176 THE SURGICAL ANATOMY OF THE HORSE 



external metacarpal bone and descending in the groove between this 

 bone and the external small metacarpal in a manner similar to the 

 internal artery. It is for a great part of its extent, however, concealed 

 by the tendon of the extensor sufFraginis muscle and by the reinforcing 

 band from the annular ligament of the knee, which joins this tendon. 



3 and 4. Tlie Internal and External Palmar Interosseous Arteries. — 

 These leave the arch on a level with the heads of the small metacarpal 

 bones, and run downwards in the grooves formed posteriorly between the 

 large and small metacarpal bones. They are thus placed one on either 

 edge of the suspensory ligament. Each terminates by anastomosing with 

 branches of the corresponding digital artery or with branches of the 

 large metacarpal artery. From one of these arteries the nutrient artery 

 of the large metacarpal bone arises. 



5 and 6. — In some subjects one or two other and very slender vessels 

 arise from the arch. These are unnamed. When both are present they 

 descend one on either edge of the perforans tendon. The inner one is 

 most frequently missing, being in fact rarely present. The outer may 

 extend as far as the lower third of the metacarpal region, where it 

 becomes lost. 



The small metacarpal artery, owing to its exposed position, is very 

 frequently injured {see " Superficial Dissection" and " Speedy Cutting"). 



The Large Metacarpal Artery. — This vessel may be regarded as the 

 continuation ot the posterior radial artery. It runs down the limb 

 beneath the fibrous carpal arch with the tendons of the superficial and 

 deep flexors of the digit. Below the knee it emerges from the tube on 

 the edge of the perforans tendon, along which it continues its downward 

 course behind the internal metacarpal vein. Behind the artery is the 

 internal plantar nerve. Just above the fetlock the artery passes out- 

 wardly, and on a level with the sesamoid bones, and between the two 

 divisions of the suspensory ligament it divides into the external and 

 internal digital arteries. 



The large metacarpal artery is in close proximity to the seat of 



