246 



ANIMAL MECHANICS. 



US = 8 inches. 

 HX = 10 „ 

 SO = 216 „ 



From which we find 



SX = 12.8 inches. 



BSX = 51° 20'. 

 XSO = 8o° 17'. 



Adding together the two angles, we find 



IJSO = .31-37'; 



or, that the arm is depressed 48 0 23' below the horizontal line, 

 when SO is perpendicular to OX. In giving a back sword 

 cut, or back-handed stroke to a racket-ball, this is the angle 

 of depression at which the moment of the force of the latissi- 

 mas dorsi round the socket S is a maximum. 



The angular velocity produced by the contraction of the 

 muscle is thus found. Let 



SO = A: XSO = 0. 



XO = x. XOS = <p, 



SX = a. 



(x) = angular velocity. 

 1 = moment of inertia of arm 

 F = force of muscle. 



We have, from the principles of Dynamics, 



(Pi) duy _ Fk sin 0 

 dF ~ ~dt ~ " 1 



but 



a 



sin dj = - 



x 



sin 



e 



a' 2 + k- - 2a£ cos 0. 



