THE ULNAR ARTERY. 789 
Branches of the third part.—(1) The princeps pollicis (a. princeps pollicis) 
branch is given off as soon as the radial artery enters the palm. It runs downwards 
in front of the first metacarpal bone, between the oblique adductor and the opponens 
pollicis, and under cover of the long flexor tendon, and divides near the lower end of the 
bone into collateral branches which run along the sides of the thumb and anastomose 
with the dorsales pollicis arteries. 
(2) The radialis indicis (a. volaris indicis radialis) is a branch which descends 
between the ulnar head of the first dorsal interosseous muscle and the transverse adductor 
of the thumb, and runs along the radial side of the index-finger to its tip, supplying the 
adjacent tissues ; not uncommonly it anastomoses with the superficial palmar arch. 
THE ULNAR ARTERY. 
The ulnar artery (a. wlnaris, Figs. 563 and 564) is the larger terminal branch, but 
the less direct continuation of the brachial. It commences in the ante-cubital fossa, 
opposite the neck of the radius, and terminates in the palm of the hand, where it 
anastomoses with the superficialis vole. to form the superficial palmar arch. 
From its origin it runs obliquely downwards and inwards, beneath the muscles 
arising from the internal condyle, to the junction of the upper and middle thirds of 
the forearm, where it comes into relation with the ulnar nerve; it then descends 
vertically, on the radial side of the ulnar nerve, to the wrist, crosses in front of the 
main part of the annular ligament to the radial side of the pisiform bone, and 
enters the palm of the hand to form the main part of the superficial palmar arch. 
Relations.—Posterior.—It rests, from above downwards, upon the lower part of the 
brachialis anticus, the flexor profundus digitorum, and the deep portion of the anterior 
annular ligament. Anterior.—In front it is crossed, in the oblique part of its course, by 
the pronator radii teres, the median nerve, which is separated from the artery by the deep 
head of the pronator, the flexor sublimis digitorum, the flexor carpi radialis, and the 
palmaris longus. In the middle third of the forearm it is overlapped by the anterior 
border of the flexor carpi ulnaris, and in the lower third it is covered by skin and fascia 
only. <A short distance above the wrist the palmar cutaneous branch of the median ncrve 
lies in front of it, and as it crosses the anterior annular ligament, it is bound down by a 
fascial expansion from the tendon of the flexor carpi ulnaris. Two ven comites, which 
frequently communicate with one another, lie one on either side of the artery. Lateral. 
On the radial side there is also, in its lower two-thirds, the flexor sublimis digitorum. On 
its wlnar side there is the flexor carpi ulnaris, from which, however, it is partially separated 
in its lower two-thirds by the ulnar nerve. 
Branches.—(1) The anterior ulnar recurrent is a small branch which arises 
in the ante-cubital fossa, frequently in common with the posterior ulnar recurrent. 
It passes upwards to the front of the internal condyle, under cover of the pronator 
radii teres, and anastomoses with branches of the anastomotic and inferior profunda 
arteries. 
(2) The posterior ulnar recurrent branch, larger than the anterior, arises in the 
ante-cubital fossa, from the outer side of the ulnar artery, and ascends on the brachialis 
anticus, and under cover of the muscles which rise from the internal condyle to the back 
of that prominence, where it passes between the humeral and olecranoid heads of the flexor 
carpi ulnaris, and anastomoses with the inferior profunda and anastomotic arteries. It 
gives branches to the adjacent muscles and to the elbow-joint. 
(3) The common interosseous artery (a. interossea communis), a short trunk 
which springs from the inner and back part of the ulnar artery in the lower part of the 
ante-cubital fossa. It passes backwards towards the upper border of the interosseous 
membrane, and divides into anterior and posterior interosseous branches. 
(3a) The anterior interosseous artery (a. interossea volaris) descends in front of the 
interosseous membrane, between the adjacent borders of the flexor longus pollicis and the 
flexor profundus digitorum, to the upper border of the pronator quadratus, where it pierces 
the interosseous membrane, and continues its descent, first on the posterior surface of the 
membrane, under cover of the extensor longus pollicis and extensor indicis, and then on 
the radius, in the groove for the extensor communis digitorum, to the back of the carpus, 
where it terminates in the posterior carpal arch. Whilst in front of the interosseous 
membrane it is accompanied by the anterior interosseous nerve, and afterwards by the 
posterior interosseous nerve. 
