two of the main
divisions of the brain--the _cerebrum_, which includes what we call the
right and left hemispheres, and the _cerebellum_.

THE CEREBRUM OR FOREBRAIN

For convenience the various lobes of the cerebrum are known as frontal,
temporal, parietal, and occipital, according to the parts of the brain
referred to: as forehead, temples, crown, or occiput. The cerebellum, or
hind brain, is also divided into two hemispheres, and is situated behind
and below the hemispheres of the cerebrum.

A system of localization has been roughly mapped out, the result of
careful laboratory work on animals and of studying the loss of various
functions in human beings as related to the location of brain injuries.

From these experiments it seems proved that consciousness belongs only
to the cortex or surface of the upper brain, and that the vast realm of
the unconscious belongs to the lower brain centers. Hence the cortex is
the organ of consciousness, and the lower centers are the repository of
the unconscious until it again becomes conscious.

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