28 THE PRINCIPLES OF MYODYNAMICS. 



(b) The myodynamic angle must be acute, 

 right, or obtuse, according to the extent of the 

 contraction of the moving muscle. 



20. The ulna may be an example of a bony 

 lever of the first order : The humerus will 

 be the fixed bone, and the triceps brachii will 

 be the contracting muscle : The myodynamic 

 angle will be between the triceps brachii and the 

 ulna. 



21. In a bony lever of the first order, let a c 

 i be a inovable bone, oca fixed bone, c their 

 joint, m the contracting muscle, whose origin 

 and insertion are at o and i : See Figs. 5, 6, 7. 



The power is at i, the fulcrum is at c, and the 

 weight is at a. The myodynamic triangle is o i 

 c. And the myodynamic angle is o i c. 



(a) The myodynamic angle is acute in Fig. 5, 

 right in Fig. 6, and ol)tuse in Fig. 7. 



(b) From the origin of the contracting muscle 

 draw a perpendicular to the long axis of the 

 movable bone — prolonged if necessary, complete 

 the rectangle o b i d, whose diagonal is the long 

 axis of the contracting muscle : Also construct 

 the rectangle d o R c, whose diagonal is the 



