104 IVORY OF THE TEETH. 



and are directed towards the outside perpendicularly, or at a 

 slightly acute angle.. These elongated globules are clearly 

 cylindrical cells. In recent teeth, the characteristic nucleus 

 with its nucleoli may be distinctly seen in them, and 

 they very closely resemble the prisms of the enamel-membrane. 

 (PI. Ill, fig. 4.) The interior of the pulp also consists of 

 round nucleated cells, bety, r een which the vessels and nerves 

 pass. When the pulp of a young tooth is detached from its 

 cavity, and the dental substance is examined (without further 

 preparation, or after the earthy matter has been withdrawn), 

 a stratum of the cylindrical cells of the pulp will be found 

 to remain attached to its internal surface, at least to the 

 lower part of it, where the newly -formed dental substance 

 is vet thin and soft. These cells are of about the same 

 size, and have the same course as the solid fibres of the 

 dental substance ; and since, on the one hand, they clearly 

 belong to the pulp, which follows from their accordance with 

 the cylindrical cells that remain attached to the rest of its 

 surface, and as, on the other hand, they are still more firmly 

 connected with the dental substance than with the pulp, and 

 remain affixed to the former, I suppose a transition to take 

 place at that part, and the cylindrical cells of the pulp to be 

 merely the earlier stage of the dental fibres, i. e. that the cells 

 become filled with organic substance, solid and ossified. In 

 some instances, these little cylinders are not found upon 

 the dental substance, but a quantity of cell-nuclei seen 

 in their place ; these are very pale, and so intimately united 

 with the dental substance, that they readily escape notice; when, 

 however, attention is once attracted to them, it is impossible to 

 mistake them, and they lie side by side with extremely 

 small interspaces. The facility with which the two struc- 

 tures may be separated, has been adduced as an argument 

 against the opinion that the dental substance is the ossified pulp, 

 and I fully acknowledge the weight of the objection. But the 

 following circumstances deprive it of at least some of its import- 

 ance. Firstly, some portion of the pulp actually remains 

 attached to the dental substance ; again, in ribs which are half 

 ossified, the cartilage may easily be separated from the ossified 

 portion; and lastly, the separation must be effected with 

 more facility in the tooth, in consequence of the greater 



