298 PHYSIOLOGY OF MUSCLES AND KEKVES. 



therefore, B h'. The small triangle Bhh' may he regarded 

 as a right-angled triangle. This gives 



Bh 



Bh' = 



sin i'/ 



The force with which the muscle-fibre strives to contract 

 in the direction A B being called k, only part of this force, 

 the component k^ lying in the direction B C, finds expression. 

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

 ponent is 



k'=-k sin /3. 



This force may be regarded as proportionate to the 

 weight which the mnscle-fibre is able to raise to the given 

 height of elevation. If we then calculate the work which 

 the muscle can accomplisli, we find, if the motion can take 

 place in the direction A B, 



A=Bbk', 

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



A = B¥ k'= ^^ ^ k sini3=Bb k. 

 sm [j 



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, consequently, 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 irie- 

 gular. The possible height of elevation is always greal:er 

 the longer the fibres are, and^ the force proj^orlionatc to the 

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

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

 rous ; these must, therefore, whatever their accidental form, 

 be regarded as short and thick muscles, possessed of small 

 elevation and great force. 



