312
UNIT TWO
Muscles That Move the Arm
The arm is one of the more freely movable parts of the body
because muscles connect the humerus to regions of the pec-
toral girdle, ribs, and vertebral column. These muscles can
be grouped according to their primary actions—flexion,
extension, abduction, and rotation (
f
gs.
9.29,
9.30, 9.31
;
reference plates 67, 68, 69;
table 9.7
). Muscles that move the
arm include the following:
Flexors
Abductors
Coracobrachialis
Supraspinatus
Pectoralis major
Deltoid
Extensors
Rotators
Teres major
Subscapularis
Latissimus dorsi
Infraspinatus
Teres minor
Flexors
The
coracobrachialis
(kor
ah-ko-bra
ke-al-is) extends from
the scapula to the middle of the humerus along its medial sur-
face. It fl exes and adducts the arm (see F
gs. 9.30 and 9.31).
The
pectoralis major
is a thick, fan-shaped muscle in
the upper chest. Its F
bers extend from the center of the tho-
rax through the armpit to the humerus. This muscle primar-
ily pulls the arm forward and across the chest. It can also
rotate the humerus medially and adduct the arm from a
raised position (see F
g. 9.28).
A small, triangular region, called the
triangle of auscultation
, is located
in the back where the trapezius overlaps the superior border of the
latissimus dorsi and the underlying rhomboideus major. This area,
near the medial border of the scapula, enlarges when a person bends
forward with the arms folded across the chest. By placing the bell of
a stethoscope in the triangle of auscultation, a physician can usually
clearly hear the sounds of the respiratory organs.
The
levator scapulae
(le-va
tor scap
u-le
¯) is a straplike
muscle that runs almost vertically through the neck, con-
necting the cervical vertebrae to the scapula. It elevates the
scapula (see F
gs. 9.27 and 9.29).
The
serratus anterior
(ser-ra
tus an-te
re-or) is a broad,
curved muscle located on the side of the chest. It arises as
fl eshy, narrow strips on the upper ribs and extends along the
medial wall of the axilla to the ventral surface of the scapula.
It pulls the scapula downward and anteriorly and is used to
thrust the shoulder forward, as when pushing something
(see F
g. 9.28).
The
pectoralis
(pek
tor-a
lis)
minor
is a thin, fl
at muscle
that lies beneath the larger pectoralis major. It extends later-
ally and upward from the ribs to the scapula and pulls the
scapula forward and downward. When other muscles F
x the
scapula in position, the pectoralis minor can raise the ribs
and thus aid forceful inhalation (see F
g. 9.28).
Trapezius
Deltoid
Pectoralis major
Linea alba
(band of connective tissue)
External oblique
Aponeurosis of external oblique
Sternocleidomastoid
Pectoralis minor
Internal intercostal
Serratus anterior
Rectus abdominis
Internal oblique
Transversus abdominis
External intercostal
FIGURE 9.28
Muscles of the anterior chest and abdominal wall. The right pectoralis major is removed to show the pectoralis minor.
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