470 ANATOMICAL AND PATHOLOGICAL OBSEKVATIONS. 



new bone will also depend very much upon the same circum- 

 stances ; for, if the centres of formation of the new shaft are 

 separated from one side only of the old bone, then an un- 

 shapely mass of new bone is thrown out on the same side, 

 for the purpose of strengthening the part during the time 

 necessary for shooting across the bridges of bone which are to 

 supply that side of the new shaft, for the formation of which 

 no osseous centres had been separated. Every possible modi- 

 fication, resulting from these principles, may be observed in 

 looking over series of necrosed long bones. 



A remarkable fact in connection with cloacae is, that they 

 are almost invariably opposite a smooth or unaltered portion 

 of the surface of the dead shaft. They result from the pus 

 thrown off from the granulating internal surface of the new 

 shaft making its way to the exterior by those parts not yet 

 closed, in consequence of having been opposite to portions of 

 the old shaft, which had not afforded separated osseous 

 centres. After the new shell has gained its full strength the 

 cloacae, like sinuses of the soft parts, are prevented from closing 

 by the continued flow of the pus. The situation of cloacse is 

 determined by circumstances in the death of the old, and kept 

 open by the continued flow of the secretions of the new shaft. 



As, therefore, it has been found impossible to separate the 

 periosteum in living animals without detaching shreds of bone 

 along with it as in necrosis of the shafts of long bones, por- 

 tions of the old osseous texture may be detected in the 

 periosteal sheath opposite ulcerations of the dead shaft and 

 as consistent with what is at present held regarding the 

 powers of capillary vessels, and the origin of the textures, we 

 are compelled to assent to the doctrine that periosteum does not 

 possess an independent power of forming osseous substance. 



The participation of the periosteum in the office of regene- 

 ration an important principle in surgery is not denied in 

 this conclusion. 



