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126 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY.
jections, between which the dentin extends. In sections this t:;ives to
the dento-en:unel jnnetion a scaUoped appearance, as shown in Fij;. lOG;
and often the deceptive a})pearance of the dentinal tubules penetratintj:
for a short distance between the enamel rods.
In many specimens made by grinding dried t(>eth large irregular
spaces are very conspicuous in the dentin. They usually occur in lines
or zones at about uniform depth from the surface. These have been
called the interglobular spaces. They are really not spaces at all, but
are areas of imperfect development in MJiich the dentin matrix has not

Fig. 109.

Secondary dentin : A, margin of primary dentin, showing a lew of the tubules continuing into the
secondary dentin ; P, pulp chamber. (About SOX.)

been calcified. The dentinal tubules pass through them ^vithout inter-
ruption. In a dried specimen the organic matrix shrinks, and the
resulting space becomes filled with the debris of grinding, so as to give
the appearance of black spaces. Fig. 107 shows two quite distinct layers
of interglobular spaces, the second much more marked than the first
and in the enamel at a position corresponding to the first is seen an im-
l^erfection of structure marked by the very dark stratification band.
This is shown best in the region of the cusp (Fig. 89) from the same
section. Interglobular spaces in the root portion of the dentin are
shown in Fig. 108, close to the granular layer of Tomes.