354 



THE TISSUES. 



rows of cartilage-cells, forming pointed tooth-like processes between 

 the individual cells, and surrounding the lower portion of the rows 

 like short tubes. (Fig. 226.) If, however, 

 this granular deposit be traced back from 

 the ossifying margin into the substance of 

 the new bone, it gradually becomes clearer, 

 more homogeneous and transparent, and 

 ultimately acquires the aspect of perfect 

 bone ; the earthy granules apparently be- 

 coming gradually fused together, and thus 

 disappearing as isolated distinguishable 

 particles. And thus the true osseous tissue 

 is developed (though not entirely, as will 

 appear), in the matrix or intercellular sub- 

 stance of the ossifying cartilage. (Fig. 225.) 

 2. But while the intercellular substance 

 thus gives place to true bony tissue, the 

 cartilage-cells also are being converted into 

 the future lacunas and pores of the bones. 

 And it may now be regarded as established 

 by Kdlliker's investigations, that each car- 

 tilage-cell becomes converted into a single 

 lacuna and its pores as follows, except 

 near the ossified surface, a. Plane w ] aere several are fused together into a corn- 



of ossification, the osseous matter 



inclosing the basis of the piiea. pound lacuna : 1. The cartilage-cells be- 

 L^ ^..r come filled with concentric layers of osse- 

 formed by the absorption of parts ous tissue, the external one being formed 

 me^iia. 6 ' ************* first, and the last or internal layers show- 

 ing imperfections or indentations. This 



proceeds till the cartilage-cell is more or less completely filled with 

 the osseous matter, though a cavity always remains (the future la- 

 cuna), containing generally the nucleus of the original cartilage- 

 cell, and a fluid plasma. 2. Minute canals (the pores) are next 

 formed by actual absorption 1 of the bone-substance; and thus are 

 completely perforated by them, both the osseous tissue deposited 

 within the cartilage-cells, and that previously found in the intercel- 

 lular substance of the cartilage. 3. Finally, the osseous tissue within 

 the cells becomes fused with that preformed between them, so that 



Vertical section through the car- 

 tilage and incipient bone of the 

 diaphysis of the femur ; in an in- 

 fant a fortnight old. a. Cartilage- 

 cells arranged in longitudinal piles 



1 The cause of this absorption is not understood. 



