NERVE FIBERS 



motor area of the brain pass them- 

 selves out as parts of the anterior 

 roots. The relay service is illus- 

 trated in Fig. 64. Here again, it is 

 seen that there is no actual joining of 

 the neurons. Whenever 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 (r) 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 

 extremities passing between epithelial 

 and other cells, and (6) in several 

 kinds of so-called tactile corpuscles. 



The motor nerves passing to vol- 

 untary 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 "inter- 

 mediary 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 con- 

 tinuous 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 contains a 



15 



s.c; 



[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 ante- 

 rior cornu; M, the muscle; 

 S, path from sensory nerve 

 roots. (Kirkes after Cowers.) 



