276 THE NERVOUS SYSTEM 



ganglia, and in the peripheral terminations of certain 

 nerve fibers. 



Fig. 122. Nerve cells from the spinal cord. 

 A nerve cell with all its processes. B body of cell, showing nucleus (N). 



409. The Axis Cylinder, or Neuraxon. One of the proc- 

 esses of the nerve cell and as a rule only one becomes 

 what is called the axis cylinder of a nerve fiber. It is a 

 protoplasmic thread continuous with the substance of the 

 cell and usually inclosed within a sheath. Axis cylinder 

 processes give off, usually at right angles, fine side 

 branches which ramify in the adjacent nerve substance 

 (Fig. 123), and the final ending of the axis cylinder 

 itself is in many minute divisions. Many or most of the 

 nerve cells have other processes which do not become 

 axis cylinders, but end in fine twiglike divisions in the 

 gray matter around them. 



410. The Nerve Fiber (Fig. 124). The essential part 

 of every nerve fiber is the central protoplasmic core, 

 which is always the axis cylinder process of a nerve cell. 

 There is hence, after all, only one fundamental form of 

 nervous matter, viz. the protoplasm of the nerve cell. 



