THE SKELETON 



73 



os iimominatum is the cavity of the acetabulum (Fig. 36), which is 

 lined inside by a thin layer of articular cartilage which has an es- 

 t remely smooth surface. The bony cup is also deepened a little by 

 a cartilaginous rim. The proximal end of the femur consists of a 

 nearly spherical smooth head, borne on a somewhat narrower neck, 

 and fitting into the acetabulum. This head also is covered with 

 articular cartilage; and it rolls in the acetabulum like a ball in a 

 socket. To keep the bones together and limit the amount of move- 



FIG. 36. Section through the hip-joint, a and b, articular cartilages; c, capsu- 

 lar ligament. 



men! , ligaments pass from one to the other. These are composed 

 of white fibrous connective tissue (Chap. IV) and are extremely 

 pliable, but quite inextensible and very strong and tough. One is 

 the capsular ligament, which forms a sort of loose bag all around the 

 joint, and another is the round ligament, which passes from the 

 acetabulum to the head of the femur. Should the latter rotate 

 above a certain extent in its socket, the round ligament and one 

 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- 



