TISSUES OF THE BODY. 



257 



It is hardly necessary to add that eacli newly formed ring must be 

 larger than the older one formed before it. And the growing bone also 

 becoming lengthened, each of these osseous tubes is likewise longer than 

 the preceding. 



The importance of the periosteum in the formation of bone has been 

 further proved by Oilier through a series of remarkable experiments. 

 Detached portions of this membrane, whether still in connection with 

 the remainder of the structure or completely separated from it, have the 

 power of generating again a complete bone; and not only in this case, 

 but even when transplanted to other parts of the body, or from one 

 animal to a second of the same species. But the deeper layer of the 

 periosteum must be carefully preserved in doing this, a precaution which 

 we will presently understand. 



If we now turn to the histology of the process (fig. 248), we must first recall 

 to mind the structure of the 

 fibrous periosteum (p. 226), 

 which is more vascular at an 

 early period than later on. 

 The latter consists internally 

 (Blasteme sous- -periosi 'ale of 

 Oilier) of a mass of young 

 connective-tissue, not fibrous, 

 but formed of fusiform and 

 stellate ceils ( b). Under this 

 appears the stratum, of Gegen- 

 baur's osteoblasts (c), which 

 generate the osseous tissue 

 here, as in the interior of cal- 

 cified cartilage, and in the 

 same manner. Both pro- 

 cesses, the intracartilaginous 

 as well as the periostea!, are 

 therefore identical. The 

 newly-formed bone (tig. 248, 

 c) is irregular, and jagged 

 towards the still soft external 

 layers, and is traversed in 

 the interior by sinuses, giving 

 it a spongy texture. These 

 are filled with medullary 

 cells, and covering the latter 

 with osteoblasts, and become 

 eventually Haversian canals. 

 Thus the osteoblasts, as in 

 the intracartilaginous formation of bone, give rise also to the production 

 of the special lamellae of the Haversian passages (a). Bundles of connec 

 tive-tissue which penetrate this new layer of bone ossify immediately, 

 and are known later as Sharpens fibres ( 142). 



During all this, however, the secondary formation of the great medul 

 lary cavity introduces new changes into the young osseous tissue. When 

 we remember the large dimensions of the former, it is easy to conceive the 

 great quantity of the latter which must undergo re-solution in its produc- 

 tion. 



Fig. 248. Formation of secondary bone. Longitudinal 

 section of the femur of a well-grown foetal sheep. , 

 the internal layer of the periosteum, consisting of con- 

 nective-tissue; 6, younger stratum, or Oilier 's layer of 

 the periosteum ; c, layer of osteoblasts ; d, newly-formed 

 osseous tissue; e, lacunae and cells. 



