In the previous chapters has been described the course of brain development including the ever increasing elaboration of neuron patterns. We have traced in a general way the development of mental processes as the nerve cell mechanism becomes elaborated from simple patterns to the most complex imaginable. We have as sumed that there is a time when this neuron develop ment becomes complete, at which time there is, so far as the brain is concerned, the possibility of the highest known mental development. Theoretically, every human being has the possibility of reaching this limiting point; but many things may intervene to stop the develop ment of the brain before it has reached this ultimate mature condition. Just as the body itself may cease to develop in stature with the result that we have dwarfs, so we have dwarfed brains with the accompanying dwarfed intelligence.