70 LABORATORY EXERCISES. 



36. STUDY OF THE JOINTS IN THE BODY. 



A. Ball-and-socket joints. 



1. Note on the articulated skeleton what bones 



form the joint at the shoulder. 



2. Point out the bones forming the hip-joint. 



3. State the points of resemblance between 



these two joints. 



4. What differences can you see in the sockets 



of the two joints? How does the head of 

 the femur differ from that of the humerus ? 



5. Move your right arm and right leg at the 



same time from a vertical position in an 

 arc sideways toward the right; state in 

 number of degrees the greatest range of 

 motion possible at the shoulder- joint and 

 at the hip- joint. 



6. In the same way move the arm and leg in an 



arc forward as far as possible ; backward 

 as far as possible. Compare the range of 

 motion at each joint. 



7. Describe a cone with the extended arm and 



leg; twist the arm and the leg at their 

 proximal ends. What kinds of move- 

 ments are, therefore, possible at these 

 joints other than those suggested in 5 

 and 6 above? 



8. Press the thumb on the hip-bone during 



these movements, then on the edge of 

 the shoulder-blade. Is either of the two 

 girdles movable? What advantages are 



