INTRODUCTION. XXXV 



are only the earlier stage of the dentinal fibres, since these cells 

 are filled with organized substance become solid and osseous. Some- 

 times these cylindricules are not found on the dentine, but then we 

 see in their place a number of cell -nuclei ; these are very pale and 

 ultimately united with the dentine so that they may be easily over- 

 looked. When once attentively observed, they are not easily mis- 

 taken, and are separated by extremely minute intervals. Against 

 the opinion that the dentine is the ossified part of the pulp, the 

 facility with which the one is separated from the other has been 

 objected, and I allow the force of that objection. But it is at least 

 weakened by the fact that a part of the pulp remains attached to 

 the dentine, and that in half-ossified ribs, the cartilage can be easily 

 detached from the ossified portion, and that in teeth the separation 

 must be so much the easier as the difference is greater between the 

 dentine and the pulp. 



There are at least sufficient grounds for going more closely 

 into the detail of this view. The pulp agrees with all the 

 other tissues of the fcetus, and more especially with cartilage, 

 inasmuch as it consists of cells ; it differs in consistence from mam- 

 malian cartilage, inasmuch as whilst the quantity of cytoblasts 

 (nucleated cells), on which the hardness of mammalian cartilage 

 depends, is very small, the cylindrical cells, at least on the surface 

 of the pulp, are closely aggregated together. In this respect the pulp 

 more nearly resembles certain cartilages in the lower animals, in which 

 the cytoblasts are present in smaller quantity and the consistence 

 of the cartilage depends upon the thickening of the walls of the cells. 

 Whether, in the presumed transition of the cells of the pulp 

 into the dentinal fibres, the obliteration of the cavity is effected 

 by the thickening of the walls of the cells, I know not, since 



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