of the Pectoral, Back and Shoulder Regions
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of the upper limb (2) | Main Anatomy
Index | Muscles of the arm
Last updated 30 March 2006
Muscles of the Pectoral, Back
and Shoulder Regions
- The pectoral region contains four muscles, all of which
are attached to the pectoral girdle and are associated
with movements of the pectoral girdle and upper limb.
Pectoralis Major Muscle (p. 507)
- This large, thick, fan-shaped muscle covers the superior
part of the thorax.
- Its lateral border forms the anterior
axillary fold and most of the anterior wall of
- The fascial sheath enclosing the pectoralis major muscle
is attached at its origin to the clavicle and sternum.
- It leaves the lateral border of this muscle to form the axillary fascia in the floor
of the axilla.
- The pectoralis major and the deltoid muscles diverge
slightly from each other superiorly and, and along with
the clavicle, form the deltopectoral
triangle (infraclavicular fossa).
- The cephalic vein, one of the
two major superficial veins of the upper limb, occupies
the furrow between the deltoid and pectoris major muscles
before it enters the deltopectoral triangle.
- Proximal attachments are: clavicular
head-anterior surface of the medial half of
clavicle; sternocostal head-anterior
surface of sternum, superior six costal cartilages, and
aponeurosis of the external oblique muscle.
- Distal attachments are: lateral lip of intertubercular
groove of humerus.
- Innervation: lateral and medial pectoral nerves;
clavicular head (C5 and C6), sternoclavicular head
(C7, C8, and T1)
- When both parts of the muscle act together, the
pectoralis major adducts and medially rotates the humerus
at the shoulder joint.
- Acting alone, the clavicular head
helps to flex the humerus and from this
position the sternocostal head
extends the humerus. When the arm is flexed,
the sternocostal head raises the ribs during forced
Pectoralis Minor Muscle (p. 507)
- This triangular muscle lies in the anterior wall of the
axilla, where it is largely covered by the much larger
- The pectoralis minor is the
landmark of the axilla.
- Along with the coracoid process of the scapula, it forms
an arch deep to which pass the vessels and nerves to the
- The pectoralis minor is surrounded by clavipectoral
fascia, a thin sheet of fibrous tissue that
runs from the clavicle superiorly to the axillary fascia inferiorly.
- Proximal attachments are: ribs 3 to 5 near their costal
- Distal attachments are: medial border and superior
surface of coracoid process of scapula.
- Innervation: medial pectoral nerve (C8 and T1)
Serratus Anterior Muscle (pp. 507, 510)
- This is a large, foliate muscle that overlies the lateral
portion of the thorax and the intercostal muscles.
- It was given its name (L. serratus, a saw) because
the saw-toothed appearance of the fleshy digitations at
its proximal attachments.
- Proximal attachments are: external surface of lateral
parts of ribs 1 to 8.
- Distal attachments are: anterior surface of medial border
- Innervation: long thoracic nerve (C5, C6, and C7).
- The serratus anterior protracts the scapula and holds or
fixes it against the thoracic wall.
- Because it is active during punching, it has been called
"the boxer's muscle".
- By fixing the scapula to the thorax, it acts as an anchor
for this bone and permits other muscles to use it as a
fixed bone to produce movements of the humerus. Inferior
fibres of the serratus anterior help to raise the glenoid
fossa of the scapula.
Injuries involving the Serratus Anterior
- When a person's serratus anterior muscle is paralysed
owing to injury to the long
thoracic nerve, the medial border of the
scapula stands out, especially its inferior angle, giving
it the appearance of a wing when the person presses
- Consequently this condition is called a "wing
scapula". When the arm is raised, the scapula is
pulled away from the thoracic wall.
- In addition the arm cannot be abducted farther than the
horizontal position because the serratus anterior is
unable to rotate the scapula and raise the glenoid fossa.
The Back and Shoulder Region
Click here for the Intrinsic
Muscles of the Back.
- The following back muscles described are the extrinsic back muscles, which
attach the upper limb to the axial skeleton. The muscles
of the shoulder are divided into three groups: (1) the
superficial extrinsic muscles (trapezius and latissimus
dorsi); (2) the deep extrinsic muscles (levator scapulae,
rhomboids, and serratus anterior); and (3) the intrinsic
muscles (deltoid, supraspinous, infraspinous, teres
minor, teres major, and subscapularis).
Extrinsic Muscles of the Back
- These muscles are supplied by the ventral rami of
cervical nerves, not by dorsal rami.
- The explanation for this is that the superficial back
muscles develop in the embryo as a ventrolateral sheet
that migrates posteriorly to gain attachment to the
Trapezius Muscle (p. 530)
- This is a large, flat, triangular muscle that covers the
posterior aspect of the neck and superior half of the
- It was given its name because the muscles of the two
sides form a trapezion
(G. irregular four-sided figure).
- The trapezius muscle attaches the pectoral girdle to the
skull and the vertebral column and assists in suspending
- Medial attachments are: medial third of superior nuchal
line; external occipital protuberance, ligamentum nuchae,
spinous processes of C7 to C12 vertebrae.
- Lateral attachments are: lateral third of clavicle,
acromion and spine of scapula.
- Innervation: spinal root of accessory nerve (CN XI) and
cervical nn. (C3 and C4).
- The superior fibres of the trapezius elevate
the scapula; its middle fibres retract the scapula, and its
inferior fibres depress the scapula
and lower the shoulder.
- The superior and inferior fibres act together in the
superior rotation of the scapula.
- The trapezius muscles brace the shoulders by pulling the
scapulae posteriorly, hence weakness of these muscles
result in drooping of the shoulders.
Latissimus Dorsi Muscle (pp. 531, 533)
- The name of this muscle is derived from the Latin meaning
"widest of the back".
- This is large, wide, fan-shaped muscle passes between the
trunk and the humerus and acts on the shoulder joint and
indirectly on the pectoral girdle.
- Medial attachments are: spinous processes of the inferior
six thoracic vertebrae, thoracolumbar fascia, iliac
crest, and inferior 3 or 4 ribs.
- Lateral attachments are: floor of intertubercular groove
- Innervation: thoracodorsal n. (C6, C7, and
- The latissimus dorsi extends,
adducts, and medially rotates the humerus at the shoulder
- When climbing, these muscles raise the trunk. In
conjunction with the pectoralis major muscle, the
latissimus dorsi muscle raises the trunk to the arm,
which occurs when performing chip-ups.
Levator Scapulae Muscle (p. 533)
- The superior third of this strap-like muscle lies deep to
the sternocleidomastoid muscle; the inferior third is
deep to the trapezius.
- Medial attachments are: posterior tubercles of transverse
processes of C1 or C4 vertebrae.
- Lateral attachments are: superior part of medial border
- Innervation: dorsal scapular (C5) and cervical (C3 and
- The levator scapulae elevates the
scapula and helps to tilt its glenoid fossa
inferiorly by rotating the scapula.
- It also helps to retract the scapula and fix it against
the trunk and to flex the neck.
- Six short muscles pass from the scapula to the humerus
and act on the shoulder joint.
Deltoid Muscle (p. 533)
- This thick, powerful shoulder
muscle covers the shoulder joint and forms the
rounded contour of the shoulder.
- As its name "deltoid" indicates, it is
triangular in outline, i.e., it is shaped
like an inverted Greek letter delta.
- Proximal attachments are: lateral third of clavicle,
acromion and spine of scapula.
- Distal attachments are: deltoid tuberosity of humerus.
- Innervation: axillary nerve (C5 and C6)
- For descriptive purposes, the deltoid may be divided into
three parts: anterior, middle, and posterior. It is
capable of acting in part or as a whole.
- The anterior part is a
strong flexor and medial rotator of the humerus.
- The middle part is the
chief abductor of the
- The posterior part is a
strong extensor and lateral rotator
of the humerus.
- In performing these movements, the deltoid works with
other muscles, e.g., the anterior part acts with the pectoralis major and
coracobrachialis muscles in flexing the arm.
- The deltoid muscle tends to stabilise
the shoulder joint and helps to hold the head
of the humerus in the glenoid fossa of the scapula during
Injuries involving the deltoid muscle
- The deltoid muscles atrophies when the axillary nerve is
severely damaged (e.g., during a fracture of the surgical
neck of the humerus).
- As the deltoid atrophies, the rounded contour of the
shoulder disappears; this gives it a flattened
- To test the strength of the deltoid clinically, the
patient's arm is abducted, and then the patient is asked
to hold it in that position against resistance. Inability
to do this indicates injury to the axillary nerve.
Teres Major Muscle (p. 533)
- The teres (L. round) major is a somewhat flattened
rectangular muscle that forms a raised oval area on the
dorsum of the scapula, beginning at the inferior angle.
- The inferior border of this rounded muscle forms the
inferior border of the posterior wall of the axilla.
- The teres major and the tendons of the latissimus dorsi form
the posterior axillary fold.
- Proximal attachments are: dorsal surface of inferior
angle of scapula.
- Distal attachments are: medial lip of intertubercular
groove of humerus.
- Innervation: lower subscapular nerve (C6 and C7)
- The teres major muscle adducts and
medially rotates the arm. It can also help to
extend it from the flexed position.
- It is furthermore an important stabiliser of the head of
the humerus in the glenoid fossa during the abduction of
Rotator Cuff Muscles
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