298 PHYSIOLOGY OF MUSCLES AND NEKVES. 



therefore, B I'. The small triangle J! I !>' may l>e regarded 

 as a right-angled triangle. Tliis gives 



BV = --^ 



817] 



The force with which the mu<e!e-libre strives to contract 

 in tin- direction A B being called /., only part of this force. 

 the component k' lying in the direction B (.'. finds expression. 

 According to the law of the parallelogram of forces, this com- 

 ponent is 



k '= k sin p. 



This force may be regarded ns proportionate to tin- 

 weight which the muscle-fibre is aide to raise to the given 

 height of elevation. If we then c.-dciilate the work which 

 the muscle can accomplish, we find, if th motion can take 

 place in the direction A B, 



Abk; 



but if motion can only occur in the direction B C, 



The value in the two cases is therefore exactly the same, 

 or, in other words, the amount of work accomplished by the 

 muscle is quite independent of the direction in which its 

 action takes place. This is, naturally, true of every other 

 muscle -fibre, and, ci >iise<jueiit 1 y, of the whole muscle. The 

 statements which we have made of parallel-fibred muscles 

 are therefore also true of those of which the fibres are irre- 

 gular. The possible height of elevation is always grea'ei- 

 the longer the fibres are, and the force proportionate to the 

 diameter or to the number of the fibres. In oblique fibred 

 muscles the fibres are generally very short, but very nume- 

 rous ; the>e must, therefore, whatever tln-ir accidental form. 

 lie regarded as short and thick muscles, possessed of small 

 ele\atinii and great f.-ive. 



