erned in perceiving facts by aid
of the body senses. Perception of size and shape by the sense of
touch, perception of weight by the muscle sense, perception of degrees
of warmth and cold by the temperature sense, are dependent on the
parietal lobe and disappear when the cortex of this region is
destroyed. It appears that there is a sort of hierarchy of centers
here, as in the motor region and probably also in the visual and
auditory regions. Skill in handling objects is partly dependent on the
"feel" of the objects and so is impaired by injuries to the parietal
lobe, as well as by injury to the frontal lobe; and knowing how to
manage a fairly complex situation, as in lighting a fire when you have
the various {64} materials assembled before you, seems also to depend
largely on this part of the cortex.

Lower Sensory Centers

[Illustration: Fig. 19.--Sensory path from the skin of any portion of
the trunk or limbs. The path consists of three neurones, the cell body
of the first lying just outside the spinal cord, that of the second
lying in the cord, and that of the third lying in the thalamus. The
last part of this path is the "Tactile path," shown in Fig. 18.
(Figure text: cortex, thalamus, cord, skin)]

As already indicated, no portion of the cortex, not even the sensory
areas, is directly connected with any sense organ. The sensory axons
from the skin, for example, terminate in the spinal cord, in what may
be called the lowest sensory centers. Here are nerve cells whose axons
pass up through the cord and brain stem to the thalamus or interbrain,
where they terminate in a second sensory center. And cells here send
their axons up to the somesthetic area of the cortex.

{65}

The thalamus is remarkable as an intermediate center for all the
senses, except smell; but exactly what is accomplished by this big
intermediate sensory center remains rather a mystery, though it
certainly appears that the thalamus has something to do with feeling
and emotion.

The Cerebellum

Regarding the cerebellum, there is much knowledge at hand, but it is
difficult to give the gist of it in a few words. On the one hand, the
cerebellum receives a vast number of axons from the lower sensory
centers; while, on the other hand, it certainly has nothing to do with
conscious sensation or perception. Its use seems to be motor. It has
much to do with maintaining the equilibrium of the body, and probably
also with maintaining the stea