The Osteon Calcification as Revealed by the Electron Microscope 145 



In contrast with the lamellae, the interlamellar cementing zones show only one 

 feature, the calcified bands are missing or very rare. The crystallites have the same 

 shape and about the same size, but they are irregularly distributed and orientated in 

 all directions forming at some points whorled figures. 



In fully calcified osteons the lamellae show no appreciable qualitative differences 

 from those of osteons in the initial stages of calcification (Fig. 4). However, compari- 



ithin longitudinal sec 



of a fully calcified osteon. Expla 



son of micrographs from osteons both at the initial stage of calcification and from 

 fully calcified ones suggests that the number of needle-shaped crystallites increases in 

 the latter. The surfaces covered by elongated crystallites as well as those covered by 

 calcified bands were measured in 56 micrographs. The results show that the areas 

 covered by needle-shaped crystallites are predominant in the osteon in the initial 

 stage of ossification and correspond to about 69 per cent. The same areas increase 

 by 14 per cent, when osteons complete their ossification going up to 83 per cent. The 

 statistical analysis shows that the differences between the two mean values are highly 

 significant, t being 6.334 for P = 0.05. This value is only indicative. In order to 

 obtain more reliable data on the actual increase of calcium it would be necessary to 

 consider the spatial distribution, density and dimensions of the calcified material in 

 the two types of apatite deposition as the cross-banding has a lower opacity to the 

 electron beam than the other calcified areas. At the moment this problem presents 

 difficulties which still have to be solved. 



In the fully calcified osteons the interlamellar cementing zones are formed almost 

 entirely of needle-shaped crystallites, which makes it difficult to establish whether the 

 calcium salts are actually increased. However, the absence or scarcity of areas covered 



yd £u,op. Symp. on Cal. Tissues 



