The Cavities.
—The body has three principal cavities: namely, the cerebro-spinal, the thoracic, and the abdominal.
The Cerebro-Spinal Cavity.
—The cerebro-spinal cavity is formed by the cranial bones, and the vertebral column. The cerebro-spinal cavity is divided into the sub-cavities, called the cranial cavity and the spinal cavity.
In the cranial cavity we find the brain. The brain is the seat of the mind, and the functions which the brain performs distinguishes man from the other animals, as man becomes a conscious, intelligent, responsible being through the action of the brain. The brain is egg-shaped, soft and yielding, closely fitting the cranial cavity. The front and top of the brain is called the cerebrum, which is the center for intelligence, reason, and will. This part of the brain is convoluted, and the depth of the convolutions to a great extent indicates the amount of intelligence.
Below the cerebrum and lying in front of the occipital bone, we find the cerebellum, which is the seat of memory and the center for the co-ordination of muscle movements. By co-ordination of muscle movement is meant that the muscles will do just what we want them to do, that they will act harmoniously, the one with the other. The condition of Saint Vitus' Dance would be an example showing a lack of co-ordination. This part of the brain is also convoluted.
Fig. 15—Brain and spinal cord.
Between the cerebrum and the cerebellum, and connecting the two, is found the pons Varolii. The word pons means bridge, and the word Varolii means to cross over. It is in this part of the brain, then, that the nerve fibers cross over to the opposite side. A person having a paralytic stroke on the right side of the body would indicate that the left side of the brain had become affected.