200 



ANATOMY FOR NURSES. [CHAP. XVI1L 



consist of two different structural elements, viz., fibres and 

 cells, both of which are enclosed and supported by a peculiarly 

 arranged connective tissue, and supplied with blood and lym- 

 phatic vessels. These fibres and cells are arranged in distinct 

 masses, called " nerve-centres," or in the form of cords, called 

 u nerves." The nervous cords are composed almost entirely of 

 the nerve-fibres, while the nerve-centres contain both fibres 



and cells. The nerves con- 

 duct or propagate nervous 

 impulses, while the nerve- 

 centres generate, transmit, 

 and store them. 



Nerve-cells. Nerve-cells 

 vary much in size and 

 shape ; many are large, 

 some being amongst the 

 largest cells met with in 

 the body ; others, again, are 

 quite small. The nucleus 

 is generally large, clear, 

 and spherical, with a single 

 large and distinct nucleolus. 

 The cell substance is finely 

 granular, sometimes is in- 

 distinctly striated. All 

 nerve-cells have at least one 

 process or branch, most 

 of them have more; and 

 they are often spoken of, in 

 consequence, as uni-polar, 

 bi-polar, and multi-polar 

 cells. In many nerve-cells 

 we recognize two distinct 

 kinds of processes : first, 

 those which, soon after 

 leaving the cell, divide and subdivide, until they become exceed- 

 ingly fine and delicate, and in some cases seem to join equally 

 processes from other cells; second, those which do not 



FIG. 115. MULTI-POLAR NERVE-CELL. 

 (Gerlach.) a, axis-cylinder, or nerve-fibre 

 process; b, pigment. 



fine 



divide and subdivide, but are prolonged as nerve-fibres. 



Nerve-fibres. These are of two kinds : those having a sheath 



