THE PRINCIPLES OF MYODYNAMICS. 



The weio-Jit is also derived from one or more 

 muscles — assisted at times by the weight of 

 some part of the head. For instance, when the 

 head is flexed, the weight of the head will co- 

 operate with the flexors in antagonizing the 

 pozuer of the extensors. (3.) In fact, any one 

 group of muscles acting on the skull may be 

 considered the power, while the antagonistic 

 group may be considered the weight. 



138. When the body and the head are in the 

 upright position, all the motor muscles of the 

 skull, above grouped, co-operate. The antago- 

 nistic groups of muscles are in equilibrium. 

 The moving components of the groips of muscles 

 antagonizing are equal. 



(i.) The moving components of the right 

 rotators equal the moving components of the 

 left rotators. (2.) The moving components of 

 the left adductors equal the moving components 

 of the right adductors. (3.) The moving com- 

 ponents of the flexors equal the moving com- 

 ponents of the extensors. 



Examples : (i.) The trachelo-mastoids will 



