CH. V.] 



STRUCTURE OF TEETH. 



75 



matter ; the proportion in a hundred parts is about twenty-eight 

 animal to seventy-two of earthy matter. The former, like the 

 animal matter of bone, may be converted into gelatin by boiling. 

 It also contains a trace of fat. The earthy matter is made up 

 chiefly of calcium phosphate, with a small portion of the carbonate, 

 and traces of calcium fluoride and magnesium phosphate. 



Structure. Under the microscope dentine is seen to be finely 

 channelled by a multitude of delicate tubes, which by their inner 

 ends communicate with the pulp-cavity, and by their outer ex- 

 tremities come into contact with the under part of the enamel and 

 cement, and sometimes even penetrate them for a greater or less 

 distance (figs. 95, 97). The matrix in which these tubes lie is 



Fig. 96. Enamel prisms. A, fragments and single prisms of the transversely-striated 

 enamel, isolated by the action of hydrochloric acid. B, surface of a small fragment 

 of enamel, showing the hexagonal ends of the fibres with darker centres, x 350. 

 (Kulliker.) 



composed of " a reticulum of fine fibres of connective tissue modi- 

 fied by calcification, and where that process is complete, entirely 

 hidden by the densely deposited lime salts " (Mummery). 



In their course from the pulp-cavity to the surface, the minute 

 tubes form gentle and nearly parallel curves and divide and sub- 

 divide dichotomously, but without much lessening of their calibre 

 until they approach their peripheral termination. 



From their sides proceed other exceedingly minute secondary 

 canals, which extend into the dentine between the tubules and 

 anastomose with each other. The tubules of the dentine, the 

 average diameter of which at their inner and larger extremity is 

 46*00 of an inch, contain fine prolongations from the tooth-pulp, 



