COMMON EXTENSOR OF THE FINGERS. 



221 



Fig. 182. 



The extensor carpi radialis brevior arises from the outer condyloid 

 eminence of the humerus by a tendon common to it and the other extensor 

 muscles, from the intervening fibrous septa, from a superficial tendinous 

 expansion, and from the external lateral liga- 

 ment of the elbow- joint. Its muscular belly 

 ends in a flat tendon, which descends with 

 that of the extensor longior, passes through 

 the same groove of the radius with it, and 

 is inserted into the base of the metacarpal 

 bone of the middle finger. A bursa is placed 

 between this muscle and the supinator brevis, 

 an:l a smaller one between the tendon and the 

 metacarpal bone. 



Fig. 182. SUPERFICIAL MUSCLES OF THE FOREARM 

 AND HAND, SEEN FROM BEHIND. 



d, olecranon ; e, external condyloid eminence ; 

 /, lower end of the ulna ; 8, main tendon of the triceps 

 extensor cubiti ; 8", its inner head ; 9, anconeus ; 10, 

 part of brachialis anticus ; 11, supinator longus; 12, 



extensor carpi radialis longior; 13, brevior; 



14, extensor communis digitorum ; 15, extensor carpi 

 ulnaris ; 15', its insertion into the fifth metacarpal 

 bone; +, between 14 and 15, extensor minimi 

 digiti ; 16, origin of the flexor carpi ulnaris by an 

 aponeurosis from the back of the ulna; 17, extensor 

 ossis metacarpi pollicis ; 17', its insertion into the 

 first metacarpal bone ; 18, extensor primi internodii 

 pollicis; 18', its insertion into the first phalanx ; + 

 and +, posterior annular ligament of the carpus or 

 retinaculum of the extensor tendons ; at +, the ten- 

 dons of the long and short radial extensors ; at +, 

 the tendon of the extensor minimi digiti ; 19, tendon 

 of the extensor secundi internodii ; 20, is placed on the 

 proximal end of the second metacarpal bone, close to 

 the insertion of the radial extensors of the carpus : 

 in the hand, the dorsal interossei muscles are shown, 

 and on the middle finger the insertion of the ex- 

 tensor tendons. 



This muscle is covered by the supinator longus 

 and extensor carpi radialis longior, and conceals the 

 supinator brevis and the insertion of the pronator 

 radii teres. The tendon of this muscle and that 

 of the extensor carpi radialis longior are crossed 

 obliquely by the extensors of the metacarpal bone 

 and first phalanx of the thumb. 



The extensor communis diyitorum, placed 

 between the extensor carpi radialis brevior 

 and the extensor minimi digiti, arises by a 

 tendon common to it and the other super- 

 ficial extensor muscles, also from the fascia of the forearm, and the 

 septa between it and the adjoining muscles. Somewhat below the middle 

 of the forearm the muscular part ends in four tendons, which pass 

 between the posterior annular ligament of the wrist and the innermost 

 broad groove on the back of the radius, and diverge as they proceed along 

 the carpus and metacarpus to reach the fingers. Here each is increased by 

 tendinous fibres derived from the lumbricales and interosseoua muscles, 



