THE JOINTS. 



The study of the articulation of the bones and the 

 ligaments holding them in place is known as syndesmol- 

 ogy. There are three general classes of articulations : 

 Synarthroses, or immovable joints; amphiarthroses, or 

 joints with slight motion; and diarthroses, or joints freely 

 movable. A synarthrodal joint is exemplified in the 

 sutures between 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 articula- 

 tion of the vertebrae the con- 

 tiguous surfaces of the bone are 

 faced by flattened discs of fibro- 

 cartilage (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 cartilagin- 

 ous 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 

 8 89 



FIG. 44. - - DIAGRAM OF A 

 DIARTHRODAL JOINT. 



ar, Afticulatory cartilage ; Ig, 

 ligament ; sn, synovial 

 membrane ; sy, synovial 

 fluid in synovial cavity; /, 

 tibia ; -v, femur. 



