THE JOINTS. 



The study of the articulation of the bones and the liga- 

 ments holding them in place is known as syndesmology. 

 There are three general classes of articulations : Synar- 

 throses, or immovable joints; amphiarthroses, or joints 

 with slight motion; and diarthroses, or joints freely mov- 

 able. A synarthrodal joint is exemplified in the sutures be- 

 tween the bones of the skull. The two surfaces of bone are 

 separated by fibrous membrane only. An amphiarthrodal 

 articulation occurs between the 

 bodies of the vertebrae and also in 

 the union of the sacrum with the 

 ilium. In the articulation of the 

 vertebrae the contiguous surfaces 

 of the bone are faced by flattened 

 discs of fibrocartilage (Fig. 21). 



The diarthrodal articulation is 

 exemplified in all joints allowing 

 free motion. Such joints are 

 composed of the following parts : 

 the ends of two bones having 

 their contiguous surfaces covered 

 with cartilage; a synovial mem- 

 brane forming a short tube whose ends are closed by the 

 cartilaginous articulating surfaces; and several ligaments 

 varying in number from two or three to a dozen (Fig. 44). 

 There are four kinds of the diarthrosis : the arthrodia, or 

 gliding joint, which occurs between the bones of the carpus : 

 the enarthrosis,, or ball-and-socket joint, such as at the hip 

 or shoulder; the ginglymus, or hinge joint, exemplified at 

 the elbow and knee; and the rotatoria, or pivot joint, formed 

 by the articulation of the axis and atlas. 

 8 73 



FIG. 44. DIAGRAM OF A 

 DIARTHRODAL JOINT. 



ar, Articulatory cartilage ; lg, 

 ligament ; sn, synovial 

 membrane ; sy, synovial 

 fluid in synovial cavity; t, 

 tibia ; v, femur. 



