The radial artery appears, from its direction, to be the continuation of the brachial, but it is smaller in caliber than the ulnar.
It commences at the bifurcation of the brachial, just below the bend of the elbow, and passes along the radial side of the forearm to the wrist. It then winds backward, around the lateral side of the carpus, beneath the tendons of the Abductor pollicis longus and Extensores pollicis longus and brevis to the upper end of the space between the metacarpal bones of the thumb and index finger. Finally it passes forward between the two heads of the first Interosseous dorsalis, into the palm of the hand, where it crosses the metacarpal bones and at the ulnar side of the hand unites with the deep volar branch of the ulnar artery to form the deep volar arch.
The radial artery therefore consists of three portions, one in the forearm, a second at the back of the wrist, and a third in the hand.
(a) In the forearm the artery extends from the neck of the radius to the forepart of the styloid process, being placed to the medial side of the body of the bone above, and in front of it below. Its upper part is overlapped by the fleshy belly of the Brachioradialis; the rest of the artery is superficial, being covered by the integument and the superficial and deep fasciæ. In its course downward, it lies upon the tendon of the Biceps brachii, the Supinator, the Pronator teres, the radial origin of the Flexor digitorum sublimis, the Flexor pollicis longus, the Pronator quadratus, and the lower end of the radius. In the upper third of its course it lies between the Brachioradialis and the Pronator teres; in the lower two-thirds, between the tendons of the Brachioradialis and Flexor carpi radialis. The superficial branch of the radial nerve is close to the lateral side of the artery in the middle third of its course; and some filaments of the lateral antibrachial cutaneous nerve run along the lower part of the artery as it winds around the wrist. The vessel is accompanied by a pair of venæ comitantes throughout its whole course.
(b) At the wrist the artery reaches the back of the carpus by passing between the radial collateral ligament of the wrist and the tendons of the Abductor pollicis longus and Extensor pollicis brevis. It then descends on the navicular and greater multangular bones, and before disappearing between the heads of the first Interosseus dorsalis is crossed by the tendon of the Extensor pollicis longus. In the interval between the two Extensores pollicis it is crossed by the digital rami of the superficial branch of the radial nerve which go to the thumb and index finger.
(c) In the hand, it passes from the upper end of the first interosseous space, between the heads of the first Interosseus dorsalis, transversely across the palm between the Adductor pollicis obliquus and Adductor pollicis transversus, but sometimes piercing the latter muscle, to the base of the metacarpal bone of the little finger, where it anastomoses with the deep volar branch from the ulnar artery, completing the deep volar arch.
Peculiarities.—The origin of the radial artery is, in nearly one case in eight, higher than usual; more often it arises from the axillary or upper part of the brachial than from the lower part of the latter vessel. In the forearm it deviates less frequently from its normal position than the ulnar. It has been found lying on the deep fascia instead of beneath it. It has also been observed on the surface of the Brachioradialis, instead of under its medial border; and in turning around the wrist, it has been seen lying on, instead of beneath, the Extensor tendons of the thumb.
Branches.—The branches of the radial artery may be divided into three groups, corresponding with the three regions in which the vessel is situated.