ANATOMY AND PHYSIOL YGY OF THE HORSE. 



159 



humeral veins; and it is covered inter- 

 nally by the large pectoral muscle, to which 

 it sends some small branches. But its prin- 

 cipal branches are — 1. One near its origin, 

 which crosses the bone to get to the flexor 

 brachii, and sends twigs to the shoulder- 

 joint. 2. A posterior branch, arising a lit- 

 tle lower down, which enters the muscle 

 called triceps. 3. Near its termination, 

 another branch to the flexor brachii. Where 

 the artery divides, it is covered by the hu- 

 meral plexus of veins, and by the absorbent 

 glands of the arm. 



The ulnar artery consists of a common 

 root, from which spring three or four ves- 

 sels of considerable size, running in waving 

 lines upon the inner side of the lower end 

 of the humerus. The upper one is directed 

 to the ulnar, splitting before it reaches the 

 bone, and sending one branch upward upon 

 the elbow, and another downward to the 

 heads of the flexors ; to which muscles 

 the other branches of this vessel are dis- 

 tributed. 



The spiral artery, the outermost division, 

 turns round the os humeri, passing under 

 the flexor brachii, and sending a recurrent 

 branch to it, to arrive at the front of the 

 radius, where it splits into several branches, 

 of which — 1. Some run into the elbow 

 joint. 2. Others, larger and more numer- 

 ous, penetrate the heads of the extensors. 

 3. Two long, slender ones descend upon the 

 radius, and give branches, in their course, 

 to the extensor muscles as low as the knee, 

 and there end in ramifications about and 

 into the joint, joining with others coming 

 from the radial. 



The radial artery, the principal division 

 humeral, continues its descent along the 

 radius, about the middle of the arm ; the 

 nerve accompanies it first on its outer side, 

 and subsequently behind it. A short way 

 above the knee, it splits into the metacarpal 

 arteries. 



The small metacarpal artery descends, 

 within a cellular sheath, along the inner and 

 back part of the knee. It continues its 

 descent along the metacarpal vein (which 

 runs to its inner side), till it gets below the 



knee, and then transmits its divisions down 

 the front of the suspensary ligament; be- 

 tween it and the canon bone, it sends off" 

 branches over the front of the knee, the 

 canon, and suspensary ligament. 



The large metacarpal artery, a continua- 

 tion of the radial trunk, continues its course 

 down the leg, by the side of the tendo per- 

 foratus, passing under the posterior annular 

 ligament, approaches the fetlock just above 

 the joint, and then splits into three vessels ; 

 from the middle division three recurrent ar- 

 teries are given out ; the side divisions be- 

 come the plantar arteries. From the arch 

 below come off" two other branches, which 

 descend into the joint. The plantar arte- 

 ries, external and internal, in the fore ex- 

 tremity, result from the fork of the meta- 

 carpal ; in the hind, from that of the 

 metatarsal. (Then* general distribution is 

 the same, both in the hind and fore feet.) 

 They descend the fetlock upon the sides of 

 the sessamoids, in company with the veins 

 which run in front of them, and with 

 the plantar nerves which proceed behind 

 them ; the artery then passes down to, 

 and into, the substance of what is called 

 the " fatty frog ; " it next passes the inner 

 and upper extremity of the coffin bone, and 

 afterwards to the foramen of the posterior 

 concavity of the bone. The branches of 

 the plantar artery are many and important. 

 After detaching some small ramifications 

 inwardly to the fetlock, posteriorly to the 

 flexor tendons, and anteriorly to the ex- 

 tensor tendon, it then sends off" — 1. The 

 perpendicular artery. 2. The transverse 

 artery. 3. The artery of the frog. 4. The 

 lateral laminal artery. 5. The cu'culus ar- 

 teriosus. From the latter arise two prin- 

 cipal sets of vessels — 1. The anterior 

 laminated arteries. 2. The inferior com- 

 municating arteries, "thirteen, and some- 

 times fourteen, in number." 3. The circum- 

 flex artery. Then, again, from this vessel 

 spring the solar arteries, which may be so 

 named from their radiated arrangement. 

 These latter are destined for the supply of 

 the sole, upon which they run in radii at 

 equal distances, whose common centre is the 



