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. 
(Pl. III, fig. 4.) The interior of the pulp also consists of 
round nucleated cells, between 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preparation, or after the earthy matter has been withdrawn), 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 yet 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, 1. 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 le 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 
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