DENTINE 241 



they are in this sense interglobular spaces, but they are not 

 apparently due, as are the interglobular spaces presently 

 to be described, to a want of complete coalescence of the 

 calcospherites but are normal structures surrounded by the 

 calcifying bodies, for the tubes enter them and do not pass 

 uninterruptedly across them as in the large interglobular 

 spaces beneath the enamel. These bodies probably afford 

 a channel of communication between the pulp and the 

 canaliculi of the cement ; they are in fact seen to do so in 



FIG. 145. Human molar. Communication of dentinal tubes 

 with spaces of granular layer. ( X250.) 



many instances (fig. 145). We should then look upon this 

 layer as part of the normal structure of dentine. They 

 are found in many Mammalia, and are very conspicuous 

 in the dentine of the Cetacea, where they are arranged in 

 concentric rows. In many teeth other much larger inter- 

 globular spaces are seen, generally situated beneath and not 

 far from the enamel in the substance of the first-formed 

 dentine (fig. 146). They are evidently formed by the want of 

 coalescence of the calcospherites which form the calcified 

 portion of the matrix. In teeth from rickety subjects, in 

 whom the calcification of the bones and teeth is very 



