2539 2539 2540 2540 2541 2541 ![A labeled diagram illustrates the anterior, posterior, and lateral views of the forearm muscles.](https://cdn.orris.care/cdss_images/102f3509ada98aaf6522dcd236e6d14ad691923c5f41a85a4249f74f12a8fe04.png) 2542 2542 2543 2543 *Fig. 7.90 Superficial Layer of Muscles in the Posterior Compartment of the Forearm. (A) Brachioradialis muscle (anterior view). (B) Superficial muscles (posterior view).* 2544 2544 2545 2545 2546 2546 2547 2547 over the superficial branch of the radial nerve and radial artery (Table 7.13). 2548 2548 2549 2549 2550 2550 ## Extensor carpi radialis longus 2551 2551 2552 2552 The extensor carpi radialis longus muscle originates from the distal part of the supraepicondylar ridge and the lateral epicondyle of the humerus; its tendon inserts on the dorsal surface of the base of metacarpal II (see Fig. 7.90). In proximal regions, it is deep to the brachioradialis muscle. 2553 2553 2554 2554 The extensor carpi radialis longus muscle extends and abducts the wrist, and is innervated by the radial nerve before the nerve divides into superficial and deep branches (see Table 7.13). 2555 2555 2556 2556 2557 2557 ## Extensor carpi radialis brevis 2558 2558 2559 2559 The extensor carpi radialis brevis muscle originates from the lateral epicondyle of the humerus, and the tendon inserts 2560 2560 2561 2561 onto adjacent dorsal surfaces of the bases of metacarpals II and III (see Fig. 7.90). Along much of its course, the extensor carpi radialis brevis lies deep to the extensor carpi radialis longus. 2562 2562 2563 2563 The extensor carpi radialis brevis muscle extends and abducts the wrist, and is innervated by the deep branch of the radial nerve before the nerve passes between the two heads of the supinator muscle (see Table 7.13). 2564 2564 2565 2565 2566 2566 ## Extensor digitorum 2567 2567 2568 2568 The extensor digitorum muscle is the major extensor of the four fingers (index, middle, ring, and little fingers). It originates from the lateral epicondyle of the humerus and forms four tendons, each of which passes into a finger (see Fig. 7.90). 2569 2569 2570 2570 On the dorsal surface of the hand, adjacent tendons of the extensor digitorum are interconnected. In the fingers, each tendon inserts, via a triangular-shaped connective tissue 2571 2571 2572 2572 *Table 7.13 Superficial layer of muscles in the posterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)* 2573 2573 2574 2574 2575 2575

Muscle	Origin	Insertion	Innervation	Function
Brachioradialis	Proximal part of lateral supraepiconydylar ridge of humerus and adjacent intermuscular septum	Lateral surface of distal end of radius	Radial nerve (C5, C6) before division into superficial and deep branches	Accessory flexor of elbow joint when forearm is midproned
Extensor carpi radialis longus