96 



HUMAN ANATOMY. 



irregular trabeculae of the calcified cartilage, bring about, through the influence of 

 their protoplasm, the deposition of a layer of bone-matrix upon the surface of the 



Fig. 126. 



Embryonal 

 cartilage 



Young periosteum 



Cartilage-cells becoming en- 

 larged and grouped 







Zone of calcification 



Osteogenetic layer of perios- 

 teum 



Central spongy bone en- 

 closing remains of carti- 

 lage 



Longitudinal section of metatarsal bone of foetal sheep, showing stages of endochondral bone-development, X 40, 



trabeculae, which thus becomes enclosed within the new bone. After the latter has 

 attained a thickness of at least the diameter of the osteoblasts, some of the cells in 

 closest apposition are gradually surrounded by the osseous matrix (Fig. 127), until, 



