1 8 THE SURGICAL ANATOMY OF THE HORSE 



button of the small metatarsal it disappears through the interval between 

 this bone and the large metatarsal to gain the back of the limb, where it 

 divides between the two divisions of the suspensory ligament into the 

 external and internal digital arteries. 



The External Digital Artery (37). — This appears behind the 

 outer division of the suspensory ligament and takes a vertical course 

 across the outer aspect of the fetlock-joint, being behind the digital 

 vein, and in front of the plantar nerve on the outer edge of the perforans 

 tendon. Near the middle of the os suffraginis it gives off the 

 perpendicular artery (43) of the pastern, which runs forwards along this 

 bone and divides into ascending and descending branches. 



The digital artery divides on the inner aspect of the lateral cartilage 

 into the plantar and preplantar (ungual) arteries. 



The Veins 



The External Digital Vein (40). — This is formed by the union 

 of vessels which drain the plexuses of the foot. One of these plexuses is 

 represented, namely, that on the outer aspect of the external lateral 

 cartilage (45). This plexus communicates with that on the deep face of 

 the cartilage through the cartilage itself. 



The vein thus formed runs upwards in front of the corresponding 

 digital artery, crossing the anterior and middle digital nerves. Above 

 the fetlock it disappears from view, since it dips in between the 

 suspensory ligament and perforans tendon, to assist in the formation of 

 the venous arch which is here placed. From this arch three veins are 

 given off, namely, the external, middle, and deep metatarsals. 



The External Metatarsal Vein (32) leaves the arch, runs outwards, 

 and appears on the edge of the perforans tendon. It takes an upward 

 course on the tendon in front of the small unnamed artery (34), which 

 descends from the tarsal arterial arch, and disappears with the tendon 

 through the tarsal sheath. 



