end of the sacrum, as the point of union of the fore hand with the hind hand. Here is the junction of these two parts, where they are united by the muscles. If there were not this union, if the volitional impulse came as far as the last dorsal vertebra and there stopped, quadrupedal locomotion would be quite impossible.
All this is assuming that the horse is free from any human interference. But if the horse's spine is carrying a load, we cannot neglect the influence of this weight upon the two parts of the body, which are, by instinct, a unit and under the same acts of will. Their point of union, in my opinion, is this centrifugal region where the forces are assembled. It is like the mechanical coupling which unites the locomotive to the loaded cars behind it. At this point all the pull of the engine is concentrated against the weight opposed to it. If the cars were not loaded, the coupling between the locomotive and the first car would not need to be so strong.
If a horse, when running or jumping, is watched during a fall, it is easy to discover that the forward part of the body gives way first. This is because the hind legs do not come forward in time to act their part as supports. But the hind legs, of themselves, have no power to come forward below the center of gravity. The failure is in the loins, the back, which have not pulled the legs forward in time to lend their support, and thus to prevent the fall of the whole body.
