DEVELOPMENT OF BONE. 127 



siderable time that both kinds of bone, those developed in 

 cartilage (primordial bones), as well as the investing bones 

 (secondary bones), when once formed, receive fresh accessions 

 of osseous tissue from the periosteal connective tissue, and that 

 they thus increase in thickness. Virchow* first pointed out 

 that in these cases the osseous tissue is developed from con- 

 nective tissue in the same way as in the development of 

 secondary bones. 



According to these different processes, three separate modes 

 of development of bone may be differentiated, the intra-carti- 

 laginous, the intra-membranous, and the periosteal; but we 

 shall see that in all these cases the osseous tissue originates in 

 an essentially similar neoplastic formation (osteogenous sub- 

 stance), and also that the connective-tissue-like deposit preced- 

 ing the formation of the several bones probably in all cases 

 proceeds from the same germs ; in short, that the above-men- 

 tioned differences refer to the place where the bone develops, 

 and to the presence or absence of cartilage, but that the process 

 of osteogenesis itself is essentially the same in all. 



In those cases where the form of the future bone is more or 

 less distinctly defined in the embryonic cartilaginous skeleton, 

 it may easily be supposed that the matrix of the bone origi- 

 nates in a metamorphosis of the matrix of the cartilage, and 

 the lacunae and corpuscles either as outgrowths of the carti- 

 lage corpuscles, or by the formation of layers of secondary 

 deposit, traversed by porous canals, occurring in the supposed 

 membrane of the cartilage cells. In regard to the formation 

 of the larger medullary spaces, we must admit a process of 

 absorption of the cartilage, or of the young bone developed 

 from it, with coincident development of the contained material. 

 These statements, which were first advanced as a matter of 

 opinion by Schwamrf- and HenleJ have obtained general ac- 

 ceptance, and for a long time were believed, in 'Germany, 

 England, and France, to be in accordance with the direct 



* Archie flir Pathol. Anat., Band v., p. 36, et seq. 



t Mikroskop. Untersuch., etc. Berlin, 1839, pp. 35 and 115. 



J Allgemeine Anatomic, 1841, p. 831. 



