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24 development of the higher mental faculties, consequent on the stimulation induced by the manipulative functions of the hand, as exemplified in the manufacture of tools and their application to the exigencies of human life. The changes produced in the human body during the first stage, being readily accomplished under the ordinary laws of organic morphology, were completed in a comparatively short time. Those of the latter, being almost co-extensive with the life-history of men on the globe, have occupied a much longer time. To convert the small increments of knowledge, gathered from experience of the laws of nature, and the working of a variety of novel mechanical contrivances, into brain substance, is a process of slow growth. Nor can any limitation be put on its duration, as it runs on parallel lines with human civilization, and is as applicable to the modern as to the early races of mankind. As evidence of the progressiveness of brain development, which went on from generation to generation during this long stage in the history of humanity, we have a series of fossil skulls showing, in chronological sequence, a gradual abandonment of simian characters, and a steady approachment to the cranial characters of the civilized races of to-day.

Among the structural changes effected in the course of this brain development was a retrocession or contraction of the facial bones, especially the jawbones, towards the central axis of the spinal column, and a backward