26 THE SURGICAL ANATOMY OF THE HORSE 



The Veins 



The Internal Metatarsal Vein (29). — This is a large vessel which is 

 given off from the venous arch formed across the limb immediately 

 above the fetlock. It runs for a short distance along the edge of the 

 perforans tendon, and then leaves the tendon to pass obliquely upw^ards 

 and forwards across the inner edge of the suspensory ligament and the 

 inner splint bone. The vein is crossed by the cutaneous branch from 

 the posterior tibial nerve, and then inclines slightly forwards, running 

 across the seat of spavin, to be continued upwards on the inner surface 

 of the shaft of the tibia as the internal saphena vein of which it forms 

 the anterior root. 



The external metatarsal vein has already been followed in the de- 

 scription of the outer aspect of the limb until it disappears in the tarsal 

 sheath. It is now represented as it leaves the sheath, where it is found 

 in front of the posterior tibial artery (15). It inclines upwards and 

 forwards, crossing the artery above the sigmoid flexure, and also the 

 flexor accessorius and popliteus muscles. Arriving at the broad upper 

 portion of the inner aspect of the tibial shaft it joins the internal saphena 

 vein of which it is regarded as the posterior root. 



The Nerves 



The Posterior Tibial Nerve (12). — This is the direct continuation of 

 the internal popliteal nerve. It is seen as it leaves the inner head of the 

 gastrocnemius muscle, being more fully displayed owing to the slight 

 displacement of this muscle. It takes a vertical course downwards in 

 front of the tendo-achilles, and just above the hock divides into the two 

 plantar nerves (22), which accompany the perforans tendon through the 

 tarsal sheath. 



About five inches above the point of the hock the nerve gives off an 

 important cutaneous branch (18), which crosses the posterior tibial 



