THE ARTERIES 173 



its course at first beneath the biceps and brachialis anticus muscles to 

 reach the front of the elbow joint. Here it meets the musculo-spiral 

 nerve, and the nerve and artery may be found deeply seated between 

 the brachialis anticus and the extensor metacarpi magnus. With the 

 musculo-spiral nerve it runs down the front of the radius, where it is 

 concealed by the extensor metacarpi magnus. Arriving at the carpus, 

 it splits up into a number of terminal branches. Some of these anasto- 

 mose inwardly with branches of the posterior radial artery. Others 

 contract outwardly anastomoses with branches of the interosseous artery 

 of the forearm. Others, again, ramify on the surface of the anterior 

 common ligament of the knee, and are distributed to the joint and to 

 the sheaths of the extensor tendons which play over it. 



A number of collateral branches are given off from the upper portion 

 of this vessel. These supply the elbow joint, the extensor metacarpi 

 magnus, and the brachialis anticus. 



The Posterior Radial Artery. — Since this division is so much larger 

 than the anterior radial, it may reasonably be looked upon as the 

 continuation of the brachial artery. It takes a downward course on the 

 internal lateral ligament of the elbow, crossing the angle formed by the 

 humerus and radius in company with the median nerve. Behind the 

 artery is its corresponding vein. The nerve, however, frequently crosses 

 the artery and is found between it and the vein. All three structures 

 are here covered by the posterior superficial pectoral muscle. The 

 artery now curves round the inner border of the radius just below its 

 upper extremity, where the bone presents a groove for the accommodation 

 of the vessel, and passes under cover of the flexor metacarpi internus 

 muscle. It now inclines slightly towards the middle line of the back of 

 the radius and descends the forearm under the muscle we have just 

 mentioned. A short distance above the carpus it emerges from beneath 

 this muscle and appears between its tendon and that of the flexor 

 metacarpi medius, and then terminates by dividing into the large and 

 small metacarpal arteries. 



