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104 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from its cavity, and the dental substance is examined (without further preparation, or after the earthy matter has been withdrawn), a stratum of the cylindrical cells of the pulp will be found to remain attached to its internal surface, at least to the lower part of it, where the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, 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 structures 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 importance. 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