THE RADIAL ARTERY. 



789 



the tendons of the extensor carpi radiahs longior and the extensor carpi radiahs 

 brevior, and anastomoses, either directly or by means of a number of small branches, 

 with the posterior ulnar carpal, forming ^i posterior carpal ai ch or net-work. 



Branches. — From the posterior carpal arch or net-work a longitudinal stem passes distally 

 in each of the three inner intermetacarpal spaces. These are the dorsal interosseous arteries 

 (aa. metacarpeae dorsales). At the upper extremity of its intermetacarpal space each interosseous 

 artery receives the corresponding perforating branch from the palmar interosseous artery, 

 and when it reaches the interval between the bases of the proximal phalanges, it divides into 

 two branches, which run forward upon the inner and outer surfaces respectively of the proximal 

 phalanges of the adjacent digits and terminate in small branches upon these phalanges. 



A slender branch, which arises either directly from the dorsal carpal arch or from the in- 

 terosseous artery of the fourth intermetacarpal space, passes along the inner border of the metacar- 

 pal and proximal phalanx of the little finger. It terminates upon the proximal phalanx of its digit. 



Variations. — Considerable variation occurs in the size of the dorsal interosseous arteries. 

 That which traverses the fourth intermetacarpal space is sometimes wanting, while that of tlie 

 second space is sometimes of considerable size and may arise directly from the radial artery. 

 Occasionally each artery undergoes a sudden increase of calibre at the point where it is joined 

 by the perforating branch from the deep palmar arch, and may appear to be the continuation of 

 the perforating branch. Where it divides into its two terminal branches, each interosseous gives 

 of? an inferior perforating branch, which passes forward to communicate with the corresponding 

 palmar digital artery ; but these perforating branches are frequently wanting, with the exception 

 of that given ofT from the artery of the second intermetacarpal space. 



5. The Dorsalis PoUicis Artery. — The dorsalis poUicis (Fig. 715) is a 

 slender artery which arises from the radial just before it passes beneath the tendon of 

 the extensor longus pollicis. It passes distally along the dorsal surface of the first 

 metacarpal and terminates upon the dorsum of the first phalanx of the thumb. 



6. The Dorsalis Indicis Artery. — The dorsalis indicis (Fig. 715) arises 

 from the radial just as it passes between the two heads of the first dorsal interosseous 

 muscle to enter the palm of the hand. It passes distally along the radial border of the 

 second metacarpal, resting upon the first dorsal interosseous muscle, and terminates 



Extensor carpi radialis longior 

 Lower extremity of radius 

 Radial artery 



Fig. 716. 



Extensor longus pollicis 



Dorsalis indicis 



Extensor ossis metacarpi pollicis 



Extensor brevis pollicis 



Dissection showins: relation of radial artery to extensor tendons in "snuff box." 



upon the first phalanx of the index-finger. It frequently gives off a small branch which 

 passes along the inner border of the metacarpal and first phalanx of the thumb. 



Variations. — The dorsalis indicis, together with the carpal portion of the radial distal to 

 the point at which the posterior radial carpal is given off, represents the dorsal interosseous 

 artery of the first intermetacarpal space The branch to the inner border of the thumb repre- 

 sents one of the terminal branches of that artery, and frequently arises directly from the radial 

 opposite the main stem of the dorsalis indicis. 



7. The Princeps Pollicis Artery. — The a. princeps pollicis (Fig. 717) arises 

 from the radial just as it emerges from between the two heads of the first dorsal inter- 

 osseous muscle and is bending horizontally inward to form the deep palmar arch. The 

 artery passes directly distally, resting upon the palmar surface of the first dorsal inter- 

 osseous muscle and being covered by the adductor pollicis. While still beneath the 



