786 HUMAN ANATOMY. 



and the skin. Posteriorly it rests successively, from above downward, upon the 

 tendon of the biceps, the supinator brevis, the pronator radii teres, the radial portion 

 of the flexor sublimis digitorum, the flexor longus pollicis, the outer border of the 

 pronator quadratus, and the anterior surface of the lower end of the radius. Inter- 

 nally it is in contact with the pronator radii teres in its upper third, and throughout 

 the rest of its course with the outer border of the flexor carpi radialis. Externally it 

 is in relation throughout its entire length with the brachio-radialis, and in the middle 

 third of its course it is in contact with the radial nerve. Two venae comites accom- 

 pany the artery, lying to its inner and outer sides. 



In its carpal portion the radial artery rests at first upon the external lateral 

 ligament of the wrist and then upon the posterior surface of the trapezium. It passes 

 beneath, successively, the tendons of the extensor ossis metacarpi pollicis, the exten- 

 sor brevis pollicis, and the extensor longus pollicis, being covered in the interval 

 between the last two and to the ulnar side of the extensor longus pollicis only by the 

 skin and fasciae, in which are some branches of the radial nerve and tributaries of the 

 radial vein. 



In its palmar portion, as it passes forward through the proximal portion of the 

 first intermetacarpal space, the artery lies between the two heads of the first dorsal 

 interosseous muscle. It then bends inward beneath the oblique head of the adductor 

 pollicis, and, either penetrating that muscle or passing between it and the transverse 

 head of the same muscle, is continued ulnarward beneath the tendons of the long 

 flexors, resting upon the bases of the metacarpal bones and upon the interosseous 

 muscles. 



Branches. — From its antibrachial portion the radial artery gives ofi numer- 

 ous 7nHscular branches to the muscles on the radial side of the forearm, and, in 

 addition, gives origin to (i) the radial recurrent, (2) the anterior radial carpal, and 

 (3) the superficial volar. 



From its carpal portion it gives rise to (4) \h^ posterior radial carpal , (5) the 

 dorsalis pollicis, and (6j the dorsalis indicis. 



From its palmar portion its branches are (7) the princeps pollicis, (8) the 

 pabnar i?iterosseous (of which there are three), and (9) the recurrent carpals. 



Variations. — The high origin of the radial has already been considered in discussing the 

 variations of the brachial artery (page 774). It is the last of the forearm arteries to be devel- 

 oped in the comparative series, and its relations with the arterial supply to the hand is due to 

 secondary anastomoses which it makes with vessels originally present, whereby it has come to 

 give origin to many branches formed before its appearance. Thus the dorsalis indicis and the 

 dorsalis pollicis are primarily digital branches from the dorsal interosseous artery of the first 

 intermetacarpal space, and this artery arose from the posterior carpal arch and has become a 

 portion of the radial by the anastomosis of that artery with the arch. Similarly the portion of 

 the radial which passes forward between the first and second metacarpals to join the deep 

 palmar arch is primarily the first posterior perforating vessel, which has secondarily become the 

 deep palmar apparent continuation of the radial, and has brought that vessel into direct con- 

 tinuity with the arch and given it the branches which originally arose from that vessel. 



The secondary anastomoses of the original radial with pre-existing vessels have, however, 

 become well established, and variations of the radial, other than its high origin, are rather 

 uncommon. It has been observed to terminate in an anastomosis with an enlarged posterior 

 carpal arch, or in the lower part of the forearm by anastomosis with the anterior interosseous 

 artery. Its absence below the point where the radial recurrent is given off has also been ob- 

 served, its territory in such cases being supplied by the interosseous. 



Occasionally it passes to the dorsal surface of the arm much higher up than usual, and in 

 such cases the superficial volar branch also arises at a much higher level than usual and passes 

 downward along the line usually occupied by the radial arter^^ It is an exceedingly slender ves- 

 sel, and, being felt at the place where the pulse is usually examined, may give rise to erroneous 

 conclusions as to the quality of that phenomenon. 



Practical Considerations. — The radial artery, like the ulnar, is the subject 

 of idiopathic aneurism only with great rarity, but a stab-wound may result in a trau- 

 matic aneurism, or may necessitate immediate ligation for control of hemorrhage. 

 The vessel may be tied in any part of its course. 



I. At the upper third of its antibrachial portion it is reached through an incision 

 made on the line described {vide stipra), which, after the deep fascia is opened up, 

 should disclose the interspace between the brachio-radialis and the pronator radii 



