Human Anatomy - Kotsan I. Ya. 2009

Muscles and Fascia of the Upper Limb
Posterior Compartment of the Forearm Muscles
Deep Layer of the Posterior Forearm Muscles

The supinator Muscle (m. supinator) lies directly on the BONES OF THE forearm and is almost entirely covered by the superficial Muscles. It originates from the lateral epicondyle of the humerus, the radial collateral ligament, and the supinator crest of the ulna, runs obliquely in a lateral direction across the forearm (wrapping around the radius posteriorly and laterally), and inserts into the upper third of the radius on its anterior and lateral sides. Function: supinates the forearm at the proximal and distal radioulnar joints and assists in extending the forearm at the elbow joint.

Innervation: radial nerve (CVI—CVIII).

The abductor pollicis longus muscle (m. abductor pollicis longus) originates from the posterior surfaces of the radius and ulna and the interosseous membrane. It curves laterally around the radius and, after passing beneath the lateral part of the extensor retinaculum onto the hand, inserts into the dorsal surface of the Base of the first metacarpal bone. Function: abducts the thumb and hand.

Innervation: radial nerve (CV-CVIII).

The extensor pollicis longus muscle (m. extensor pollicis longus) has a fusiform shape and originates from the posterior surface of the ulna and radius, as well as the interosseous membrane of the forearm. The tendon of the muscle passes beneath the extensor retinaculum in a separate synovial sheath through a groove on the posterior surface of the radius and inserts into the dorsal surface of the base of the distal phalanx of the thumb. Function: extends the thumb and partially abducts it.

Innervation: radial nerve (CV—CVIII).

The extensor pollicis brevis muscle (m. extensor pollicis brevis) is unique to humans (genetically part of the abductor pollicis longus). It originates from the posterior surface of the radius and the interosseous membrane. Its tendon runs alongside the tendon of the abductor pollicis longus in a separate synovial sheath beneath the extensor retinaculum and inserts into the dorsal surface of the base of the proximal phalanx of the thumb. Function: extends the proximal phalanx of the thumb and abducts the thumb.

Innervation: radial nerve (CV—CVIII).

The extensor indicis muscle (m. extensor indicis) originates from the dorsal surface of the ulna and the interosseous membrane. It inserts into the distal and middle Phalanges of the index finger. Function: extends the index finger and assists in extension of the entire hand.

Innervation: radial nerve (CV—CVIII).



Last update: 08/08/2026

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