654 TBE ARTERIES 



by their inner face and the posterior face of the principal metacarpal bone, 

 terminating- at the inferior extremity of the lateral bones, by anastomosing in 

 full canal with a branch of the collateral of the cannon. They furnish some 

 ramifications to the suspensory ligament which covere them, and several tendinous 

 and cellulo-cutaneous twigs ; one supplies the nutrient aitery of the large meta- 

 carpal bone (Fig. 377, 7). 



b. The anterior interosseous arteries arise from nearly the same point as the 

 preceding — one outwards, the other inwards — turning back round the head of 

 the lateral metacaqjals to place themselves in the groove which separates these 

 from the large metacarpal bone, on their external or dorsal face, after having 

 thrown off several anastomosing ramuscules that communicate between the two 

 arteries in front of the upper extremity of this bone, or with the terminal 

 branch of the anterior radial and the interosseous arteries of the forearm. By 

 their terminal extremity, these two arteries anastomose with a branch of the 

 collateral of the cannon — that which receives the posterior interosseous arteries 

 (Figs. 376, 7; 377, 11). 



The doi-sal interosseous arteries, although much finer than the palmar — in 

 Solipeds these arteries are qiyte rudimentary — nevertheless furnish collateral 

 divisions for the anterior tendons of the metacarpus, the periosteum, the con- 

 nective tissue, and the skin. They often communicate with the posterior arteries 

 by deep branches, which cross the intermetacarpal ligaments. 



Variations. — The existence of the interosseous metacarpal arteries, their 

 position, and their anastomoses with the inferior extremity of the collateral of 

 the cannon, are constant ; though this is not the case with regard to their origin, 

 or the source whence they are derived. In the tyjiical description given, we have 

 considered them all as being furnished by the radio-palmar artery ; but it is 

 necessary to add that one of the four — the external dorsal — often comes directly 

 from the arterial branch that, from the siqjra-carpal arch, descends along the 

 carpus to concur in forming the infra-carpal arch, by anastomosing with the 

 radio-palmar, or rather with a branch of the interosseous of the forearm. It is 

 also necessary to add that these metacarpal arteries sometimes arise together 

 from one large branch furnished by the collateral of the cannon, at the superior 

 extremity of the metacarpus (Fig. 377), and which receives the now rudimentary 

 radio-palmar artery, as well as that given off by the supra-carpal arch ; so that 

 we may have two superposed supra-carpal arches. We have met other anomalies 

 which need not be noticed here, as they are without interest. 



2. Second Terminal Branch of the Posterior Radial, or Collateral 

 Artery of the Cannon ^ (Figs. 376, 9 ; 377, 2). 



The collateral artery of the cannon (or large metacarpal artery) (Fig. 376, 9) 

 continues by its volume and direction, the posterior radial artery. It passes, 

 with the flexor tendons, under the carpal arch, and descends on the inner side of 

 these tendons, accompanied by the internal plantar nerve, to above the fetlock 

 and near the sesamoid bones, where it bifurcates into the digital arteries. 



Collateral branches. — We observe : 



1. Near the origin of the artery, and very often from the posterior radial 

 artery itself, a branch which anastomoses above the pisiform bone with the ulnar 

 artery, forming an arch, the convexity of which is inferior (Figs. 376, 10 ; 377, 



> This artery, the mperficial plantar of Rigot, represents one of the metacarpal palmar 

 hranches furnished by the superficial palmar arcli in Mau and other pentadactylous animals. 



