32 



THE HUMAN BODY. 



Inuominate. 



PARTS WHICH COMPOSE A JOINT. 



3. In a joint there are 



L Tivo or more bones, each covered, where they come 



in contact, with a thin, 

 smooth layer of cartilage 

 or gristle. Cartilage is 

 more elastic than bone, 

 and serves as a spring 

 in the joint. 



2. Ligaments which 

 bind the ends of the 

 bones firmly together. 

 A ligament is a white, 

 glistening band, very 

 strong, and generally 

 not elastic. When we 

 examine it with a mi- 

 croscope, we find that it 

 is made of fine white 

 fibers, lying side by side 



like the threads of a ribbon, only there are no cross- 

 fibers. They all run lengthwise. 



3. The cavity of the joint has a thin lining, called a 

 synovial membrane. This membrane gives out a fluid 

 called syncJvia, or joint-water. This serves the same pur- 

 pose that the oil we put in the joints of machinery serves. 

 But while these need constant attention, and soon wear 

 out, the living joint oils itself, and may be in constant 

 use for seventy years or more without causing a thought 

 in the mind of its owner. 



If, however, joints become diseased, they are very 



Femur , 



Fig. 21. 

 THE HIP-JOIXT. 



