THE BONES AND JOINTS. 



733 



On the other hand, there may be irregular branching channels through 

 the bone across the lamellae, which appear to be due to the enlargement 

 and coalescence of the lacunas and caualiculi, without the direct influence 

 of blood-vessels or other cells than the fixed cells of the bone. 



The tissue which replaces the absorbed bone may be very rich in 

 small spheroidal cells, or it may be more or less fibrillar. 



As a result of this process irregular islets of bone tissue may be 

 entirely separated from adjacent bone and surrounded by a more or less 



> I 



*,<&-', :':'^j ;?:.. ..:,--;:-;-}ffr_ ** 





FIG. 485. RAREFYING OSTEITIS IN ULNA OF CHILD. 

 o, Isolated bone fragment with rough edges ; b, marrow tissue; c, Howship's lacunae with osteoclasts. 



fibrillar vascular tissue ; this is most apt to occur in the cancellous tissue. 

 Or the originally compact bone may become traversed by a series of larger 

 and smaller irregular branching, communicating channels with ragged 

 walls. These progressive alterations may cease, and be succeeded by a 

 new formation of bone along the edges of the channels or cavities. 



Earefyiug osteitis may occur as an independent process from unknown 

 causes; it is often associated with scrofula, with diseases of the joints, 

 with fractures or other injuries to the bone ; it often forms a predominant 

 feature in tuberculous inflammation of the bones. It is chiefly by a 

 rarefying osteitis that bone tissue is eroded and destroyed in the vicinity 

 of tumors, aneurisms, etc., which exert pressure on the bones. By the 

 same process the sharp ends of fractured bone may be rounded off as 

 healing proceeds. 



"When this form of inflammation occurs in cancellous bone tissue the 

 marrow is red or gelatinous, and the bony septa may disappear altogether, 

 so that in extreme cases there may be, instead of cancellous bone, a mass 

 of granulation tissue. When the process occurs in the articular extrem- 

 ity of a bone the granulating medulla may send little offshoots through 

 the articular cartilage. These may become fused together and iuflam- 



