MOVEMENT OF ANIMALS, viii.-ix. 



so attached ; for the stick becomes a kind of detached 

 member. The origin of movement, therefore, cannot 

 be situated in any origin which is the termination of 

 something else, nor in any other part which is farther 

 from it ; for example, the origin of movement of the 

 extremity of the stick is in the hand, but the origin 

 of the movement of the hand is in the wrist." And 

 so if the origin of movement is not in the hand, be- 

 cause it is still higher up,* neither is it in this higher 

 position ; for, again, if the elbow is at rest, the con- 

 tinuous part below it can be set in motion as a whole. 

 IX. Now since there is similarity in the left and the 

 right sides of the body, and the opposite parts can be 

 moved simultaneously, so that it is impossible for the 

 right side to move just because the left is at rest or vice 

 versa, and the origin of movement must be in that 

 which lies above both sides, it necessarily follows that 

 the origin of movement in the moving soul must be 

 between them ; for the middle is the Hmit of both 

 extremes. And it stands in the same relation to the 

 movements above as to those below, to those, for 

 example, which proceed from the head and to those 

 which proceed from the spine in animals which have 

 a spine. And there is good reason for this ; for we 

 say that the organ of sensation is also situated in 

 the centre of the body ; and so if the region round 

 about the origin of movement is altered by sense- 

 perception and undergoes change, the parts which 

 are attached to it change with it by extension or con- 

 traction, so that in this way movement necessarily 

 takes place in animals. And the central part of the 



dpxai in relation to the parts below them, but the true apx-n 

 is situated in the soul, which lies in the centre of the body. 

 * i.e. the wrist. 



471 



