82 



CONNECTIVE TISSUE CARTILAGE BONE 



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Primordial Mar- 

 row ('a cities. The 

 absorption of the 

 cartilage matrix re- 

 sults in the forma- 

 tion of broad spaces 

 into which osteo- 

 genic buds of prim- 

 itive marrow tissue 

 push their way from 

 the perichondrium. 

 Thus the primordial 

 marrow cavities are 

 formed. The fetal 

 marrow which now 

 occupies these cav- 

 ities is derived from 

 the osteogenic layer 

 of the primitive peri- 

 osteum. The oste- 

 ogenous tissue of this 

 layer, containing os- 

 teoblasts, osteoclasts, 

 a n d developing 

 blood-vessels, grows 

 into the cartilage in 



the form of budlike 

 cords which are pre- 

 ceded by absorption 

 of the adjacent car- 

 tilage matrix. This 

 so-called 'eruptive 

 tissue promptly 

 reaches the center of 

 ossification 411 d bur- 

 rows its way into the 

 enlarged cartilage 

 lacunas whose cells are now replaced by jirimari/ osteogenic marrow. The 

 destruction of cartilage is initiated and maintained by agency of the 

 osteogenic tissue, presumably through specific cells, the so-called clion- 



FIG. 93. RECONSTRUCTION OF CARTILAGE INTO BONE. 



car. c., cartilage cells in successive stages of degenera- 

 tion; ost, osteoblasts; gi. c., giant cells (osteoclasts); 6, 

 young bone; bl. c., blood cells. (From Dahlgren and 

 Kepner.) 



