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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.
On account of the great size of the cerebrum, the midbrain is entirely concealed from view when the other parts occupy their normal positions. The midbrain carries upon its back and upper surface four small rounded masses of cell-bodies, called the corpora quadrigemina.
If a pencil were placed over the ear, what portions of the brain would be above it and what below? Describe briefly the cerebrum, the cerebellum, the midbrain, the pons, and the bulb. Locate and describe the cortex. State purpose of the convolutions. State the general differences between the cranial and the spinal nerves. Locate and give the number of the dorsal-root ganglia.
In reflex action the impulses are mainly through the spinal cord, but to some extent through the bulb, pons, and midbrain. In voluntary action they pass through the cerebrum—a condition that leads to important modifications in the results.
This is the plan in the cerebrum and cerebellum, and here are found devices for increasing the surface: the cerebrum having convolutions, the cerebellum transverse ridges. That of collections of cell-bodies into rounded masses. Such masses are found in the bulb, the pons, the midbrain, and the base of the cerebrum. That of arrangement in a continuous column. This is the plan in the spinal cord.
There were the cerebral lobes, or largest part of the forebrain, enormously developed and overhanging the cerebellum, or great lobe of the hindbrain, and completely covering the lobes of the midbrain. On the cerebrum I even thought I could detect for I have a smattering of anatomy the usual convolutions, and the grooves dividing the cerebrum into two hemispheres.
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.
In the midbrain, bulb, and spinal cord fibers are found: first, that connect these parts with the cerebrum and cerebellum above; second, that pass into and become a part of the nerves of the body; and third, that connect the opposite sides of these parts together.
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.
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