315
CHAPTER NINE
Muscular System
surface. It connects the scapula to the greater tubercle of the
humerus and abducts the arm (see F
gs. 9.27 and 9.29).
The
deltoid
(del
toid) is a thick, triangular muscle that
covers the shoulder joint. It connects the clavicle and scap-
ula to the lateral side of the humerus and abducts the arm.
The deltoid’s posterior F bers can extend the humerus, and
its anterior F
bers can fl
ex the humerus (see F
g. 9.27).
A humerus fractured at its surgical neck may damage the axillary
nerve that supplies the deltoid muscle (see F
g. 7.43). If this occurs,
the muscle is likely to shrink and weaken. To test the deltoid for such
weakness, a physician may ask a patient to abduct the arm against
some resistance and maintain that posture for a time.
Extensors
The
teres
(te
re
¯z)
major
connects the scapula to the
humerus. It extends the humerus and can also adduct and
rotate the arm medially (see F
gs. 9.27 and 9.29).
The
latissimus dorsi
(lah-tis
ı
˘-mus dor
si) is a wide, trian-
gular muscle that curves upward from the lower back, around
the side, and to the armpit. It can extend and adduct the arm
and rotate the humerus medially. It also pulls the shoulder
downward and back. This muscle is used to pull the arm back
in swimming, climbing, and rowing (see F gs. 9.27 and 9.30).
Abductors
The
supraspinatus
(su
prah-spi
na-tus) is located in the
depression above the spine of the scapula on its posterior
Trapezius
Deltoid
Short head of
biceps brachii
Long head of
biceps brachii
Clavicle
Subscapularis
Coracobrachialis
Medial border
of scapula
Brachialis
Biceps brachii
(short and long
heads)
Subscapularis
Coracobrachialis
Brachialis
(a)
(c)
(d)
(b)
FIGURE 9.31
Muscles of the shoulder and arm. (
a
) Muscles of the anterior shoulder and the arm, with the rib cage removed. (
b, c,
and
d
) Isolated
views of muscles associated with the arm.
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