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80 EMBRYOLOGY OF THE DENTAL TISSUES.

forming cell. These pass through the soft substance of the odonto-
blasts (protoplasm and seem to be a part of them, but in fresh, young
)
sections the so-called processes move in the substance of the odonto-
blasts bv j>ressure on the cover-glass, and the fibril may be traced to
a i)ear-shaped cell beyond (Fig. 62). There will usually be found as
manv })rocesses going out from sides or ends of the odontoblasts toward
the pulp as there are going into the matrix from the dentin end of the
cell. In cross sections of the odontoblasts, delicate light spots are seen
in the substance, which are probably the cut fibers. When the layer
of odontoblasts is teased away from the forming dentin, fibrils are seen
bridging the gap, apparently offshoots from the odontoblasts ; but on
careful examination there will usually be found a decided line of demar-
cation across the fiber at the point where it meets the square end of the

Fig. 63.

Section of growing tooth of calf at birth; odontoblasts that were square and abrupt against the
They are
forming dentin, showing the line of demarcation between the cell and the fibril.
attached to the pulp.
odontoblast (Fig. 63). This line seems to show that the fibril was not
continuous with the protojilasm of the cell. Other sections which have
been separated by teasing, show odontoblasts having their side masses
of protoplasm drawn away from the fibril which apparently has run
through it. Some of this protoplasm is left upon the fibril, giving it
a ragged appearance as it passes from a canal in the matrix across to
the separated pulp tissue, bridging the gap.
The pear-shaped cell has perhaps a more important function than
the odontoblast proper. It is to supply the life and nourishment to
the whole of the calcified matrix, as the bone corpuscle within its
lacuna supplies life and nourishment to bone and cementum.
Minute calcium globules or calco-spherites are seen to be arranging
themselves against the already formed matrix, where they collect in large