10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
MUSCLES OF THE POSTERIOR THORAX
(Figure 10.14c–e)
Trapezius
(trah-pe
9
ze-us)
(
trapezion
5
irregular
four-sided figure)
Most superficial muscle
of posterior thorax; flat
and triangular in shape;
upper fibers run inferiorly
to scapula; middle fibers
run horizontally to scapula;
lower fibers run superiorly
to scapula
O—occipital bone,
ligamentum nuchae,
and spinous processes
of C
7
and all thoracic
vertebrae
I—a continuous insertion
along acromion and
spine of scapula and
lateral third of clavicle
Stabilizes, raises, retracts,
and rotates scapula
; mid-
dle fibers retract (adduct)
scapula; superior fibers
elevate scapula (as in
shrugging the shoulders)
or help extend head with
scapula fixed; inferior
fibers depress scapula
(and shoulder)
Accessory nerve
(cranial nerve XI); C
3
and C
4
Levator scapulae
(skap
9
u-le)
(
levator
5
raises)
Located at back and side
of neck, deep to trapezius;
thick straplike muscle
O—transverse processes
of C
1
–C
4
I—medial border of
scapula, superior to spine
Elevates/adducts scapula
in concert with superior
fibers of trapezius; tilts
glenoid cavity downward
when scapula is fixed,
flexes neck to same side
Cervical spinal nerves
and dorsal scapular
nerve (C
3
–C
5
)
Rhomboids
(rom
9
boidz)—major and
minor
(
rhomboid
5
diamond
shaped)
Two roughly diamond-
shaped muscles lying deep
to trapezius and inferior to
levator scapulae; rhomboid
minor is the more superior
muscle
O—spinous processes
of C
7
and T
1
(minor)
and spinous processes
of T
2
–T
5
(major)
I—medial border of
scapula
Stabilize scapula
; act to-
gether (and with middle
trapezius fibers) to retract
(adduct) scapula, thus
“squaring shoulders”;
rotate scapula so that
glenoid cavity is down-
ward (as when lowering
arm against resistance;
e.g., paddling a canoe)
Dorsal scapular nerve
(C
4
and C
5
)
MUSCLE GALLERY
Table 10.8
Superficial Muscles of the Anterior and Posterior Thorax:
Movements of the Scapula and Arm
(Figure 10.14)
(continued)
Trapezius
(c)
Levator
scapulae
Supraspinatus
Clavicle
Spine of
scapula
Infraspinatus
Teres minor
Humerus
Deltoid
Teres
major
Latissimus
dorsi
Rhomboid
minor
Rhomboid
major
Figure 10.14
(continued)
Superficial
muscles of the thorax and shoulder
acting on the scapula and arm.
(c)
Posterior view. The superficial
muscles are shown on the left side of
the illustration. Superficial muscles are
removed on the right side to reveal the
deeper muscles acting on the scapula,
and the rotator cuff muscles that help
stabilize the shoulder joint.
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