207 



The granular condition of the intercolumnar tissue and of the ceil 

 itself often renders the observation of this stage very difficult ; but 

 in rfckety bone it is very readily shown, as in this disease there is a 

 tendency for the cells to assume their permanent form before the 

 deposit of bone-earth in any considerable quantity. To cells thus 

 composed of an outer thickened cell wall and an inner granular cell 

 (the cartilage nucleus of authors) which contains within it a nucleus 

 (the nucleolus of writers), v/hich stands in the relation of a nucleus 

 to the future lacuna, the authors have given the name of " lacunal 

 cells," while the term granular cell has been applied to that which 

 is us^ually designated the nucleus. In transverse sections of bone 

 immediately below the line of ossification, the lacunal cells may be 

 seen presenting different characters under different circumstances. 

 Where two cells come into contact, the processes or canaliculi may 

 be seen extending across from one to the other ; but where the cell 

 is surrounded by intercolumnar tissue, the processes are short and do 

 not extend beyond the walls of their own cell ; or if cells join at one 

 point while the remainder is inverted with intercolumnar tissue, the 

 canaliculi will anastomose at the point of junction ; while elsewhere 

 they are few, short, and do not extend beyond the cell. 



In the further process of development the cells and intercolumnar 

 tissue become fused together so as no longer to be recognised as 

 distinct parts ; and the granular ceil appears as a perfect lacuna with 

 a large cavity and numerous large canaliculi. To bone in this con- 

 dition the term primary bone has been applied. It speedily however 

 undergoes a change preparatory to the formation of the more per- 

 manent secondary bone. Here and there in the line of ossification 

 portions are removed by absorption, the spaces left being filled with 

 small somewhat granular cells lying in a transparent blastema, through 

 the agency of which the absorption has been in all probability effected. 

 It would appear as though the cells grew at the expense of the sur- 

 rounding tissue. These spaces correspond entirely to the Haversian 

 spaces before described ; and in them the secondary bone is in the 

 first instance formed. The process of formation of secondary bone 

 appears to be everywhere- essentially the same, whether in the ab- 

 sorbed spaces, or on the surfaces, or in the membranes of the foetal 

 cranium, except that in the two latter cases there is a pre-existing 

 fibrous tissue, which, before ossification begins, undergoes a change 

 similar to that which occurs in the bone itself and is converted into 

 a cellular mass. So that at the border where ossification is advan- 

 cing there is only an arrangement of cells ; while a little beyond 

 that point the cells have fibrous tissue abundantly mixed up with 

 them ; and there is in fact a resemblance to fibrous tissue in an early 

 state of formation. The formation of perfect bone is effected by 

 means of cells, perhaps identical with those which are found repla- 

 cing the previous tissue, but at all events undistinguishable from 

 them by any microscopical characters. To these cells, which take 

 part in the formation of bone, the authors have given the name of 

 *' osteal cells." In the case of laminated bone they arrange them- 

 selves side by side, and, together with the transparent blastema in 



