270 



MICROSCOPIC AX A TOM)' OF THE ORGAXS. 



from freed cartilage cells. Some of the cells form the elements 

 of the future bone-marrow ; a part, on the contrary, play the 

 important role of bone-formers or osteoblasts. These are large, 

 often-branched cells, which as a rule form a layer on the 

 inner surface of the periosteum, and are carried into the mar- 

 row cavity along with the periosteal buds. Thus we find in 

 the areas of ossification, first, proliferation of the cartilage cells 

 and a calcification of the ground substance, and then a de- 



FIG. 194. 



Cartilage cell^ !& 



Periosteum 



Perichon d ral. ^*>jt^.* 

 bone 



The place marked x in the preceding figure with stronger magnification. X 185. 



struction of this cartilage by the ingrowth of periosteal buds. 

 In long bones the marrow cavity increases in size by a gen- 

 eral breaking down of the calcified bone. 



The cartilage lying at both ends of the diaphysis shows 

 characteristic relations (Figs. 195 and 196). We may notice 

 in this several zones which are well marked off from one 

 another. The part most distant from the marrow cavity shows 

 no changes, containing spindle-shaped cavities with small cells. 

 The cells lying nearer the medullary cavity are larger and 



