DEEP PALMAR ARfH 543 



interosseous muscle between the extensor tendons to the level of the metacarpo- 

 phalangeal joint, Avhere it divides into two small branches, like the other dorsal 

 interosseous arteries, for the sui)ply of the sides of the contiguous fingers on their 

 dorsal aspect. At the base of the second interosseous space it communicates with 

 the posterior perforating branch of the deep arch, which here runs ))ackwards 

 between the heads of the second dorsal interosseous muscle, and at the fore part of 

 the space it anastomoses through the anterior perforating brancli with the fourth 

 digital artery. 



The dorsal digital arteries, the terminations of the metacarpal artery and 

 dorsal interosseous arteries, extend along the sides of the fingers as far as the first 

 inter})halangeal joint, where they anastomose with the dorsal l^ranches of the col- 

 lateral digital arteries. 



(8) The dorsalis pollicis arises from the radial just before it sinks between 

 the two heads of the first dorsal interosseous muscle. It runs downwards on the 

 ulnar side of the extensor secundi internodii pollicis, along the metacarpal l:)one, 

 and divides into two branches for the supply of the radial and ulnar side of the 

 thumb on its dorsal aspect. These branches sometimes come off separately from 

 the radial artery. 



(4; The dorsalis indicis arises from the radial just as that artery sinks Ix'- 

 tween the two heads of the first dorsal interosseous muscle, usually below the origin 

 of the dorsalis pollicis, but sometimes as a common trunk with the latter vessel. 

 It runs downwards along the radial side of the metacarpal bone of the index 

 finger, and can be traced along the radial side of that finger as far as the first inter- 

 phalangeal joint, where it anastomoses with the dorsal branch of the radialis 

 indicis. 



III. The Radial Artery in the Palm (the Deep Palmar Arch) 



The radial artery enters the palm between the first and second metacarpal bones 

 at the base of the first interosseous space, by passing between the two heads of the 

 first dorsal interosseous muscle. It then runs inwards between the adductor 

 pollicis and inner head of the flexor brevis pollicis, and continuing its course, in a 

 slight curve with the convexity forwards, across the base of the metacarpal l^ones 

 and interosseous muscles, it anastomoses with the deep branch of the ulnar, 

 forming the deep palmar arch. The arch thus formed may be said to extend from 

 the first interosseous space to the base of the metacarpal lione of the little finger, 

 and is a finger's breadth nearer the wrist than the superficial arch. It is covered 

 by the superficial and deep flexor tendons, by the inner head of the flexor brevis 

 pollicis, and by part of the flexor brevis minimi digiti. It is accompanied by the 

 deep l)ranch of the ulnar nerve, and two small venae comites. 



Variations in the Deep Palmar Arch 



(A) The deep palmar arch may be larger than u.sual, and its interosseous branches supply 

 the })lace of one or more of the digital arteries by dividing at the cleft of the fingers into collat- 

 eral digital branches. (B) It may be reinforced by enlarged jidsterior perforating branches fium 

 the radial and its branches on the back of the hand, or by a large anterior intero.sseou.s. (C) The 

 radial may join the deep arch by passing through the second instead of the first intero.sseous space. 

 (D) The princeps pollicis and radialis indicis may come nff from the supei-ficial arch or from the 

 superficial volar, or from a separate branch of the radial wliich passes through the first intero.sseous 

 space. 



The branches of the deep palmar arch are: — O) The princeps pollicis; (2) 

 the radialis indicis; (3) the palmar interosseous (three in number); (4) the recur- 

 rent carpal; (5) the posterior perforating. The first two are usually spoken of as 

 coming off from the radial artery in the palm; the last three from the deep palmar 

 arch. 



(1) The princeps pollicis arises from the radial artery as it enters the palm, 

 between the two heads of the abductor indicis. It passes downwards between the 

 adductor transversus pollicis and abductor indicis, parallel to the metacarpal bone, 

 and between the tAvo ])ortions of the flexor brevis pollicis under cover of the flexor 



