254 



MANUAL OF HISTOLOGY. 



whole life through. Others again, it is supposed, become filled with 

 neutral fats after increasing in size, thus constituting the fat-cells of the 

 yellow medulla eventually (e). This last view, however, requires con- 

 firmation. 



But other of these cells have a higher destiny : they become the gene- 

 rators of the osseous tissue. H. Miiller supposed this to take place imme- 

 diately, the roundish lymphoid cell becoming transformed into a bone- 

 cell; but Gegenbaur recognised an intermediate form, a modification of 

 the medullary cell, to which he gave the name "osteoblast" (figs. 245, 246). 

 There is but little difficulty in recognising that the irregular medullary 

 cavities are lined by these cells in a manner similar to the arrangement of 



epithelium (fig. 245, c). 

 Crowded together (fig. 246, 

 I, 6), round, polygonal, or 

 more or less cylindrical in 

 form, with single or mul- 

 tiple nucleus, and consider- 

 able variation as to size, 

 these osteoblasts secrete 

 externally a thin layer of 

 a homogeneous opalescent 

 matter, which covers the 

 internal surface of the un- 

 dulating walls of the cavity 

 (fig. 245, d), or a part of 

 their membraneless body 

 may be continuous with 

 this substance. Both these 

 views have found defend- 

 ers. For the last Waldeyer 

 has entered the lists, fol- 

 lowed byRottettand Stieda; 

 and for the first, Gegenbaur, 

 Landois, Koelliker. We 

 must declare ourselves in- 

 clined to look on Gegen- 

 baur 's interpretation of the 

 appearances presented as 

 the more correct, although 



245. Transverse section from the femur of a human 

 embryo of about eleven weeks old. a, a medullary sinus 

 cut transversely, and 6 another longitudinally; c, osteoblasts; 

 a, newly-formed osseous substance of a lighter colour; e that 

 C greater age;/, lacunae with their cells; a, a cell still 

 united to an osteoblast. 



.. . . 



we do not regard the difierence of views as anything essential. 



But this layer of osteoblasts supplies not only the material for the 

 ground-substance of the osseous tissue, but the cells of the latter like- 

 wise. Advancing from the ranks of these osteoblasts, either single and 

 entire cells or parts of the same sink themselves into the newly-formed 

 lamella (fig. 245, g,f, fig. 246, c), where they may be recognised in everv 

 stage of growth up to the stellate form, on assuming which they are not 

 untrequently connected by means of their processes with contiguous cells. 



Hey are, however, larger and poorer in ramifying processes than the 

 structures of a later period. 



These processes are repeated over and over again. On the completion 

 ol the first homogeneous lamella with its contained cells, there follows 



tt Y?^ with new Cell3 > and so on > and the 



thicker and thicker, assuming a laminated appearance i 



n conse- 



