324 ' SPECIAL HISTOLOGY. 



§ 105. Elementary 2it"ocesses in the Layers formed from the Perios- 

 teum. — The periosteum of the priiuarilj cartilaginous bones, is propor- 

 tionally very thick and vascular, consisting, as early as at the fifth 

 month, of common connective tissue and fine elastic filaments, the latter 

 of which in process of time become stronger and stronger, occasionally 

 assuming the nature of elastic fibres. On the inner aspect of this fully 

 formed periosteum, there is now deposited an ossific blastema firmly ad- 

 herent to the bone (Fig. 133, B) ; so that when the periosteum is re- 

 moved, it generally remains upon it as a moderately thick, soft, whitish 



yellow lamella, in which, microscopic ex- 

 amination shows the existence of a fibrous 

 tissue, with a not particularly distinct 

 fibrillar formation, something like imma- 

 ture connective tissue, and granular, oval, 

 or round nucleated cells, measuring 0-006 

 -0*01 of a line. When this lamella is 

 raised from the bone, it is found to be 

 very intimately connected with the most 

 superficial layers, and on its internal sur- 

 face a few little detached fragments of 

 bone, and scattered masses of reddish, soft medulla, from the most su- 

 perficial cancellar spaces, will be observed. The bone thus laid bare, 

 when the removal of the periosteal layer has been carefully conducted, 

 presents a rough, and as it were porous surface, with numerous medul- 

 lary spaces, and remains, superficially, in spots of greater or less extent, 

 quite soft, pale-yellow, and transparent, whilst more internally it becomes 

 firmer and whiter, ultimately acquiring the usual appearance of perfect 

 osseous tissue. When it is inquired, how the formation of bone, which 

 indubitably takes place in this situation, is effected, we refer to the blas- 

 tema just described, the cells of which, scattered in the fibrillated con- 

 nective tissue, have not the least resemblance to those of cartilage, but 

 appear exactly like the foetal medulla-cells, or formative cells of the 



Fig. 133. — Transverse section from the surface of the shaft of the metatarsus of the Calf; 

 magnified 45 diam. : j1, periosteum : B, ossifying blastema ; C, young layer of bone, with 

 wide cavities, a, in which are lodged remains of the ossifying blastema, and reticular spi- 

 culse, b, which towards the blastema present a tolerably abrupt border; D, more developed 

 layer of bone, with Haversian canals, c, which are surrounded by their lamellae. 



distinct bodies, we must call to mind the fact already referred to, that in cartilage, the wall 

 of the cavities have frequently undergone less change than, or a different change from, the 

 surrounding matrix; and therefore appear both optically and chemically distinct, though 

 they are by no means so, morphologically: and, therefore, that there is no difficulty in sup- 

 posing the same thing to occur in bone. The chemical diiierentiation of the wall of the 

 lacuna is, in fact, exactly comparable to that of the wall of the cavity which contains the 

 " nucleus" in connective tissue, and in fibro-cartilage ; and which gives rise to the formation 

 of the elastic element in those tissues. — Trs.] 



