82 FEACTUKES AND DISE^.SES OF BONES. 



and togetlier constituting the provisional callus. The external 

 ring, embracing both fragments, and the plug, within the 

 medullary canal, constitute nature's provision for keeping the 

 fragments in apposition and at rest. The substance between the 

 fragments is, during this stage, changed into fibro-cartilage. 



In the fourth stage, extending to the fifth or sixth month, it 

 is converted into bone, constituting the permanent or definitive 

 callus. 



In the fifth stage, extending from the fifth or sixth month to 

 the tenth or twelfth, the provisional callus, being no longer 

 necessary, disappears, and the medullary canal is restored. 

 Such are the views of Dupuytren ; and such is the method by 

 which fractures are repaired in the lower animals. The only 

 exceptions which I have observed, have been the union of 

 fractures of the lower maxillary bone, when the fracture has 

 been longitudinal, and bound so firmly as to admit of no motion 

 whatever between the fragments. Doubtless, the fractures of 

 our patients would unite, as those of the bones of the human 

 being, by the reparative material being thrown out between the 

 broken ends — that is, by intermediate or permanent callus — pro- 

 vided the parts could be kept in a state of complete repose ; but 

 this being impossible, nature has provided a method by which 

 they are held in a state of quietude, until the permanent callus 

 is finally deposited between the broken fragments. 



The latter part of the process of repair is that of the shaping 

 and the modelling of the fragments and their bond of union. 

 These consist of — (1.) The removal of sharp projecting points 

 and edges from the fragments ; (2.) The closing or covering of 

 the exposed ends of the medullary tissue ; (3.) The formation 

 of a compact external wall and cancellous interior for the new 

 bone ; and (4.) The making of these continuous with the walls 

 and cancellous tissue of the fragments. The first is effected by 

 the absorption of the offending points and angles, and in the 

 absorption of bone the earthy matters are first removed. The 

 closing or covering of the parts of the broken medullary tube, 

 which are exposed in fractures with much displacement, is 

 slowly accomplished by the formation of a thin layer of com- 

 pact tissue similar to that which covers the cancellous tissue at 

 the articular ends of bones. 



The callus, before ossifying, may become, according to Paget, 



