THE DENTAL TISSUES. 



seen to be bifurcated, while the central mass of the tooth 

 is composed of dentine permeated by pulp canals which 

 pursue a longitudinal course ; a slight further modification 

 brings us to the structure of the dentine of the Labyrin- 

 thodon, in which a maximum of complexity is attained, 

 although a clue to its intimate structure is afforded by the 

 teeth of Varan us or of Lepidosteus. 



The laminse of pulp, with their several systems of den- 



FIG. 39 



b' 



tinal tubes, instead of passing out in straight lines like the 

 spokes of a wheel, pursue a tortuous course as they run 

 from the central small pulp chamber towards the surface. 

 Not only do they undulate, but they also give off lateral 



(*) Transverse section of a tooth of Labyrinthodon. (After Owen.) 

 ft ; The letter a is placed in the centre pulp chamber ; the letter b marks 

 the lines of separation between the system of dentinal tubes which belong 

 to each lamina of pulp ; these lines of demarcation were formerly sup- 

 posed to be occupied by cementum. 



