42 



GENERAL PART. 



found 

 teeth 



in osseous fishes, and quite universally as the dentine of 

 (fig. 32). 



With regard to its development, 

 bone is preceded by soft connective 

 tissue or by cartilage. In the first 

 case, it develops by the transfor- 

 mation of the connective tissue 

 cells into bone corpuscle-, and by 

 the hardening of the intermediate 

 tissue. More frequently it is pre- 

 ceded by cartilage ; and this holds for 

 a great part of the vertebrate skele- 

 ton. Formerly great importance was 

 attached to this difference in the origin 



o 



D 



FIG. 32. Section through. *he root of a 

 tooth (after Kolliker). C, cement ; 

 J, interglobular spaces D, dentine 

 with deutinal tubes. 



of bones ; and a primary was 

 distinguished from a second- 

 ary method of bone develop- 

 ment. In reality the two Fl ' 33 '~ A Section f ossif r ill e cartilage (after 



Frey). a, Smaller marrow spaces placed in the 

 processes resemble each other cartilage; b, ditto, with cells of the cartilage 



closelv For in the latter marrow ; , remains of the calcified cartilage ; 



d, larger marrow spaces ; e, osteoblasts. 



case, in conjunction with a 



precedent deposition of lime, and partial destruction or reduction 

 of the cartilage, there is a new formation of a soft connective 

 tissue-substance (osteogenic substance) from the centre outwards, thr 

 cells (osteoblasts) of which give rise to bone corpuscles and the 

 intermediate tissue becomes the hard basis of bone (fig. 33). More- 

 over, cartilage bones grow in thickness at the expense of the 



