388 GENERAL ANATOMY. 



but the hardening of the latter is retarded during the whole of 

 the time necessary for the reproduction of its vascular envelope. 



When things have thus occurred, i. e. when it is a new bone 

 that is formed, the separated piece has the same volume and 

 appearance as the original bone, presenting the same processes, 

 impressions, lines, and inequalities. 



Other pathologists, and in particular MM. Leville, Riche- 

 rand, and recently Dr. Knox,* maintain that in all cases, 

 the necrosis in question is confined to an internal portion of 

 the substance of the walls of the medullary canal, and that the 

 new bone simply results from the outer part of the original 

 bone which the necrosis has not affected, and which has only 

 undergone changes of volume and consistence. 



It is certainly so in many cases, and then the sequestrum 

 has a diameter sensibly less than the original bone, and its sur- 

 face is rough and uneven. 



The extremities of the long bones become affected with ne- 

 crosis, and are reproduced much less frequently than their bo- 

 dy. It is hot uncommon, however, to observe these pheno- 

 mena at the upper extremity of the humerus. They have also 

 been observed at the lower extremity of the bones of the fore- 

 arm. I have extracted from the interior of a new bone the 

 lower extremity of the tibia, which had become affected with 

 necrosis after a fracture which happened two or three years 

 previously. The articular cartilage was all that was wanting 

 at this extremity. 



The broad bones are also subject to necrosis, but their re- 

 production is rare or imperfect. The scapula, however, after 

 being affected with necrosis, has been seen to be replaced by 

 two other bones. 



Necrosis of the short bones is much more common than is 

 supposed. It commonly exists under the form of a seques- 

 trum inclosed at the centre of the bone. This constitutes many 

 of the alleged cases of caries of the bones of the tarsus, car- 

 pus, &c. 



* Edinburgh Medical and Surgical Journal, 1822 and 1823. 



