The motor zone of the cortex we now know to be situated in the convolutions bordering the fissure of Rolando. Vision is evidently excited from the occipital lobes, though not yet conclusively proved. Smell, presumably, is located in the temporal lobes. Considered action is directed from the upper hemispheres only. It is significant that the hemispheres of the cerebrum are also accepted as the seat of memory for man--that intellectual quality which makes him capable of acting from absent stimuli, stimuli only present to memory; which makes it possible for him to reason the present from the experiences of the past. But in all animal life, except the higher forms, the control of action is from the lower brain centers, centers which respond only to present objects. With them memory, as man knows it, is lacking; but the reactions of the past are indelibly imprinted upon motor nerves and muscles, so that when the present object presses the button, as it were, calling forth the experience of the race, the animal instinctively reacts. But of what use to man, then, are the lower brain centers? In man, as in lower animals, they care for the vegetative functions of life, so that our blood continues to circulate, the air enters and leaves our lungs, digestion is carried on, with no assistance from the upper centers, the hemispheres of the cerebrum being thus left free for concentration on the external world of matter, which it can transform into a world of thought. It is the lower or vegetative brain that may still exist and keep life intact when the functions of the cerebrum are destroyed. We can say, then, of the brain as a whole that it is the organ of the mind, the _sine qua non_ of the mind, the apparatus for the registration of sense impressions. The senses themselves are the rudiments of mind, are the means by which stimuli alighting on sense organs enter consciousness; for the nerves of special sense immediately carry the impetus to the brain, where it is recognized as the "not me," the _something_ definitely affecting the _me_, and demanding reaction from the _me_. The functions of the cerebrum we find grouping themselves in three classes: _intellect_, _emotion_, and _volition_, more simply, thinking, feeling, and willing; and we find no mental activity of the normal or abnormal mind which will not fall into one of these groupings. This does not mean that one part of the brain thinks, another part wills, another part feels; for in the performance of any one of these functions the mind acts as a whole. Our thinking or our willing may be permeated with feeling, but the entire mind is simply reacting simultaneously upon various stimuli. CHAPTER V THE NORMAL MIND