CHAPTER XVIII 



THE NERVOUS SYSTEM OF MAN 



161. Parts of the Nervous System. — The nervous system 

 of man consists of the same general parts as the nervous 

 system of the frog (See page 118). There is a brain and 

 spinal cord, from which nerves extend to the special 

 senses, the muscles, the heart, and the stomach. When 

 the brain of man is compared with that of the frog, it is 

 obvious that the cerebrum of man is proportionately larger. 

 Although some of the other parts of the brain appeal 

 unlike the corresponding regions in the frog, scientists 

 tell us that they are really the same. 



162. The Nerve Cell. — The nervous system of man con- 

 sists of many thousands of nerve cells which differ from all 

 other cells in having more parts and branches (Figures 

 223, 224, 225). The nerve cells are unlike other evils 

 in appearance, although they have the usual parts. Ex- 

 amination shows that the nerve cells have a prominent 

 nucleus surrounded by cytoplasm, which grows out into a 

 number of branches called fibers. The shorter branches 

 divide and form, together with the branches from the 

 neighboring nerve cells, a mass of tangled fibers. There 

 is usually one unbranched fiber, perhaps several feet Long, 

 which ends either in the skin, in some muscle, or in tin- 

 nervous system. When this long liber readies the muscle 

 or skin, it divides into several fine branches. All of these 

 branches which arise from a nerve cell belong to it, and in 

 this connection the word cell includes all the branches, 

 the nucleus, and the cytoplasm. 



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