CIRCULATORY SYSTEINJ. 185 



as the continuation of the radial trunk, continues its course down 

 the leg by the side of the tendo perforatus, passing along with it 

 at the knee under the posterior annular ligament, but inclosed 

 within a cellular sheath of its own. As it proceeds, it inclines 

 to the side of the tendo perforans, and, in approaching the fetlock, 

 gets in advance of that tendon. Immediately above the joint, 

 where it is situated between the tendo perforans and the suspen- 

 sory ligament, it splits into three vessels. The middle division 

 slides into the interval between the bifurcated terminations of the 

 ligament, and between them and the bone forms a transverse 

 arch, from which three recurrent arteries retrace in a flexuous 

 line the suspensory ligament, and form communications with the 

 small metacarpal artery : the lateral divisions become the plantar 

 arteries. From the arch, below, come off two lateral branches 

 which descend into the joint. 



The plantar arteries, one external, one internal, in the 

 fore extremity result from the bifurcation of the metacarpal, in 

 the hind from that of the metatarsal artery : I prefer this appel- 

 lation for them, because it denotes their destination at once, and 

 because it saves us the useless division of a trunk only six inches 

 in length into three nominal arteries ; and because our descrip- 

 tions and memories are not clogged by it as they are by the 

 " large pastern," and the " small pastern," and the " coffin 

 arteries." Their general distribution is the same both in the fore 

 and hind feet. 



The plantar arteries, in emerging from their common origin be- 

 hind the flexor tendons, describe two sides of the figure of a 

 triangle, the base of which, turned downward, is represented by 

 a line drawn across the backs of the sesamoid bones, the apex 

 being the point of bifurcation. They descend the fetlock upon 

 the outer sides of the sesamoids, in company with their corres- 

 pondent veins which run in front of them, and with the plantar 

 nerves which proceed behind them : in this part of their course, 

 they describe correlative curves outward, to conform to the pro- 

 minences of the fetlock, and henceforward continue to pursue pre- 

 cisely the same uniformity both in course and distribution, so that 

 we need only in the progress of our description make mention of one. 

 In its passage over the sesamoid, the outer edge of that bone is 

 found to rise between the vessel and the flexor tendon ; but in quit- 

 ting the fetlock, the artery again approaches the tendo perforatus, 

 and subsequently runs alongside of it to its implantation in the 

 head of the os coronse, at which place the artery sinks down behind 

 the cartilage into the substance of what is called the " fatty frog." 

 Inclining forward in its subsequent descent, the artery next passes 

 the inner and upper extremity of the ala of the os pedis, where it 

 u 1) 



