DEVELOPMENT OF BONE. 75 



If we examine the cartilage at a considerable 

 distance from the line of ossification, we find the 

 ordinary appearance of hyaline cartilage with more 

 or less flattened cells. Approaching now the zone 

 of ossification, we find that the cells are larger, are 

 arranged in rows or groups of frequently four, eight, 

 or sixteen, etc., the intercellular substance being less 

 in amount, corresponding to the increase in size and 

 number of the cells. Further inward, we find the 

 cells still more plainly arranged in rows, very large, 

 sometimes globular or flattened against one another, 

 and the basement substance reduced to quite thin 

 septa, enclosing spaces in which the rows of large 

 cartilage-cells lie. Then comes a narrow zone, in 

 which the septa of the basement substance are filled 

 with fine granules of lime salts calcification zone. 

 Here the cartilage-cells have assumed a peculiar 

 granular character. Finally, still nearer we find that 

 the lime salts have disappeared from the septa, and 

 that the spaces which contained the large granular 

 cartilage-cells have become continuous with the 

 advancing vascular, bone-walled marrow-cavities, 

 above described. It is to be distinctly understood 

 that the calcification zone is not bone, but only cal- 

 cified cartilage ; the true bone being first formed 

 after this lime has disappeared, on the surface of the 

 septa in which it was temporarily deposited for 

 what purpose we do not know. 



Turning our attention now to the exact way in 



