Royal Society. 471 



is usually 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 invested 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 cell 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, and 

 through the agency of which the absorption has been m all probability 

 effected. It would appear as though the cells grew at the expense 

 of the surrounding 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 

 absorbed spaces, or on the surfaces, or in the membranes of the fcEtal 

 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 

 which they lie, become impregnated with ossific matter, and perma- 

 nently fused with the bone tissue with which they lie in contact. 

 By the linear arrangement of these osteal cells lamination is pro- 

 duced. In the case of non-laminated bone the cells are simply os- 



* The views here brought forward of the removal and replacement of tissue 

 tlirougli the agency of cells arc, so far as the authors know, entirely new ; and 

 may have an important bearing on many iioints of physiology and pathology. 

 Indeed, this is perhaps the first time that the fact (which has been generally 

 assumed) of the entire absorption of tissue in the processes of nutrition, and its 

 replacement by new tissue, has been demonstrated. 



