HISTOLOGY 



155 



exceedingly fine canals penetrating the matrix and putting any one 

 lacuna into communication with neighboring lacunae. 



The external surface of cartilage is invested by a membrane, the peri- 

 chondrium, consisting of collagenous connective-tissue fibers, densely 

 arranged and for the most part parallel to the surface of the cartilage. 



Capsule. 



Perichond 



Matnx. 



Bl.v. 



Fig. 118. — 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. (From Bremer, 

 Text-book of Histology.) 



The perichondrium contains blood vessels but they do not penetrate into 

 the cartilage. Hence cartilage cannot occur in thick masses. 



In growing cartilage, cells from the adjacent surface of the peri- 

 chondrium become cartilage cells and add cartilage to the exterior of the 

 mass already formed. At the same time growth may take place within 

 the mass. A deep cartilage cell divides. The resulting two cells secrete 

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

 of its own. In growing cartilage, therefore, the matrix substance is not 

 so firmly "set" that it may not expand as a result of such internal or 

 interstitial growth. 



