52 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



Permanent Teeth. 



MIDDLE LINE OF JAW. 



Incisor, Canine. P^rT' 



The age at which each permanent tooth is cut is indicated in this table in years 



Structure. A tooth is generally described as possessing a crown, neck, 

 and root or roots. The crown is the portion which projects beyond the 

 level of the gum. The neck is that constricted portion just below the crown 

 which is embraced by the free edges of the gum, and the root includes all 

 below this. 



On making longitudinal and transverse sections through its center, figure 

 6 1, A, B, a tooth is found to be principally composed of a hard superficial 



FIG. 60. Normal Well-formed Jaws, from which the Alveolar Plate has been in great 

 part removed, so as to expose the Developing Permanent Teeth in their Crypts in the Jaws. 

 (Tomes.) 



material, dentine or ivory, which is hollowed out into a central cavity which 

 resembles in general shape the outline of the tooth, and is called the pulp 

 cavity. 



The tooth pulp is composed of fibrous connective tissue, blood vessels, 

 nerves, and large numbers of cells of varying shapes. On the surface in 



