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124 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY.
The hrniiclics lliroiighout their length are few and small, and are given
oiV at an acute angle to the direction of" the tul)ule; hut just helure tlie
enamel is reaeiied tlie tnhnles fork and hrancli, producing an a[)|)earanee
similar to the delta of a river. These hranches are given otf from the
tubules for some little distance hack from the enamel, and they anasto-
mose with other tubules very freely. The braneiiing of the tubules in
their outer portion causes the spreading of caries just beneath the
enamel, the micro-organisms growing through the branches from tube

Fig. 107.

Interglobular spaces in dentin: 7(7, first line of interglobular spaces; 7.9', second line of inter-
globular spaces. (About 30 >^.)

to tube, and so spreading sideways beneath the enamel plates, and then
penetrating the dentin in the direction of the tubules. Fig. 104 shows
the penetration of caries in the dentin. It will be noticed that in decay
starting at the contact point there has been more spreading under the
enamel than in that starting at the gingival line, but in both ])ositions
the penetration has followed the direction of the tubules.
In the root portion the tubules pass out from the pulp canals at right
angles to the long axis of the tooth and pass directly out to the cemen-
tum, showing only the secondary curves. Throughout their course they