REPARATION OF BONE. 281 



Osseous tissue, though of a very imperfect kind, is often formed in the substance 

 of Fibrous tumors, by the calcification of their organic base ; and it is curious 

 that this should usually contain a very large proportion of calcareous matter, 

 as much as 81 per cent, having been found in a specimen transmitted to John 

 Hunter as a calculus, and the proportion of carbonate of lime being much 

 greater than in normal bone. Where perfected Osseous structure presents itself 

 in a Tumor, it is usually as an outgrowth from true Bone. It is curious, how- 

 ever, that the osseous plates not unfrequently found in the dura mater, possess 

 a structure (as pointed out by Mr. Tomes, loc. cit.) much more closely allied to 

 that of true bone, than that which presents itself in most adventitious forma- 

 tions of this kind ; and this seems related to the fact, that, in some of the lower 

 Mammalia, especially of the Carnivorous order, certain parts of this membrane 

 (the falx and tentorium) are normally ossified. 



270. The Regeneration of Bone, after loss of its substance by disease or 

 injury, is extremely complete; in fact, there is no other structure of so complex 

 a nature, which is capable of being so thoroughly repaired. Much discussion 

 has taken place, with respect to the degree in which the different membranous 

 structures, that surround bone and penetrate its substance, contribute to its 

 regeneration ; but the fact seems to be, that any or all these membranes may 

 contribute to the formation of new bone, in proportion to their vascularity the 

 new structure, however, being most readily produced in continuity with the old. 

 Thus, when a portion of the shaft of the bone is entirely removed, but the peri- 

 osteum is left, the space is filled up with bony matter in the course of a few 

 weeks ; though, if the periosteum also be removed, the formation of new osseous 

 matter will be confined to a small addition in a conical form to the two extremi- 

 ties, a large interspace being left between them. The production of new bony 

 tissue, in this experiment, as in cases where the periosteum has been detached 

 by disease, and remains alive while the shaft dies, is in continuity with minute 

 spicula of original bone, which still adhere to the membrane; and it is well 

 known that, in comminuted fractures, every portion of the shattered bone that 

 remains connected with the vascular membranes, whether these be internal or 

 external, becomes the centre of a new formation; the loss of substance being 

 filled up the more rapidly in proportion to the number of such centres. 



271. The most extensive reparation is seen, when the shaft of a long bone is 

 destroyed by disease. If violent inflammation occur in its tissue, the death of 

 the fabric is frequently the consequence; apparently through the blocking up of 

 the canals with the products of inflammatory action, and the consequent cessa- 

 tion of the supply of nutriment. It is not often that the whole thickness of 

 the bone becomes necrosed at once ; more commonly this result is confined to 

 its outer or to its inner layers. When this is the case, the new formation takes 

 place from the part that remains sound ; the external layers, which receive their 

 vascular supply from the periosteum, and from the Haversian canals continued 

 inwards from it, throwing out new matter on their interior, which is gradually 

 converted into bone; whilst the internal layers, if they should be the parts remain- 

 ing uninjured, do the same on their exterior, deriving their materials from the 

 medullary membrane, and from its prolongations into the Haversian canals. 

 But it sometimes happens that the whole shaft suffers necrosis; and as the 

 medullary membrane and the entire Haversian system have lost their vitality, 

 reparation can then only take place from the splinters of bone which may remain 

 attached to the periosteum, and from the living bone at the two extremities. 

 This is consequently a very slow process; more especially as the epiphyses hav- 

 ing been originally formed as distinct parts from the shaft, do not seem able to 

 contribute much to the regeneration of the latter. 



272. When the shaft of a long bone of a dog, rabbit, or bird has been fractured 



