ounces for women. Other things being equal, the size and weight of the
brain bear a general relation to the mental power of the individual. As a
rule, a large, healthy brain stands for a vigorous and superior intellect.
The brains of many eminent men have been found to be 8 to 12 ounces above
the average weight, but there are notable exceptions. The brains of
idiots are small; indeed, any weight under a certain size, about 30
ounces, seems to be invariably associated with an imbecile mind.

The human brain is absolutely heavier than that of any other animal,
except the whale and elephant. Comparing the size of these animals with
that of man, it is instructive to notice how much larger in proportion to
the body is man's brain. The average proportion of the weight of the brain
to the weight of the body is greater in man than in most animals, being
about 1 to 36. In some small birds, in the smaller monkeys, and in some
rodents, the proportional weight of the brain to that of the body is even
greater than in man.

267. The Cerebrum. The three principal masses which make up the brain
when viewed as a whole are:

1. The cerebrum, or brain proper.
2. The cerebellum, or lesser brain.
3. The medulla oblongata.

The cerebrum comprises nearly seven-eighths of the entire mass, and
fills the upper part of the skull. It consists of two halves, the right
and left cerebral hemispheres. These are almost separated from each
other by a deep median fissure. The hemispheres are united at the bottom
of the fissure by a mass of white fibers passing from side to side. Each
of these hemispheres is subdivided into three lobes, so that the entire
cerebrum is made up of six distinct lobes.

The cerebrum has a peculiar convoluted appearance, its deep folds being
separated by fissures, some of them nearly an inch in depth.

It is composed of both white and gray matter. The former comprises the
greater part of the mass, while the latter is spread over the surface in a
layer of about 1/8 of an inch thick. The gray matter is the portion having
the highest functions, and its apparent quantity is largely increased by
being formed in convolutions.

The convolutions of the cerebrum are without doubt associated with all
those higher actions which distinguish man's life; but all the
convolutions are not of equal importance. Thus it is probable that only
the frontal part of the brain is the intellectual region, while certain
convolutions are dev