CARTILAGE. 



121 



the microscope. Fibro-cartilage is ctaracterised by a matrix of 

 fibrous tissue ; while the cellular variety consists of an aggrega- 

 tion of cells without a matriz. 



Hyaline cartilage is distinguished by the following names, 

 according to the purpose it serves : — Articvlar, when it encrusts 

 the articular surfaces of bones, helping to form joints by supplying 

 a smooth elastic cushion, which diminishes both concussion and 

 friction ; Costal, when it supplies elastic prolongations (hsemapo- 

 pbyses) to the ribs, connecting them distally with the sternum ; 

 Membraniform, when it appears as thin plates, forming per- 

 manently open tubes, — the trachea or wind-pipe is composed of 

 this kind of cartilage. 



In articular or encrusting cartilage the matrix is abundant, 

 and the cells vary in form, those near the surface being flatter 

 and more numerous. It is 

 always thickest in the young, 

 becoming thinner as the sub- 

 jacent ossification proceeds. It 

 is thickest in the centre of 

 convexities, thinnest in the 

 centre of cavities. In the adult 

 it is non- vascular, being nour- 

 ished by a vascular zone in 

 the synovial membrane, called 

 the circulus articuli vasculosus, 

 from which the nutritive ma- 

 terial is conveyed. The blood- 

 vessels of the bone underneath the cartilage also assist iw 

 supplying nourishment to the latter. All hyaline cartilage,' 

 except the articular kind, is covered by a membrane called the> 

 perichondrium. 



Fibro-cartilage consists of cartilage cells and fibrous tissue,) 

 which may be white or yellow, the former being tough and strong,! 

 the latter highly elastic. White fibro-cartilage is much the more 

 plentiful, and presents the following varieties : — It .is called Inter- 

 articular when it appears as a pad interposed between the two 

 articular cartilages which form a joint ; such a pad is termed a 

 TYieniscus, and the temporo-maxillary and femoro-tibial joints are! 

 furnished with such. Circumferential, where it surrounds andl 

 deepens an articular cavity, as the acetabulum. Connecting,] 

 when it is interposed between bones and firmly connects them, asl 



Fia. 41. 

 Section of hyaline cartilage, a, Four separatin^^ 

 cells ; b, Two cells in apposition ; c c. Nuclei ; 1 

 d. Cavity in the matrix containing three cells. 



