74 



HISTOLOGY. 



Their diameter increases toward the inner surface where it is from 2 to 4 p. 

 They branch freely, as shown in Figs. 84 and 85, and terminate blindly 

 or by connecting with neighboring canaliculi. Sometimes they are pro- 

 longed into the enamel for a short distance; they may end abruptly as if 

 the terminal part had been destroyed or, in the permanent teeth, the 

 enamel may form knobs invading the dentine. Ordinarily the contact 

 between enamel and dentine is smooth. 



The calcification of dentine begins shortly before the formation of 

 enamel and spreads from the crown over the neck and root (Fig. 86). 

 The calcified portion increases in thickness, and contour lines, indicative 

 of stratification, are sometimes seen. Near the enamel there are large 

 irregular spaces of uncalcified matrix which occur in the course of the 



Enamel prisms. 



Dentine. 



Enamel. 



FIG. 84. FROM A LONGITUDINAL SECTION OF THE LAT- 

 ERAL PART OF THE CROWN OF A HUMAN MOLAR 

 TOOTH. X 240. 



i, Dental canaliculi, some extending into the enamel; 2, 

 dental globules projecting toward the interglobular 

 spaces, 3. 



Cement. 



FIG. 85. FROM A LONGITUDINAL SECTION 

 OF THE ROOT OF A HUMAN MOLAR 

 TOOTH. X 240. 



I, Dental canaliculi interrupted by a 

 stratum with many small inter- 

 globular spaces, 2. 3, bone lacunae 

 and canaliculi. 



contour lines if such are apparent. The spaces, which in section suggest 

 bone lacunae, are bounded by rounded masses of calcified dentine, and 

 are therefore called interglobular spaces (Fig. 84). The reason for their 

 persistence is unknown. The interglobular spaces of the root are much 

 smaller and more numerous than in the crown. As seen in Fig. 85 they 

 occur in a layer of dentine not far from its outer surface, and because with 

 low magnification they appear as dots this layer is sometimes named 

 the "granular layer." The compact dentine beyond it is closely joined to 

 the substantia ossea, their canaliculi having been said to communicate. 

 The epithelial sheath which bounded the dentine in early stages becomes 

 reduced to fragments, thus allowing the cement and dentine to unite. 



The pulp of the adult tooth is a very vascular connective tissue of 

 embryonic type. It suggests reticular tissue since its fibrils do not form 



