THE ARTERIES 749 
posterior circumflex. Its other branches resemble those of the horse. (2) The 
anterior circumflex artery in about half the cases arises from the brachial. (3) 
The deep brachiai artery arises about a third of the way down the arm. (4) The 
bicipital artery (for the biceps) is given off at the distal third of the arm. (5) The 
proximal collateral ulnar artery arises almost opposite to the preceding vessel. It 
ramifies chiefly in the distal part of the triceps, and sends a superficial branch to the 
medial and posterior surfaces of the proximal part of the forearm. (6) The proxi- 
mal collateral radial artery (not present in the horse) arises at the distal fourth of 
the arm, crosses over the terminal part of the biceps, descends on the extensor 
carpi radialis, and concurs with a branch of the volar interosseous artery in forming 
the rete carpi dorsale. It often supplies the bicipital artery. (7) The distal col- 
lateral radial artery is very small; it accompanies the deep branch of the radial 
nerve on the dorsal surface of the forearm and supplies branches to the elbow joint 
and the brachialis, supinator, and extensor muscles. (8) The common interosseous 
artery is given off from the median a little below the elbow. It supplies 
branches to the flexor muscles and gives off the dorsal interosseous artery, 
which passes through the interosseous space, gives branches to the extensor muscles, 
and by its terminal twigs concurs in the formation of the rete carpi dorsale. The 
direct continuation of the trunk is the volar interosseous artery, which descends 
along the interosseous space under cover of the pronator quadratus, gives off a 
branch to the rete carpi dorsale and the fifth volar metacarpal artery, and termin- 
ates by joing the volar branch of the radial artery to form the deep volar arch. 
(9) The volar antibrachial artery (Ramus volaris antibrachii) arises below the 
interosseous and descends at first under the flexor carpi radialis, then between the 
heads of the deep flexor, and divides into ascending and descending branches which 
ramify in the muscles mentioned. 
The radial artery, the smaller terminal of the median, descends along the 
medial border of the radius, and divides near the carpus into dorsal and volar 
branches. The dorsal branch assists in forming the rete carpi dorsale. The larger 
volar branch descends behind the medial border of the carpus and joins the end of 
the volar interosseous in forming the deep volar arch. The arch extends across 
the interossei at the proximal part of the metacarpus. From this arch three deep 
volar metacarpal arteries descend in the second, third, and fourth intermetacarpal 
spaces and concur with the corresponding superficial volar and the dorsal meta- 
carpal arteries to form the common digital arteries. 
The ulnar artery is much the larger of the two terminal branches of the median. 
Tt descends with the median nerve along the medial border of the deep flexor of the 
digit, and sends a connecting branch to the radial above the carpus. It then in- 
clines somewhat laterally and passes between the superficial and deep flexor tendons. 
Near the middle of the metacarpus it gives off the first volar metacarpal artery and 
divides into the second, third, and fourth superficial volar metacarpal arteries. 
The first volar artery unites with the corresponding dorsal artery to form the first 
common digital artery, which supplies proper digital arteries for the opposed sur- 
faces of the first and second digits. The superficial volar arteries descend in the 
spaces between the other metacarpal bones, and unite near the metacarpo-phalangeal 
joints with the corresponding deep volar and dorsal metacarpal arteries to form 
three common digital arteries. Each of the latter divides after a short course into 
two proper digital arteries, which run along the opposed surfaces of the second to 
the fifth digits. The lateral digital artery of the fifth digit comes from the super- 
ficial volar arch formed by the union of a branch of the volar interosseous with the 
fourth superficial volar metacarpal artery. 
The rete carpi dorsale gives off four dorsal metacarpal arteries which descend 
in the intermetacarpal spaces and unite near the metacarpo-phalangeal joints with 
the volar arteries to form the common digitals. 
