The biceps brachii is a large, thick, fusiform muscle of the arm located in its anterior compartment. As its name suggests, it has two heads - a laterally located long head and a medially located short head. Both heads merge into a single distal body that crosses the elbow joint and inserts into the radial tuberosity of the radius.

The long head arises from the supraglenoid tubercle of the scapula via a long, cylindrical tendon. This tendon lies within the intracapsular space of the shoulder joint but remains extrasynovial. It passes between the supraspinatus and subscapularis. When reaching the head of the humerus, it makes a sharp turn over the humeral head, which allows it to reach the intertubercular or bicipital groove. Further, the tendon passes inferiorly through the groove and exits it distally to join the short head. The transverse humeral ligament secures the tendon within the groove.

The short head originates from the apex of the coracoid process of the scapula and descends vertically down the arm. The two heads unite in the middle third of the arm, forming a single muscle belly. Shortly before insertion into the radial tuberosity, the biceps tendon gives rise to the bicipital aponeurosis, which is a flat, broad tendinous expansion that inserts into the antebrachial fascia.

The biceps brachii is an antagonist to the triceps brachii. Its origin and insertion sites allow it to act on two joints - the elbow joint and the shoulder joint. Both heads contribute to flexion of the forearm at the elbow joint and supination of the forearm at the proximal radioulnar joint. Additionally, the short head is responsible for flexion of the arm at the shoulder joint, while the long head assists in abduction of the arm at the same joint.

Overall, the biceps brachii lies superficial to the brachialis muscle and musculocutaneous nerve, with the coracobrachialis located medial and deep. The brachial artery, basilic vein, and median nerve also run medial to the muscle, while the cephalic vein lies laterally. The deltoid partially covers the long head of the biceps.

Anatomical variations of the biceps are relatively common. About 30% of adults have variations in the origin of the muscle, with the third head arising from the humerus being the most frequent. Rarely, supernumerary heads may vary in number anywhere from 4 to 7. Variations in the distal tendon are also observed - it may be bifurcated or completely separated. Importantly, these variants do not impair arm functions, though they may be mistaken for tendon tears on imaging.

Origin: long head - supraglenoid tubercle of the scapula; short head - apex of the coracoid process of the scapula.

Insertion: radial tuberosity of the radius. The bicipital aponeurosis arises from the tendon of the biceps brachii and inserts into the antebrachial fascia.

Action: flexion of the forearm at the elbow joint and supination of the forearm at the proximal radioulnar joint; short head - flexion of the arm at the glenohumeral (shoulder) joint; long head - abduction of the arm at the glenohumeral joint.

Innervation: musculocutaneous nerve (C5 - C6).

Blood supply: branches of the brachial artery and anterior circumflex humeral artery (both are branches of the axillary artery).

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Biceps brachii muscle