ear the middle line
of the head (and just about where the phrenologists located their
"bump of veneration"!), is the center for the legs; next below and to
the side is the center for the trunk, next that for the arm, next that
for head movements, and at the bottom, not far from the ears, is the
center for tongue and mouth.

[Illustration: Fig. 14.--The nerve path by which the motor area of the
cortex influences the muscles. The upper part of this path, consisting
of axons issuing from the giant pyramids of the motor area and
extending down into the spinal cord, is the pyramidal tract. The lower
part of the path consists of axons issuing from the motor cells of the
cord and extending out to the muscles. The top of the figure
represents a vertical cross-section of the brain, such as is given, on
a larger scale, in Fig. 18. (Figure text: cortex, cord, muscles)]

The largest nerve cells of all are found in the motor area, and are
called, from their shape, the "giant pyramids". They have large
dendrites and very long axons, which latter, {53} running in a thick
bundle down from the cortex through the brain stem and cord,
constitute the "pyramidal tract", the principal path of communication
from the cerebrum to the lower centers. The motor area of the brain
has no direct connection with any muscle, but acts through the
pyramidal tract on the lower centers, which in turn act on the
muscles.

How The Brain Produces Muscular Movements

The motor area is itself aroused to action by nerve currents entering
it through axons coming from other parts of the cortex; and it is by
way of the motor area that any other part of the cortex produces
bodily movement. There are a few exceptions, as, for example, the
movements of the eyes are produced generally by the "visual area"
acting directly on the lower motor centers for the eye in the brain
stem; but, in the main, any motor effect of brain action is exerted
through the motor area. The motor area, as already mentioned, acts on
the lower motor centers in the cord and brain stem, and these in turn
on the muscles; but we must look into this matter a little more
closely.

A lower motor center is a group of motor and central neurones, lying
anywhere in the cord or brain stem, and capable of directly arousing a
certain cooerdinated muscular movement. One such unit gives flexion of
the leg, another gives extension of the leg, a third gives the rapid
alternation of flexion and extens