362 THE TISSUES. 



firmer skeleton is required, and the greater part of the cartilaginous 

 skeleton therefore becomes replaced by bone; while equally firm 

 bones are at the same time developed from the softer blastema be- 

 fore described. Thus there appears to be no necessity for cartilage 

 as a matrix for the development of bone, unless required on account 

 of its greater firmness; and Meyer's assumption that everything 

 in which bone is formed is cartilage, is both a begging of the ques- 

 tion, and, at the same time, incorrect. 



3. The manner of development of bone is, however, essentially the 

 same, whether cartilage or a soft blastema be the matrix. In both 

 cases it is developed as an entirely new tissue, and the pre-existing 

 tissue disappears and gives place to it. It has been seen that the 

 true osseous tissue is first developed in the intercellular substance of 

 the cartilages, and finally the whole of it appears to be converted 

 into bone. There are, however, no facts indicating that chondrine 

 can be converted into glutin, or cartilageine into osteine (p. 100). 

 This element of the cartilage is 'therefore merely replaced ly the 

 osseous tissue. On the other hand, it has been seen that the carti- 

 lagG-cavities remain for a time, increasing in size and changing their 

 forms ; but the cartilage-ceZfc within them, after increasing in num- 

 ber, disappear (except probably their nuclei), the lacunae (and pores) 

 taking their place in part (p. 354, 2). 



Again, while the secondary bones are forming in the membranous 

 expansion of collagenous tissue, the latter disappears, being replaced 

 by them (p. 359). It is apparently only the soft and still unorgan- 

 ized blastema in contact with the collagenous tissue that can be 

 converted directly into osseous tissue. And the probable reason 

 why the latter is transparent when first formed in the case of the 

 periosteal layers, is, that perfect osseous tissue is at once formed ; 

 while, when formed in cartilage, the earthy matter only is first de- 

 posited, and the osteine is subsequently formed and combined 

 with it. 



In both cases, therefore, the cartilage and the collagenous tissue 

 respectively are merely the matrix in which the bone is formed, and 

 which disappears progressively with the formation of the latter. 

 ISTor can the idea that the same modified plasma may be developed 

 into the collagenous tissue on the one hand, and the osseous on the 

 other, be deemed singular. Both contain the same organic imme- 

 diate principle (osteine) ; and the latter differs from the former more 

 especially in containing a greater amount of mineral constituents. 



