56 THE FROG CHAP. 



ment (cps. Ig), forming a short, fibrous tube. The other 

 end of this tube is fixed to the femur, just below the 

 head, the ligament being continuous, in each case, with 

 the perichondrium. There is thus a space between the 

 head of the thigh bone and the acetabulum, closed all 

 round by the capsular ligament. This space is filled with 

 a delicate, fibrous, closed bag, the synovial capsule (sy. 

 cps), one side of which fits closely into the acetabulum, 

 while the other as closely invests the head of the femur. 



jp. esf c j 



jo.chrf actb 



FIG. 15. Horizontal section of the Frog's hip-joint, (x 5.) 



actb. acetabulum ; cps. Ig. capsular ligament ; lid. head of femur ; il. ilium ; med. 

 marrow ; p. chd. perichondrium ; p. ost. periosteum ; pu. pubis ; sh. shaft of 

 femur ; sy. cps. synovial capsule. 



The capsule is filled with a watery fluid, the synovia, 

 and thus forms a buffer or water-cushion between the 

 adjacent parts of the skeleton. Thus the synovial 

 capsule keeps the two parts slightly apart and prevents 

 friction, while the capsular ligament keeps them together 

 and prevents dislocation. 



It is obvious that, in such a joint as this, movement is 

 possible in all directions. The femur can be inclined 

 either upwards, downwards, or sideways, and is capable 

 of a certain amount of rotation. The joint is, in fact, a 

 cup-and-ball joint, and is capable of movement in any 



