312 



Muscles of the Arm. 



M. triceps 



brachii 



Epicoiidylus 

 lateralis 



Olecranon 



IM. anconaeus 



isr. extensor 

 carpi uliiaris 



M. extensor 

 digitorum 

 communis 



LigauHii 

 carpi do 



M. extensor 

 arpi radialis lirevis 



M. extensor 

 tar]]i raili.alis longus 



M. biceps 

 brachii 



braeliialis 



357. Muscles of the 

 right forearm, 



viewed from the radial side. 



M brachio- 

 radialis 



M. extensor 

 -carpi radialis 

 lonarus 



M. extensor 



carpi radialis 



brevis 



tcndinuiii. Ench 

 hocdiiie attacbod 

 ii.-md and tlio 2"'^ 



tendon presents 

 mm. liimbricales 



M. extensor carpi radialis breyis 



(see also Figs. 352, 358 and 359). 

 Form: spindle -shajwd. Position: 

 usually superficial on the radial side 

 of the forearm, coming in contact in 

 front with th(> m. extensor carpi radia- 

 lis longus, behind with the m. extensor 

 digitorum communis. Origin: epi- 

 condylus lateralis humeri and fascia 

 antihrachii, fused with its neighbors. 

 Insertion: the fibers go downward 

 and converge, becoming attached in 

 the middle of the forearm to a flat, 

 long tendon which goes close behind 

 that of the m. extensor carpi radialis 

 longus through the second compartment 

 of the lig. carpi dorsale to the dorsal 

 surface of the basis oss. metacarpalislll: 

 there, between the tendon and the bone, 

 lies the bursa m. extensoris carpi 

 radialis brevis (see Fig. 360), rarely 

 absent. The tendon is partially crossed 

 uver by the same muscles as is that of 

 the m. extensor carpi radialis longus 

 (see also Fig. 361). Action: it ex- 

 tends the hand. In n e r v a t i o n : ramus 

 profundus n. radialis. 



M. extensor digitorum commu- 

 nis (see also Figs. 358 and 361). 

 Form: oblong - spindleshaped. Posi- 

 tion: superficial on the back of the 

 forearm, radialwavd bounded by the 

 ra. extensor car]i radialis brevis, ulnar- 

 ward by the m. extensor carpi ulnaris. 

 Origin: epicondylus lateralis humeri 

 and fascia antihrachii, fused with its 

 neighbors. Insertion: the fibers run 

 parallel downward and in the middle 

 of the forearm become separated into 

 four single bellies. Each of these goes 

 over into a long, flat tendon ; these pass 

 together through the fourth compartment 

 of the lig. carpi dorsale and then di- 

 verge to go to the dorsal surface of 

 the first phalanx of the 2"d 5th fin- 

 ger; each becomes attached by three 

 processes, one in the middle going to 

 the base of the second plialanx and 

 two at the side converging in frunt and 

 going to the base of the third. The 

 four tendons are connected -ndth on(^ 

 another upon the ossa metacarpalia by 

 means of three o\iYu{\whA\\A?,.JH)icturae 

 a triangidar exj^ansion upon the first phalanx to which 

 and interossei (see Fig. 368). Action: it extends the 



abductor pollicis 

 longus 



extensor pollicis 

 brevis 



M. extensor 

 pollicis bi'evis 



M. abductor 

 pollicis longus 



M. extensor 

 pollicis 



loilKUS 



-5'''i finger. Innervation: ramus profundus u. radialis. 



