144 THE CONNECTIVE TISSUES, BY A. ROLLETT. 



trabeculse of a secondary bone, proceeding from different 

 centres of ossification, unite with one another at a later period. 

 They form broad transverse trabeculse, parallel to the surface 

 of the bone on which new layers are deposited, causing the 

 bone to become thickened, as in the periosteal increase of bones 

 developed from cartilage. 



When we thus follow the three above-named modes of de- 

 velopment of osseous tissue, it is seen that we meet only with 

 variations that gradually pass into one another. 



In the case of intra-cartilaginous ossification, the substitu- 

 tion from the first of a new tissue for the cartilage which sub- 

 sequently calcifies, removes the difficulty of explaining the 

 molecular difference between the matrix of cartilage and the 

 organic matrix of bone which was formerly experienced, when 

 the impregnation of cartilage with salts of lime was regarded 

 as the essential condition of the ossifying process. 



There further occurs a complete agreement between the 

 origin of the first rudiments of true bone and the primary 

 layers by which growth is effected. In reference to the latter, 

 it is found that they only partially succeed one another in a 

 centrifugal direction, leading to a change of form in the bone, 

 whilst they are chiefly superimposed centripetally towards 

 the cavities which were bounded by the first deposits, leading 

 probably in all instances to a relative increase or diminution of 

 the sclerosed as well as of the soft parts contained in a given area. 

 We do not possess any macroscopic observations which tend to 

 the supposition that, in bone once formed, growth may occur 

 by intus-susception. The microscopic observations instituted 

 in reference to this point are open to various interpretations, 

 and we shall only remark here that objections have been 

 recently raised against the well-known experiment of Hunter, 

 negativing an interstitial increase of bone, because two orifices 

 made in the shaft of the long bone of a young animal did not 

 retreat from one another. 



We have seen in our microscopic investigations how intricate 

 the relations are in regard to centrifugal and centripetal de- 

 position of new bone, and how the formerly described perios- 

 teal development of the complex long bones, in which the 

 greater part of the intercalated and investing lamellse, and the 



