FORMATION OP CALLUS AFTER FRACTURE. 485 



is shivered, a number of little medullary spaces are 

 naturally opened. In the neighbourhood of these, the 

 still closed medullary spaces are seen nearly invariably, 

 when matters follow a regular course, to become filled 

 with callus, new lamellae of bone attaching themselves to 

 the internal surface of the osseus trabeculae which bound 

 the spaces, just as in the ordinary growth of bone in 

 thickness, the originally pumicestone-like layers become 

 compact by the deposition of concentric lamellae. In 

 this manner it happens, that after some time a larger 

 or smaller new layer of bone is found, filling up the end of 

 the medullary canal of each fragment, so as to occasion its 

 occlusion. This is a kind of a new formation which has 

 nothing in common with the former one, as far as their 

 starting points are concerned, but has its origin in quite 

 another tissue, and is altogether different in its palpable 

 result, inasmuch as it produces, within the confines of 

 its own bone, a condensation of that portion of the mar- 

 row which lies in the immediate vicinity of the fracture. 

 Even in cases where the ends of the bones perfectly co- 

 incide, an internal formation of bone such as I have 

 described takes place in the medullary canal of each 

 fragment, producing its occlusion. 



These two kinds are the usual and normal ones. 

 Around the two fractured ends the swelling takes place, 

 in the interior, the condensation. Gradually, in pro- 

 portion as the extravasated blood is absorbed the new 

 masses of tissue which have been developed between 

 the broken ends draw nearer to one another, and round 

 about the fracture forms a bridge- or capsule-like com- 

 munication by means of the ossification of the soft parts. 

 There is therefore- but little reason to ask whether the 

 callus proceeds from free exuded. or extravasated ma,t- 

 ter. No doubt an extravasation takes place in the first 

 instance into the space between the fractured ends, but 



