362 



SPECIAL HISTOLOGY. 



(fig. 133, B) ; so that when the periosteum is removed, 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 particu- 

 larly distinct fibrillar formation, 

 something like immature connec- 

 tive tissue, and granular, oval, or 

 round nucleated cells, measuring 

 0-006— 0-01'". 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 surface 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 medullary 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 blastema just 

 described, the cells of which, scattered in the fibrillated connec- 

 tive tissue, have not the least resemblance to those of carti- 

 lage, but appear exactly like the foetal medulla-cells, or forma- 

 tive cells of the embryo. In fact, it is now, not difficult to show, 

 that the outermost, still soft bone-lamellse pass into the blastema 

 in question, with their separate spiculse and projections, and 

 that (1.) the matrix of the bone arises from its fibrous tissue, 

 by the simple uniform deposition of calcareous salts, although 

 usually, as it seems, without the previous appearance of cal- 

 careous granules ; and (2.) that the bone-cells are formed out of 



Fig. 133. Transverse section from the surface of the shaft of the metatarsus of 

 the Calf, x 45 diam.: A, periosteum ; B, ossifying Diastema; C, young layer of bone, 

 with wide cavities, a, in which are lodged remains of the ossifying blastema, and 

 reticular spiculae, 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 lamella;. 



