

MECHANICS OF MUSCLE 



363 



muscle in succession or at different times. Most muscles are, however, in a mechanical 

 sense units. But in either case the muscle fibers constitute the elementary motor 

 elements. 



FIG. 361 



The Direction of the Muscle Pull. In those muscles where the fibers always run 

 in a straight line from origin to insertion in all positions of the joint, a straight line 

 joining the middle of the surface of origin with the middle of the insertion surface 



FIG. 362 



will give the direction of the pull (Fig. 361). If, however, the muscle or its tendon 

 is bent out of a straight line by a bony process or ligament so that it runs ove^r a 

 pulley-like arrangement, the direction of the muscle pull is naturally bent out of 



FIG. 363 



line. The direction of the pull in such cases is from the middle point of insertion 

 to the middle point of the pulley where the muscle or tendon is bent. Muscles or 

 tendons of muscles which pass over more than one joint and pass through more than 



