HIP-JOIXT. 61 



a socket. If the hard bones came into direct contact they 

 would be apt to chip one another when a sudden move- 

 ment was made, especially if the hip-joint were so far bent 

 as to knock the thigh-bone against the rim of the acetabu- 

 lum; the elastic and yielding cartilage forms a protecting 

 cushion between the bones and prevents this. 



To keep the bones in place and limit the range of 

 movement, ligaments pass from one to the other ; they are 

 composed of connective tissue, are extremely pliable but 

 cannot be stretched, and are very tough and strong. One 

 is the capsular ligament, which forms a bag all round the 

 joint, and another is the round ligament, L. T., Fig. 26, 

 which passes from the rim of the acetabulum to the head 

 of the femur ; from the rim of the socket it passes to 

 the center of the acetabulum along a groove in the bone, 

 and then turns out to be fixed to the thigh-bone. 



Covering the inside of the capsular ligament and con- 

 tinued over the cartilages of the joint is the synovial mem- 

 brane, very thin and composed of a layer of flat cells. 

 This pours out into the joint a very small quantity of 

 synovial liquid, which is somewhat like the white of a raw 

 egg in consistency, and plays the part of the oil moisten- 

 ing those surfaces of a machine which glide over one 

 another ; it lubricates the joint and enables all to run 

 smoothly and with but little friction. 



In the natural state of the parts the synovial membrane 



What is the-use of the cartilage lining the bones which move over 

 one another in a joint? 



What is the use of ligaments? Of what are they composed? 

 What are their properties? Name some ligaments of the hip-joint. 

 Where does the capsular ligament lie? Where the round ligament? 

 What membrane lines the joint? Of what is it composed? What 

 does it pour into the joint? What is synovial liquid like? What is 

 its use? Illustrate by au example. 



