HUMAN ANATOMY. 



TOOTH-STRUCTURE. 



In principle, and among the lower vertebrates in fact as well, teeth may be 

 regarded* hardened papilla of the oral mucous membrane ; they consist, therefore, 

 of two chief parts, the connective-tissue core and the epithelial capping. < 

 three constituents present in typical mammalian teeth, the enamel is the derivative of 

 the ectoblastic epithelium, the dentine, with the pulp, and the cementum being con- 

 tributions of the embryonal connective tissue. . 



The Enamel. This, the hardest tissue of the body, covers the crown, being 

 thickest on the cutting edge or grinding surface of the tooth. It gradually thins away 



FIG. 1306. 



Stripes of Retzius (longitudinal) 



Contour lin 

 Schreger's li 



Neck 



Prism-stripes of Schreger (light and 

 dark) 



Gum 



Pulp-tissue 



Dentine 



Cementum 

 Alveolar periosteum 



Z Osseous tissue of jaw 



Root-canal 



Sagittal section of canine tooth in situ. Semi-diagrammatic. 



the neck, around which its terminal border appears as a more or less distinct 

 ami nl'trii serrated eil-e. The external surface of the enamel, especially in young 

 teeth, nfti-n <-\hil>its a line ^triation composed of horizontally disposed lines. Under 

 a hand-ijas^ tin >< lines are seen to be minute elevations, the enamel-ridges, which 

 encircle the (i-own. The remarkable hardness of this tissue is due to the large amount 

 (97 per cent.) of earthy material ami the small proportion of organic matter, which 

 latter in adult enanx 1 averages only about 3 per cent.; in infantile enamel the amount 

 of animal material i- from h\e to six times greater ( Hoppe-Seyler). 



