The tendon of the long head passes through the glenohumeral joint superior to the head of the humerus and then passes through the intertubercular sulcus and enters the arm. In the arm, the tendon joins with its muscle belly and, together with the muscle belly of the short head, overlies the brachialis muscle.
The long and short heads converge to form a single tendon, which inserts onto the radial tuberosity.
As the tendon enters the forearm, a flat sheet of connective tissue (the bicipital aponeurosis) fans out from the medial side of the tendon to blend with deep fascia covering the anterior compartment of the forearm.
The biceps brachii muscle is a powerful flexor of the forearm at the elbow joint; it is also the most powerful supinator of the forearm when the elbow joint is flexed. Because the two heads of the biceps brachii muscle cross the glenohumeral joint, the muscle can also flex the glenohumeral joint.
The biceps brachii muscle is innervated by the musculocutaneous nerve. A tap on the tendon of the biceps brachii at the elbow is used to test predominantly spinal cord segment C6.
The brachialis muscle originates from the distal half of the anterior aspect of the humerus and from adjacent parts of the intermuscular septa, particularly on the medial side (Fig. 7.64 and Table 7.8). It lies beneath the biceps brachii muscle, is flattened dorsoventrally, and converges to form a tendon, which attaches to the tuberosity of the ulna.
The brachialis muscle flexes the forearm at the elbow joint.
Innervation of the brachialis muscle is predominantly by the musculocutaneous nerve. A small component of the lateral part is innervated by the radial nerve.
The only muscle of the posterior compartment of the arm is the triceps brachii muscle (Fig. 7.65 and Table 7.9). The triceps brachii muscle has three heads:
The long head originates from the infraglenoid tubercle of the scapula.
The medial head originates from the extensive area on the posterior surface of the shaft of the humerus inferior to the radial groove.
The lateral head originates from a linear roughening superior to the radial groove of the humerus.
The three heads converge to form a large tendon, which inserts on the superior surface of the olecranon of the ulna.
The triceps brachii muscle extends the forearm at the elbow joint.
Innervation of the triceps brachii is by branches of the radial nerve. A tap on the tendon of the triceps brachii tests predominantly spinal cord segment C7.
The major artery of the arm, the brachial artery, is found in the anterior compartment (Fig. 7.66A). Beginning as a continuation of the axillary artery at the lower border of the teres major muscle, it terminates just distal to the elbow joint where it divides into the radial and ulnar arteries.
In the proximal arm, the brachial artery lies on the medial side. In the distal arm, it moves laterally to assume a position midway between the lateral epicondyle and the medial epicondyle of the humerus. It crosses anteriorly to the elbow joint where it lies immediately medial to the tendon of the biceps brachii muscle. The brachial artery is palpable along its length. In proximal regions, the brachial artery can be compressed against the medial side of the humerus.
Branches of the brachial artery in the arm include those to adjacent muscles and two ulnar collateral vessels, which contribute to a network of arteries around the elbow joint (Fig. 7.66B). Additional branches are the profunda brachii artery and nutrient arteries to the humerus, which pass through a foramen in the anteromedial surface of the humeral shaft.