THE RADIAL ARTERY. 



785 



The variations in the formation of the superficial palmar arch are frequent and numerous, 

 and may be grouped in two classes : ( i ) those in which additional branches from the forearm 

 participate in the formation of the arch or replace the radial in its composition, and (2) those in 

 which there is no true arch, the arteries which should participate in its formation, and in some 

 cases additional ones also, failing to anastomose and each giving rise independently to a certain 

 number of digital branches. To the first of these classes belong the cases in which the median 

 or anterior interosseous artery anastomoses directly with the arch formed by the superficial 

 volar and the ulnar, and also those in which the superficial volar fails to reach the ulnar, the arch 

 being formed by the union of the latter vessel with the median or the anterior interosseous. 

 And, finally, the arch may be formed by the ulnar artery alone, no direct communication taking 

 place between it and the arteries mentioned. 



In the second class of cases— that in which there is no true arch — the ulnar and the super- 

 ficial volar, on reaching the palm, divide in a somewhat fan-like manner to give rise to the digital 

 branches. The superficial volar may contribute the fourth digital, as well as the vessels to the 



c 



Variations of palmar arteries replacing: superficial arch. ( /aschtschtnski). 



thumb and radial side of the index (Fig. 714, A ), or it may be limited to the latter vessels, all 

 four normal digitals being derived from the ulnar. With the absence of the arch there may be 

 associated an extra development of the median artery, which continues distally into the palm 

 as the fourth digital vessel, the remaining digitals and the radialis indicis and princeps polhcis 

 being supplied by the ulnar and radial respectively ( C). Or, finally, with the extra development 

 of the median there is associated an absence, more or less complete, of the superficial volar, 

 the median giving off the branches to the radial digit as well as the fourth digital [B ) . 



THE RADIAL ARTERY. 



The radial artery (a. radialis) (Figs. 710, 712) is the smaller of the two terminal 

 branches of the brachial, whose course it continues downward through the forearm. 

 It arises at the bend of the elbow and passes down the outer border of the forearm to 

 the level of the styloid process of the radius, where it bends outward, curving around 

 the external lateral ligament of the wrist. It then extends downward over the pos- 

 terior surface of the trapezium until it reaches the interval between the first and second 

 metacarpal bones, and here it again changes its direction and passes forward into the 

 palmar surface of the hand, across which it is continued inward over the anterior sur- 

 faces of the second, third, and fourth metacarpals, forming what is termed the deep 

 palmar arch (arcus volaris profundus). It terminates opposite the proximal part 

 of the fourth metacarpal interspace by anastomosing wath the deep palmar branch of 

 the ulnar. 



In accordance with its position with reference to the bony axis of the forearm 

 and hand, the radial artery may be regarded as consisting of three parts. In its first 

 or antibrachial portion it is preaxial in position, in the second or carpal portion it is 

 postaxial, and in the third or palmar portion it is again preaxial. 



Relations. — In its antibrachial portion the course of the artery may be indi- 

 cated by a line drawn from a point midway between the two condyles of the humerus 

 to a point about i cm. internal to the styloid process of the radius. In its upper 

 half it is overlapped in front by the inner border of the brachio-radialis (supinator 

 longus) muscle, but lower down it is covered only by the deep and superficial fasciae 



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