46 THE CONNECTIVE TISSUES [CH. v - 



produced, form bone corpuscles. On the bony trabeculse first formed, 

 layers of osteoblastic cells from the osteogenetic layer of the perios- 

 teum repeat the process just described ; and as this occurs in several 

 thicknesses, and also at the edges of the spicules previously formed, 

 the bone increases, both in thickness, length and breadth. The pro- 

 cess is not completed by the time the child is born ; hence the fonta- 

 nelles or still soft places on the heads of infants. Fig. 60 represents 

 a small piece of the growing edge of a parietal bone. 



FIG. 60. Part of the growing edge of the developing parietal bone of a foetal cat. sp, Bony spicules with 

 some of the osteoblasts imbedded in them, producing the lacuna 1 ; of, osteogenetic fibres prolonging 

 the spicules with osteoblasts (ostj between them and applied to them. (Schafer.) 



The bulk of the primitive spongy bone is in time converted into 

 compact bony tissue, with Haversian systems. Those portions in the 

 interior not converted into bone become filled with the red marrow 

 of the cancellous tissue. 



Ossification in Cartilage. Under this heading, taking the femur 

 or any other long bone as an example, we have to consider the process 

 by which the solid cartilaginous rod which represents the bone in the 

 foetus is converted into the hollow cylinder of compact bone with 

 expanded ends formed of cancellous tissue of which the adult bone is 

 made up. We must bear in mind the fact that this foetal cartila- 

 ginous femur is many times smaller than even the medullary cavity 

 of the shaft of the mature bone, and, therefore, that not a trace of the,- 



