Attachment of the Upper Extremity to the Trunk

The scapula and the clavicle make up the pectoral girdle, which provides the connection between the upper extremity and the axial skeleton. The bones of the pectoral girdle are shown in Fig. 7-1. Muscles anchor the upper extremity and the pectoral girdle to the trunk of the body. These muscles can be divided into three groups.

One group of muscles extends from the trunk to the scapula. In appropriate combinations, the muscles in this group can move the scapula upward, downward, forward, backward, clockwise, or counterclockwise. These actions assist in movement of the shoulder.

A second group of muscles extends between the scapula and the humerus. These muscles move the arm at the glenohumeral (shoulder) joint. The muscles and tendons that extend over the shoulder strengthen and stabilize the joint.

A third group extends from the trunk to the humerus. This group, which includes the pectoralis major and the latissimus dorsi, adducts the arm. Table 7-1 summarizes the muscles associated with the trunk, the scapula, and the humerus.

Axilla

The space at the junction of the arm and the thorax, between the upper limb and the chest wall, is called the axilla The anterior wall of the axilla is formed by the pectoralis major muscle and the pectoralis minor muscle Predominant structures in the posterior wall are the scapula and the subscapularis muscle Medially, the axilla is delineated by the ribs, the intercostal muscles, and the serratus anterior muscle. The narrow lateral wall is formed by the head of the humerus; specifically, it is formed by the intertubercular (bicipital) groove, where the anterior and posterior walls converge. The long head of the biceps brachii muscle is located in the intertubercular groove. The short head of the biceps brachii muscle and the coracobrachialis muscle are closely associated in this same region. The boundaries of the axilla are illustrated in Fig. 7-2.

The axilla functions as a passageway for vessels and nerves that pass between the root of the neck and the arm. The vessels in this region include the axillary artery and vein, together with their branches. The nerves that pass through the axilla are branches of the brachial plexus and innervate the upper extremity. The axilla also contains numerous lymph nodes, which are drained by axillary lymph vessels that pass through this region. The axillary lymph nodes are of particular significance because a large portion of the lymphatic drainage from the breast filters through these nodes, and they are frequently involved with breast cancer.

The region from the shoulder to the elbow is the arm, or brachium. The only bone in this region is the humerus, which is the longest bone in the upper extremity. The features of the humerus are shown in Fig. 7-3.

Muscular Components.

The muscles of the arm, or brachium, are arranged in anterior and posterior compartments, which are separated by an intermuscular septum of fascia (Fig. 7-4). The muscles of the arm are summarized in Table 7-2.

TABLE 7-2

Muscles Located in the Arm

Muscle	Origin	Insertion	Action	Innervation
Anterior Compartment
Biceps brachii	Long head: supraglenoid tubercle Short head: coracoid process	Radius and ulna	Flex and supinate forearm	Musculocutaneous
Coracobrachialis	Coracoid process	Medial humerus	Flex and adduct shoulder	Musculocutaneous
Brachialis	Distal humerus	Ulna	Flex forearm	Musculocutaneous
Posterior Compartment
Triceps brachii	Long head: infraglenoid tubercle Lateral head: proximal shaft of humerus Medial head: distal shaft of humerus	Olecranon process of ulna	Extend arm at elbow and stabilize shoulder	Radial

The anterior muscle compartment consists of three muscles that act as flexors and are innervated by the musculocutaneous branch of the brachial plexus. The largest of the muscles is the biceps brachii muscle As the name implies, the biceps brachii has two heads of origin. The short head originates on the coracoid process of the scapula, and the long head originates from a tubercle just above the glenoid cavity (supraglenoid tubercle). The two heads merge to form a single muscle belly that inserts on the radial tuberosity and on the ulna by way of an aponeurosis. In addition to being a flexor of the forearm at the elbow, the biceps brachii is a supinator of the forearm. The muscle originates superior to the shoulder and passes over the joint; it therefore helps stabilize and strengthen the shoulder joint. The biceps brachii muscle also acts as a flexor of the arm at the shoulder.

The coracobrachialis is a short muscle on the medial surface of the superior part of the arm. It has a common origin with the short head of the biceps brachii on the coracoid process of the scapula, and it inserts on the medial side of the humerus near the midpoint of the shaft. The coracobrachialis, along with the biceps brachii, acts as a weak flexor and adductor of the shoulder. This muscle is visible only in sections through the upper part of the arm. The coracobrachialis is the only muscle that, although predominantly located in the arm, acts on the shoulder joint.

The third muscle of the anterior compartment is the brachialis muscle This is a deep muscle, underlying the biceps brachii. It has an extensive origin along the anterior surface of the distal half of the humerus, and it terminates on the coronoid process of the ulna. The brachialis is a strong flexor of the forearm at the elbow joint. It is seen only in sections through the lower part of the arm.

The posterior compartment of the arm is occupied by a single, large muscle, the triceps brachii. As the name implies, this muscle has three heads of origin. The long head originates via a tendon from the infraglenoid tubercle. The lateral head attaches to the posterior surface of the proximal shaft of the humerus. The medial head is deep to both the long and the lateral heads. Its origin is on the posterior surface of the shaft of the humerus, distal to the origin of the lateral head. All three heads merge to form a single muscle belly that inserts on the olecranon process of the ulna via a single tendon. An olecranon bursa is located between the tendon and the olecranon process. The triceps brachii muscle is a powerful extensor of the elbow. The long head spans the shoulder joint; consequently, it also helps stabilize that joint. The radial nerve innervates the triceps brachii.

Vascular Components.

The primary arterial blood supply to the arm is the brachial artery and its branches. The brachial artery begins at the inferior border of the teres major muscle, as a continuation of the axillary artery, and ends in the cubital fossa, where it divides into the radial and ulnar arteries. The vessel is superficial throughout its length, and it runs its course in the fascia of the medial intermuscular septum, which divides the muscles into the anterior and posterior compartments. In the septum, it is associated with the basilic vein, the median nerve, and the ulnar nerve Numerous branches supply the muscles of the arm.

One, or possibly two, brachial veins accompany the brachial artery These deep veins ascend through the arm to continue as the axillary vein. In addition to the deep brachial vein, two important superficial veins are in the arm. The cephalic vein is in the superficial fascia, anterolateral to the biceps brachii muscle. As it courses superiorly, it passes between the deltoid and the pectoralis major muscles to empty into the axillary vein. The basilic vein is in the superficial fascia on the medial side of the arm. About one third of the way up the arm from the elbow, the basilic vein passes deep to the superficial fascia and continues upward to merge with the brachial vein to form the axillary vein. Both the superficial cephalic and basilic veins are frequently visible through the skin. Fig. 7-5 shows some of the vascular relationships in the arm.

Cubital Fossa

The cubital fossa, a triangular area on the anterior side of the elbow joint, contains vessels and nerves that pass from the arm to the forearm. The base of the triangular area is an imaginary line between the lateral and medial epicondyles of the humerus. The two sides are formed by the brachioradialis muscle laterally and the pronator teres muscle

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