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Pectoral Region and Axilla
I.
Landmarks
A. jugular (suprasternal) notch: at the T2 / T3 intervertebral level
B. clavicle:
1. most frequently broken bone ion the body
2. subcutaneous throughout its length
3. its anterior aspect is convex medially and concave laterally
4. it articulates medially with the manubrium of the sternum and laterally with the
acromion process of the scapula
C. acromion process: the point of the shoulder and extension of the spinous process
of scapula
D. sternum: consists of the manubrium, body (gladiolus), and xiphoid process
E. sternal angle (angle of Louis): at the junction of the manubrium and body of
sternum, also it is at the level of the 2nd rib anteriorly and the T4 /T5 intervertebral
level posteriorly
F. xiphosternal junction: at the level of T9
G. costal arch: the lower anterior margin of the chest wall consisting of the costal
cartilages of ribs 7 – 10
H. anterior axillary fold: formed by the pectoral muscles
I. mid-clavicular line: a vertical line through the midpoint of the clavicle
II.
Osteology: the skeleton of the thorax consists of the sternum, 12 pairs of ribs, and
the 12 pairs of ribs
A. sternum
1. manubrium articulates with the clavicles, first two ribs, and sternal body
2. body articulates with ribs 2 – 7, manubrium, and xiphoid process
3. xiphoid process articulates only with the body of the sternum. It is recessed
and may have a hole in it and remains cartilagenous longer.
B. ribs (12 pairs of which 7 are true ribs and 5 pair are false ribs)
1. ribs 3 – 9 are considered typical
2. each typical rib has the following components
a. head - articulates with corresponding vertebrae and the vertebrae above
b. neck
c. tubercle – articulates with the transverse process of corresponding vertebrae
d. body or shaft
e. angle – most dorsal component of rib
f. costal cartilage
3. each rib articulates
a. with the bodies of two vertebrae by means of the head
b. with the transverse process of a corresponding vertebrae with the tubercle
c. with the sternum for ribs 3 – 7
4. ribs 8, 9, and 10 articulate with the rib above through its costal cartilage
2
5. the first rib is the shortest, most sharply curved, broadest, and articulates only
with the first thoracic vertebrae
a. it has a scalene tubercle for attachment of the anterior scalene muscle that
separates anterior and posterior grooves for the subclavian vein and artery,
respectively.
6. ribs 11 and 12 are called floating ribs
7. articulation between the first rib and the sternum is a cartilagenous joint with all
of the other sternocostal articulations of the true ribs having a synovial joint
III.
Breast
A. development
1. starts with a thickening of epithelium called mammary (milk) line
a. extends from the upper to the lower limb 7 weeks post conception
b. 15 to 25 cords of cells grow into the superficial fascia
2. at puberty, in the female, the mammary gland enlarges primarily due to and
increase in lactiferous ducts
3. breasts enlarge after the second month of pregnancy, and by 6 months the ducts
are fully developed
a. alveoli (spherical collections of milk secreting epithelial cells) and secreting
are become fully developed during the last three months of pregnancy due to
hormones that stimulate the alveoli
4. after cessation of lactation, the breasts diminish in size to their non-pregnancy
state and at menopause, they atrophy mostly due to the loss of alveoli, not ducts
B. location
1. the breast extends from the second to the 6th or 7th rib and from the sternum to
the axilla
2. about 2/3 lies on the pectoralis major muscle and the other 1/3 on the serratus
anterior muscle
3. it is confined to the superficial fascia and consists mostly of fat, except during
pregnancy
C. structure
1. nipple: may be inverted, flat, or project outward
2. has 15 to 25 ducts, one from each lobule (a milk gland consisting of many
alveoli) that open separately
a. polythelia (extra nipples) is more common than polymastia (extra breasts)
3. areola – pigmented area around the nipple containing many sebaceous glands
4. connective tissue between the lobules send bundles out to the skin as
suspensory (Cooper's) ligaments
5. the lobules drain into the lactiferous ducts that have near their termination at
the nipple, lactiferous sinuses, which are dilations of the ducts
6. breasts are only loosely attached to the underlying deep (pectoral) fascia
D. blood supply
1. anterior perforating branches of the internal thoracic artery
2. perforating branches from the intercostal arteries
3. pectoral branches from the thoracoacromial trunk
4. lateral thoracic branches of the axillary artery
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E. lymph drainage
1. about ¾ of the lymphatic drainage is to the axillary nodes
2. medially, drainage is to the internal thoracic (parasternal) nodes
3. some drainage may go to the nodes of the opposite side
4. also, drainage can be to the abdomen and subperitoneal lymphatics
IV.
Muscles of the pectoral region
A. pectoralis major muscle
1. origin – medial part oaf the clavicle, sternum, costal cartilages of ribs 2 – 5,
and the upper rectus sheath
2. insertion – greater tubercular crest of the humerus
3. action – Flexes, adducts, and rotates the arm medially. If the arm is at the side,
the clavicular portion draws the arm or shoulder cranialward, ventrally, and
medially; the sternocostal portion draws the arm or shoulder caudalward,
ventrally, and medially.
4. innervation – lateral (C5, 6, 7) and medial (C8, T1) pectoral nerves
5. blood supply
a. thoracoacromial trunk
b. lateral thoracic artery
c. perforating intercostal branches
d. anterior perforating branches of the internal thoracic arteries
B. pectoralis minor muscle – deep to the pectoralis major
1. origin – from ribs 2 – 4 or 3 – 5
2. insertion – the coracoid process of the scapula
3. action – protracts and depresses the shoulder
4. innervation – medial pectoral nerve that after passing through the pectoralis
minor muscle continues forward to the pectoralis major muscle
C. subclavius muscle
1. origin – from the first rib and its cartilage at their junction
2. insertion – after projecting upwards and laterally, the inferior surface of the
clavicle
3. action – depresses the clavicle
4. innervation – nerve to the subclavius off the lateral trunk of brachial plexus
V.
Fascias
A. pectoralis major fascia is sheathed in the pectoral fascia extending from clavicle
B. a separate fascia that extends from the clavicle to the axillary fascia and surrounds
both the subclavius and pectoralis minor muscles is called the clavipectoral fascia
1. costocoracoid membrane
a. that portion of the clavipectoral fascia that spans between the costocoracoid
ligament and upper border of the pectoralis minor muscle
b. costocoracoid ligament – thickened portion of the costocoracoid membrane
that forms a strong band that is attached to the coracoid process, clavicle,
and the first rib
c. defects or holes in the costocoracoid membrane allow for passage of the
thoracoacromial artery and vein, cephalic vein, and the lateral pectoral nerve
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2. suspensory ligament of the axilla – that portion of the clavipectoral fascia
from the lower border of the pectoralis minor muscle to the axillary fascia
VI.
Intercostal spaces (interspaces) – the spaces between two ribs
A. muscles
1. external intercostal muscle
a. extends from the rib above to the rib below
b. occupies an intercostal space from the tubercles of the ribs posteriorly to
to the cartilages of the ribs anteriorly
(1) where they end anteriorly they are replaced by external intercostal
membranes that continue to the sternum
(a) usually, internal intercostal muscles can be seen through them
c. direction of the muscle fibers
(1) at the back the fibers extend downward and laterally
(2) at the sides, the fibers extend downward and forward
(3) in the front they extend downward and medially
d. action – elevates the ribs to increase the thoracic cavity volume
2. internal intercostal muscle
a. also extend between the ribs
b. occupies the interspaces between the costal cartilages anteriorly to the
angles of the ribs posteriorly
c. from the angle of the ribs to the vertebral column posteriorly they are
substituted with posterior intercostal membranes in the interspaces
d. these muscle fibers run perpendicular to the external intercostal muscles
e. action – lowers the ribs to decrease thoracic cavity volume
3. neurovascular bundle
1. intercostal nerve and vessels in the costal groove on the inferior surface of
each rib
2. the arrangement of the neurovascular bundle from above to below is
a. vein
b. artery
c. nerve
3. and as it travels in the substance internal intercostal muscle it partitions off
that muscle into another part call the innermost intercostal muscle, which
lies deep to the neurovascular bundle
VII. Sternoclavicular joint
A. a synovial joint that contains a fibrocartilagenous disc, which partitions the joint
cavity into two compartments
B. a joint capsule surrounds the all of the elements of the sternoclavicular joint
C. interclavicular ligament intervenes between the medial end of each clavicle
1. strengthens the superior surface of the joint capsule
D. anterior and posterior sternoclavicular ligaments
1. strengthens the anterior and posterior surfaces of the joint capsule
E. costoclavicular ligament – a strong ligament that joins the clavicle to first rib
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VIII. Axilla (armpit)
A. space or fossa between the lateral chest wall and medial side of the arm
1. continuous with the posterior triangle of the neck through the cervicoaxillary
canal (prevertebral fascia forming the axillary fascia or sheath)
2. shaped like a shortened pyramid
3. contents
a. brachial plexus
b. axillary artery
c. lymph nodes
d. fat
B. surface anatomy
1. anterior axillary fold – formed by pectoralis major and minor muscles
2. posterior axillary fold – formed by the latissimus dorsi (mostly), teres major
and subscapularis muscles, plus the scapula
3. axillary fossa (armpit) – between the anterior and posterior axillary folds
4. midaxillary line – a vertical line on the lateral side of the midway between
the axillary folds
C. boundaries
1. apex – cervicoaxillary canal (axillary sheath), bounded by the lateral border
of the first rib, clavicle, and base of the coracoid process
2. anterior wall – subclavius, pectoralis minor and minor muscles and their
related fascias
3. medial wall – serratus anterior muscle covering the thoracic wall
4. posterior wall – from above downwards, the subscapularis, teres major, and
latissimus dorsi muscles
5. lateral wall – coracobrachialis and biceps brachii muscles
6. base or floor – skin and axillary fascia
D. description of muscles that form the boundaries of the axilla
1. pectoralis major and minor muscles – described in section IV of these notes
2. subscapularis muscle
a. arises from the subscapular fossa of the scapula
b. passes directly in front of the shoulder joint, fuses with its capsule and
inserts on the lesser tubercle of the humerus
c. action – medial rotator of the arm
d. innervation – upper and lower subscapular nerves (both are C5 & 6)
e. blood supply – a couple or more subscapular vessels
3. teres major muscle
a. arises from the inferior angle and adjacent axillary border of the scapula
b. passes anterior to the long head of the triceps brachii muscle to insert on the
lesser tubercular ridge of the humerus
c. action – adducts and medially rotates the arm
d. innervation – lower subscapular nerve
e. blood supply – subscapular vessels
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4.. latissimus dorsi muscle
a. described in section VI of notes of the Back
b. It crosses the inferior angle of the scapula, crossing the origin of the teres
major muscle and as it goes under the teres major muscle its fibers rotate.
This rotation results in most of its fibers of origin to be reversed at the
site of insertion; in the bottom of the intertubercular sulcus of humerus
c. at its insertion, the tendon of the latissimus dorsi muscle is anterior to that
of the teres major muscle with both being separated by a bursa
5. serratus anterior muscle
a. origin – the upper eight ribs
b. insertion – the vertebral border of the scapula
c. action – Rotates the scapula, raising the point of the shoulder as in full
flexion and abduction of the arm. Draws the scapula forward as in the act
of pushing or punching.
d. innervation – long thoracic nerve (C5, 6, and 7)
e. blood supply - lateral thoracic artery
6. long and short heads of the biceps – will be described in notes on Scapular
Region and Arm
E. vessels
1. axillary artery: partitioned into three parts
a. first part begins at the lateral border of the first rib as a continuation of
subclavian artery
b. it ends at the lower border of the teres major muscle by becoming the
brachial artery
c. its three partitions are created by the anteriorly positioned pectoralis muscle
(1) 1st part has one branch
(a) superior thoracic artery supplying the first two costal interspaces
(2) 2nd part has two branches
(a) thoracoacromial trunk – arises from behind the upper margin of
the pectoralis minor muscle, pierces the clavipectoral fascia
(costocoracoid membrane part), and quickly divides into four
branches
i. acromial branch – supplies region of the acromion process
ii. pectoral branch – supplies pectoralis major and minor muscles
iii. clavicular branch – small artery going to subclavius muscle
iv. deltoid branch – enters the deltopectoral triangle then travels
distally with the cephalic vein
(b) lateral thoracic artery
i. arises behind the lower margin of the pectoralis minor muscle
ii. supplies the lower anterior and medial aspects of the axilla and
mammary gland
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(3) 3rd part has three branches
(a) subscapular artery – largest branch off the axillary artery
i. circumflex scapular artery
(i) goes around the lateral border of the scapula, traversing the
triangular space between the teres major, the subscapularis,
and long head of the triceps muscles
(ii) it enters the infraspinous fossa between the teres minor
muscle and the scapula staying close to the bone
(iii) it ends deep to the infraspinatous muscle where it joins the
suprascapular artery forming a collateral route for blood to
flow from the 1st part of the subclavian artery to the 3rd
part of the axillary artery
ii. thoracodorsal artery – travels with the nerve of the same name
to the latissimus dorsi muscle
(b) anterior humeral circumflex artery – small and passes anterior
to the humerus
(c) posterior humeral circumflex artery – larger and passes posterior
to humerus with the axillary nerve through the quadrangular space
2. axillary vein
a. lies anterior and inferior to the axillary artery
b. receives tributaries comparable to branches of the artery, but additionally,
there are extra vessels with varying locations
c. lateral thoracic vein anatomoses with the superficial epigastric vein to
form the thoracoepigastric vein
(1) forms a collateral route (portocaval shunt) for blood between the
inferior and superior vena cava, usually in liver disease
IX.
Brachial plexus
A. formed from the anterior primary rami of the spinal nerves C5 – T1 in the
posterior triangle of the neck
B. basic elements from medial to lateral are:
1. roots or ventral rami – there are five
2. trunks – there are three
3. divisions – there are three posterior and three anterior
4. cords – there are three
5. nerves - several of them
C. nerves
1. dorsal scapular nerve to rhomboid and levator scapulae muscles – from
anterior primary ramus of C5: pierces the scalenus medius muscle
2. long thoracic nerve to serratus anterior muscle – from anterior primary rami of
C5, 6, 7: pierces the scalenus medius muscle
3. suprascapular nerve to supraspinatous and infraspinatous muscles – from the
superior trunk – goes through the scapular notch, C5 & 6
4. nerve to the subclavius muscle – from the superior trunk, C5 & 6
5. lateral pectoral nerve to the pectoralis major muscle – from lateral cord: goes
through the costocoracoid membrane, C5, 6, 7
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6. medial pectoral nerve to both the pectoralis major and minor muscles – from
the medial cord, C 8 & T1
7. medial brachial cutaneous nerve to anterior arm – from the medial cord, T1:
has an association with the intercostobrachial nerve, T2 intercostal nerve
8. medial antebrachial cutaneous nerve to forearm – from medial cord, C8, T1
9. upper subscapular nerve to subscapularis – from posterior cord, C5 & 6
10. thoracodorsal (middle subscapular) nerve to latissimus dorsi – from
posterior cord, C6, 7, 8
11 lower subscapular nerve to subscapularis and teres major muscles – from the
posterior cord, C5 & 6
12. axillary nerve to deltoid and teres minor muscles – from posterior cord, C5, 6
13. radial nerve to all dorsal muscles of upper limb – from posterior cord, C5 – T1
14. musculocutaneous nerve to anterior part of the arm – from lateral cord, C5 – 7
15. median nerve which is a major nerve to anterior forearm and minor nerve to
the hand – from both medial and lateral cords, C5 – T1
16. ulnar nerve that is a minor nerve to anterior forearm and a major nerve to the
hand – from the medial cord, C7, 8 & T1
X.
Lymph nodes – lymph nodes are found throughout the axilla, but there are five
regional groups
A. pectoral or anterior nodes
B. brachial or lateral nodes
C. subscapular or posterior nodes
D. central nodes
E. apical or subclavian nodes