The radial artery, (latin : a. radialis, french : artère radiale) in direction, though not in size, appears to be the continuation of the brachial. It extends from the bifurcation of the latter, obliquely along the front of the fore-arm as far as the lower end of the radius, below which it turns round the outer border of the wrist, and then descending to the back of the space between the metacarpal bones of the thumb and fore-finger, passes forwards to the palm of the hand, which it crosses towards the inner side, so as to form the deep palmar arch. From the change in its course at the lower end, the directions and connections of the radial artery may be separately described in the fore-arm, on the wrist, and in the hand.
In the fore-arm, the direction of this artery is from the point of bifurcation of the brachial opposite to the neck of the radius towards the fore part of the styloid process of that bone. It descends at first somewhat obliquely outwards in a line with the brachial artery, and then nearly vertically along the outer part of the front of the fore-arm, its course being indicated by a line drawn from the middle of the bend of the elbow to the narrow interval between the trapezium bone and the tendons of the extensors of the thumb, which can be readily felt towards the outer border of the wrist. Placed at first to the inner side of the radius, the vessel gradually inclines to the front of that bone, on which it lies below ; it is in this part of the vessel that the pulse is usually felt during life. The radial artery is nearer to the surface than the ulnar, and is covered only by the common integument and fascia, except where it is overlapped by the fleshy part of the supinator longus, which must be drawn aside in order to bring the vessel into view. At first it rests on the tendon of the biceps, and is then supported by the branches of the musculo-spiral nerve, and some cellular tissue, which separate it from the short supinator muscle. It next passes over the insertion of the pronator teres, and the thin radial origin of the flexor sublimis; after which, it lies on the flexor pollicis longus and pronator quadratus, until it reaches the lower end of the radius. To the inner side of this vessel lie the pronator teres in the upper part of its course, and in the rest, the flexor carpi radialis; and on the outer side, in its whole course along the fore-arm, is the supinator longus or the tendon of that muscle.
The artery is accompanied by venae comites, which have the usual arrangement of those veins.
The radial branch of the musculo-spiral nerve is placed on the outer side of the artery in the middle third of its course. At the elbow that nerve is separated from the artery by a considerable interval; and towards the lower end of the fore-arm, it turns backwards beneath the tendon of the supinator longus, to reach the dorsal aspect of the arm, and thus loses all connection with the artery. Some filaments of the external cutaneous nerve pierce the fascia to reach the lower part of the artery, which they accompany to the back of the carpus.
At the wrist, the radial artery turns outwards between the styloid process of the radius and the carpus, beneath the tendons of the extensors of the metacarpal bone and of the first phalanx of the thumb, and upon the external lateral ligament of the wrist-joint, to reach the back of the carpus. It then runs downwards for a short distance, lying in the angular interval between the tendons of the two extensors of the thumb just alluded to, and that of the extensor of its second phalanx; and soon, being crossed by this last-named tendon, the vessel reaches the upper end of the space between the first and second metacarpal bones, where it turns forwards into the palm of the hand, by passing between the heads of the first dorsal interosseous muscle.
As it turns round below the end of the radius the artery is deep-seated, but afterwards comes nearer to the surface. It is accompanied by two veins and by some filaments of the external cutaneous nerve, and is crossed by subcutaneous veins and by filaments of the radial nerve.
From Quain's Anatomy.