OH. V.] 



DEVELOPMENT OF BONE. 



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

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

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

 osteoblasts 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 con- 



ir. 



fig. go. Ossification in cartilage xhowing Ntage of irruption. The shrunken cartilage-cells 

 are seen in the primary areolae. At ir an irruption of the subperiosteal tismiu has 

 penetrated the subperiosteal bony crust. (After Lawrence.) 



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

 The calcareous deposit creeps up between the rows of cartilage- 

 cellf, enclosing them in calcined boxes containing one, two, or 

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

 formation of primary areolrc. 



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 



ri 



