586 THE BLOOD-VASCULAR SYSTEM 



rete [rete carpi dorsale]. From this rete are given off the second, third, and fourth dorsal 

 metacarpal arteries to the second, third, and fourth intermetacarpal spaces respectively. These 

 vessels run downward on the dorsal interosseous muscles as far as the flexure of the fingers, and 

 there divide into two branches (dorsal digital), which run along the sides of the contiguous 

 fingers on theu* dorsal aspect. Near their proximal ends they anastomose with the dorsal 

 perforating branches of the deep volar arch. Distally they are connected by volar perforating 

 branches with the digital arteries or the corresponding spaces. The branches which run along 

 the backs of the fingers anastomose with the dorsal branches of the first dorsal digital arteries 

 derived from the volar common digital vessels (fig. 476). 



(2) The first dorsal metacarpal (figs. 472, 476) is given off by the radial shortly before it 

 passes between the two heads of the first dorsal interosseous muscle. It quickly divides into 

 two branches which supply the dorsal surface of the thumb and the radial side of the index- 

 finger toward its dorsal surface. 



III. The Radial Artery in the Palm (Deep Volar 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 medially between the 

 transverse and oblique heads of the adductor pollicis muscle and continuing its 

 course in a slight curve with the convexity forward, across the base of the meta- 

 carpal bones and interosseous muscles, it anastomoses with the deep branch 

 of the ulnar, forming the deep volar arch [arcus volaris profundus]. The arch 

 may be said to extend from the first interosseous space to the base of the meta- 

 carpal bone 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 fiexor tendons, by the 

 superficial head of the flexor pollicis brevis, and by part of the flexor quinti 

 digiti brevis. It is accompanied by the deep branch of the ulnar nerve, and two 

 small venae comitantes (figs. 472, 473). 



The branches of the deep volar arch are: — (1) The princeps pollicis; (2) the 

 radialis indicis; (5) the volar metacarpals (.three in number); (4) the recurrent 

 carpal; (3) the dorsal perforating. The first two are usually spoken of as coming 

 off from the radial artery in the palm; the last three from the deep volar arch. 



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

 the two heads of the first dorsal interosseous muscle. It passes downward between the adductor 

 pollicis transversus and the first dorsal interosseous muscle, parallel to the metacarpal bone, 

 and between the two portions of the flexor pollicis brevis under cover of the flexor pollicis 

 longus. Opposite the metacarpo-phalangeal joint it usually divides into two branches, one 

 of which is distributed to each side of the thumb on its volar aspect. These vessels anasto- 

 mose with each other at the end of the thumb, like the other digital arteries. 



(2) The arteria radialis indicis comes off from the radial artery a little lower than the former 

 vessel, or as a common trunk with it, and passes forward between the first dorsal interosseous 

 and adductor pollicis transversus, parallel to the radial side of the second metacarpal bone. 

 After emerging from beneath the adductor pollicis transversus it continues its course along the 

 radial side of the index-finger, on its volar aspect, as far as the tip, anastomosing in this course 

 with the digital artery on the opposite side of the finger in a way similar to that of the other 

 digital arteries. It frequently communicates, at the lower border of the adductor pollicis, 

 with the superficial volar arch and princeps pollicis. It gives off a dorsal branch, which anasto- 

 moses with the branch fron the first dorsal metacarpal to the index finger. 



(3) The volar metacarpal arteries [aa. metacarpea) volarcs], three in number, come off from 

 the convexity of the deep arch, and, coursing downward in the centre of the second, third, and 

 fourth interosseous spaces on the interosseous muscles, terminate near the cleft of the fingers 

 by anastomosing with the digital arteries from the superficial arch. These vessels supply the 

 interosseous muscles and the bones, and the second, third, and fourth lumbricales. 



(4) The recurrent branches come off from the concavity of the arch, and consist of two or 

 three small vessels which run vipward toward the wrist, and anastomose with the volar branch 

 of the volar interosseous, and the volar radial and ulnar carpal arteries. 



(.')) The dorsal perforating branches (rr. pnrforantes), wiiich arc usually three in number, 

 pass from the arch directly through the second, third, and fourth interosseous spaces between 

 the two heads of the corresponding dorsal intero.sseous muscle, and join the proximal ends of 

 the first dorsal interosseous, and the second, third, and fourth dorsal metacarpal arteries re- 

 spectively. 



THE THOHACIC AORTA 



The thoracic aorta [aorta thoracalis] (fig. 477) is the thoracic portion of the 

 aorta desf^cndcns. It extends from the t(;rmination of the aortic arch at the 

 lower border of tlie body of the fourtli thoracic vertebra to the lower ])or(ler of 

 the body of the twelfth thoracic vertebra, where it passes between the medial 



i 



