80 THE ANATOMY OF THE HORSE. 



The Perforating Metatarsal Artery, the smaller branch resulting 

 from the division of the anterior tibial artery, passes from the front to 

 the back of the tarsus by the canal between the cuboid, scaphoid, and 

 cuneiform bones. Here it unites with the outer and inner plantar 

 divisions of the posterior tibial, which descend in the tarsal sheath, one 

 on each side of the perforans tendon. Of the four vessels that spring 

 from the arch thus formed, the two that descend with the plantar 

 nerves at the side of the flexor tendon are unnamed and slender (Plate 

 19). The other two are termed the plantar interosseous metatarsal 

 arteries. This may be regarded as the most typical arrangement of the 

 arteries here, but it is not constant. Sometimes the inner plantar 

 artery is directly continued as the satellite vessel of the internal plantar 

 nerve in the metatarsus, the outer plantar artery alone uniting with 

 the perforating metatarsal artery. 



The External Plantar Interosseous Artery is very slender. It 

 descends, as beforesaid, between the outer splint bone and the edge of 

 the suspensory ligament ; and above the fetlock it anastomoses with a 

 recurrent twig from the large metatarsal artery. 



The Internal Plantar Interosseous Artery, a vessel of consider- 

 able size, descends between the inner splint bone and tjie edge of the 

 suspensory ligament. Above the lower extremity of that bone it in- 

 clines towards the middle of the limb to join the large metatarsal artery. 

 It supplies the nutrient artery of the large metatarsal bone. 



The Digital Arteries (Plate 19). These arteries separate at an 

 acute angle, in passing backwards between the branches of bifurcation 

 of the suspensory ligament. For the remainder of their course they 

 are identical with the homonymous vessels of the fore limb. For their 

 description turn to page 28. 



The Digital Veins (Plate 19). These are the satellites of the digital 

 arteries, in front of which they ascend. They drain away the blood 

 from the venous plexuses within the hoof; and, uniting with one 

 another above the fetlock, they form an arch between the deep flexor and 

 the suspensory ligament. From this arch spring the metatarsal veins. 



The Metatarsal Veins are three in number : — 



1. The Internal Metatarsal Vein ascends in front of the inner edge of 

 the deep flexor tendon, in company with the internal plantar nerve and 

 a slender artery. The vein is the most anterior of the three structures, 

 and the slender artery is between the vein and the nerve. At the 

 upper third' of the metatarsus the vein deviates forwards, crossing the 

 inner splint bone and the large metatarsal obliquely, to gain the inner 

 side of the hock, above which it is continued as the anterior root of the 

 internal saphena vein. The course of the vein over the hock is generally 

 apparent in the living animal, and when very prominent it constitutes 

 the so-called "blood spavin." 



