538 THE BLOOD-VASCULAR SYSTEM. 



From this description it will be observed that the anastomotica magna is the 

 vessel most engaged, the only part of the anastomosis in which it is not employed 

 being that in front of the external condyle. 



Radial Artery (Fig. 304). 



The Radial Artery appears, from its direction, to be the continuation of the 

 brachial, but in size it is smaller 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, round the outer side of the 

 carpus, beneath the extensor tendons of the thumb, to the upper end of the space 

 between the metacarpal bones of the thumb and index finger, and, finally, passes 

 forward, between the 'two heads of the First dorsal interosseous muscle, into the 

 palm of the hand, where it crosses the metacarpal bones to the ulnar border of the 

 hand, to form the deep palmar arch. At its termination it inosculates with the 

 deep branch of the ulnar artery. The relations of this vessel may thus be con- 

 veniently divided into three parts viz., in the forearm, at the back of the wrist, 

 and in the hand. 



Relations. In the forearm this vessel extends from opposite the neck of the 

 radius to the fore part of the styloid process, being placed to the inner side of the 

 shaft of the bone above and in front of it below. It is overlapped in the upper 

 part of its course by the fleshy belly of the Supinator longus muscle ; throughout 

 the rest of its course it is superficial, being covered by the integument, the super- 

 ficial and deep fasciae. In its course downward it lies upon the tendon of the 

 Biceps, the Supinator brevis, the Pronator radii tores, the radial origin of the Flexor 

 sublimis digitorum, the Flexor longus pollicis, the Pronator quadratus, and the 

 lower extremity of the radius. In the upper third of its course it lies between 

 the Supinator longus and the Pronator radii teres ; in its lower two-thirds, between 

 the tendons of the Supinator longus and the Flexor carpi radialis. The radial 

 nerve lies close to the outer side of the artery in the middle third of its course, 

 and some filaments of the musculo-cutaneous nerve, after piercing the deep fascia, 

 run along the lower part of the artery as it winds round the wrist. The vessel is 

 accompanied by venae comites throughout its whole course. 



PLAN OF THE RELATIONS OF THE RADIAL ARTERY IN THE FOREARM. 



In front. 



Skin, superficial and deep fasciae. 

 Supinator longus. 



/" ~"\ 



Inner side. \ Outer side. 



Pronator radii teres. J ^i^drwirm 7 Supinator longus. 



Flexor carpi radialis. Radial nerve (middle third). 



Behind. 



Tendon of Biceps. 

 Supinator brevis. 

 Pronator radii teres. 

 Flexor sublimis digitorum. 

 Flexor longus pollicis. 

 Pronator quadratus. 

 Radius. 



At the wrist, as it winds round the outer side of the carpus from the styloid 

 process to the first interosseous space, it lies upon the external lateral ligament, 

 and then upon the scaphoid bone and trapezium, being covered by the extensor 

 tendons of the thumb, subcutaneous veins, some filaments of the radial nerve, and 

 the integument. It is accompanied by two veins and a filament of the musculo- 

 cutaneous nerve. 



