DEVELOPMENT OF THE BONES. 



353 



Where, however, the ossification ex- Fi g- 225 



tends in all directions from a centre, 

 the cartilage-cavities are confusedly 

 grouped in roundish or oval, irregular 

 little masses, as in the short bones, and 

 the epiphyses of the long bones. In 

 both these cases, however, the cavities 

 containing the cells (the latter being 

 in a single or double linear series, or 

 in a more globular mass), are the elon- 

 gated original cartilage-cavities. The 

 thickness of the layer around and be- 

 yond the bone, which presents the ar- 

 rangement of cells just described, varies 

 in the different cartilages ; being J 5 to 

 2*4 of an inch in the shafts of the long 

 bones, and very thin around the os- 

 seous centres, in the epiphyses, and in 

 the short bones. It is always yellowish, 

 streaky, transparent, and apparently 

 fibrous; while the surrounding cartilage 

 is, as usual, bluish-white, with a hya- 

 line or granular intercellular substance. 



III. The preparations for ossification 

 being completed by the development 

 of the vessels and the arrangement of 

 the cartilage-cells just described, the 

 osseous tissue now begins to appear. 

 And as true cancellated bone-substance consists originally of only 

 the lacunae and pores and the surrounding true osseous tissue, and 

 the cancelli (with their marrow and its vessels), we have to inquire 

 how these are developed respectively. 



1. The true osseous tissue is usually developed before the lacunae 

 and pores are formed; and its formation occurs mainly in the inter- 

 cellular substance of the cartilage, its cells still remaining unchanged. 

 The first apparent change in this is the deposit of very fine granules 

 of the earthy constituents of bones, varying in size from an im- 

 measurable minuteness up to T2 &^ to g ^V^ of an inch in diameter. 

 When the cells are disposed in rows at the ossifying border, this 

 disposition of earthy matter always forms columns between the 



Vertical section of cartilage at seat of 

 ossification. The clusters of cells are 

 arranged in columns, the intercellular 

 spaces between them being l-3250th of 

 an inch in breadth. At the lower end 

 of the figure osseous fibres are seen oc- 

 cupying the intercellular spaces, at first 

 bounding the clusters laterally, then 

 splitting them longitudinally, and en- 

 circling each separate cell. The greater 

 opacity of this portion is due to a three- 

 fold cause : the increase of osseous fibres, 

 the opacity of the contents of the cells, 

 and the multiplication of oil-globules. 



