OSSIFICATION IN CARTILAGE 



49 



thelium-like layer on the calcified trabeculae and deposit a layer of bone, 

 and ensheath them. The encased trabeculae are gradually absorbed by 

 the osteodasts of Kolliker. 



These stages are precisely similar to what goes on in the growing shaft 

 of a bone which is increasing in length by the advance of the process of ossifi- 



/c, 



sv. 



FIG. 58. Transverse Section through the Tibia of a Fetal Kitten, semidiagrammatic. 

 X 60. P, Periosteum. O, Osteogenetic layer of the periosteum, showing the osteoblasts 

 arranged side by side, represented as pear-shaped black dots on the surface of the newly 

 formed bone. B, The periosteal bone deposited in successive layers beneath the peri- 

 osteum and ensheathing E, the spongy endochondral bone; represented as more deeply 

 shaded. Within the trabeculse of endochondral spongy bone are seen the remains of the 

 calcined cartilage trabeculae represented as dark wavy lines. C, The medulla, with V, V, 

 veins. In the lower half of the figure the endochondral spongy bone has been completely 

 absorbed. (Klein and Noble Smith.) 



cation into the intermediary cartilage between the diaphysis and epiphysis. 

 In this case the cartilage cells become flattened and, multiplying by division, 

 are grouped into regular columns at right angles to the plane of calcification 

 while the process of calcification extends into the hyaline matrix between 

 them. 



