DENTINE 239 



be approximately the same, the manner in which they are 

 bound together in the dental tissues may vary considerably. 

 The Dentine Matrix. This is a clear, more or less homo- 

 geneous looking substance traversed by the dentinal tubes. 

 In young teeth, where the deposition of the dentine is still 

 proceeding, the denser part of the tissue is bordered by a clear 

 layer between it and the odontoblasts in which the tubes are 

 clearly seen but not so sharply defined (fig. 143) ; this is the 

 odontogenic zone (the pradentine of Continental authors), 

 and is occupied by tissue on the borderland of calcification 

 in which the salts are not yet fully deposited. The calcified 



p 



FIG. 143. Human tooth near open end. d. Dentine ; o odontogenic 

 zone ; od. odontoblasts ; p. pulp. ( x 150.) 



dentine has a festooned outline towards this zone, made up 

 of rounded bodies, the contours of which are formed by 

 the calcospherites or spherical masses of lime salts which 

 build up the fully calcified substance of the dentine, as will 

 be more fully described in treating of its development. 

 Delicate fibres derived from the connective tissue of the pulp 

 are present in the matrix and form its fibrillar basis, the 

 existence of which is usually completely veiled by the dense 

 calcification ; but it appears occasionally in parts acted upon 

 by the acids of caries, the slow action of the weak acid 

 gradually undoing, as it were, the process of development 

 and revealing the foundation substance. At the borders 

 of carious cavities a very fine lamination is sometimes 



