231 



tella 



projections or depressions which fit into corresponding de- 

 pressions or elevations on the bones with which they articu- 

 late. In addition to this the articular surfaces are quite 

 smooth and dense, having no Haversian canals, and they 

 are covered with a layer of cartilage. Strong ligaments 

 pass from one bone to- the other to hold each in its place 

 {A, Fig. 103). Some of these consist simply of bands, con- 

 necting the joint on its 

 different sides, while 

 others form continuous 

 sheaths around the joint. 

 The interior of the 

 joint, except where the 

 bone surfaces rub upon 

 each other, is covered 

 with a serous lining, called 

 the synovial membrane 

 (B, Fig. 103). This se- 

 cretes a thick, viscid of nee jointTendons. 2. Liga- 

 liquid, the synovial fluid, merits. 3. Cartilage. 4. Space contain- 

 which prevents friction. in g synovial fluid. This space is lined, 

 ~,, . , i except upon the articular surfaces, by the 



Ihe synovial membrane 



* synovial membrane. 



does not cover the ends 



of the bones, but passes around the joint and connects 

 with the bones at their edges so as to form a closed sac 

 in which the fluid is retained. 



Kinds of Movable Joints. The different kinds of mova- 

 ble joints are the ball and socket joint, the hinge joint, the 

 pivot joint, the condyloid joint, and the gliding joint. 

 These are constructed and admit of motion, as follows: 



i. In the ball and socket joint the ball-shaped end of 

 one bone fits into a cup-shaped cavity in another bone, 

 called the socket. The best examples of such joints are 



FIG. 103. Outside and inside view 



