222 



MUSCLES OF THE UPPER LIMB. 



forming a fibrous expansion, which covers the back of the first and second 

 digital phalanges, and terminates upon the third phalanx. It is attached to 

 the second and third phalanges in the following manner. Opposite the first 

 bone the tendon divides into three fasciculi ; the central one is much thinner 

 than the others, and is inserted into the base of the second phalanx ; the 

 two lateral parts, continuing onwards, are joined together towards the 



middle or fore part of the second phalanx, 

 and, having passed beyond this, are inserted 

 into the last phalanx. On the index and 

 little fingers the tendons are joined before 

 their division, by the special extensor tendons 

 of those digits. 



Fig. 183. DEEP POSTERIOR MUSCLES OF THE 

 FOREARM. 



a, posterior surface of the humerus above tlie 

 olecranon fossa; 6, upper and back part of the 

 olecranon ; c, outer and back part of the middle 

 of the radius ; d, lower part of the ulna, grooved for 

 the tendon of the extensor carpi ulnaris ; e, base of 

 the second metacarpal bone ; 1, anconeus muscle ; 2, 

 surface of the flexor digitorum profundus, exposed 

 by the removal of the aponeurotic tendon of 3, the 

 flexor carpi ulnaris ; 4, extensor carpi radialis 

 brevior, and 5, the cut tendon of the extensor carpi 

 radialis longior, both descending to their insertion at 

 e, into the second and third metacarpal bones ; 6, 

 extensor ossis metacarpi pollicis; 6', its insertion 

 into the first metacarpal bone ; 7, extensor primi 

 interned ii pollicis ; 7', its insertion into the base of 

 the first phalanx ; 8, extensor secundi internodii 

 pollicis ; 8', its insertion into the base of the last 

 phalanx ; 9, extensor indicis ; 9', its junction with 

 the tendon of the common extensor, which is cut 

 short : in the metacarpal spaces the four dorsal 

 interossei muscles are represented, the tendons of 

 the common extensor having been removed ; and at 

 10, the insertion of the second and third dorsal 

 iuterossei, by a triangular expansion, into the tendon 

 of the extensor communis, as well as the mode of 

 insertion of that tendon into the middle and last 

 phalanges, are shown. 



On the back of the hand the tendon of the 

 ring-finger gives off two processes, one on 

 each side, which pass obliquely downwards 

 to join the tendons of the middle and little 

 fingers : in consequence of this arrange- 

 ment it follows that, if those two fingers be 

 flexed, the tendon to the ring-finger is held 

 downwards, and it becomes impossible to 

 extend that finger by the action of the muscle. 

 The tendon of the index-finger is only united 



to that of the middle finger by a loose, transverse, semitransparent band of 



fibres, and is free in its action. A synovial membrane invests the tendons 



of this muscle as they pass under the annular ligament. 



The extensor minimi digiti is a slender muscle which is placed between the 



extensor communis digitorum and the extensor carpi ulnaris, and arises 1 y 



