(3.) Arteria anterior carpi radialis. — This is ordinarily a minute branch vvhich comes oft from the radial, either very close to the pre ceding, or a little above it. It runs directly inwards in contact with the anterior ligament of the wrist joint, or on the radius at a level just above this ; to join with a similar branch from the ulnar on the opposite side of the wrist, and with the terminations of the an terior interosseous artery. It supplies the carpal bones and the articulation.
(4.) The arteria dorsalis carpi radialis, or posterior carpal branch, is considerably larger than the preceding, and is given off from the radial at a lower level, generally while the artery lies in the deep groove formed by the tendons of the extensors of the thumb. Its course is, like that of the anterior carpal, di rectly inwards beneath the tendons of the different fingers; and like it, at about the middle of the wrist, it terminates by uniting with a similar branch from the ulnar artery, and svith the terminal ramifications of the in terosseous vessels. Its size and arched shape are usually much more distinct than those of the anterior carpal vessels.
Other small branches are given off from the radial immediately previous to its entering the palm. Thus an arteria dorsalis pollicis is usually present, and divides, after a short course, into a branch for each side of the thumb ; and there generally exists a similar twig for the radial side of the index finger, either as a separate branch from the radial artery, or from the ulnar division of the bi furcation just mentioned. A larger branch runs along the interosseons muscle in the second metacarpal space, to divide at its an terior extremity into branches for the opposed sides of the index and middle fingers. The vessels occupying the third and fourth spaces, with the same ultimate distribution, rarely arise from the radial ; more usually they come from the posterior carpal arch, and sometimes from the previous metacarpal vessel, or from a similar ulnar branch lying in the fourth space. All these metacarpal branches unite, at the superior extremity of the interosseous space, with the deep arch by means of its posterior perforating branches ; and at its inferior termination, with the digital branches from the more superficial arch of the ulnar vessel. Their distribution to the fingers cor responds to that of the arteria dorsalis polli cis.
The arteria magna seu prineeps pollids is the first branch given off from the radial in the palm, and, as its name intimates, it is usually of considerable size. From the point of its origin it runs downwards beneath the flexor brevis pollicis and tendon of the flexor longus, lying on the metacarpal bone of the thumb, until near the metacarpo-phalangeal joint ; where it divides into two branches, one of which occupies each border of the phalanges, and joins that opposite in the ordinary manner beneath the sentient cushion which forms the extremity of the thumb.
The arteria radialis indieis —also given off' beneath the flexor brevis pollicis, runs yet more vertically downwards than the pre ceding, beneath that muscle and the adductor pollicis, and on the abductor indicis or first dorsal interosseous muscle, to become super ficial at their lower borders. Here it gives off a tolerably large communicating branch to the superficial palmar arch of the ulnar artery, and from this point it passes along the radial side of the 'second metacarpal bone and index finger to its extremity, having a distribution in all respects like that of the digital branches of the palmar arch ; its description is deferred to them.
From the arch itself are given off' few branches of any size. Those which proceed downwards, lying on the palmar interossei, are three in number, one for each space, and anteriorly they end by inosculating with the digital branches from the ulnar, like the small twigs already referred to as occupying the same interosseous position on the dorsum of the hand. They have been named " ante rior interosseous " branches. The remaining branches of the radial are the posterior per forating, three twigs which perforate the supe rior extremity of the same metacarpal spaces, to anastotnose on the back of the hand with the posterior carpal and metacarpal branches.
The ulnar artery.— The remaining terminal branch of the brachial is usually much larger than the preceding, with which it is also contrasted by the more linear direction of its course, and by its situation in the different regions through which it passes ; since it oc cupies the front of the limb from its com mencement to its termination, and is placed less superficially in the forearm than in the hand.