The long head of the biceps brachii muscle is the larger of the two muscle bodies that forms the entire biceps brachii muscle. The biceps brachii gets its name from the Latin words for “two-headed” and “arm” which describe its structure and location. The long and short heads of the biceps brachii work together to achieve the same functions. From the merger point, the entire muscle continues beyond the distal end of the humerus and inserts on the radial tuberosity of the radius. Together with the short head, the long head of the biceps brachii acts as a flexor of the arm at the elbow joint and a supinator of the forearm. The biceps brachii, brachialis, and brachioradialis muscles all act as flexors of the arm at the elbow, with the brachialis acting as the agonist and the biceps brachii and brachioradialis acting as synergists. At the radioulnar joint in the forearm, the biceps brachii acts as a supinator to turn the palm of the hand upwards.
The short head of the biceps brachii is the shorter and medial of the two bodies that form the biceps brachii muscle in the upper arm. Like the long head of the biceps brachii, the short head is a flexor and supinator of the elbow joint. At the shoulder joint, the short head aids in adduction of the humerus. The biceps brachii muscle gets its name from its two origins, or immovable ends. The long head arises from the supraglenoid tubercle of the scapula, while the short head arises from the coracoid process of the scapula. From its origin, the short head passes anterior to the head and shaft of the humerus and fuses with the long head around the middle of the humerus. The fused biceps brachii muscle crosses the elbow joint along its anterior surface and inserts on the radius at the radial tuberosity.