VOLUNTARY MOTION. 475 



If the sensorial functions had been limited to 

 mere sensation and perception, conjoined with the 

 capacity of passive enjoyment and of suffering, the 

 purposes of animal existence would have been but 

 imperfectly accomplished ; for in order that the 

 sentient being may secure the possession of those 

 objects which are agreeable and salutary, and 

 avoid or reject those which are painful or injurious, 

 it is necessary that he should possess the power of 

 spontaneous action. Hence the faculty of Volun- 

 tary Motion is superadded to the other sensorial 

 functions. The muscles which move the limbs, 

 the trunk, the head, and organs of sense, — all those 

 parts, in a word, which establish relations with the 

 external world, are, through the intermedium of a 

 separate set of nervous filaments, totally distinct 

 from those which are subservient to sensation,* 

 made to communicate directly with the sensorium, 

 and are thereby placed under the direct control and 

 guidance of the will. The mental act of volition 

 is doubtless accompanied by some corresponding 

 physical change in that part of the sensorium, 

 whence the inotor jierves, or those distributed to the 

 muscles of voluntary motion, arise. Here, then, 

 we pass from mental phenomena to such as are 

 purely physical; and the impression, whatever may 

 be its nature, originating in the sensorium, is pro- 

 pagated along the course of the nerve to those 

 muscles, whose contraction is required for the pro- 

 duction of the intended action. Of the function of 

 voluntary motion, as far as concerns the moving 



* On this subject I must refer the reader to the researches of Sir 

 Charles Bell, and Magendie, who have completely established the 

 distinctioii between these two classes of nerves. 



