evel; and it may
surprise the uninitiated to know that not only is the mind quite "out
of it" so far as these functions are concerned, but that the brain
proper is "out of it" also. Most of these reflexes not only go on when
the brain is removed from the skull, but it is an interesting detail
that they are generally exaggerated under these conditions. This shows
that while the third or lowest level does its own work, it is yet in a
sense under the weight--what physiologists call the inhibiting
action--of the higher brain masses. It is not allowed to magnify its
part too much, nor to work out of its proper time and measure. The
nervous apparatus involved in these "third-level" functions may be
called the "reflex circuit" (see Fig. 2), the path being from the
sense organ up to the centre by a "sensory" nerve, and then out by a
"motor" nerve to the muscle.

[Illustration: FIG. 2.--_s c mt_ = reflex circuit; _s c sp mp c mt_ =
voluntary circuit.]

Going upward in the nervous system, we next find a certain group of
bodies within the gross mass of the brain, certain centres lying
between the hemispheres above and the medulla and spinal cord below,
and in direct connection by nervous tracts with both of these. The
technical names of the more important of these organs are these: the
"corpora striata," or striped bodies, of which there are two, the
"optic thalami," also two in number, and the "cerebellum" or little
brain, situated behind. These make up what is called the "second
level" in the system. They seem to be especially concerned with the
life of sensation. When the centres lying above them, the hemispheres,
are removed, the animal is still able to see, hear, etc., and still
able to carry out his well-knit habits of action in response to what
he sees and hears. But that is about all. A bird treated thus, for
example, these second-level centres being still intact while the
hemispheres are removed, retains his normal appearance, being quite
able to stand upon his feet, to fly, walk, etc. His reflexes are also
unimpaired and his inner physiological processes; but it soon becomes
noticeable that his mental operations are limited very largely to
sensations. He sees his food as usual, but does not remember its use,
and makes no attempt to eat it. He sees other birds, but does not
respond to their advances. He seems to have forgotten all his
education, to have lost all the meanings of things, to have
practically no intelligen