562 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



as the dorsal interosseous artery. This vessel (A. interossea dorsalis) passes down 

 between the anterior and lateral extensors of the digit and concurs with the anterior 

 radial in forming a network on the anterior surface of the carpus, the rete carpi 

 dorsale. From the latter arise two small vessels, the internal antl external dorsal 

 metacarpal arteries (A. metacarpea dorsalis meclialis, lateralis), which run distally 

 in the grooves between the large and small metacarpal bones and anastomose 

 with the volar metacarpal arteries. 



4. The artery of the rete carpi volare (A. retis carpi volaris) is a small vessel 

 which arises at the distal third of the forearm and passes downward to the posterior 

 surface of the carpus, where it concurs with branches of the volar metacarpal 

 arteries in forming the rete carpi volare. 



5. The external volar metacarpal artery (A. metacarpea volaris lateralis) is a 

 small vessel which arises just above the carpus under cover of the flexor carpi 

 medius and anastomoses with the ulnar artery, forming the supracarpal arch. 

 From the latter a branch descends with the outer branch of the median nerve, 



inclines outward toward the posterior bor- 

 der of the accessory carpal bone, and arrives 

 at the head of the external metacarpal bone. 

 Here it is connected with the internal volar 

 metacarpal artery, usually by two transverse 

 branches, thus forming the deep volar or 

 subcarpal arch (Arcus volaris profundus). 

 One of these branches lies between the sub- 

 carpal check ligament and the suspensory 

 ligament; the other (not always present) 

 lies beneath the latter on the large meta- 

 carpal ])one. A small branch descends to 

 the fetlock with the external metacarpal 

 nerve. Below the arch the artery pur- 

 sues a flexuous course downward on the 

 posterior face of the large metacarpal bone 

 alongside of the external small metacarpal 

 and under cover of the suspensory liga- 

 ment. At the distal third of the meta- 

 carpus it commonl^^ unites with the cor- 

 responding vessel of the inner side to form 

 a short trunk which passes backward 

 through the angle of divergence of the 

 branches of the suspensory ligament and 

 joins the external digital or the common digital arter}'. 



6. The internal volar or small metacarpal artery (A. metacarpea volaris 

 medialis) is given off from the posterior radial at an acute angle, usually a little 

 above the external one or by a common trunk with it. It passes down the inner 

 side of the carpus behind the tendon of the flexor carpi internus and embedded in 

 the posterior annular ligament. Arriving at the i)roximal end of the inner meta- 

 carpal bone it becomes more deeply jjlaccd and is connected with the external volar 

 artery by one or two transverse branches as stated above. It then pursues a 

 flexuous course downward alongside of the inner small metacarpal bone, like the 

 corresponding external artery, with which it commonly unites as described al)Ove. 

 It is larger than the external artery and supplies the nutrient artery to the large 

 metacarpal bone. 



Fig. 446. — Cross-section op Middle of Right 

 Metacarpus of Horse. 

 a, Common digital (or large metacarpal) 

 artery; b, internal metacarpal vein; c, internal 

 metacarpal nerve; d, external metacarpal nerve; 

 e, branch of external volar metacarpal artery; 

 /, external metacarpal vein; g, g, g, deep volar 

 or interosseous metacarpal arteries; h, tendon of 

 anterior extensor; ?', tendon of lateral extensor; 

 k, anastomotic branch connecting metacarpal 

 nerves; I, deep flexor tendon; m, check ligament; 

 n, superficial flexor tendon; o, suspensory liga- 

 ment; p, large metacarpal bone; q, (j, small 

 metacarpal hones; r, skin. (After EUenberger, 

 in Leisering's Atlas.) 



The foregoing account (icscrihc.s the most common arrangement of the dorsal and volar 

 metacarpal arteries. Variations in their origin and connections are connnon, but have no great 

 surgical importance. Collateral branches are omitted for the same reason. In some cases the 



