30 HIP-JOINT. * 



muscle are attached to separate bones, between which 

 a joint is placed; and when the muscle contracts it pro- 

 duces movement at the joint. The joints and muscles 

 are the chief organs of movement. 



3. Joints. As an example of a joint we may take 

 that at the hip (Fig. 13). 



FIG. 13. The hip-joint, sawed through its middle. The rounded head of the 

 thigh-bone is seen to fit into the cup or socket of the hip-bone. , cartilage lin- 

 ing socket; , cartilage covering end of femur; c, c, capsular ligament; LT, round 

 ligament. 



On the outer side of the hip-bone (s, Fig. 3) is a cup- 

 like hollow which receives the round upper end of the 

 thigh-bone. Lining the cup is a thin layer of cartilage, 

 and covering the end of the thigh-bone is another. The 

 cartilage is extremely smooth and is kept moist by a few 

 drops of joint-oil, or synovial liquid, so that the end of the 



3. Describe the hip-joint, 

 vial fluid? The ligaments ? 



What use is the cartilage ? The syno- 



