Magnified 20 diameters. 

 Perpendicular section of the ossifying margin 

 of the shaft of the femur of a child, two weeks 

 old. a, cartilage and its cells ; b, margin of 

 ossification ; the dark stripes represent the ossi- 

 fication of the intercellular substance, which 

 precedes that of the cartilage cells indicated by 

 the lighter portions ; c, compact osseous layer 

 near the ossifying margin ; d, spongy substance 

 with cancelli e, formed by the absorption of 

 the bony substance. 



Magnified 300 diameters. 



Section of the margin of ossification of the condyle of the femur o f 

 a child two years old, affected with rickets, a, cartilage-cells, single 

 and multiplying, in series ; b, c, more or less striated intercellular 

 substance ; d, cartilage-cells at the very commencement of their 

 conversion into bone-cells ; e, the same in a more advanced state, 

 with greatly thickened walls, indications of the canaliculi, and 

 commencing deposition of calcareous salts in the walls, hence their 

 darker colour, the nuclei still distinct ; /, still more developed and 

 ossified bone-cells imbedded in the intercellular substance g, which 

 is also becoming ossified. 



or incineration, the organic substance or 

 cartilage may be separated. 



In the development of bone, a temporary 

 cartilage closely resembling the permanent 

 cartilages in structure and chemical compo- 

 sition is usually first formed, and in this the 

 inorganic matter is subsequently deposited ; 

 in a few instances, however, a soft blastema, 

 consisting of areolar tissue, with nucleated 

 cells, is substituted for the cartilage. The 

 process of ossification commences at one or 

 more points in the internal portions of the 

 temporary cartilage ; these are called the 

 centres of ossification. Just before the 



deposition of the earthy matter takes place, 

 the cells of the cartilage multiply by endo- 

 genous cell-growth. The earthy or inorganic 

 matter is then deposited in a finely granular 

 form, and first in the intercellular substance ; 

 so that in a section of ossifying cartilage, the 

 earthy matter is seen extending into the 

 intercellular substance beyond the adjacent 

 cartilage corpuscles (fig. 74). 



The deposition next takes place in the 

 cells themselves, and in the same manner as 

 the secondary deposit in the cells of plants ; 

 the spaces left between the portions of sub- 

 stance forming the secondary deposit, corre- 



