VH Dissector: Upper Limb: Axilla

Rotate to a right lateral view of the thoracic cage and identify the the components of the apex of the axilla which is formed by the convergence of the bones in its three major walls; clavicle in the anterior wall, scapula in the posterior wall, and the first rib in the medial wall. This convergence creates an opening at the apex called the cervicoaxillary canal through which the major nerves and vessels pass. Identify the following structures: clavicle, scapula, first rib

Add the intercostal muscles.

Add the serratus anterior muscles.

Add the subscapularis muscles.

Add the teres major muscles.

Add the latissimus dorsi muscles.

Add the humerus and see how each of these muscles insert into the humerus

Add the coracobrachialis muscles.

Add the pectoralis minor muscles.

Add the pectoralis major muscles.

Identify the opening at the axillary apex called the cervicoaxillary canal through which the major nerves and vessels pass. Rotate the cadaver to build a better understanding of this canal.

Begin with the Pectoral girdle with the pectoral muscles removed.

Add the Ventral Primary Rami of C5 and C6.

C5 and C6 unite to form the superior trunk.

Add the Ventral Primary Rami of C7.

C7 continues as the middle trunk.

Add the Ventral Primary Rami of C8 and T1.

C8 and T1 unite at the neck of the first rib to form an inferior trunk. The inferior trunk lies on the first rib posterior to the subclavian artery.

Add the anterior division of the superior trunk.

Add the posterior division of the superior trunk

Add the anterior division of the middle trunk

Add the anterior division of the inferior trunk

Add the posterior division of the inferior trunk.

The three posterior divisions unite to form the posterior cord.

The anterior divisions of the superior and middle trunks unite to form the lateral cord.

The anterior division of the inferior trunk continues as the medial cord.

Observe that the cords of the brachial plexus derive their names by virtue of their relationship to the axillary artery.

The Dorsal Scapular Nerve – from C5; supplies rhomboid muscles and levator scapulae muscles

The Long Thoracic Nerve – from C5, C6, C7; supplies the serratus anterior muscle.

The Nerve to Subclavius – from C5 and C6; supplies the subclavius muscle. (This nerve is not visualized on the 3D cadaver)

The Suprascapular Nerve – arises from the superior trunk of the brachial plexus, receiving fibers from C5, C6; passes through the suprascapular notch (where it may become entrapped); supplies the supraspinatus and infraspinatus muscles (both rotator cuff muscles).

The Lateral Pectoral Nerve – from C5 – C7 and supplies the pectoralis major muscle.

The Musculocutaneous Nerve – one of the two terminal branches of the lateral cord. Supplies the muscles of the anterior arm (coracobrachialis, biceps brachii, and brachialis). It, typically, pierces the coracobrachialis muscle and travels distal deep to the biceps brachii muscle. Just proximal to the elbow it emerges superficial, lateral to the distal biceps tendon and is now called the lateral antebrachial cutaneous nerve (or lateral cutaneous nerve of the forearm)

The Lateral Root of the Median Nerve – the other terminal branch of the lateral cord; joined by the medial root of the median nerve to form the median nerve. (This nerve is not visualized on the 3D cadaver)

The Medial Pectoral Nerve – (C8, T1) enters the deep surface of the pectoralis minor to supply this muscle and part of the pectoralis major. (This nerve is only visualized on the left side of the 3D cadaver)

The Medial Brachial Cutaneous Nerve (medial cutaneous nerve of the arm) – supplies the skin over the medial surface of the arm – purely sensory. It unites with the intercostal brachial nerve (2nd intercostal nerve) to supply this area.

The Medial Antebrachial Cutaneous Nerve (medial cutaneous nerve of the forearm)– supplies skin over the medial surface of the forearm – purely sensory.

The Ulnar Nerve - (C7*, C8, T1) A terminal branch of the medial cord of the brachial plexus; supplies one and one-half muscles in the forearm, most of the intrinsic muscles of the hand, and some sensory.

The Medial Root of the Median Nerve – other terminal branch of the medial cord; joins the lateral root to form the median nerve which supplies most of the flexor muscles of the forearm and some of the muscles of the hand. Innervates some of the skin of the hand..

The Upper Subscapular Nerve – (C5, C6) supplies the supscapularis muscle.

The Thoracodorsal Nerve – (C6, C7, C8) supplies the latissimus dorsi muscle; arises between the upper and lower subscapular nerves.

The Lower Subscapular Nerve – (C5, C6) supplies part of the subscapularis muscle and all of the teres major muscle.

The Axillary Nerve – (C5, C6) one of the terminal branches of the brachial plexus; passes to the posterior aspect of the arm through the quadrangular space along with the posterior circumflex humeral vessels; supplies articular branches to the glenohumeral joint; after emerging from the quadrangular space it winds around the surgical neck of the humerus to supply the deltoid and teres minor muscles; it terminates as the superior lateral brachial cutaneous nerve supplying sensory to the superior lateral aspect of the skin covering the deltoid muscle.

The Radial Nerve – (C5-T1) The other terminal branch of the posterior cord; provides the major nerve supply to the extensor muscles of the arm and forearm; as it leaves the axilla the radial nerve runs between the long and lateral heads of the triceps brachii muscle to enter the radial (spiral) groove of the humerus; gives off the posterior brachial cutaneous and posterior antebrachial cutaneous nerves. As it enters the forearm it branches into a superficial and deep branch. The deep branch travels under the supinator muscle and emerges as the posterior interosseous nerve. The superficial radial nerve travels to the hand where it supplies sensory to part of the thumb and dorsum of the hand.

The First Part of the Axillary Artery – located between the lateral border of the first rib and the superior border of the pectoralis minor muscle. The first part of the artery is enclosed in the axillary sheath along with the axillary vein and the brachial plexus. The first part has one branch, the superior (supreme) thoracic artery, which helps supply the first and second intercostal spaces and the superior part of the serratus anterior muscle.

The Second Part of the Axillary Artery – lies deep to the pectoralis minor; has two branches: the thoracoacromial and lateral thoracic arteries. The thoracoacromial artery divides into four branches: acromial, deltoid, pectoral, and clavicular. The lateral thoracic artery supplies parts of the pectoral muscles and in the female is an important source blood to the lateral mammary gland. The lateral thoracic artery typically runs along the superficial surface of the serratus anterior muscle with the long thoracic nerve.

The Third Part of the Axillary Artery – has three branches: subscapular, anterior circumflex humeral, and posterior circumflex humeral arteries. The subscapular artery ends by bifurcating into the circumflex scapular and thoracodorsal arteries. The circumflex scapular artery passes around the lateral border of the scapula to supply muscles on the dorsum of the scapula. The thoracodorsal artery supplies the latissimus dorsi muscle. The anterior and posterior circumflex humeral arteries pass around the surgical neck of the humerus. The posterior circumflex humeral artery passes through the posterior wall of the axilla via the quadrangular space with the axillary nerve to supply the deltoid and teres minor muscles.

The Branches of Axillary Artery are named according to their distribution rather than by their point of origin. There are extensive arterial anastomoses around the scapula. The surgical importance of the collateral circulation becomes apparent during ligation of an injured axillary or subclavian artery. The axillary artery may be ligated between the thyrocervical trunk and the subscapular artery. In this case, the direction of blood flow in the subscapular artery is reversed and blood reaches the distal portion of the axillary artery first. Note that the subscapular artery receives blood via several anastomoses with the suprascapular artery, deep transverse cervical artery (dorsal scapular artery), and some intercostal arteries. Ligation of the axillary artery distal to the subscapular artery cuts off the blood supply to the arm.

The Axillary Vein – lies on the antero-medial side of the axillary artery. The axillary vein begins at the inferior border of the teres major muscle

Where the Basilic Vein joins with the venae comitantes (deep brachial veins accompanying the brachial artery).

The Axillary Vein ends at the lateral border of the first rib, where it becomes the Subclavian Vein. This vein receives tributaries that correspond to the branches of the axillary artery.

However, there are two veins for each artery in the limbs. Superior to the pectoralis minor the axillary vein is joined by the Cephalic Vein.

The Axillary Sheath – the axillary artery, vein, and cords of the brachial plexus are enveloped in the thin fascial sheath. Anterior to the subclavian artery the prevertebral layer of cervical fascia is prolonged laterally, where it forms the axillary sheath. The sheath follows the cervicoaxillary canal.

The Axillary Lymph Nodes – comprised of 20 – 30 nodes which are the main lymph nodes of the upper limb. These nodes are arranged in five principal groups. The lymph node groups on the 3D cadaver are not divided into the following groups, however you can get a sense of what the grouping are from the accompanying diagram and the cadaver. 

1. The pectoral group of axillary lymph nodes – receive lymph mainly from the anterior thoracic wall including the breast. Efferent vessels pass from these to the central and apical groups of nodes.

2. Lateral group of axillary lymph nodes – receive lymph from most of the upper limb.

3. Subscapular group of axillary lymph nodes – receive lymph from the posterior aspect of the thoracic wall and scapular region. Efferent vessels pass from these to the central group of nodes.

4. Central group of axillary lymph nodes – receive lymph from the other groups of axillary nodes (pectoral, lateral, subscapular). Efferent vessels from this group pass to the apical group of nodes.

5. Apical group of axillary lymph nodes – situated in the apex of the axilla; receive lymph from all other axillary lymph nodes. Efferent vessels from this group unite to form the subclavian lymphatic trunk which joins the jugular and bronchmediastinal trunks to form the right lymphatic duct. On the left side, the subclavian lymphatic trunk joins the thoracic duct.