THE STRUCTURE AND ECONOMY OF BONE. 67 



dary cartilage corpuscules remaining as centres, or the sources of 

 new centres of nutrition, of the future bone, their progeny form- 

 ing the cellular mass which becomes enclosed in the capsules of 

 compact primary bone. When these capsules have opened into 

 one another to form the haversian canals, a process similar to the 

 mode of developement of gland ducts, and capillaries, the cellu- 

 lar mass surrounds the vessels in their course, and separates them 

 from the walls of the canals. 



That this cellular layer plays an important part in the economy 

 of bone, appears probable from the prominent position it holds in 

 its developement, and from the intimate connection of the haver- 

 sian canals with all the morbid changes of bone. Its existence, 

 great extent, and probable powers, cannot be overlooked in any 

 question regarding the economy of bone in health or disease. 



The cellular mass, just described, fills the cancelli, or enlarged 

 haversian chambers, of foetal bones, and, in this situation, has not 

 been overlooked by former observers. In adult bones, it is in the 

 medullary cavity, cancelli, and, to a certain extent, in the larger 

 haversian canals, replaced by fat cells. 



On the surface of young and vigorous bones I have observed 

 numerous cells, flattened, elongated, and more or less turgid, 

 belonging doubtless to the system of haversian cells. 



J. G. 



