Biceps
| Pronuncation | BYE-seps |
| Derivation | Bi, two; ceps, head; the two-headed muscle. The full name is biceps brachii (BRAY-kee-ee, referring to the arm) which distinguishes it from biceps femoris on the leg. |
| Origin | Two points (one for each head) on the deep anterior, superior part of the scapula. These points are the glenoid fossa and the coracoid process. |
| Insertion | Anterior surface of the radius below the head. |
| Action | Bends the arm at the elbow and turns the forearm palm-up. |
Biceps comprises most of the mass of the front of the upper arm. The short head is on the medial side, and the long head is on the lateral side. The short head rests lower on the arm than the long head.
It emerges from under the lateral part of pectoralis and the deltoid, and its tendon disappears between the extensor mass and the flexor mass of the forearm (specifically, between brachioradialis and pronator teres). Because the two heads are mostly covered by the deltoid, they cannot usually be distingished on the surface, especially when the muscle is relaxed.
Besides the main tendon of the biceps, there is also tendinous ribbon, the bicipital (bye-SIP-it-al) aponeurosis , which extends over the flexors. Its binding action sometimes creates a plane break there, dividing the shape of the flexor mass into a short curve and a long curve.
Biceps changes its shape dramatically when tensed. The belly becomes rounder and rises, becoming more spherical. Sometimes the division between the heads can be seen on the upper end in front.
The tendons become prominent, and a depression forms between them. The tendons form a flat plane with a sharp break on the medial side.