The extensor digitorum is a long bipennate muscle which is located near the medial border of posterior side of forearm. Having a spindle-shaped belly, it arises from the lateral epicondyle of humerus, the capsule of the elbow-joint, and the antebrachial fascia. Then the extensor digitorum runs downwards, along the full length of forearm. Being part of the superficial layer of muscles, it lies directly under the skin, stretching over the supinator, the abductor pollicis longus, and extensor pollicis longus muscle.
Before it reaches the distal third portion of forearm, the belly of extensor digitorum divides into four tendons which travel under the extensor retinaculum. Then these tendons are enclosed, together with the extensor indicis tendon, in a common synovial sheath. Finally, having reached the metacarpal bone, each one of the tendons ends in a tendinous expansion which fuses with the capsule of the metacarpophalangeal joint. Each one of the tendinous expansion in turn separates into three slips, with the lateral two being inserted into the base of the distal phalanx and the middle one into the base of the middle phalanx.
Action
This bipennate muscle of forearm extend the four fingers and assists the extension of hand at the wrist.
Innervation
The extensor digitorum muscle is innervated by the posterior interosseous branch of the radial nerve (C6-C7-C8).
Blood Supply
This muscle is supplied by branches of the posterior interosseous artery, which is arises from the common interosseous and this, from the ulnar.
Below, the superficial muscles of right forearm, showing the extensor muscles
