CHAPTER V.
THE NERVOUS SYSTEM.
The nervous system, which regulates all the vital processes
of the body, physical and chemical, and which is
situated partly in the head and partly in the trunk, may
well form the connecting link between the description of
the head and that of the trunk. It has two divisions,
the cerebro-spinal system and the sympathetic system.
The former consists of the cerebrum or brain proper, the
cerebellum or little brain, the pons Varolii, the medulla
oblongata, the spinal cord, and the cranial and spinal
nerves; the latter of a series of ganglia or aggregations
of nerve centers. The brain, which includes the cerebrum,
cerebellum, pons, and medulla, occupies the cranium
and the spinal cord is contained within the bony
framework of the spinal column. In the male the brain
weighs about 49 ounces and in the female 44, while in
an idiot it seldom weighs more than 23 ounces.
The cerebrum or brain proper has two parts or hemispheres, roughly oval in shape, each of which has five lobes separated by fissures, the frontal, parietal, occipital, and temporo-sphenoidal lobes, and the central lobe or island of Reil at the base of the brain. The chief fissures are the longitudinal fissure, the fissure of Sylvius at the base of the brain, and the fissure of Rolando between the frontal and parietal lobes. There are also five serous cavities called ventricles, the two lateral and the third, fourth, and fifth ventricles, of which the first two, one in either hemisphere, are the most important. Around these cavities is the brain substance, which is made up of two tissues, the white and the gray, the latter forming the outer part of the brain to the depth of
