Vitality Supreme

It is an interesting fact that the spine is the central and fundamental structure of all the higher organisms on this earth. In the course of the evolution of life on this planet there developed from the very simplest forms of animal organisms two different higher forms of life--on the one hand the vertebrate animals, possessing an internal skeleton, and on the other hand the insects, clams, crustaceans and other creatures that have their skeletons on the outside, as one may say, in the form of shells. The legs of an insect, for instance, are small tubes with the muscles inside. The limbs of vertebrate animals, on the other hand, have the muscle outside the bone. Invertebrates commonly have the main nerve trunk in front, or underneath, instead of at the back, and likewise often have their brains in their abdomens. Some of them, such as the grasshopper, even hear with their abdomens. But all vertebrata have the great nerve trunk at the back, contained in the spine and with a bulb on the front or upper end constituting the brain. In fact, a vertebrate animal is primarily a living spine, and all other parts of the body are in the nature of appendages. The limbs, for instance, and in the higher animals the ribs and other parts of the skeleton, are simply attached to the spine, or are offshoots from it. In the fishes these limbs take the shape of fins. In the higher developments of life they assume the form of legs.