MOVEMENT OF ANIMALS, viii. 



Now that which first causes movement in the 

 animal must be situated in a definite beginning. 

 Now it has already been stated that the joint is the 

 beginning of one thing and the end of another ; where- 

 fore nature employs it sometimes as one and some- 

 times as two. For when movement is being origin- 

 ated from it, one of its extreme points must be at 

 rest, while the other must move ; for we have already 

 said that what causes movement must be supported 

 on something which is at rest. The extremity, there- 

 fore, of the forearm is moved and does not cause 

 movement, but in the elbow-joint one part, namely 

 that which is situated in the actual whole which is in 

 motion, is moved, but there must also be something 

 which is unmoved ; and this is what we mean when 

 we say that a point is potentially one but becomes 

 actually two. So if the forearm were a living creature, 

 it is somewhere near this point that the origin of move- 

 ment set in motion by the soul would be situated. 

 Since, however, it is possible for an inanimate object 

 to bear this same relation to the hand,° for instance 

 if one moves a stick in one's hand, it is clear that the 

 soul could not be situated in either of the extremities, 

 neither in the extremity of that which is moved ^ nor 

 in the other origin of movement (apX'D ^ '» ^^^ ^^^ stick 

 has an end and a beginning (opxv) ^ hi relation to the 

 hand. So, for this reason, if the origin of movement 

 set up by the soul is not situated in the stick, it is not 

 situated in the hand either ; for the extremity of the 

 hand * bears the same relation to the wrist as the 

 latter does to the elbow. For there is no difference 

 between what is attached by growth and what is not 



• i.e. the point where the hand joins the stick. 



469 



