THE OSSEOUS SYSTEM, 3G3 



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

 however, the transformation cannot be followed stop by step, 

 as in rachitic bones. This much, however, is always apparent, 

 that the bone-cells at first present larger cavities, less developed 

 ravs, and more distinct nuclei (the latter, as we know, remain- 

 ing), and, as their occasionally 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 connexion with the bone ; it does not, however, take place 

 in connected but in interrupted, reticular lamella. 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 nothing else than the rudi- 

 ments of the Haversian or vascular canals of the compact sub- 

 stance, 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 

 Avliich, having once formed a junction, they remain continuous 

 during the entire growth of the bone in thickness, so that the 

 formation of the spaces in the bone is, at least afterwards, pre- 

 indicated 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 con- 

 nective tissue, the bone-cavities of the periosteal layers also con- 

 tain round, elongated, or dentate, flattened, faintly granular 

 cellular corpuscles of 0-01 — 002" or more in size, with from 3 

 to 12 or more vesicular nuclei and nucleoli, which are probably 

 referable to the multiplication of the medulla-cells (vid. § 11). 



