8 ELEMENTARY PHYSIOLOGY. 



The bones are united to each other in 

 United, different ways. Those which are quite 



movable are connected by joints. Some 

 of these are called hinge-joints because they work 

 like the hinge of a door. These (arm) bones 

 which meet at the elbow are hinge-jointed. Eaise 

 and lower your forearm and notice particularly how 

 the joint acts. The joints in the fingers and the 

 knee are also hinge-joints. Another kind is called 

 the ball and socket joint, where the round end of one 

 bone moves in a hollow place of another. Here (a) 

 at the hip is a good example of a ball and socket 

 joint, where the round head of this large upper bone 

 of the leg moves in a deep hollow of this lower bone 

 of the main body. The bones of the head meet each 

 other with jagged edges forming a seam-like junc- 

 tion called a suture. One of these is clearly shown 

 on this skeleton (12). Between the bones of the 

 back are placed cushions of cartilage. This is a 

 substance softer than bone and quite elastic, like 

 rubber. This cushion arrangement between the 

 bones of the back, is nicely shown on this plate. 

 (Refer to cartilages between lumbar vertebrae.) 



The bones are bound to one another 



Bound To- . _ 



Bother by by ligaments. These are very strong 

 Ligament*. and hol( j foe bones firmly in position. 

 Some of these stout bands or ligaments are shown on 

 this plate. Here (XVI) are the ligaments which 

 bind together the bones of the hip. These (XXV, 

 XXVI) are the ligaments of the elbow joint 



