THE OSSEOUS SYSTEM. 325 



embryo. In fact, it is now, not difficult to show, that the outermost, 

 still soft bone-lamellae pass into the blastema in question, with their 

 separate spiculsQ and projections, and that (1.) the matrix of the bone 

 arises from its fibrous tissue, by the simple uniform deposition of cal- 

 careous salts, although usually, as it seems, without the previous ap- 

 pearance of calcareous granules ; and (2.) that the bone-cells are formed 

 out of the formative cells of the blastema. With respect to the latter, 

 however, the transformation cannot be followed step by step, as in 

 rachitic bones. This much, however, is always apparent, that the bone- 

 cells at first present larger cavities, less developed rays, and more dis- 

 tinct nuclei (the latter, as we know, remaining), and, as their occasion- 

 ally visible outlines prove, correspond entirely in size with the cells just 

 mentioned, so that I do not for a moment doubt, that they are formed 

 in this situation exactly as they are elsewhere. With respect to the 

 development of the ossifying blastema itself, it is at least clear, that it 

 is derived from the numerous vessels of the foetal and young periosteum ; 

 the origination of its fibres from fusiform cells, I have very frequently 

 observed in man and in animals, but with respect to the cells, can only 

 state that they occur of various sizes, and occasionally intermixed with 

 free nuclei. 



The formation of bone in this blastema occurs wherever it is in con- 

 nection with the bone ; it does not, however, take place in connected but 

 in interrupted, reticular lamellce. The roundish or elongated spaces 

 (Fig. 133, a), which, from the first, remain between the layers of osseous 

 tissue, and in the different layers communicate with each other, are no- 

 thing else than the rudiments of the Haversian or vascular canals of 

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

 first is obviously nothing more than the unossified portion of the ossific 

 blastema, although it sometimes contains more formative cells than 

 connective tissue. The cells of these spaces are very soon transformed 

 into the usual, light-reddish medulla-cells, and partly into vessels which 

 communicate with those of the interior of the bone, and in part also 

 with those of the periosteum, with which, having once formed a junction, 

 they remain continuous during the entire growth of the bone in thick- 

 ness, so that the formation of the spaces in the bone is, at least after- 

 wards, preindicated by those, which, in accordance with what has been 

 said, proceed from the periosteum through the ossific blastema to the 

 bone. Besides medulla-cells and vessels as well as some connective 

 tissue, the bone-cavities of the periosteal layers also contain round, 

 elongated, or dentate, flattened, faintly granular cellular corpuscles of 

 0*01-0'02 of a line, or more in size, with from 3 to 12 or more vesicu- 

 lar nuclei and nucleoli, which are probably referable to the multiplica- 

 tion of the medulla-cells (vid. 11). The periosteal layers, which, 

 agreeably to what has been stated, are from the first deposited in the 



