XXXVl INTRODUCTION. 



I have not observed this transition. If it really so happens, 

 then the cavities of the cells so completely disappear, as to leave 

 no trace of the cartilage-corpuscles. From the observations 

 of Retzius it might be supposed that some of the cells retained their 

 cavity and even were converted into radiated cells, since Retzius 

 observed true bone corpuscles in the dentine. If, then, the super- 

 ficial layer of the pulp, consisting of cylindrical cells, is converted 

 by ossification into the dentine, then the subjacent layer of the pulp's 

 parenchyme, consisting of round cells, must first be converted into 

 cylinders, the vessels of this layer become obliterated, and this layer 

 then become ossified, &c. 



" What then are the dentinal tubes ? Retzius compares them 

 with the calcigerous tubes that radiate from the bone-corpuscles, and 

 I was at first of the same opinion, and accordingly I regarded them 

 as prolongations of the cells, the bodies of which lay in the pulp. If 

 the pulp be drawn out of the pulp- cavity of a hog's tooth and the 

 margin of the pulp be examined, it is seen that each of the superficial 

 cylindrical cells is prolonged, opposite the dentine, into a short fine 

 fibre and that these fibres correspond in diameter with the dentinal 

 tubes projecting from the surface of the pulp, I once believed that 

 they projected into the dentinal tubes, and that the intertubular tissue 

 was merely the intercellular substance between these elongations 

 of the cells. But I have given up these ideas since I observed nothing 

 of the kind in human teeth, and since this explanation brings with it 

 a difficulty in regard to the teeth of the pike. In these teeth, accord- 

 ing to Retzius, there is a direct transition from dentine to bone. 

 If one of the large teeth of the lower jaw be sawed ofi", the earth 

 dissolved by muriatic acid, and fine longitudinal sections removed, 

 the dentine is seen to form a hollow cone which is filled by bone. 



