Human Anatomy - Kotsan I. Y. 2009

Muscles and fasciae of the upper limb
Posterior group of forearm muscles
Superficial layer of the posterior forearm muscles

The extensor carpi radialis longus Muscle (m. extensor carpi radialis longus) is located superficially beneath the Skin, originating from the lateral epicondyle and the lateral border of the humerus, as well as the lateral intermuscular septum of the arm. In the forearm, the muscle occupies the space between the brachioradialis and the extensor carpi radialis brevis. Approximately at the middle of the forearm, the muscle belly transitions into a flat tendon which, after passing beneath the extensor retinaculum and the tendon of the extensor pollicis longus, inserts into the dorsal surface of the Base of the second metacarpal bone. Function: extends the hand; acting in simultaneous contraction with the flexor carpi radialis, it abducts the hand. Furthermore, because the resultant line of force of the muscle passes very close to the frontal axis of the elbow joint (anterior to it), it may also participate to a minor extent in the flexion of the forearm.

Innervation: radial nerve (С_V—С_VIII).

Class="center">

Fig. 120. Posterior muscle group of the forearm (right arm)

1 — brachioradialis, 2 — extensor carpi radialis longus, 3 — extensor carpi radialis brevis, 4 — abductor pollicis longus, 5 — extensor pollicis brevis, 6 — extensor digitorum, 7 — extensor pollicis longus, 8 — extensor retinaculum, 9 — intertendinous connection, 10 — tendons of the extensor digitorum, 11 — extensor carpi ulnaris, 12 — extensor digiti minimi

Fig. 121. Deep Layer of the posterior muscle group of the forearm (right arm)

1 — supinator, 2 — abductor pollicis longus, 3 — extensor pollicis brevis, 4 — extensor pollicis longus, 5 — tendon of the extensor carpi radialis longus, 6 — tendon of the extensor carpi radialis brevis, 7 — extensor indicis

The extensor carpi radialis brevis muscle (m. extensor carpi radialis brevis) is partially covered by the preceding muscle, originating from the lateral epicondyle of the humerus, the radial collateral ligament, and the forearm fascia. It inserts into the dorsal surface of the base of the third metacarpal bone. Function: extends the hand; upon simultaneous contraction with the flexor carpi radialis, it abducts the hand.

Innervation: radial nerve (С_V—С_VIII).

The extensor digitorum muscle (m. extensor digitorum) lies medial to the radial wrist extensors, originating from the lateral epicondyle of the humerus, the radial collateral ligament, and the forearm fascia. At the middle of the forearm, the muscle belly divides into 4 tendons which, after passing beneath the extensor retinaculum onto the hand, extend toward the dorsal surface of digits 2–5. Each tendon, in turn, splits into three slips: the middle slip inserts into the middle phalanx, while the two lateral slips insert into the distal phalanx. Function: extends digits 2–5; extends the hand.

Innervation: radial nerve (С_V—С_VIII).

The extensor digiti minimi muscle (m. extensor digiti minimi) originates from the lateral epicondyle of the humerus and the forearm fascia. The slender tendon of this muscle passes onto the hand beneath the extensor retinaculum within a separate synovial sheath and inserts into the dorsal surface of the bases of the middle and distal Phalanges of the little finger (on the dorsum of the little finger, the bundles of this muscle merge with the fourth tendon of the extensor digitorum). Function: extends the little finger.

Innervation: radial nerve (С_VI—С_VIII).

The extensor carpi ulnaris muscle (m. extensor carpi ulnaris) is located most medially among the posterior group of Muscles, lies adjacent to the ulna along its entire length, and can be easily palpated in individuals with well-developed musculature. The muscle originates from the lateral epicondyle of the humerus, the radial collateral ligament, and the forearm fascia. The tendon of the extensor carpi ulnaris passes through a separate synovial sheath beneath the extensor retinaculum, occupying a groove on the posterior surface of the distal end of the ulna. The muscle inserts into the base of the fifth metacarpal bone. Function: extends the hand; acting together with the flexor carpi ulnaris, it adducts the hand.

Innervation: radial nerve (С_VI—C_VIII).