OSSIFICATION IN CARTILAGE. 



277 



cartilaginous continues to grow at the same time, increasing in every dimension. 

 The part already osseous increases also in circumference ; fresh bone being 

 continually deposited in the subperiosteal membranous tissue outside that which 

 is first formed on the surface of the cartilage (figs. 313, 318). The subperiosteal 



Fig. 316. SMALL PORTION OF A SECTION OF DEVELOPING BONE, TAKEN AT THE JUNCTION OF THE 



BONE AND CARTILAGE, AND EXAMINED IN THE FRESH CONDITION. MAGNIFIED ABOUT 140 DIAMETERS. 



(Sharpey.) 



a, b, two of the new-formed osseous tubes or areolse, with a few shrunken cartilage- cells lying in them ; 

 c, cartilage-cells near the ossifying surface, large and clear and filling the cavities in the matrix ; on the 

 left of the figure some of them are shrunken. 



Fig. 317. PART OF A LONGITUDINAL SECTION OF THE DEVELOPING FEMUR OF THE RABBIT. DRAWN 

 UNDER A MAGNIFYING POWER OF 350 DIAMETERS (from Klein and Noble Smith). 



a, rows of flattened cartilage-cells ; 6, greatly enlarged cartilage-cells close to the ad Dancing bone, the 

 matrix between is partly calcified ; c, d, already formed bone, the osseous trabeculje being covered with 

 osteoblasts (e), except here and there, where a giant-cell or ostoclast (/), is seen, eroding parts of the 

 trabeculae ; g, h, cartilage-cells which have become shrunken and irregular in shape. From the middle of 

 the figure downwards the dark trabeculae, which are formed of calcified cartilage matrix, are becoming 

 covered with secondary osseous substance deposited by the osteoblasts. The vascular loops at the extreme 

 limit of the bone are well shown, as well as the abrupt disappearance of the cartilage-cells. 



deposit takes place in the same way as in the formation of a membrane bone. Bony 

 spicules prolonged by bunches of osteogenic fibres (fig. 318) project out from the 

 previously formed layer, into the intervals between the blood-vessels. By the union 

 of the spicules the vessels become in like manner enclosed in channels whose walls 

 are gradually thickened by deposits of osseous substance, between which some of 



