Learning
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Figure 9-8A Some muscles of the head and neck (anterior
view).
Muscles of Mastication
Mastication (mass-tih-KAY-shun) or chewing is caused
by some very strong muscles. Table 9-2 lists the muscles of
mastication and the functions they perform. The mas-
seter (mass-SEE-ter) and the temporalis (tim-poh-
RAL-is) are the main muscles that close your jaw by
bringing up the mandible in a bite grip. They are assisted
by the pterygoid (TEHR-ih-goyd) muscles.
Muscles of the Eye
The muscles that move the eyes are unique in that they do
not insert on bone; instead they insert on the eye-ball.
-Table 9-2 lists the muscles that move the eyes and the
functions they perform. The superior rectus raises the
eye; the inferior rectus lowers the eye. The medial
rectus rolls the eye medially, and the lateral rectus rolls
the eye laterally. The superior and inferior oblique
muscles rotate- the eyeball on an axis.
Muscles Moving the Head
The main muscle that moves the head is the sternoclei-
domastoid (stir-noh-kyle-doh-MASS-toyd) muscle (see
Figure 9-8). Table 9-3 lists the muscles of the head and the
functions they perform. Contraction of both sterno-
cleidomastoids causes flexion of the neck; contraction of
one at a time results in rotation to the left or right. Other
muscles of the neck assist the sternocleidomastoid in
moving the head.