oted to the service of the senses.

The cerebrum is the chief seat of the sensations, the intellect, the will,
and the emotions. A study of cerebral injuries and diseases, and
experiments upon the lower animals, prove that the hemispheres, and more
especially the gray matter, are connected with mental states. The
convolutions in the human brain are more prominent than in that of the
higher animals, most nearly allied to man, although some species of
animals, not especially intelligent, have marked cerebral convolutions.
The higher races of men have more marked convolutions than those less
civilized.

A view of the under surface of the brain, which rests on the floor of the
skull, shows the origin of important nerves, called the cranial
nerves, the cerebellum, the structure connecting the optic
nerves (optic commissure), the bridge of nervous matter (pons
Varolii) connecting the two hemispheres of the cerebellum, and lastly
numerous and well-marked convolutions.

268. The Cerebellum. The cerebellum, or lesser brain, lies in
the back of the cranium, and is covered over in man by the posterior lobe
of the cerebrum. It is, at it were, astride of the back of the
cerebro-spinal axis, and consists of two hemispheres joined by a central
mass. On its under surface is a depression which receives the medulla
oblongata. The cerebellum is separated from the cerebrum by a
horizontal partition of membrane, a portion of the dura mater. In some
animals, as in the cat, this partition is partly bone.

The cerebellum is connected with other parts of the nervous system by
strands of white matter on each side, radiating from the center and
divided into numerous branches. Around these branches the gray matter is
arranged in a beautiful manner, suggesting the leaves of a tree: hence its
name, arbor vitae, or the tree of life.

The functions of the cerebellum are not certainly known. It appears to
influence the muscles of the body so as to regulate their movements; that
is, it serves to bring the various muscular movements into harmonious
action. The mechanism by which it does this has not yet been clearly
explained. In an animal from which the cerebellum has been removed, the
functions of life do not appear to be destroyed, but all power of either
walking or flying straight is lost.

[Illustration: Fig. 115.--A Vertical Section of the Brain.

A, frontal lobe of the cerebrum;
B, parietal lobe;
C, parieto occipital lobe with fissu