MUSCLES OF THE HAXD. 225 



the common extensor through a compartment of the annular ligament, 

 comes into contact with the tendon from that muscle destined for the index 

 finger, and unites with it to form the expansion already described. 



Fig. 185. TRANSVERSE SECTION OF THE RIGHT 

 HAND BETWEEN THE CARPUS AND META- 

 CARPUS, SHOWING THE ANTERIOR ANNULAR 



LIGAMENT OP THE CARPUS, AND THE PLACES 

 OP THE VARIOUS EXTENSOR AND FLEXOR 

 TENDONS, SEEN FROM THE DISTAL SIDE. 4 



This figure is also designed to show the 

 transverse arch formed by the second row of 

 carpal bones, a, metacarpal articular surface 

 of the trapezium for the metacarpal bone of 

 the thumb; a', palmar ridge of the trapezium ; 

 b, articular surface of the trapezoid bone for 

 the second metacarpal bone ; c, the surface 

 of the os magnum for the middle metacarpal ; 



d, the surface of the unciform for the fourth, and e, that for the fifth metacarpal 

 bone ; e', unciform process ; between a' and e', the cut edge of the annular ligament 

 is represented, the ends attached to the projecting parts of these bones, and sending 

 another process towards the trapezium at 11, by which the tendon, of the flexor carpi 

 radialis is enclosed in the groove of the trapezium ; 1, tendon of extensor ossis metacarpi 

 pollicis ; 2, extensor primi internodii ; 3, extensor secundi internodii ; 4, extensor 

 indicia; 5 and 6, long and short radial extensors of the carpus; 7, the four divi- 

 sions of the tendon of the common extensor of the fingers, the middle two belong to 

 the third aud fourth fingers ; 8, extensor minimi digiti ; 9, extensor carpi ulnaris ; 

 10, flexor carpi radialis; 11, flexor longus pollicis; 12, the first on the ulnar side of 

 the tendons of the flexor superficial digitorum ; 13, the same of the flexor profundus ; 

 14, the median nerve; 15, points to the middle of the cut margin of the palmar 

 aponeurosis stretched across the annular ligament ; 16, the fibres of the palmaris brevis 

 muscle ; 17, cut surface of the muscles of the ball of the thumb ; 18, muscles of the 

 little finger. 



MUSCLES OF THE HAND. 



Besides the tendons of the long muscles and the lumbricales already 

 described, there are placed in the hand one superficial muscle called 

 palmaris brevis, the short muscles of the thumb and little finger, and the 

 interossei muscles. 



The palmaris brevis is a thin flat subcutaneous muscle, which arises from 

 the inner margin of the palmar fascia and annular ligament ; its fibres pro- 

 ceed transversely inwards, and are inserted into the skin along the inner 

 border of the palm. 



The palmaris brevis crosses the muscles of the little finger and covers the ulnar 

 artery and nerve. It is -subject to considerable variation in its breadth and thickness, 

 consisting sometimes of only a few scattered fibres. 



MUSCLES OF THE THUMB The fleshy mass which forms the thenar pro- 

 minence, or ball of the thumb, consists of four muscles. 



The abductor pollicis (abductor brevis pollicis, Alb.), superficial and flat, 

 arises from the annular ligament and from the ridge of the os trapezium, 

 and, proceeding outwards and forwards, is inserted by a tendon into the 

 radial border of the first phalanx of the thumb at its base. 



The opponens pollicis, placed behind the abductor, arises from the 

 annular ligament and from the os trapezium and its ridge, and is inserted 

 into the whole length of the metacarpal bone of the thumb at the radial 

 border. 



Q 



