166 A MANUAL OF DENTAL ANATOMY. 



from the interior of the dentine cap. Osteoblasts clothe, 

 like an epithelium, the trabeculae and the connective tissue 

 fibres attached to them, and by the calcification of these the 

 osteodentine is formed. 



The process is exactly like the calcification of any mem- 

 brane bone, and the connective tissue bundles remind one 

 of those which are believed to be the occasion of the 

 formation of Sharpey's fibres in bone. In the case of teeth 

 which are going to be anchylosed to the subjacent bone, 

 these fibres run continuously from the interior of the dentine 

 cap down to the bone, and calcification in and around them 

 binds the two inseparably together. 



It is interesting to note, especially in connection with 

 the fact that some observers believe Sharpy's fibres to be 

 elastic, that the hinged teeth of the pike (see fig. 88) owe 

 their power of resilience entirely to the elasticity of these 

 connective tissue bundles, which do not become completely 

 calcified, although at an early stage it would be quite im- 

 possible to say whether the tooth under observation was 

 going to be anchylosed, or to be a hinged tooth tied down by 

 elastic strings. 



The Calcification of Cementum. Just as is the case 

 with bones elsewhere in the body, cementum may be formed 

 in two distinct ways, by membranous ossification, and by 

 ossification in a fibro-cartilage, the former method obtaining 

 upon the roots of teeth, and the latter upon those crowns 

 where the cement organ described by Magitot exists. 



At the time when the crown of a tooth appears through 

 the gum, it alone is complete, and the root has yet to be 

 calcified ; as each portion of dentine of the root is completed 

 it is coated with a closely adherent vascular membrane which 

 is in fact the follicle wall, and which is to become, when the 

 cement is formed, the alveolo-dentar periosteum. 



The inner or dentinal face of this membrane presents a 

 layer of large cells, the osteoblasts of Gegenbaur, and it is 



