AXILLARY ARTERY AND ANASTOMOSIS AROUND SCAPULA

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Here is a comprehensive account of the axillary artery and the anastomosis around the scapula, based on Gray's Anatomy for Students and the THIEME Atlas of General Anatomy.

Axillary Artery

Overview and Extent

The axillary artery is the direct continuation of the subclavian artery. It begins at the lateral margin of rib I and ends at the inferior margin of teres major, where it continues as the brachial artery. It passes through the axilla, accompanied medially/anteriorly by the axillary vein, and is surrounded by the cords of the brachial plexus.

Three parts of the axillary artery, divided by pectoralis minor

Parts of the axillary artery - Gray's Anatomy for Students

Three Parts (Divided by Pectoralis Minor)

The pectoralis minor muscle crosses anterior to the axillary artery and divides it into three parts:

Part	Position relative to pectoralis minor	No. of branches
1st part	Proximal (medial) to pectoralis minor	1 branch
2nd part	Posterior (behind) pectoralis minor	2 branches
3rd part	Distal (lateral) to pectoralis minor	3 branches

A useful mnemonic: 1-2-3 rule (1st part = 1 branch, 2nd part = 2 branches, 3rd part = 3 branches).

Branches

1st Part (1 Branch)

1. Superior thoracic artery

Small vessel from the anterior surface
Supplies the upper medial and anterior walls of the axilla

2nd Part (2 Branches)

2. Thoraco-acromial artery

Originates just posterior to the medial (superior) margin of pectoralis minor
Curves around the superior margin of the muscle, pierces the clavipectoral fascia
Immediately divides into 4 branches: pectoral, deltoid, clavicular, and acromial
Pectoral branch contributes to breast supply; deltoid branch accompanies the cephalic vein in the deltopectoral (clavipectoral) triangle

3. Lateral thoracic artery

Arises from the anterior surface, posterior to the lateral (inferior) margin of pectoralis minor
Follows the muscle to the thoracic wall
Supplies medial and anterior walls of the axilla
In women, contributes branches to the breast around the inferior margin of pectoralis major

3rd Part (3 Branches)

4. Subscapular artery - the largest branch of the axillary artery

Arises from the posterior surface, follows the inferior margin of subscapularis
Divides into two terminal branches:
- Circumflex scapular artery - passes through the triangular space (between subscapularis, teres major, and long head of triceps), enters the infraspinous fossa, and anastomoses with the suprascapular and dorsal scapular arteries
- Thoracodorsal artery - follows the lateral border of the scapula to the inferior angle; supplies the posterior and medial axillary walls (and latissimus dorsi)

5. Anterior circumflex humeral artery

Small; from the lateral side of the 3rd part
Passes anterior to the surgical neck of the humerus
Anastomoses with the posterior circumflex humeral artery
Supplies the glenohumeral joint and head of humerus

6. Posterior circumflex humeral artery

Larger; from the lateral surface of the 3rd part, just posterior to the anterior circumflex humeral artery
Passes through the quadrangular space (bounded by teres minor, teres major, long head of triceps, and surgical neck of humerus) along with the axillary nerve
Curves around the surgical neck of the humerus
Anastomoses with the anterior circumflex humeral artery, profunda brachii, suprascapular, and thoraco-acromial arteries

Branches of the axillary artery with named vessels

Branches of the axillary artery - Gray's Anatomy for Students

Anatomical Variants (Lippert & Pabst)

Normal pattern (40% of cases): all 6 branches arise as described above
Thoraco-acromial artery arises from the lateral thoracic artery (10%)
Common origin of lateral thoracic artery and subscapular artery (10%)
Posterior circumflex humeral artery arises from the subscapular artery (20%)
Common origin of anterior and posterior circumflex humeral arteries - the "common circumflex humeral artery" (20%)

Anastomosis Around the Scapula (Scapular Arcade)

This is a clinically important collateral network on the posterior scapular surface, formed by the anastomosis of three vessels:

Scapular arcade - posterior view showing all anastomosing vessels

Scapular arcade - THIEME Atlas of Anatomy

The Three Contributing Arteries

Artery	Origin	Route
Suprascapular artery	Thyrocervical trunk (branch of subclavian)	Passes over the superior transverse scapular ligament (nerve passes under); enters supraspinous fossa, then passes under inferior transverse ligament (often absent) into the infraspinous fossa
Circumflex scapular artery	Subscapular artery (from 3rd part of axillary)	Passes through the triangular space (medial axillary foramen) to reach the infraspinous fossa
Dorsal scapular artery (deep branch of transverse cervical artery)	Transverse cervical artery (from thyrocervical trunk)	Runs along the medial border of the scapula

Anastomotic Network

All three vessels converge and anastomose in the infraspinous fossa, forming a rich anastomotic arcade around the posterior scapula.

Clinical Significance

This anastomosis is critically important because:

If the axillary artery is ligated or occluded (e.g., trauma, surgery), the scapular arcade provides a collateral pathway to reconstitute blood flow to the distal upper limb
The collateral blood can flow: subclavian artery → suprascapular artery / dorsal scapular artery → scapular arcade → circumflex scapular artery → subscapular artery → axillary artery (distal to occlusion)
This is why ligation of the axillary artery proximal to the subscapular artery origin is generally safe and compatible with limb viability
The anastomosis also explains why the suprascapular nerve passes under the superior transverse scapular ligament (while the artery passes over it) - this spatial separation is a classic exam point

Neurovascular Passageways Around the Scapula

Space	Boundaries	Structures transmitted
Triangular space (medial axillary foramen)	Teres minor (above), teres major (below), long head of triceps (lateral)	Circumflex scapular artery
Quadrangular space (lateral axillary foramen)	Teres minor (above), teres major (below), long head of triceps (medial), humerus (lateral)	Posterior circumflex humeral artery + axillary nerve
Triceps hiatus (triangular interval)	Teres major (above), long head of triceps (medial), humerus (lateral)	Deep artery of arm (profunda brachii) + radial nerve

Sources:

Gray's Anatomy for Students, pp. 853-855
General Anatomy and Musculoskeletal System, THIEME Atlas of Anatomy, pp. 375, 404, 410

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