88 



HISTOLOGY 



around which ossification has begun. On either side of the shaft of 

 hyaline cartilage, the matrix of which stains blue with haematoxylin, 

 there is a strip of bone, the matrix of which is stained red with eosin. 

 These strips are sections of a band of bone which completely encircles 

 the middle part of the cartilage. It has been formed by osteoblasts which 

 developed in the perichondrium. The portion of the cartilage which is 

 surrounded by bone has begun to degenerate. Its capsules have been 



Enlarged 



cartilage 



cells. 



Endochondrial 

 bone. 



Perichondrial 

 bone 



Periosteum. 



Perichondrial 

 bone. 



FIG. 75. A DORSO-PALMAR LONGITUDINAL SECTION OF A MIDDLE-FINGER PHALANX, 

 FROM A HUMAN EMBRYO OF THE FOURTH MONTH. X 60. 



resorbed, and the enlarged lacunae are beginning to coalesce. The matrix 

 of the cartilage in this region takes a deeper stain, and calcareous granules 

 are being deposited within it. 



On the left of Fig. 74, a bud of perichondrial tissue is seen entering 

 the shaft of the cartilage, and similar buds may invade it from other 

 sides. Within the cartilage the ingrowing perichondrial tissue forms the 

 primary marrow, which is a very vascular connective tissue. As it ad- 

 vances, the walls of the lacunae are resorbed, setting free the cartilage 

 cells. Formerly it was thought that these cartilages cells became osteo- 

 blasts, but they are now considered to be dying cells, without further 

 function. 



