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SECT. XVIII. 



OF THE VOLUNTARY MOTIONS. 



283. We have seen that the nerves perform two 

 offices (220) — the one of feeling, the other of moving. 

 The former we have already considered ; we shall now 

 say something with respect to the latter. 



284. All the motions of the body may be divided 

 into voluntary and involuntary. 



The pulsation of the heart, and the peristaltic mo- 

 tion of the intestines and other viscera, are commonly 

 adduced as instances of involuntary motion. 



The action of by far the greater number of the other 

 muscles is voluntary. 



Respiration, sneezing, the tension of the membrana 

 tympani, the action of the cremaster, are regarded by 

 some as belonging to the former class ; by others, to 

 the latter ; and by others, as of a mixed nature. 



285. If this division is narrowly examined, it will be 

 found embarrassed by so many difficulties that the limits 

 of each class cannot well be determined. 



For, on the one hand, few functions can be termed 

 truly involuntary, especially if we consider the con- 

 nection of the imagination and passions with the will. 



Again, on the other hand, there are few voluntary 

 motions that may not be rendered involuntary by the 

 force of habit, whose influence upon our animal mo- 

 tions is immense. 



