334 THE NERVE SYSTEM 



Small buds are seen at times along the course of 

 dendrites. They are called gemmules. 



Axone, or Axis-cylinder. This arises from the 

 body of the neurone, or nerve cell, as a cone-shaped 

 process, and is seen as a very delicate fiber. In 

 structure it differs from the dendrites. Each axone 

 is uniform in diameter; and consists of fine fibrillse, 

 embedded in a clear protoplasmic substance (neuro- 

 plasm). Axones may be very short or as much 

 as a meter in length. As a rule, only one axone 

 is given off from a cell, and this form is termed mon- 

 axic neurones ; however, more than one is present; as 

 two axones, they are termed diaxonic neurones; and 

 several axones, polyaxonic neurones. 



Axones in certain portions of the nerve system 

 (brain and spinal cord) possess fine branches called 

 collaterals; they have the same structure as the axone 

 from which they arise. Some axones, as Golgi cells, 

 break up into branches after leaving the cell body, 

 called dendraxones. The minute endings of the axis- 

 cylinders and collaterals, which spread out like the 

 branches of a tree, are termed telodendria. 



The axone is the functional element of the nerve 

 system which acts as the distributive or emissive 

 conductor of nerve impulses. 



Nerve Fibers. Nerve fibers are simply continua- 

 tions of the axis-cylinder or axorie given off from the 

 cell body of a neurone, with their surrounding invest- 

 ments, the myelin and neurilemma. They are classi- 

 fied into two varieties, according to whether or not 

 the axis-cylinder possesses a medullary or myelin 

 sheath, viz., medullated or myelinic nerve fibers and 

 non-medullated or amyelinic nerve fibers. 



Medullated Nerve-fibers. These possess three distinct 

 minute anatomical portions, when subjected to stain- 

 ing methods and examined under the microscope, 

 namely: An external investing sheath, the neurilemma; 



