OH. V.] 



DEVELOPMENT OF BONE. 



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 cartilaginous 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 original cartilage can be present 



Fig. 88. Part of the growing: edge of the developing parietal bone of a foetal cat. sp, 

 bony gpicules with some of the osteoblaats imbedded in them, producing the lacunae ; 

 o/, oirteogenic fibres prolonging the spiculea with oateoblaste (ost) b?tween them and 

 applied to them. (O. Lawrence.) 



in the femur of the adult. Its purpose is indeed purely tem- 

 porary ; and, after its calcification, it is gradually and entirely 

 absorbed. 



The cartilaginous rod which forms the precursor of a foetal long 

 bone is sheathed in a membrane termed the perickondrium, which 

 exactly resembles the periosteum described above ; it consists of 

 two layers, in the deeper one of which spheroidal and branched 

 cells predominate and blood-vessels abound, while the outer layer 

 consists mainly of fibres. 



Between the cartilaginous prefigurement of which the foetal 

 K.P. 



