DISEASES OP BONES 165" 



there may be a fibrous capsule, -wliicb after some time may 

 secrete a serous fluid for lubrication of tbe broken ends of the 

 bone, -wbich. may be smooth, and eburnated and possibly- 

 covered by hyaline cartilage, in this instance forming a new 

 joint. 



Describe the process of ossification of a callus. 



The ossification of the granulation is either a direct or- 

 indirect one. The former is the result of direct ossification 

 by the osteoblasts of the periosteal and myeloginous granula- 

 tion tissue (the embryonic tissue following inflammation of 

 the periosteum and marrow). In the indirect process of" 

 ossification of the granulation tissue, this latter first becomes, 

 cartilage, which in turn becomes bony tissue. About the 

 third or fourth day after the fracture occurs, little foci of 

 osteoid tissue exhibit themselves at the point of fracture (due< 

 to the action of osteoblasts). In the second week the external, 

 callus is still soft ; by the end of the third week the periosteal, 

 callus consists of pretty firm, spongy bone. The internal- 

 callus undergoes the same changes. 



In four to five weeks the provisional callus begins to- 

 be converted into a permanent cicatrix (permanent callus), 

 the superficial and deeper portions of the provisional callus 

 become absorbed — mainly by the action of the osteoclasts ; 

 finally, the medullary cavity of the bone is more or less 

 restored and the surface of the bone shows but little of the 

 large ovoid mass, the original callus. 



How is the regular callus formation interfered with 9 



By constitutional diseases, as osteoporosis, osteomalacia,, 

 infectious diseases, by marked displacement of the bony frag- 

 ments, infection of the tissues at the point of fracture, decided: 

 splintering of the bone ; by the lodging of soft tissues between. 



