232 OF ARTICULATIONS. 



CHAPTER IV. 



A GENERAL ACCOUNT OF ARTICULATIONS, AND OF 



Of Articulations. 



THOSE surfaces of bones which form the movable articula- 

 tions are covered with cartilaginous matter which has been 

 already described.* 



In many of the immovable articulations, as the sacro-iliac 

 symphysis for instance, a thin lamen of cartilaginous matter, 

 with all the other appurtenances of joints, are likewise met 

 with. The connexion between the articular cartilage and the 

 bones is strong, but its nature is not well known. None of 

 the vessels of the bone pass into the cartilage, but terminate in 

 its immediate neighborhood. Gerdy, (page 29) considers it 

 a secretion from these vessels, and that its formation is like 

 that of the cuticle, from the vessels of the skin. This, however, 

 is but a mere opinion, unsustained by proof. It presents the 

 appearance of a couch of white wax spread over the end of 

 the bones, though it is composed of vertical fibres like the frill 

 of velvet, so crowded together as to leave no sensible interval 

 between them, and presenting a free extremity to the cavity of 

 the joint. The cartilages terminate insensibly at their circum- 

 ference on the surface of the bone. On the heads of the bones 

 they are thicker at the central part, than at their circumference ; 

 in the corresponding socket, the cartilaginous coating is thickest 

 at the margin, and sometimes spreads out into a sort of carti- 

 laginous rim. 



On the formation of the epiphysis of the long bones, and its 

 covering cartilage. In the foetus and young subject, there is 

 no distinction between the cartilage that is to become the bone 

 of the epiphysis and that which is to remain as articular carti- 



* See page 36. 



