FORMATION OF BONE FROM CONNECTIVE TISSUE. 475 



oneself at the spots, where calcareous salts are really 

 deposited in them. Whilst the periphery of such calcified 

 trabeculae (Fig. 131) offers a brilliant, almost cartilagi- 

 nous appearance, in their middle an opaque, finely gra- 

 nular matter presents itself which pervades the intercel- 

 lular substance, and towards the interior of the trabecuke 

 passes into a nearly homogeneous, calcareous layer, in 

 which at intervals the osseous corpuscles may be recog- 

 nized. Here we have therefore already a complete 

 osseous network, and at the same time an exact picture 

 of the regular growth of bone in thickness. 



If, however, the spots are very carefully examined, 

 where the borders of these trabeculae and bands of bone 

 come into contact with the fibrous substance of the 

 meshes, it is seen that no perfectly defined limit exists 

 there, but that the intercellular substance of the osteoid 

 tissue is gradually lost in the intercellular substance of the 

 fibrous marrow, so that here and there a few of the con- 

 nective-tissue-corpuscles of the fibrous connective tissue 

 are included in the sclerotic substance of the trabeculae. 

 Hence you may infer, that the formation of the real osse- 

 ous substance from connective tissue is essentially effected 

 by the gradual change of the intercellular substance, and 

 that this loses its originally fibrous nature and becomes 

 converted into a dense, shining, cartilaginous mass, with- 

 out its ever really attaining however to the structure of 

 cartilage. Here there is never a stage exactly corres- 

 ponding to any of the known forms of cartilage, but it is 

 out of connective tissue that we see the osteoid substance 

 directly arise, which in cartilage also and marrow is the 

 first to arise when they become bone. This is so far very 

 important, that you can from all these instances acquire 

 the conviction that people have been mistaken in speak- 

 ing of the cartilage of bone (Knochenknorpel). Cartilage 

 as such can only calcify ; when it is to become bone, a 



