146 ANSWERS TO PRACTICAL QUESTIONS 



This seems to the author 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 we use when 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, page 48.) 



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 attachment near the elbow. 



5. What class of lever is used in bending 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 extremity of the fingers. 



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

 with our toes ? 



(See Physiology, Fig. 14, .) 



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 gastrocnernius muscle at its 

 attachment to the heeh 



