THE SKELETON 



69 



side of the capsular ligament are put on the stretch, and any fur- 

 ther movement which might dislocate the femur (that is ; remove 

 the head from its socket) is checked. Covering the inside of the 

 capsular ligament and the outside of the round ligament is a layer 

 of flat cells, which are continued in a modified form over the ar- 

 ticular cartilages and form the synovial membrane. This, which 

 thus forms the lining of the joint, is always moistened in health 

 by a small quantity of glairy synovial fluid, something like the 



FIG. 39. Section through the hip-joint, a and 6, articular cartilages; c, capsu- 

 lar ligament. 



white of a raw egg in consistency, and playing the part of the oil 

 with which the contiguous moving surfaces of a machine are mois- 

 tened; it makes all run smoothly with very little friction. 



In the natural state of the parts, the head of the femur and the 

 bottom and sides of the acetabulum lie in close contact, the two 

 synovial membranes rubbing together. This contact is not main- 

 tained by the ligaments, which are too loose and serve only to 

 check excessive movement, but by the numerous stout muscles 

 which pass from the thigh to the trunk and bind the two firmly 

 together. Moreover, the atmospheric pressure exerted on the sur- 

 face of the Body and transmitted through the soft parts to the 

 outside of the air-tight joint helps also to keep the parts in contact. 

 If all the muscles and ligaments around the joint be cut away, it is 



