arts occupy their normal positions. However, if the
cerebrum is pulled away from the hindbrain, it is brought into view
somewhat as in Fig. 130.

The midbrain carries upon its back and upper surface four small rounded
masses of cell-bodies, called the _corpora quadrigemina_. The upper two of
these bodies are connected with the eyes; the lower two appear to have
some connection with the organs of hearing. On the front and under
surface, the midbrain separates slightly as if to form two pillars, which
are called the _crura cerebri_, or cerebral peduncles. These contain the
great bundles of nerve fibers that connect the cerebrum with the parts of
the nervous system below.

*The Hindbrain* lies beneath the back portion of the cerebrum, and
occupies the enlargement at the base of the skull. It forms about one
eighth of the entire brain, and is composed of three parts--the cerebellum,
the pons, and the bulb.

*The Cerebellum* is a flat and somewhat triangular structure with its
upper surface fitting into the triangular under surface of the back of the
cerebrum. It is divided into three lobes--a central lobe and two lateral
lobes--and weighs about two and one half ounces. In its general form and
appearance, as well as in the arrangement of its cell-bodies and axons,
the cerebellum resembles the cerebrum. It differs from the cerebrum,
however, in being more compact, and in having its surface covered with
narrow, transverse ridges instead of the irregular and broader
convolutions (Fig. 132).

*The Pons*, or pons Varolii, named from its supposed resemblance to a
bridge, is situated in front of the cerebellum, and is readily recognized
as a circular expansion which extends forward from that body. It consists
largely of bands of nerve fibers, between which are several small masses
of cell-bodies. The fibers connect with different parts of the cerebellum
and with parts above.

[Fig. 132]

Fig. 132--*Human brain* viewed from below. _C._ Cerebrum. _Cb._ Cerebellum.
_M._ Midbrain. _P._ Pons. _B._ Bulb. I-XII. Cranial nerves.

*The Bulb*, or medulla oblongata, is, properly speaking, an enlargement of
the spinal cord within the cranial cavity. It is somewhat triangular in
shape, and lies immediately below the cerebellum. It contains important
clusters of cell-bodies, as well as the nerve fibers that pass from the
spinal cord to the brain.

*The Spinal Cord.*--This division of the centra