253 



PHYSIOLOGY AND HEALTH. 



their faces always moist and slippery. This is the living 

 joint, which prepares and pours out this oily fluid, as the skin 

 pours out perspiration ; and if the joints are properly used, 

 and in good health, this fluid is of the due proportion and 

 consistency. But in some cases of disease or injury, it be- 

 comes abundant, and fills the sac of the joint, as a bladder, 

 with water. This happens most frequently in the knee, from 

 a blow or a strain. Then this lining membrane takes an un- 

 natural and increased action, and throws out much more fluid 

 than is needed, and so fills the sac of the joint that the knee 

 is swelled and lame. 



612. The ligaments and the c apsides Jiold the bones together 

 at the joints. The capsule encloses the whole joint : it sur- 

 rounds the end or the seat of junction of each bone, and is 



FIG. XLVI. Knee, Capsule^and Ligaments. 



a, Tendon of the great muscle of the thigh, 

 attached to the knee pan. 



b, Knee pan. 



c, Tendon connecting the knee pan with the 

 bones of the leg. 



d, d t Capsule covering all the joint. 



e, f, Lateral ligaments extending from the 

 thigh to the bones of the leg. 



ff, Thigh bone. 



h, i, Bones of the leg. 



attached to both. In the knee, (Fig. XLVI. J, d,) the cap- 

 sule surrounds-, and is attached to, the lower end of the thigh 

 bone : it passes over the space between the bones, and in like 

 manner it surrounds, and is attached to, the upper ends of the 

 bones of the leg. The synovial membrane within this cap- 

 sule prepares and throws into the joint the synovial fluid that 

 moistens and oils it. 



There are other ligaments within and without the joints. 

 Some of those within the knee are seen in Fig. XLVII. The 



