924 THE VASCULAK SYSTEM. 



distally, on the dorso-lateral aspects of the fingers which bound the third and fourtl 

 interosseous spaces, and they anastomose with the special volar digital branches of th 

 volar digital arteries. 



Arcus Volaris Superficialis. The superficial volar arch (O.T. superficia 

 palmar) (Fig. 768) includes the terminal portion of the ulnar artery, and is usuall; 

 completed on the radial side by the superficial volar, or by the volaris indici 

 radialis or the princeps pollicis branches of the radial artery. It extends fron 

 the ball of the little finger to the ulnar border of the superficial head of th 

 flexor pollicis brevis, and reaches distally to a line drawn across the palm at th 

 level of the distal border of the fully abducted thumb. It is accompanied b; 

 venae comites and it is covered by the integuments and the central portion o 

 the palmar aponeurosis, and, on the ulnar side of the palm, by the palmaris brevis 

 It is in contact dorsally with * the flexor brevis and opponens digiti quinti, an< 

 with the common digital branches of the ulnar and median nerves, as well a 

 with the flexor tendons and the lumbrical muscles. 



Branches. Four volar common digital arteries arise from the convexity of the arc): 

 The most ulnar of the four passes along the ulriar border of the little finger, accompanie< 

 by the common digital branch of the ulnar nerve ; the other three pass distally superficia 

 to the common digital nerves, one along the middle of each of the ulnar three interosseou 

 spaces, towards the interdigital clefts, just proximal to which each common digital arter 

 divides into two special digital arteries which supply the contiguous sides of the finger 

 bounding the cleft. As the special digital branches pass along the sides of the fingers the; 

 lie superficial to the corresponding special digital nerves, and supply branches to the joints 

 to the flexor tendons and their sheaths, and to the skin and subcutaneous tissues on th 

 volar surfaces of the fingers ; they give off" dorsal branches also which anastomose wit' 

 the dorsal digital arteries and supply the tissues on the dorsal aspects of the second an 

 terminal phalanges. Some of the dorsally directed branches form a plexus in the matri 

 of the nail. In the pulp of the finger-tips anastomosing twigs join to form arches fror 

 which numerous branches are given off to the skin and subcutaneous fat. 



Each of the three most radial special digital arteries is joined, immediately proximal t 

 its division, by a volar metacarpal artery from the deep volar arch and a distal perforatin: 

 artery from a dorsal metacarpal artery. The most ulnar digital artery is joined by 

 branch which arises either from the most ulnar volar metacarpal artery or from the dee 

 volar arch. 



Arcus Volaris Profundus. The deep volar arch (O.T. deep palmar) (Fig. 769 

 extends from the base of the metacarpal bone of the little finger to the proxima 

 end of the first interosseous space, and is formed by the terminal part of the radia 

 artery anastomosing with the profunda branch of the ulnar. It is from 12 t 

 18 mm. (half to three-quarters of an inch) proximal to the level of the superficia 

 volar arch. It lies deeply in the palm, in contact with the proximal ends of th 

 bodies of the metacarpal bones and on the origin of the interossei muscles, and dee; 

 to the long flexor tendons and their synovial sheaths. 



Branches. (a) The proximal perforating : three small arteries which pass dorsall) 

 through the ulnar three interosseous spaces and between the origins of the dorss 

 interosseous muscles. They anastomose on the dorsum of the hand with the dorsal meta 

 carpal arteries. 



(b) Small irregular recurrent branches pass proximally and unite with the vola 

 carpal arch. 



(c) The articular to the adjacent articulations. 



(d) The volar metacarpal arteries are three vessels which pass distally, on th 

 interosseous muscles of the three ulnar interosseous spaces, deep to the flexor tendons 

 They terminate by anastomosing with the volar digital arteries just before the latte 

 vessels divide into special volar digital branches. 



(e) The communicating, a small irregular branch which passes ulnarwards betweei 

 the flexor tendons and the short muscles of the little finger to anastomose with the ulna 

 volar digital artery. 



BRANCHES OF THE DESCENDING THORACIC AORTA. 

 The branches given off from the thoracic portion of the descending aorta ar 

 distributed chiefly to the walls of the thorax and to the thoracic viscera. The 



