278 



BONE OR OSSEOUS TISSUE. 



the osteoblasts are left behind as bone-corpuscles in lacunae, whilst others remain 

 surrounding the blood-vessels within the meshes. 



The question whether bone can be directly formed from cartilage by a transfor- 

 mation of the cartilage-matrix into osseous tissue, whilst the cartilage-cells become 

 bone-corpuscles (metaplastic ossification), is one which has been much discussed of 

 late years and can hardly as yet be said to be definitely decided. But although the 

 cells of a calcified cartilage in the neighbourhood of advancing ossification some- 

 times appear stellate and simulate bone- corpuscles, and the calcified fibrous matrix 



*> p p 

 Fig. 318. PART OF A TRANSVERSE SECTION OP A DEVELOPING LONG BONE, RATHER MORE ADVANCED 



THAN THAT REPRESENTED IN FIG. 313, AND UNDER A HIGHER MAGNIFYING POWER (E. A. S.). 



From a drawing by Mr. J. Lawrence. 



cb, endochondral hone which began as a calcification of the cartilage-matrix, parts of which still 

 remain (c) covered over by secondary osseous deposit ; o, secondary areolae, occupied by vessels, foetal 

 marrow, and osteoblasts ; pb, periosteal bone deposited in the form of irregular trabeculas, prolonged 

 externally by bony spicules passing into bunches of osteogenic fibres. These, which are everywhere 

 covered with osteoblasts, become lost in the external fibrous layer of the periosteum, p ; bl, bl, blood- 

 vessels variously cut. 



Fig. 319. LONGITUDINAL SECTION THROUGH THE PERIOSTEAL THICKENING OP A BONE AT ABOUT THE 

 SAME STAGE OF DEVELOPMENT AS THAT REPRESENTED IN FIG. 313. From a drawing by Mr. J. 

 Lawrence. (E. A. S. ) 



c, cartilage with the cells in rows ; the tissue of the periosteal thickening is sharply marked off from 

 it except near the surface ; p, outer layer of the periosteum ; i, p, inner layer of the periosteum or 

 subperiosteal tissue, with osteogenic fibres, and osteoblasts. One or two blood-vessels are observed cut 



of the cartilage may in like manner simulate osseous tissue, there is not sufficient 

 evidence to show that true lamellar bone is formed in any other way than through 

 the agency of osteoblasts. 



The first formed bony tissue is different in its general appearance from the bony 

 tissue of the adult, being reticular and not regularly lamellar, and, for a long while, 

 even the shafts of the long bones are rather cancellated, than compact in their 

 texture. The more obviously lamellated condition does not begin to appear until 

 about the sixth month after birth, when the periosteum deposits a succession of 

 entire lainellse around the embryonic bone. The blood-vessels which pass from 



