34 



PHYSIOLOGY AND TEMPERANCE. 



they are intended. Some joints allow of motion in every 

 direction, for example, the shoulder joint; others have only 

 a to-and-f ro motion, like the elbow while others again have 



but little motion, as, for 

 instance, the slight move- 

 ment) of each individual 

 spine upon its next neigh- 

 bor. Let us examine the 

 construction of a joint. 



Fig. 12 represents the 

 knee after the skin and 

 fat have been removed. 

 The ends of the bones 

 coming together to form a 

 joint are covered with car- 

 tilage, more or less elastic, 

 according to its thickness. 

 This acts, in a measure, 

 like a buffer, to arrest jara 

 in jumping or in falling. 

 The cartilage, in turn, is 

 covered by a smooth lining, 

 the synovial membrane, 

 which is folded over the 

 inner surface of the joint 

 from one bone to the other, 

 and forms a closed sac. 

 Within the sac is a small 

 quantity of fluid, the syno- 

 via, secreted by the membrane. This fluid lubricates the 

 joint, like oil in machinery, and promotes free motion with- 

 out friction. Outside this is a strong cap, holding the bones 

 together. There are also extra bands, like bands of ribbon, 

 stretching from one bone to another. Still outside all this 



FIG. 12. The Right Knee Joint, showing how 

 . firmly it is bound about by ligaments. 



