On Muscular Motion and Animal Spirits 285 



In the second place, if one end of the string to be 

 contracted were free but the other end fixed, that the 

 free end and also all parts of the string would in 

 contraction be drawn towards the fixed end ; as is 

 shown in Plate III., Fig. 4, which represents the string 

 so arranged and the same when contracted. For in 

 the said figure not only the free end of the string, 

 c, but also its middle point, a^ and so also all parts of 

 it, are drawn in the contraction of the string towards 

 the end, 3, which we suppose fixed. And similarly 

 we infer that if a greater weight be attached to the 

 one end and a smaller weight to the other, the 

 smaller weight will in the contraction of the string, 

 be drawn towards the greater as to a fixed end. 



From what has been said, it will not be difficult to 

 understand the motion of the shortened muscle-s and 

 fibres. For if a fibre, fibril, or muscle, both of the 

 ends of which are free, undergoes contraction, it is 

 not to be doubted that both its ends will approach 

 the centre ; but if one of the ends is attached to an 

 immovable part, as is the case with the muscles which 

 serve for local motion, the contraction will be 

 altogether to the more fixed part ; and the movable 

 end, which in a muscle is called the termination, is 

 drawn in contraction towards the immovable end, or 

 what is the same thing, the head of the muscle. And 

 this also occurs in the contractions of the fibres or 

 fibrils. I am quite aware that the learned Dr Willis 

 has expressed a contrary opinion in his treatise 

 On Muscular Motion^ for that distinguished man 

 altogether denies that the fibres contract from the 

 termination towards the origin ; and indeed affirms 

 that when they are shortened, both of their ends are 

 drawn towards the middle. But with all respect to 

 such a man, when one end of a fibre is fixed to an 



