198 OSSEOUS SYSTEM. [sect. 1 04. 



and successfully detached, has a rough and, as it were, porous surface, 

 with numerous medullary spaces; and, in its outermost part, is, 

 for a greater or less extent, still quite soft, pale yellow, and trans- 

 lucent ; further inwards, on the contrary, it continually increases 

 in firmness and whiteness, till at last it assumes the usual appear- 

 ance of fully-developed bone. The formation of bone, which un- 

 doubtedly here takes place, is effected through means of the 

 above-mentioned blastema, the cells of which, scattered among 

 the delicate fibres, have not the slightest resemblance to cartilage- 

 cells, but have exactly the same appearance as foetal marrow-cells, 

 or the formative cells of the embryo. In fact, it is now not very 

 difficult to demonstrate, that the outermost, still soft osseous 

 layers, with their trabecular and projections, pass into the blastema 

 in question; and that, 1st, the fundamental substance of the bone 

 arises from its fibrous tissue by the simple uniform deposition of 

 calcareous salts, but, as it would seem, without the previous ap- 

 pearance of calcareous granules ; and 2nd, that the bone-cells 

 become developed from the formative-cells of the blastema ; still, 

 with reference to the latter, the metamorphosis cannot be followed 

 step by step, as in the rachitic bones. According to Virclwid's 

 discovery, which I can fully confirm, these cells, without previously 

 presenting secondary membranes, like the cartilage-capsules, gra- 

 dually acquire a stellate form, and, when the surrounding matrix 

 ossifies, become directly transformed into stellate bone-cells, which, 

 accordingly, are not contained in bone;capsules. With reference 

 to the development of the ossifying blastema itself, see the note 

 at the end of this section. 



The formation of bone in the above-mentioned blastema occurs 

 in all places where the latter is in connection with the bone ; it 

 does not, however, take place in uniformly continuous but in reticu- 

 lated interrupted lamellae. The rounded and elongated spaces (fig. 

 86 a), which from the first remain in the intervals of the osseous 

 tissue, and communicate with each other in the different layers, are 

 in reality the rudiments of the Haversian or vascular canals of the 

 compact substance, and contain soft reddish medulla, which, at 

 first, is evidently merely the non-ossifying portion of the ossific 

 blastema, but soon contains more formative cells than connective 

 tissue. The cells of these spaces soon take on the form of or- 

 dinary, slightly reddish marrow-cells. A part of them are also 

 transformed into vessels which communicate with those of the 

 interior of the bone, and especially also with those of the peri- 

 osteum, with which, having once entered into connection, they 



