THE STRUCTURE OF THE NERVE SYSTEM 339 



however, a tracing of the axones of these nerves for 

 a distance into the gray substance of the brain or 

 spinal cord, where they originate, will end in the 

 nerve centre, which is termed the deep origin of a 

 nerve. 



Endings of Nerves. It must be remembered that 

 the course or appearance of a nerve has nothing to do 

 with its function, for from all external or microscopic 

 examination an efferent nerve cannot be differenti- 

 ated from an afferent nerve. Nerves end in several 

 ways, which vary in different situations. 



The Efferent or Centrifugal Nerves. This variety 

 is motor and conveys nerve impulses away from the 

 brain and spinal cord. Upon reaching their final 

 ending, these lose both the neurilemma and myelin 

 sheath. The axis-cylinder divides and gives off 

 branches (collaterals) which join with other axones. 

 These axis-cylinders come in direct contact with the 

 tissue cells and are termed end arborizations, or 

 telodendria, also end-organs, terminal organs, or end- 

 tufts. 



In muscles of the skeleton the axones of the nerves 

 lose their neurilemma and myelin sheath; at the 

 point they join the muscle fiber, and after giving off 

 branches within the sarcolemma, appear to lie in a 

 mass of sarcoplasm and nuclei which forms the 

 motor-plate. 



In the muscles of the viscera (involuntary) the 

 nerve fibers are non-medullated, and belong to the 

 sympathetic system or other neurones. The axones 

 divide and subdivide to form plexuses which invest 

 the muscle-cell bundles. Other branches are given 

 off from the latter which finally come in intimate 

 relation with each cell, upon the surface of which 

 they are seen as granular masses. 



In the glands the nerve fibers are derived from the 

 sympathetic and other neurones; the axones reach 



