General Anatomy

PECTORAL REGION (including Infraclavicular region)

Superior: clavicle,

Lateral: deltoidopectoral sulcus,

Inferior: inferior margin of the pectoralis major,

SKIN INNERVATION:

Medial and intermediate supraclavicular nerves (from the cervical plexus),

Anterior cutaneous branches of the intercostal nerves.

Just underneath the skin is the superficial pectoral fascia (covering the pectoralis major) which continues in the axillary region to become the superficial axillary fascia (base-floor of the axillary fossa together with the skin). By removing the fascia, we will find the pectoralis major muscle.

The pectoralis minor muscle lies deep to the pectoralis major. It must be cut to dissect the axil¬lary artery, vein, and the cords of the brachial plexus. By lying over the middle of the axillary artery, it divides the artery into three parts (proximal to the muscle, covered by the muscle, and distal to the muscle).

Axillary artery: 1st part: Superior thoracic artery + thoracoacromial artery

2nd part: Lateral thoracic artery + subscapular artery

3rd part: Anterior and posterior circumflex humeral arteries.

The largest branch is the subscapular artery, giving the branches circumflex scapular and thora¬codorsal arteries.

The axillary vein is medial to the axillary artery which is surrounded by the cords of the brachial plexus.

Brachial plexus: It comes from the ventral rami of the spinal nerves C5-T1. The spinal nerves come out from the vertebral canal through the intervertebral foramen. When they come out, they divide into anterior (ventral) and posterior (dorsal) rami.

Above the clavicle, the brachial plexus forms three trunks:

Superior trunk: C5-C6

Middle trunk: C7

Inferior trunk: C8-T1

The lateral cord is formed by the superior and middle trunks, the medial cord by the inferior trunk, and the posterior cord from all three.

The musculocutaneous nerve pierces through the coracobrachialis muscle, and it goes below the brachialis muscle. At the distal end, it becomes the lateral antebrachial cutaneous nerve that comes out from below the biceps at the lateral side of the tendon (running together with the cephalic vein).

The Median nerve arises from the medial and lateral cords (having the appearance of a V-shaped nerve), and it runs through the medial bicipital groove on the arm together with the ulnar nerve, the medial brachial cutaneous and medial antebrachial cutaneous nerves, and the brachial artery. Then, it goes to the cubital fossa (at the middle), and it is the most medial structure of the cubital fossa. The middle structure is the brachial artery, and the lateral structure is the tendon of the biceps muscle. The median nerve (after the cubital fossa) goes to the forearm between the flexor digitorum superficialis (in its fascia) and the flexor digitorum profundus in the midline of the forearm (that's why it's called the median nerve). Then, it goes through the carpal canal. In the palmar region, it is covered by the pal¬maris longus tendon. If this muscle is missing, the nerve runs between the flexor carpi radialis tendon and the flexor digitorum tendons. In the palm, it divides into superficial and the deep branches. The deep branch innervates the thenar muscles (except the adductor) and the 1st and 2nd lumbricals. The superficial branch innervates the skin of the palm and the lateral 3½ fingers by seven digital branches.

The Ulnar nerve arises from the medial cord of the brachial plexus and runs though the medial bicipital groove on the arm, but leaves the groove and pierces through the medial intermuscular septum and goes to the sulcus nervi ulnaris. Then, it reaches the forearm between the two heads of the flexor carpi ulnaris muscle. In the inferior 1/3 of the forearm, we can find the ulnar nerve covered by the flexor digitorum profundus together with the ulnar artery. The ulnar artery, in the superior 1/3 of the forearm, is between the deep and the superficial muscles, and afterward it joins the ulnar nerve.

The ulnar nerve goes into the palm in front of the flexor retinaculum (it doesn't pass through the carpal canal) together with the ulnar artery, where it gives superficial and deep branches. The deep branch innervates the interossei muscles, the 3rd and 4th lumbricals, the adductor pollicis, and the hypothenar muscles. The superficial branch innervates the ulnar 1½ fingers, the ulnar 1/2 of the palm, and the palmaris brevis.

The medial brachial and antebrachial cutaneous nerves arise from the medial cord of the brachial plexus and are found in the medial bicipital groove. The medial antebrachial cutaneous nerve pierces the brachial fascia through the basilic hiatus and joins the basilic vein. The medial brachial cutaneous nerve anastomoses with the 1st, 2nd (and sometimes 3rd) intercostal nerves. This anastomosis is called the intercostobrachial nerve (innervates the skin of the axilla).

The Radial nerve arises from the posterior cord of the brachial plexus. It is located in front of the tendon of latissimus dorsi muscle and the teres major, runs to the superior part of the sulcus bicipitalis medialis, and leaves the sulcus (it is not a structure of the sulcus) where it goes to the extensor muscles of the arm between the triceps (medial and lateral head) into the sulcus nervi radialis. Then, it comes forward again in the cubital region (not into the cubital fossa) in the lateral side between the brachialis and brachioradialis muscles. You must move apart those two muscles to find the nerve.

There it divides into two branches (superficial and deep). The superficial branch innervates the radial 2½ fingers (by digital nerves) and skin at the dorsal side of the hand. The deep branch pierces through the superficial muscles (supinator) and innervates the extensor muscles.

The Axillary nerve arises from the posterior cord of the brachial plexus and gives skin branches (lateral cutaneous branches) that are not dissectable.

AXILLARY REGION

The region basically consists of the axillary fossa; however, it also includes the skin covering the walls of the fossa. If described as a surface region of the anterior side of the body (as it is usually presented), the axillary region is a triangular wedge (the most lateral portion of the Pectoral region):

Lateral: Deltopectoral sulcus