450 THE ARTERIES OF THE TIPPER LIMB. 



joint. It then runs downwards for a short distance over the scaphoid bone and 

 trapezium, being: crossed by the tendon of the extensor longus pollicis, and reaches 

 the upper end of the space between the first and second rnetacarpal bones, where it 

 turns forwards into the palm of the hand, by passing between the heads of the first 

 dorsal interosseous muscle. 



As it turns round below the end of the radius the artery is deeply seated, but 

 afterwards it comes nearer to the surface. It is accompanied by two veins and by 

 some filaments of the external cutaneous nerve, and is crossed by subcutaneous veins 

 and by branches of the radial nerve. 



BKANCHES. 1. The posterior radial carpal is a small but constant branch 

 It arises beneath the extensor tendons of the thumb, and running inwards on the 

 back of the carpus anastomoses with the posterior ulnar carpal branch, completing 

 the posterior carpal arch, horn which the dorsal interosseous arteries of the third and 

 fourth spaces spring. It anastomoses, also, with the terminal branch of the anterior 

 interosseous of the forearm. 



2. The first dorsal interosseous artery, arising beneath the extensor tendons 

 of the thumb, frequently in common with the posterior carpal branch, passes to the 

 interval between the second and third metacarpal bones, receives the first superior 

 perforating branch of the deep palmar arch, and descends on the second dorsal 

 interosseous muscle to the level of the metacarpo-phalangeal articulations. It here 

 sends forwards a slender inferior perforating branch to join the corresponding palmar 

 digital artery, and ends by dividing into two dorsal digital branches which ramify 

 on the adjacent margins of the index and middle fingers, as far as the base of the 

 second phalanx, and anastomose on the sides of the fingers with the palmar collateral 

 arteries. 



The second and third dorsal interosseous arteries, springing from the posterior 

 carpal arch, are distributed in a similar manner in the third and fourth interdigital 

 spaces, but their inferior perforating branches are often wanting. 



3. The dorsal arteries of the thumb, two small branches, arising separately 

 or together opposite the base of the metacarpal bone, run upon the dorsal aspect of 

 the thumb-bones, one at the radial, the other at the ulnar border. 



4. The dorsal artery of the index finger, a very small branch, arises below 

 the preceding, and, sending branches to the abductor indicis, runs along the radial 

 side of the back of the index finger. 



IN THE HAND. The radial artery, entering the palm between the heads of the 

 abductor indicis muscle, immediately gives off, under cover of the adductor obliquus 

 pollicis, the large artery of the thumb and the radial branch of the index finger, and 

 turns inwards to form the deep palmar arch by inosculating with the deep branch of 

 the ulnar artery. 



The large artery of the thumb (art. princeps pollicis) passes downwards in 

 front of the abductor indicis, between the metacarpal bone of the thumb and the 

 muscles covering it, to the space between the heads of the flexor brevis pollicis. At 

 that point, and beneath the tendon of the long flexor, it divides into two collateral 

 branches, which course along the borders of the phalanges, on their palmar aspect, 

 and unite in front of the last phalanx, to form an arch similar in arrangement to 

 that on the other fingers. 



The radial branch of the index finger (art. radialis indicis) descends 

 between the abductor indicis and adductor pollicis muscles, and continues along the 

 radial border of the index finger, forming its radial collateral branch, and anasto- 

 mosing in the usual manner on the last phalanx with the ulnar collateral branch 

 derived from the superficial palmar arch. This artery sometimes arises by a common 

 trunk with the foregoing, or more frequently is united with the inner collateral 

 artery of the thumb. 



