146 ANSWESS TO PRACTICAL QUESTIONS 



to be an example of the first or second class of lever. Huxley 

 gives it as an illustration of the third class. 



3. What class of lever do ive use wJien we lift the foot 

 while sitting down ? 



The third class. The fulcrum is the knee-joint ; the weight 

 is at the center of gravity of the foot and leg, and the power 

 is applied by the ligament which passes over the patella. 



4. Explain the swing of the arm from the shoulder. 



(See Physiology, p. 34 ) 



The third class. The fulcrum is the shoulder- joint ; the 

 weight is at the center of gravity of the arm and hand, and 

 the power is applied by the biceps or triceps muscle at its at- 

 tachment near the elbow. 



5. What class of lever is used in betiding our fingers ? 



The fulcrum is at the junction of the finger with the palm ; 

 the weight is at the center of gravity of the finger, and may 

 play about the fulcrum as stated in second question. It is the 

 third class of lever, especially when force is exerted at the ex- 

 tremity of the fingers. 



6. What class of lever is our foot when we tap the 

 ground with our toes ? 



(See Physiology, Fig. 14, Tc.) 



The first class. The weight is at the toe when the force is 

 exerted ; the fulcrum is at the ankle ; and the power is applied 

 by the gastrocnemius muscle at its attachment to the heel. 



7. Wliat class of lever do we use when we raise our- 

 selves from a stooping position ? 



The third class. See second question. If we are attempt- 

 ing to lift a heavy burden, the bones act on the principle of 

 the toggle-joint. "When one stoops to take a heavy weight 

 upon his back or shoulder, he puts both the knee and the hip- 

 joints into the condition that the toggle-joint is when it is bent; 

 and then, as he straightens up, the weight is raised by an ac- 

 tion of the joints precisely similar to that of the toggle-joint in 

 machinery. In the case of the knee, the straightening of the 



