THE SKELETAL SYSTEM 51 



these joints. Furthermore, it has been stated that these surfaces 

 in the hving animal are covered with a layer of cartilage. In 

 addition to these articular cartilages, in some joints an accessory 

 cartilage is found which plays an important part in the work of the 

 joints. At the hip-joint this arrangement is seen in the form of a 

 marginal ring of fibrocartilage, which very appreciably deepens the 

 acetabulum and makes dislocation extremely difficult if not im- 

 possible. 



The stifle-joint, which corresponds to the knee-joint of man, is 

 the largest and most elaborate of all the articulations. This is 

 because it comprises two joints, the femoropatellar and the femoro- 

 tibial. Two C-shaped cartilages are placed between the femur 

 and tibia to adapt them more properly to each other (see Fig. 61). 



Synovia is a viscid, straw-colored fluid which gives an alka- 

 line reaction. It contains proteins, salts, and mucin. The latter 

 gives synovia its viscidity and lubricating property. The amount 

 of synovia increases and diminishes to a certain extent under nor- 

 mal conditions. When an excessive quantity is present a puffy 

 swelling occurs in the region of the joint. Bog spavin is a good 

 example of an excess in the hock-joint. 



