48 



THE CONNECTIVE TISSUES 



[CH. V. 



after layer of true bone; this is formed exactly in the same way 

 as in such a bone as the parietal ; by the agency of the osteoblasts, 

 osteogenetic fibres, and then spicules of bone, are formed by deposit 

 of calcareous matter. As the layers are formed, some of the osteo- 

 blasts get walled in between the layers and become bone-cells. 



In the later part of this stage the calcareous deposit between the 

 cartilage-cells cuts them off from nutrition, and they in consequence 

 waste, leaving spaces that are called the primary areolce. The 

 calcareous deposit creeps up between the rows of cartilage-cells, 



ir. 



FIG. (>2. Ossification in cartilage showing stage of irruption. The shrunken cartilage-cells are seen 

 in the primary areolae. At ir an irruption of the subperiosteal tissue has penetrated the sub- 

 periosteal bony crust. (After Lawrence.) 



enclosing them in calcified boxes containing one, two, or more cells 

 each. The wasting of the cells leads here also to the formation of 

 primary areolae. 



We may roughly compare the two sets of cells engaged in the 

 process to two races of settlers in a new country. The cartilage-cells 

 constitute one race, and so successfully build for themselves calcareous 

 homes as to be completely boxed up ; so they waste and disappear, 

 leaving only the walls of their homes enclosing the spaces called 

 primary areolse. The osteoblasts, the other race of cells under the 



