Vessels which carry blood from the heart to the tissues are called =arteries=, while those which return the blood to the heart from the tissues are called =veins=. Arteries and veins are connected by very small, thread-like vessels called _capillaries_, which originate in the smallest arteries and are so minute that they can not be seen without the aid of a microscope. The capillaries penetrate the soft tissues in every direction, and finally unite to form small veins. For our purpose we need consider only the arteries and veins. The =arteries= carrying blood from the heart ramify and subdivide in all parts of the body, and thus reach the foot. They are thick-walled, very elastic tubes, =without valves=, and carry =bright-red= blood, which flows in spurts, as can be seen when an artery is cut. If a finger be pressed lightly over an artery lying near the surface, the blood-wave can be felt as a light stroke (pulse). The character of the pulse is important, because in inflammations of the pododerm or horn-producing membrane of the foot we can ascertain by feeling that the pulse is stronger than usual in the large arteries carrying blood to the inflamed foot. On either side of the phalanges below the fetlock-joint there lies an artery called the _digital artery_ (Fig. 25, _a_). The pulse can be felt in it as it passes over the fetlock at _A_, Fig. 25. It gives off the following collateral (side) branches: 1. The _artery of the first phalanx_ (perpendicular artery), with anterior and posterior branches. 2. The _artery of the plantar cushion_, which supplies with blood the plantar cushion, the velvety tissue of the sole and frog, the bar portion of the coronary band, and the sensitive laminæ of the bars. 3. The _coronary artery_, which carries blood to the coronary band, os coronæ, ligaments of the coronary and pedal joints, flexor tendons, and skin. The terminal branches of the digital arteries are the _preplantar_ and _plantar ungual arteries_. The preplantar artery passes through the notch in the wing of the os pedis, then along the preplantar fissure, splitting up into many branches, which spread over and penetrate the porous surface of the os pedis. The plantar artery courses along the plantar fissure, enters the plantar foramen, and passes into the semilunar sinus of the os pedis, where it unites with the terminal branch of the opposite digital artery, forming the _semilunar arch_. [Illustration: FIG. 25.