CHAPTER V. 

 THE NERVOUS SYSTEM. 



The nervous system, which regulates all the vital pro- 

 cesses 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 cere- 

 brum, cerebellum, pons, and medulla, occupies the cran- 

 ium 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 hem- 

 ispheres, roughly oval in shape, each of which has five 

 lobes separated by fissures, the frontal, parietal, occip- 

 ital, 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 Syl- 

 vius 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 



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