MUSCLES ON THE DORSAL SURFACE OF THE FOREARM. 39' 



Triceps braehii (insertion) 



Biceps braehii (insertion) 



Supinator muscle 

 (insertion) 



Abductor pollicis longus 

 (origin) 



Pronator teres 

 (insertion) 



M. Extensor Digitorum Communis. The extensor digitorum communis 



arises from the common tendon, from the lateral epicondyle of the hurnerus, from 

 the fascia over it, and fro,m -intermuscular septa on either side. Extending along 

 the dorsum of the forearm it ends, proximal to the wrist, in four tendons, of which 

 the most lateral often has a separate fleshy belly. After passing under the 

 dorsal carpal ligament, in a compartment along with the extensor indicis 

 proprius, the tendons separate on 

 the dorsum of the hand, where 

 the three most medial tendons are 

 joined together by two obliquely 

 placed bands. One passes distally 

 and laterally, and connects to- 

 gether the third and second ten- 

 dons ; the other is a broader and 

 shorter band, which passes also 

 distally and laterally, and joins 

 the fourth to the third tendon. 

 In some cases a third band is 

 present which passes distally and 

 medially from the first to the 

 second tendon ; and, frequently, 

 the tendon for the little finger is 

 joined to the tendon for the ring 

 finger, and separates from it only 

 a short distance above the distal 

 end of the metacarpal bone. 



The tendons are inserted in 

 the following manner: On the 

 finger each tendon spreads out so 

 as to form a membranous expan- 

 sion over the knuckle and on the 

 dorsum of the first phalanx. The 

 border of the tendon is indefinite 

 over the metacarpo - phalangeal 

 articulation, of which it replaces 

 the dorsal ligament. On the dorsum 

 of the first phalanx the tendon 

 receives at its sides the insertions 

 of the interosseous and lumbrical 

 muscles. At the distal end of the 

 first phalanx it splits into ill-de- 

 fined median and collateral slips, 

 which pass over the dorsum of the 

 first inter-phalangeal articulation, 

 where they replace the dorsal 

 ligament. The median slip is 

 inserted into the dorsum of the carpi uin 

 base of the second phalanx, while 

 the two lateral pieces become 

 united to form a membranous 

 tendon on the dorsum of the 

 second phalanx, which, after passing over the second inter-phalangeal articula- 

 tion, is inserted into the base of the terminal phalanx. 



The muscle is placed superficially in the forearm, between the extensors of the 

 carpus and the proper extensor of the little finger. 



Nerve-Supply. The dorsal interosseous nerve (C. (5.) 6. 7. 8.). 



Actions. The muscle extends the elbow, wrist, and fingers. On account of the attachment 

 together of the tendons to the third, fourth, and fifth fingers by accessory bands in the dorsum of 

 the hand, these three fingers can only be fully extended together, while extension of the first finger 



Flexor 

 digitorum 

 profundu 

 (origin) 



Extensor pollicis brevis 

 (origin) 



Brachioradialis 

 /(insertion) 



Groove for tendons of 



radial extensors of 



carpus 



Groove for extensor 



pollicis longus 



Groove for extensor digitorum com- 

 munis and extensor indicis proprius 



FIG. 355. MUSCLE- ATTACHMENTS TO THE RIGHT RADIUS 

 AND ULNA (Dorsal Aspect). 



