116 PHYSIOLOGY. 



15. The chief net-ioorJcs or ganglia are four in number. 

 The first which is called cervical, is formed from the second, 

 third and fourth cervical nerves ; lies on the side of the neck 

 about its middle ; and it gives rise to four large nerves which 

 go to the head, neck and upper part of the chest. The 

 second plexus lies under the pit of the arm, and gives rise to 

 eight principal branches which go to the chest, shoulder and 

 arms. The other two plexuses lie in the pelvis, and give off 

 branches which supply the viscera contained in it, and also 

 the lower extremities^ 



16. A second division of the nervous system, as I have 

 stated, has been called by anatomists ganglionic, or the ner- 

 vous system of organic life. (A ganglion is a small grayish 

 white body, of a roundish or oval shape, varying in size, 

 from a pin's head to an almond) These ganglions are chief- 

 ly siliiated on the sides of the spinal column, throughout its 

 whole length, and are connected by nervous threads, which 

 pass from one to the other, and also with the nerves which 

 come out from the spine. {&ix of these ganglions are found 

 in the head ; three in the neck ; twelve in the dorsal region ; 

 Jive in the lumbar ; and three in the sacral region.) 



17. The principal of the plexuses are formed by nervous 

 filaments proceeding from these ganglions. These are the 

 cardiac plexus, the pulmonary plexus, and the great solar 

 plexus. {"The whole ganglionic system of nerves is called 

 the great sympathetic nerve.) jThis is connected with the brain 

 by the sixth cerebral nerve and a branch of the fifth. It 

 also receives branches from the seventh, eighth, and ninth, 

 and all the spinal nerves, to the lower part of the spine, be- 

 low which it terminates^ We are now prepared to consider 

 the functions of the nervous system. 



18. The brain being the centre of the nervous system, is 

 the most important organ of the human body; pfo the lowest 

 order of animals, we find but imperfect rudiments of a ner- 

 vous system } but as we ascend in the scale of animal exist- 

 ence, we find it more and more developed as we advance, till 



