BONE. 309 



Haversian canal, and its wall to constitute ultimately the 

 outer lamina of such canal. 



The arguments adduced in disproof of the opinion that the 

 nuclei of the cartilage cells become converted into bone cor- 

 puscles, apply with equal force against the idea of the calcifi- 

 cation of the walls of the cartilage cells. 



Bone Cells. Bone cells, then, according to the views of 

 the author, are not transformed nuclei of cartilage corpuscles, 

 but take their origin in distinct granular cells, which may be 

 clearly seen in the growing spiculae of bone dispersed amongst 

 the fibres in which the earthy matter of bone is first deposited, 

 and which at length become entirely imbedded in the earthy 

 deposition. 



As, however, it is most probable that a development of 

 bone cells and new laminaa of bone are ever in progress even 

 in adult bones, we should expect to encounter in the cancelli of 

 bones of every age fibres of cellular tissue and granular cells ; 

 both these do occur in them, and especially the latter, which 

 are met with in great numbers. 



These granular nucleated cells are more numerous in foetal 

 and young bones^than in those of older formation ; in the 

 former, indeed, they almost entirely fill up the cavities of the 

 cancelli : in the latter, although they are still numerous, their 

 place is supplied with fat vesicles, which are not present in 

 the former. 



It seems to me to be not improbable that two kinds of 

 granular cells may exist in the medullary spaces, &c., one 

 consisting of rudimentary bone cells, and the other connected 

 with the elaboration of the marrow, which occupies the me- 

 dullary cavity, medullary cells, and larger Haversian canals. 



It might be supposed that these granular cells were the 

 white corpuscles of the blood escaped from the ruptured 

 vessels, the red blood discs having been absorbed ; this no- 

 tion is, however, disproved by the fact that many of them 

 are much larger than the colourless corpuscles of the blood. 

 (See Plate XXXIII. fig. 5.) 



The existence of a granular blastema in the cancelli, &c. 



