22 THE ANATOMY OF THE HORSE. 



following muscles: — (1) the anterior head of the middle flexor of the 

 metacarpus; (2) the ulnar head of the same muscle ; (3) the superficial 

 flexor of the digit (perforatus) ; (4) the ulnar origin of the deep flexor 

 (ulnaris accessorius). In the fore-arm it descends in close company 

 with the vessels of the same name, and at the carpus it gives off" the 

 cutaneous hranch already described (page 20). At the upper border of 

 the pisiform bone, and beneath the tendon of the middle flexor, 1 it joins 

 a branch from the median to form the external plantar nerve. 



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

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

 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 T , it inclines forwards and disappears 

 with the median nerve between the radius and the internal flexor of 

 the metacarpus. 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 Interosseous 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 will 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 Blanches. 



The Posterior Radial Veins. The artery is accompanied by three 

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

 freely w T ith 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 



1 In Plates 6 and 9 the termination of the nerve has been pulled slightly forwards to 

 show its junction with the branch from the median. 



