THE MUSCLES 



127 



7 



between the power (P) and the weight ( W). In the lever 



of the second order the weight is between the other two, and 



in the lever of the third order the power 



is between the others. In Fig. 116 the 



biceps muscle acts on the radius and ulna 



fastened together as one, turning at the 



elbow as a fulcrum ; the weight to be 



lifted is in the hand. This is evidently a 



lever of the third order with the power 



between the other points. In this case it 



takes a force in the muscle equal to about 



six pounds to raise one pound in the hand. 



216. Figure 120 shows how the muscles 

 may act as levers upon the bones to pre- 

 vent the bones from turning upon the joints 

 as fulcrums; thus the body is held erect. 

 Where are the muscles located that keep 

 the body from falling or bending forward 

 (Fig. 120)? From falling backward? 

 (Which of the two sets is in front ?) What 

 kind of lever is illustrated by the head tilted 

 upon the atlas (Fig. 121)? 



217. Names and Positions of Muscles. 

 A few of the important muscles are here 

 mentioned: The scalp muscle (Fig. 122) 



passes over the top of the head ; it raises FlG- I20 . Diagram 

 the skin over the eyes, and (in some 

 persons) moves the scalp. The two pairs 

 of chewing muscles are the temporal and 

 masseter (Fig. 122). You can feel the temporal muscle 

 swell and harden if you place your finger on the temple and 

 close your mouth forcibly. In the same manner you may 

 feel the contraction of the masseter by placing the fingers 

 just below the cheek bone. The muscle used in bowing 

 passes obliquely down on the side of the neck to the 



of the Muscles that 

 keep the Body 

 erect. 



