Biceps

The biceps or biceps brachii (Latin: musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle belly which is attached to the upper forearm. While the long head of the biceps crosses both the shoulder and elbow joints, its main function is at the elbow where it flexes and supinates the forearm.

Structure

The biceps is one of three muscles in the anterior compartment of the upper arm, along with the brachialis muscle and the coracobrachialis muscle, with whom the biceps shares a nerve supply. The biceps muscle has two heads, the short head and the long head, distinguished according to their origin at the coracoid process and supraglenoid tubercle of the scapula, respectively. From its origin on the glenoid, the long head remains tendinous as it passes through the shoulder joint and through the intertubercular groove of the humerus. Extending from its origin on the coracoid, the tendon of the short head runs adjacent to the tendon of the coracobrachialis. Unlike the other muscles in the anterior compartment of the arm, the long head of the biceps muscle crosses two joints, the shoulder joint and the elbow joint.

Both heads of the biceps join in the middle upper arm to form a single muscle mass, usually near the insertion of the deltoid, to form a common muscle belly; although several anatomic studies have demonstrated that the muscle bellies remain distinct structures without confluent fibers. As the muscle extends distally, the two heads rotate 90 degrees externally before inserting onto the radial tuberosity.