The Axilla

Question 1

Identify the boundaries of the axilla.

Answer 1

Apex/cervico-axillary canal: It is a passageway between
the neck and axilla. It is directed upwards and medially
into the root of the neck and corresponds to the triangular
space bounded in front by the clavicle, behind by the
upper border of the scapula and medially by the outer
border of the first rib (Fig. 4.3). The axillary artery and
brachial plexus enter the axilla from neck through this
gap, hence it is also termed cervico-axillary canal. The axillary vein enters the neck from the axilla through this canal.
Base/floor: it is formed by the axillary fascia. bounded anteriorly by the anterior axillary fold formed by the lower border pectoralis major muscle. posteriorly by the posterior axillary fold formed by the tendon of latissimus dorsi and teres major muscles. Medially by the lateral aspect of the chest wall.
Anterior wall: formed by pectoralis major, subclavius and pectoralis minor muscles.
Posterior wall: formed by subscapularis muscle above and latissimus dorsi and teres major muscles below.
Medial wall: formed by the upper 4 or 5 ribs with their corresponding intercostal spaces covered by the serratus anterior muscle.
Lateral wall: formed by the tendon of biceps brachii in the bicipital groove of the humerus and the short head of biceps brachii muscle.

Question 2

What are the contents of the axilla?

Answer 2

1. Axillary artery and its branches
2. Axillary vein and its tributaries
3. Cords of the brachial plexus
4. Axillary lymph nodes
5. Axillary tail of breast ( axillary tail of spence)
6. Fibrofatty tissue
7. Long thoracic and intercostobrachial nerves

Question 3

Describe the course, parts, and branches of the axillary artery.

Answer 3

Axillary artery is the main artery of the upper limb. It begins at the outer border of the first rib as a continuation of the subclavian artery and ends by becoming the brachial artery at the lower border of the teres major muscle. In axilla it runs from apex to the base near the anterior wall. in the axilla it is crossed by the pectoralis minor muscle which divides it into 3 parts. The axillary vein is medial to the artery and the cords are arrange around the 2nd part of the artery, which is the part deep to the pectoralis minor (lateral cord being lateral, medial cord being medial and the posterior cord being posterior)
Parts of the axillary artery: divided into 3 by the pectoralis minor muscle.
1. First part - superior to the muscle.
2. Second part - posterior to the muscle.
3. Third part - Inferior to the muscle.
Branches: Screw The Lawyer, Save A Patient/She Tastes Like Sweet Apple Pie.
1. First part: Superior thoracic artery - arises near subclavius, passes between pectoralis major and minor and supplies them and medial wall of axilla.
2. Second part: (a) Thoraco-acromion artery - emerges from the upper border of pectoralis minor, pierces clavipectoral fascia and divides into 4 branches. (i) Pectoral branch - supplies the pectoral muscles. (ii) Deltoid branch - ends up joining anastomosis over the acromion. (iii) acromion branch (iv) Clavicular branch - supply the sternoclavicular joint.
(b) Lateral thoracic artery - emerges at and runs along the inferior border of pectoralis minor, supplying the branches to pectoralis major and minor and serratus anterior muscles. In the females, the lateral thoracic artery is large and provides important supply to the breast through its lateral mammary branches.
3. Third part: (a) Subscapular artery, the largest branch of axillary artery, runs along the lower border of the subscapularis and ends near the inferior angle of the scapula.
(b) Anterior circumflex humeral artery, a small branch,
passes in front of surgical neck of humerus and anastomoses with the posterior circumflex humeral artery to form an arterial circle around the surgical neck of humerus. It gives an ascending branch, which runs upwards into the intertubercular sulcus of humerus to
supply the head of humerus and shoulder joint.
(c) Posterior circumflex humeral artery, larger than the
anterior circumflex humeral artery, passes backwards, along with axillary nerve through the quadrangular intermuscular space, crosses the posterior aspect of surgical neck of humerus to anastomose with the anterior circumflex humeral artery. It supplies the deltoid muscle and shoulder joint.

Question 4

Identify the branches that form the anastomoses around:
1. The body of scapula.
2. Over the acromion process of the scapula.

Answer 4

1. Around the body of scapula: It occurs between the
   (a) suprascapular artery, a branch of the thyrocervical
   trunk from the first part of the subclavian artery,
   (b) circumflex scapular artery, a branch of the
   subscapular artery from the third part of the axillary
   artery, and
   (c) deep branch of the transverse cervical artery, a branch
   of the thyrocervical trunk.
2. Over the acromion process: It occurs between the
   (a) acromial branch of the thoraco-acromial artery,
   (b) acromial branch of the suprascapular artery, and
   (c) acromial branch of the posterior circumflex humeral
   artery.

Question 5

Describe the course of the axillary vein.

Answer 5

The axillary vein is formed at the lower border of the teres major muscle by the union of basilic vein and venae comitantes of brachial artery. It runs upward along the medial side axillary artery and ends at the outer border of the 1st rib by becoming the subclavian vein.
Tributaries: 1. veins, which correspond to the branches of the axillary artery, namely; lateral thoracic vein and subscapular vein
2. Cephalic vein

Question 6

Identify the different groups of the axillary lymph nodes and areas of the body they drain.

Answer 6

They are divided into the following five groups:
1. Anterior or pectoral group: They lie along the lateral
thoracic vein at the lower border of the pectoralis minor.
They receive the lymph from the upper half of the trunk
anteriorly and from the major part of the breast.
2. Posterior or subscapular group: They lie on the posterior
axillary fold along the subscapular vein. They receive the
lymph from the upper half of the trunk posteriorly, and
from the axillary tail of the breast.
3. Lateral group: They lie along the upper part of the
humerus in relation to the axillary vein. They drain the
lymph from the upper limb.
4. Central group: They are situated in the upper part of the
axilla. They receive the lymph from the other groups and
drain into the apical group (vide infra). The
intercostobrachial nerve passes amongst these nodes.
Therefore, enlargement of these nodes such as in cancer
may compress this nerve, causing pain in the area of
distribution of this nerve, i.e., along the inner border of
the arm.
5. Apical or infraclavicular group: They are situated deep
to the clavipectoral fascia at the apex of the axilla along
the axillary vein. They drain into
subclavian lymph trunk on the right side and into the
thoracic duct on the left side.