EVOLUTION OF THE BRAIN. 13
The relative size of the brain has become immensely expanded. That means the dominance of brain over body, of spirit over matter, of the higher over the lower life.
As we ascend in our survey of the scale of life, not only does the brain become relatively larger, but the spinal cord becomes shorter at its lower end. In some of the huge saurians belonging to the age of reptiles we find the cord a hundred feet in length. Well might such animals be taken by sacred writers as symbols of evil, as types of all that is horrid and repulsive. The serpents of our own time are examples of very long spines and a great deal of repulsive power.
These facts of evolution are now accepted by the leading scientific men of our day. They have been
verified by a vast array of facts, in both geology and biology.
THE BRAIN AND NERVOUS SYSTEM DEVELOP FROM THE BASE TO THE TOP AND FROM THE BACK TO THE FRONT. The high im
port of this law will appear as we proceed. It forms one essential basis for a true social science.
The life of the individual fore
shadows the life of the race. It shows corresponding phases of growth. It is therefore necessary to study the development of the brain both before and after birth.
In the early stages of prenatal life the brain appears as three little vesicles, marked A, M and B in this
engraving. In the lower figure a little point, P, projects downward from the front vesicle, A. As the growth of the brain proceeds, this process turns up and then over backward in the direction of the arrows in the upper figure. It goes on expanding until it forms the cerebrum, the larger mass of the brain. Although it thus turns backward, yet the line of the vital forces from the spinalis is forward and upward. The back vesicle, B, sends out a process which becomes the cerebellum or little brain, marked Cer. 1. m, in the upper figure. In the fully developed brain the three primary vesicles become central or subordinate parts.
From the first phase to the close of fetal life the brain presents a constant increase in its complexity of structure. At different parts of this period the brain resembles, in succession, those of an ascending series of the lower animals. But the brains of these lower animals are arrested, some at a lower, some at a higher point; that of man alone passes onward to completion.
In all the vertebrates, the highest division of the animal kingdom, the first part to attain a definite structure is the brain and spinal cord. On a previous page this is shown as the "Primitive Trace." And in the whole scale of life, the rank of each species of animal is determined by its development of the nervous system and of the muscles which are the direct instruments through which the brain and nerves must express themselves.
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