OSSIFICATION IN CARTILAGE 4? 



Stage of Proliferation and Calcification. The cartilage cells in and near 

 the center of ossification become enlarged, proliferate, and arrange them- 

 selves in rows in the long axis of the fetal cartilage, figure 57. Lime salts are 

 next deposited in fine granules in the hyaline matrix of the cartilage, and this 

 gradually becomes transformed into calcified trabeculae, figure 57. The en- 

 larging cartilage cells become more transparent, and finally disintegrate, 

 the spaces occupied by them forming the primordial marrow cavities. During 



FIG. 57. Developing Bone of Femur of the Rabbit. (Schafer, from Klein.) X 35- a, 

 Cartilage cells; b, cartilage cells enlarged in the region of calcifying matrix; c, d, trabeculae of cal- 

 cifying cartilage covered- with e, osteoblasts; /, osteoclasts eroding the trabeculae; g, h, disappear- 

 ing cartilage cells. The osteoblasts are seen to be depositing layers of bony substance. Loops 

 of blood-vessels extend to the limit of the region in which the bone is forming. 



this stage the perichondrium has become the periosteum, and is beginning 

 to deposit bone on the outside of the cartilage. 



Stage of V ascularization of the Cartilage. Processes from the osteo- 

 genetic layer of the periosteum containing blood-vessels break through the 

 bone into the primordial marrow cavities and form the primary marrow, 



