NERVE FIBERS 



The relay service is illustrated in Fig. 

 64. Here again, it is seen that there is 

 no actual joining of the neurons. When- 

 ever it is said that a nerve cell is 

 " joined" to another, or that the axis 

 cylinder of a cell "joins" another cell, 

 no actual continuity of tissue is meant. 

 Different neurons communicate only by 

 contiguity. 



Peripheral Nerve Terminations. 

 Nerves terminate peripherally (i) in 

 muscles, (2) in glands, (3) in special 

 organs connected with the senses of 

 sight, hearing, smell and taste, (4) in 

 hair-follicles, (5) in simple free ex- 

 tremities passing between epithelial and 

 other cells, and (6) in several kinds of 

 so-called tactile corpuscles. 



The motor nerves passing to volun- 

 tary muscles form first a "ground 

 plexus" for each group of muscle 

 bundles this plexus being made of 

 the axis-cylinder fibrillae. From this 

 plexus fibrils pass to form an "interme- 

 diary plexus" corresponding to each 

 muscle bundle. These fibrils are still 

 medullated, and when a branch from 

 the intermediary plexus enters a muscle 

 fiber its sheath becomes continuous with 

 the sarcolemma of that fiber, and the 

 axis-cylinder fibrils form a network on 

 the surface of the muscle fiber. This 

 is called an end motorial plate. It con- 

 tains a number of nuclei, and sends off 

 15 



[M 



FIG. 68. Diagram of an 

 element of the motor path. 



U. S, upper segment; L. 

 S, lower segment ; C. C, cell of 

 cerebral cortex; S. C, cell of 

 spinal cord , in anterior cornu ; 

 M, the muscle; S, path from 

 sensory nerve roots. (Kirkes 

 after Cowers.) 



