Arterial structure:AxillaryAxillary

The **axillary artery** represents the continuation of the subclavian artery and is a major artery of the upper limb

   The axillary artery enters the axilla by passing behind the midpoint of the clavicle on the outer edge of the first rib. The axillary artery is divided into three parts by its relation to pectoralis minor:

* the first part lies proximal to pectoralis minor
* second part lies posterior to pectoralis minor
* third part distal to pectoralis minor

The axillary vein is anterior to the arter.

First Part

The first part of the axillary artery has one branch:

* **superior thoracic artery** - runs anteriorly to supply pectoralis major and minor

Second Part

The second part of the axillary artery has two branches:

* **thoracoacromial artery** - runs over pectoralis minor to pierce the clavipectoral fascia and supply the clavicle, deltoid, acromion and pecs (CAPD) via its four terminal branches. Acromia travels to the acromion; deltoid runs down the delto-pectoral groove; pectoral supplies the pectoral muscles; clavicular sends a branch to the sterno-clavicular joint and the subclavius.

* **lateral thoracic artery** - runs laterally along the lower border of pectoralis minor with long thoracic nerve to supply serratus anterior and both pectoralis muscles, also an important blood supply to the breast in the female.

Third Part

The third part of the axillary artery has three branches:

* **subscapular artery** - largest branch of the axillary artery, travels along the posterior wall of the axilla. Distally, it divides into circumflex scapular artery which supplies the infraspinatus fossa and the thoracodorsal artery which runs with the thoracodorsal nerve to enter and supply the latissimus dorsi.
* **anterior circumflex humeral artery** - runs deep to coracobrachialis and biceps, gives an ascending branch as an important supply to the head of the humerus, then passes around the surgical neck of humerus and anastamoses with the posterior circumflex artery
* **posterior circumflex humeral artery** - passes through the posterior wall of the axilla with the axillary nerve via the quadrangular space to supply deltoid; it also supplies triceps brachii andglenohumeral joint.

Relations

The cords of the brachial plexus are closely related to the axillary artery 1:

* at the **first part** of the axillary artery, the lateral and posterior cords lie superolaterally, whereas the medial cord lies posteriorly; a loop connecting the medial and lateral pectoral nerves also lies anterior to the axillary artery
* at the **second part** of the axillary artery, the posterior, lateral and medial cords embrace the artery as per their names
* at the **third part** of the axillary the cords then branch into their respective peripheral nerves

Variant anatomy

Branches from the axillary artery are highly variable. In one study, variations of the subscapular artery and posterior circumflex humeral artery were noted in ~65% of the cases, and could be grouped into five main categories:

* high origin of the subscapular artery from the second part of the axillary artery
* common trunk for subscapular artery and posterior circumflex humeral artery from the second part of the axillary artery
* common trunk for subscapular artery and posterior circumflex humeral artery from the third part of the axillary artery
* common trunk for subscapular artery and posterior circumflex humeral artery with the thoracodorsal artery originating directly from the axillary artery
* common trunk for subscapular artery, posterior circumflex humeral artery and deep brachial artery

The thoracoacromial artery though, appeared to originate from the first or second part of the axillary artery in all cases.