i6 THE SURGICAL ANATOMY OF THE HORSE 



disappears to the inner side of the lateral cartilage, where it divides into 

 the preplantar and plantar (ungual) vessels. About the middle of the os 

 suffraginis it gives off the perpendicular artery of the pastern, which 

 runs forwards at right angles to the parent vessel to be distributed on 

 the lateral aspect of the first phalanx. 



The Veins 



The veins of the foot unite to form the plexuses of the foot. One 

 of these plexuses is seen on the outer aspect of the lateral cartilage (48). 

 From the plexuses the blood is drained by the internal and external 

 digital veins. The latter is represented in the plate. It takes a course 

 upwards in front of the digital artery across the fetlock, above which 

 joint it disappears by dipping inwardly between the suspensory ligament 

 and the perforans tendon. Here is formed a venous arch by the union 

 of the external and internal digital veins. From this arch three veins 

 are given off. One of these, the external metacarpal vein, is shown in the 

 plate (32). It runs directly upwards in front of the plantar nerve and 

 its accompanying artery. At the knee it splits up into a number of 

 vessels, forming a plexus from which the ulnar vein and posterior 

 radial veins (three or four) are given off. 



The Nerves 



The Ulnar Nerve. — This nerve emerges from beneath the posterior 

 head of the flexor metacarpi medius. It runs on the back of the fore- 

 arm on the tendon of the flexor accessorius and along the line of 

 apposition of the middle and external flexors of the metacarpus. About 

 four inches above the knee it disappears between the last two muscles, 

 and joins the branch of the median to form the external plantar nerve. 



Immediately above the knee a cutaneous branch of the ulnar nerve 

 appears between the tendons of the flexor metacarpi medius and flexor 



