258 COMPARATIVE ANATOMY 



This not only insures some degree of elasticity at the joint but also pro- 

 vides a means of lubrication. As the cartilage wears down through use, 

 the cartilage cells are converted into one of the best lubricants known to 



man. 



In the development of some joints, a cartilaginous disc primarily 

 divides the liquid-filled cavity in two. Later this disc disappears and a 

 single cavity is formed. 



