104 NATURE OF MUSCULAR ACTION. 



same moment, an impression retrograde to the 

 course of that influence which is going from the 

 brain to the muscle ? If we had no facts in anatomy 

 to proceed upon, still reason would declare to us 

 that the same filament of a nerve could not convey 

 a motion, of whatever nature that motion may be, 

 whether vibration or motion of spirits, in opposite 

 directions at the same moment of time. 



" 1 find that, to the full operation of the muscular 

 power, two distinct filaments of nerves are neces- 

 sary, and that a circle is established between the 

 sensorium and the muscle ; that one filament or 

 single nerve carries the influence of the will towards 

 the muscle, which nerve has no power to convey an 

 impression backwards to the brain ; and that another 

 nerve connects the muscle with the brain, and, act- 

 ing as a sentient nerve, conveys the impression of 

 the condition of the muscle to the mind, but has no 

 operation in a direction outwards from the brain to- 

 wards the muscle, and does not therefore excite the 

 muscle, however irritated."* 



This consciousness of the state of the muscles, or 

 muscular sense, as it may be truly called, is of great 

 importance both to man and to animals, as it is 

 necessarily by information thence derived that 

 every subsequent exertion is directed and appor- 

 tioned in intensity to the effort required to be made. 

 If we had no such sense, the delicate and well- 

 directed touches of the engraver, painter, and sculp- 

 tor, or of the ingenious mechanic, would be at the 

 mercy of hazard ; and a single disproportioned move- 

 ment might ruin the successful labour of months, 

 supposing success in reality to be compatible with 

 chance. Without this sense, man could not deliber- 

 ately proportion the muscular efforts to his real 

 wants ; and, even in walking, his gait would be un- 

 steady and insecure, because there would be no 



* Bell's Anatomy seventh edition. voL ii. p. 372. 



