TEETH. 315 



Dentine. The dentine is constituted of numerous tubes 

 imbedded in an intertubular substance; these tubes commence 

 at the pulp cavity, on the surface of which they open, and 

 from which they proceed in a radiate manner, terminating 

 on the borders of the dentine ; those arising from the upper 

 part of this cavity ascend almost vertically, those from the 

 sides more obliquely, and those from the lower portion pass 

 either horizontally outwards, or else descend somewhat. 



These tubes diminish in size from their commencement to 

 their termination : they are branched ; at first they divide in 

 a dichotomous manner ; their subsequent ramifications are 

 numerous, minute and arborescent, and they inosculate freely 

 with the similar branches proceeding from the adjacent tubes : 

 those tubes which proceed towards the cementum are remark- 

 able for the very great number of branches into which they 

 divide. 



The tubes of the dentine in their passage outwards do not 

 run in straight lines, but describe in their transit two or 

 three large curves, and each of these primary curves, when 

 examined with a higher power of the microscope, will be ob- 

 served to be made up of numerous smaller and secondary 

 curves ; both the large and small curvatures of one tube corre- 

 spond with those of another. 



Such is the usual course and distribution of the tubes of 

 the dentine : several modifications of them, however, still re- 

 main to be noticed. 



Thus sometimes a tube in its passage will dilate into a 

 bone cell, and again proceed onwards to its destination as a 

 tube ; at others a number of them, even in the centre of the 

 dentine, will break up and form a cluster of bone cells ; again 

 at others the tubes frequently become transformed into or 

 terminate on the margin of the dentine in bone cells. This 

 gradual transformation of the dentinal tubes into bone cor- 

 puscles, and their termination in the same, is especially seen 

 in tha.t portion of the dentine contiguous to the cementum. 



The usual method of termination of the dentinal tubes, is in 

 fine and inosculating branches on the surface of the dentine. 

 Sometimes, however, the tubes anastomose in a peculiar 



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