These fibers connect
with the cell-bodies in the cortex (Fig. 131).
The cerebrum is a double organ, consisting of two similar divisions,
called the _cerebral hemispheres_. These are separated by a deep groove,
extending from the front to the back of the brain, known as the _median
fissure_. The hemispheres, however, are closely connected by a great band
of underlying nerve fibers, called the _corpus callosum_.
[Fig. 131]
Fig. 131--*Microscope drawing* of a neuron from cerebral cortex. _a._ Short
segment of the axis cylinder with collateral branches.
At the base of the cerebrum three large masses of cell-bodies are to be
found. One of these, a double mass, occupies a central position between
the hemispheres, and is called the _optic thalami_. The other two occupy
front central positions at the base of either hemisphere, and are known as
the _corpora striata_, or the striate bodies.
*The Midbrain* is a short, rounded, and compact body that lies immediately
beneath the cerebrum, and connects it with the hindbrain. On account of
the great size of the cerebrum, the midbrain is entirely concealed from
view when the other parts occupy their normal positions. However, if the
cerebrum is pulled away from the hindbrain, it is brought into view
somewhat as in Fig.
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