and mental activity. That the cerebrum is the seat of
the reasoning powers, and all the higher intellectual functions, is
proved by three facts. (1.) If this portion of the brain is removed, it
is followed by the loss of intelligence. (2.) If the human cerebrum is
injured, there is an impairment of the intellectual powers. (3.) In the
animal kingdom, as a rule, intelligence corresponds to the size of the
cerebrum. This general law of development is modified by differences in
the cerebral texture. Men possessing comparatively small brains may have
a vast range of thought and acute reasoning powers. Anatomists have
found these peculiarities to depend upon the quantity of gray matter
which enters into the composition of the brain.

In the cerebro-spinal system there are three different kinds of reflex
actions. (1.) Those of the spinal cord and medulla oblongata are
performed without any consciousness or sensation on the part of the
subject. (2.) The second class embraces those of the tuber annulare,
where the perception gives rise to motion without the interference of
the intellectual faculties. These are denominated purely _instinctive_
reflex actions, and include all those operations of animals which seem
to display intelligent forethought; thus, the beaver builds his
habitation over the water, but not a single apartment is different from
the beaver homestead of a thousand years ago; there is no improvement,
no retrogression. Trains of thought have been termed a third class of
reflex actions. It is evident that the power of reasoning is, in a
degree, possessed by some of the lower-animals: for instance, a tribe of
monkeys on a foraging expedition will station guards at different parts
of the field, to warn the plunderers of the approach of danger. A cry
from the sentinel, and general confusion is followed by retreat. Reason
only attains its highest development in man, in whom it passes the
bounds of ordinary existence, and, with the magic wand of love, reaches
outward into the vast unknown, lifting him above corporeal being, into
an atmosphere of spiritual and divine Truth.

[Illustration: Fig. 60.
Section of the brain and an ideal
view of the pneumogastric nerve
on one side, with its branches, _a_.
Vertical section of the cerebrum.
_b_. Section of the cerebellum, _c_.
Corpus callosum. _d_. Lower section
of medulla oblongata. Above
_d_, origin of the pneumogastric
nerve. 1. Pharyngeal branch. 2.
Superior laryngeal