THE TEETH. 361 



the lingual side. The papilla grows still deeper into the 

 pear-shaped body, or stellate reticulum, as it is now termed, 

 because of the stellate-shaped cells it contains, and thus 

 forms a double cap over the papilla, the lower tunic 

 of which is the enamel organ, consisting of cylindrical 

 epithelial cells, Which probably absorb the stellate cells, 

 becoming calcified, forming the enamel prisms, and so 

 the process goes on from within outward, until the 

 enamel is completely calcified. 



While the enamel is thus being calcified the same 

 process is taking place with the dental papillae, but in 

 the opposite direction. The continuous layers of odon- 

 toblasts which now occur here calcify from without in 

 the papilla, receding till it forms the future pulp in- 

 closed within its now formed pulp cavity and canal, with 

 its minute apical foramen for the transmission of the 

 nerves and vessels so essential to the future welfare of 

 the tooth. It is important to remember that the com- 

 plete formation of the apical foramen does not take place 

 for some years after the eruption of the tooth. 



The cementum is formed from the soft connective 

 tissue of the dental sac. When the tooth is erupted the 

 enamel is also covered by a thin layer of cement, which 

 wears off. It is about the ^IT^JT mc ^ m thickness and 

 is named Nasmyth's membrane. 



Table of Eruption of Temporary Teeth. 



Central incisors, lower, . . 5 to 7 months. 



Central incisors, upper, . . 7 to 8 " 



Lateral incisors, lower, . . 8 to 9 " 



Lateral incisors, upper, . . 9 to 10 " 



First molars, lower, . . . 11 to 12 " 



First molars, upper, . . 13 to 14 " 



Cuspids or canines, lower, . . 17 to 18 " 



Cuspids or canines, upper, . 19 to 20 " 



Second molars, . . . . 23 to 30 " 



