THE NERVOUS SYSTEM. 465 



the Cerebrum, Cerebellum, the Crura cerebri, the Pons Varolii, and the 

 so-called Basic ganglia; the Medulla Oblongata; and the Spinal cord, 

 with the nerves proceeding from them. Its fibres are chiefly, but not 

 exclusively, distributed to the skin and other organs of the senses, and 

 to the voluntary muscles. 



(II.) The Sympathetic System consists of : (1) A double chain 

 of ganglia and fibres, which extends from the cranium to the pelvis, 

 along each side of the vertebral column, and from which branches are 

 distributed both to the cerebro-spinal system, and to other parts of the 

 sympathetic system. With these may be included the amall ganglia in 

 connection with those branches of the fifth cerebral nerve which are dis- 

 tributed in the neighborhood of the organs of special sense: namely, the 

 Ophthalmic, Otic, Spheno -palatine, and Submaxillary ganglia. (2) 

 Various ganglia and plexuses of nerve-fibres which give off branches to 

 the thoracic and abdominal viscera, the chief of such plexuses being the 

 Cardiac, Solar, and Hypogastric; but in intimate connection with these 

 are many secondary plexuses, as the Aortic, Spermatic, and Renal. To 

 these plexuses, fibres pass from the praevertebral chain of ganglia, as well 

 as from cerebro-spinal nerves. (3) Various ganglia and plexuses in the 

 substance of many of the viscera, as in the Stomach, Intestines and 

 Urinary bladder. These, which are, for the most part, microscopic, also 

 freely communicate with other parts of the sympathetic system, as well 

 as, to some extent, with the cerebro-spinal. (4) By many, the ganglia 

 on the Posterior roots of the spinal nerves, on the Glossopharyngeal and 

 Vagus, and on the Sensory root of the Fifth cerebral nerve (Gasseriam 

 ganglion), are also included as sympathetic-nerve structures. 



We have already considered the functions of nerve-fibres; we must 

 now turn to those of the Nerve-centres, which are made up not only of 

 nerve-fibres but also of nerve-cells. 



IV. FUNCTIONS OF NEBVE- CENTRES. 



The functions of nerve-centres may be classified as follows: 1. Con- 

 duction. x5. Transference. 3. Reilection. 4. Automatism. 5. Aug- 

 mentation. 6. Inhibition. 



1. Conduction. 



Conduction in or through nerve-centres may be thus simply illus- 

 trated. The food in a given portion of the intestines, acting as a 

 stimulus, produces a certain impression on the nerves in the mucous 

 membrane, which impression is conveyed through them to the adjacent 

 ganglia of the sympathetic. In ordinary cases, the consequence of such 



an impression on the ganglia is the movement by reflex action of the 

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