92 HUMAN PHYSIOLOGY. 



NERVOUS SYSTEM. 



The Nervous System coordinates all the various organs and tissues 

 of the body, and brings the individual into conscious relationship with 

 external nature by means of sensation, motion, language, mental and moral 

 manifestations. 



The Nervous Tissue may be divided into two systems, the Cerebro- 

 spinal and the Sympathetic. 



(1) The Cerebro-spinal System, occupies the cavities of the cranium 

 and spinal canal, and consists of the brain, the spinal cord, the cranial and 

 spinal nerves. It is the system of animal life, and presides over the func- 

 tions of sensation, motion, etc. 



(2) The Sympathetic System, situated along each side of the spinal 

 column, consists (i) of a double chain of ganglia, united together by nerve 

 cords, and extends from the base of the cranium to the coccyx ; (2) of various 

 ganglia, situated in the head and face, thorax, abdomen, pelvis, etc. All 

 the ganglia are united together by numerous communicating fibres, many 

 of which anastomose with the. fibres of the cerebro-spinal system. It is 

 the nervous system of organic life, and governs the functions of nutrition, 

 growth, etc. 



Nervous Tissue is composed of two kinds of matter, the gray and 

 white, which differ in their color, structure and physiological endowments ; 

 the former consists of vesicles or cells which receive and generate nerve 

 force; the latter consists of fibres which simply conduct it, either from the 

 periphery to the centre or the reverse. 



Structure of Gray matter. The gray matter found on the surface of 

 the brain in the convolutions, in the interior of the spinal cord, and in the 

 various ganglia of the cerebro-spinal and sympathetic nervous systems, 

 consists of a fine connective tissue stroma, the neuroglia, in the meshes of 

 which are embedded the gray cells or vesicles. 



The cells are grayish in color, and consist of a delicate investing capsule 

 containing a soft, granular, albuminous matter, a nucleus, and sometimes a 

 nucleolus. Some of the cells are spherical or oval in shape, while others 

 have an interrupted outline, on account of having one, two or more pro- 

 cesses issuing from them, constituting the tint-polar, bi-polar or multi-polar 

 nerve cells. Cells vary in size ; the smallest being found in the brain, the 



