88 NERVOUS 81' STEM. 



Looking at the associated movements in their relations 

 to the mode of action of the motor nerves, it seems prob- 

 able that, as a rule, the anatomical relations of the nerves 

 are such that a motor stimulus, or an effort of the will, can- 

 not be conducted to a portion only of a muscle, but must act 

 upon the whole muscle, and the same is true, probably, of 

 certain restricted sets of muscles ; but the association of 

 movements of corresponding muscles upon the two sides 

 of the body, with the exception, perhaps, of the muscles of 

 the eyes, is due mainly to habit, and may be greatly modi- 

 fied by education. 



Mode of Action of the Sensory Nerves. The sensory 

 nerve-fibres, like the fibres of the motor system, are en- 

 tirely independent of each other in their action; and in 

 the so-called anastomoses that take place between sensory 

 nerves, the fibres assume no new relations, except as regards 

 contiguity. 



As motor fibres convey to their peripheral distribution 

 the stimulus engendered by an irritation applied in any por- 

 tion of their course, so an impression made upon a sensitive 

 nerve is always referred to the periphery. A familiar 

 example of this is afforded by the very common accident of , 

 contusion of the ulnar nerve as it passes between the ole- 

 cranon and the condyle of the humerus. This is attended 

 with painful tingling of the ring and little finger and other 

 parts to which the filaments of this nerve are distributed, 

 without, necessarily, any pain at the point of injury. More 

 striking examples are afforded in neuralgic affections depend- 

 ent upon disease or pressure on the trunk of a sensitive 

 nerve. In such cases, excision of the nerve is often practised, 

 but no permanent relief follows unless the section be made 

 between the affected portion of the nerve and the nerve- 

 centres ; and the pain produced by the disease is always re- 

 ferred to the termination of the nerve, even after it has been 

 divided between the seat of the disease and the periphery, 



