324 



Basic Structure of Vertebrates 



The external surface of cartilage is invested by a connective-tissue 

 membrane, the perichondrium (Fig. 266), which contains blood- 

 vessels, but they do not penetrate into the cartilage. Hence cartilage 

 cannot occur in thick masses. 



In growing cartilage, cells from the perichondrium become cartilage- 

 cells and add cartilage to the exterior of the mass already formed. At 

 the same time, deep cartilage-cells divide. The resulting cells secrete 

 matrix substance whereby they become separated, each to lie in a 

 lacuna of its own. Therefore cartilage grows by a combination of ex- 

 ternal addition and internal expansion. 



Most cartilage, containing little or no fibrous material, is bluish 

 and clear — hence known as hyaline cartilage (Fig. 266). In fibro- 

 cartilage the matrix contains fibers similar to those of ordinary con- 



Capsule 



Fig. 26o. Hyaline cartilage, with perichondrium; from human trachea. (Bl.v.) 

 Blood-vessel; (X) cartilage-cell whose nucleus is not in section; (Y) new matrix 

 forming between two cells resulting from a recent division of a cartilage-cell. 

 (Courtesy, Bremer: "Text-Book of Histology," Philadelphia, The Blakistou 

 Company.) 



