ANIMAL MECHANICS 



109 



neither gain nor loss of work due to the penniform arrange- 

 ment. 



In the Nylghau, the muscular fibres of the biceps humeri 

 are 1.84 inches in length, and make an angle of 50 0 with the 

 central line. These penniform fibres will therefore act like 

 the prismatic fibres of an ordinary biceps muscle, whose 

 length is 



I = 1.84 x sec 50 0 = 2.85 inches. 



The actual length of the biceps in the Nylghau is 6 inches, 

 and yet the total amount of its contraction is only that due to 

 a muscle of 2.85 inches in length. The intention of this ar- 

 rangement of penniform fibres is to produce a powerful pull 

 through a small space. In the brachiceus muscle of the same 

 animal, the fibres run parallel together through the entire 

 length of the muscle, which is prismatic, and wound spirally 

 round the humerus. The length of the fibres is 8 inches, and 

 from their parallel, and not penniform arrangement, this 

 muscle is capable of a contraction nearly three times greater 

 than that of the penniform biceps. 



In the Ass, the length of the penniform fibres of the 

 biceps humeri is 1.06 inches, and they form with the tendinous 

 axis an angle of about 24 0 . Hence the action of this penni- 

 form biceps will be similar to that of a prismatic muscle 

 whose length is 



I = 1.06 x sec 24 0 =1.15 inches. 



The actual length of the biceps muscle in the Ass is 6.6 inches. 

 The fibres of the brachiceus muscle in the Ass are parallel, and 

 run along its entire length, which is 9 inches. Hence the 

 brachiceus is capable of a contraction nearly eight times 

 greater than that of the biceps muscle. 



Let it be required to find a prismatic muscle, whose action 



