CHAPTER IX. 



GENEKAL HISTOLOGY OF THE NERVOUS SYSTEM. 



WE may gain a clear conception of the nervous system in 

 its general outlines by remembering that it consists essentially 

 of a series of delicate cords which, on the one hand, proceed 

 from the nucleated bodies of the gray matter, conveying voli- 

 tional impulses to the periphery of the organism ; or, on the 

 other hand, of sensitive peripheral extremities that take up the 

 impression of external objects and carry them back to the cen- 

 tral gray substance. 



In either case both the conducting cords and the central 

 corpuscles of the gray matter possess no distinctive differences, 

 such as may be appreciated by the microscope, while, on the 

 other hand, the peripheral termini appear under many different 

 forms, the peculiarity of ending being dependent in part upon 

 the type of tissue in which they are found, partly upon the 

 office they have to perform, and partly upon other causes that 

 are unknown to us. The nerve-centres are located in the brain, 

 spinal cord, and in the ganglia of the cerebro-spinal and sym- 

 pathetic system. 



The methods of nerve- terminations that have been described 

 may be briefly enumerated here. They are by (1) peculiar 

 terminal bodies, (2) loops, (3) networks, (4) end bulbs, (5) proto- 

 plasmic bodies (cells), (6) free or pointed extremities. 



Nerve-fibres. Of these there are three kinds that have 

 distinctive differences : 1. The myelinic or medullated fibres. 

 2. Fibres of RemaJc. 3. Ultimate fibrils. Intermediate forms, 

 such as have been described by various writers, under the names 

 of protoplasmic processes, primitive fasciculi or naked axis- 

 cylinders, varicose cylinders, etc., will be noticed in other con- 

 nections. 



Myelinic fibres. These are also known as the medullated. 



