22 THE ANATOMY OF THE HORSE. 



The Posterior Radial Artery (Plate 6) is one of the terminal 

 branches of the brachial. It is so much larger than the other tenninal 

 branch (the anterior radial), that it might be described as the direct 

 continuation of the brachial, whose direction it prolongs. Beginning 

 above the inner condyle, it descends on the bone, and then lies over the 

 internal lateral ligament of the elbow-joint, and posterior to the tendon 

 of insertion of the biceps. It is here covered by the posterior superficial 

 pectoral, and is related to the median nerve, which lies close behind it, 

 and to its satellite veins. At this point it is favourably placed for taking 

 the pulse, and its situation and relations should be carefully noted. 

 After crossing the elbow, it inclines forwards and disappears with the 

 median nerve between the radius and the internal flexor of the meta- 

 carpus. In this position it descends to within a short distance of the 

 carpus, where it divides into two terminal branches of unequal size — 

 the large and small metacarpal arteries. It gives off the following 

 collateral branches : — 



1. Articular Branches to the elbow-joint. 



2. The Interonseous Artery of the fore-arm, which reaches the outside of 

 the limb by passing through the radio-ulnar arch. It then descends along 

 the outer side of the line of junction of the radius and ulna (Plate 7), 

 where it Avill be followed in the dissection of the front of the fore-arm. 



3. Muscular Branches to the flexors of the metacarpus and digit. 



4. Cutaneous Branches. 



The Posterior Radial Veins. Tlie artery is accompanied by three or 

 four satellite veins, which surround it and the nerve, and anastomose 

 freely Avith each other. They begin at the carpus, where they anasto- 

 mose with the metacarpal veins, and at the elbow-joint they unite with 

 the basilic and ulnar veins to form the brachial vein. They receive 

 branches corresponding more or less exactly to those of the artery. 



The Median Nerve in the fore-arm (Plate 6). This nerve has already 

 been followed in the dissection of the arm, where it was seen descending 

 in front of the brachial artery. It preserves the same relationship to the 

 first few inches of the posterior radial artery, but at the elbow it crosses 

 the artery superficially to take up a posterior position. Below the joint 

 it again changes its position by mounting on the surface of the artery, 

 or it may even again place itself in front. At a variable point in the 

 fore-arm it terminates by dividing into two branches, one of which is 

 continued as the internal plantar nerve, while the other joins the ulnar 

 to form the external plantar. In the subject from which Plate 6 was 

 taken, the division took place considerably above the middle of the fore- 

 arm, but more frequently it occurs in the lower third. Immediately 

 below the elbow the nerve furnishes a branch to the internal flexor of 

 the metacarpus, and branches to the deej) flexor of the digit (humeral 

 and radial heads). 



