60 THE ESSENTIALS OF HISTOLOGY 



fibres are covered with osteoblasts, and as the bone forms, some of 

 these become left as bone-corpuscles within lacunae. Thus in every 

 particular the development of these bones resembles that of the sub- 

 periosteal layer of endochondral bone, which is also to be considered 

 as an instance of intramembranous ossification, although taking place 

 on the surface of cartilage. Moreover, it is the same subperiosteal 

 tissue which deposits the true or secondary bone upon those parts 

 of the calcified cartilage -matrix which have escaped absorption ; and 

 this must also, therefore, be reckoned as developed according to the 

 same type. In fact, even in intracartilaginous ossification, very little 

 of the calcified cartilage-matrix eventually remains ; this being almost 

 wholly replaced by true or fibrous bone which has been formed by 

 osteoblasts. 



