204 DETAILED SYNTHESIS. 



motion ; at the elbow and knee are examples of hinge- 

 joint ; that of the wrist is a compound hinge, like the 

 ankle, while in the lower arm and neck there are rotary 

 joints. Other joints allow a still more limited motion, 

 to which attention will be drawn. 



271. THE LIGAMENTS that bind the bones together 

 are of three kinds : the flat or strap, the round, and the 

 capsular. The first is the most common. They are all 

 arranged so as to permit desirable motion, but to check 

 all other. (See Fig. 2, PL 17 and PL 18.) 



272. Remark. The action of muscles also tends to bind the organs 

 together at the joints. The pressure of the air is of considerable effect, 

 for if all the ligaments of a hip-joint should be cut, it would require a 

 weight of forty pounds to draw the bone from its socket. 



273. THE JOINTS AEE LINED WITH serous membrane, 

 that continually secretes the glairy, anti-friction synovia 

 or synovial fluid. In early life this membrane covers the 

 entire surface of the cartilages of a joint ; but in later 

 years the cartilages themselves appear to touch, and the 

 synovial membrane is found lining only the sides of the 

 joint. Sometimes the membrane is laid in folds and 

 fringes in the sides of the joint, as in the knee, so that 

 it may form a larger quantity of fluid. (Fig. 6, PI. 17.) 



274. IN SOME OF THE JOINTS THERE is an extra or 

 friction cartilage, to promote freedom of motion in the 

 joint. (See Fig. 162.) 



FIG. 156. 



Fig. 156 represents the 

 Periosteum peeled up 

 from a part of the bone 

 upon and to which it 

 grew. 



275. THE BONES AND CARTILAGES ARE COVERED 

 with a thin, dense, finely-textured membrane of sinewy 

 tissue, called periosteum on the bones, and perichondrium 



271. How nmny kinds of - ? 272. What said of air ? 273. How ? 274 What 

 ? Describe Fig. 156. 275. How -? 



