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CALCIFICATION. 75
oval and lies in that part of the cell farthest from the dentin, and is
sometimes prolonged toward the dentinal processes so as to be ovoid
or almost pointed. The dentinal process passes into the canals of the

Fig. 55. Fig. 56.

Section of developing tooth, embryo of pig: Section of jaw, embryo of pig: 1, ameloblasts
1, stellate reticulum of enamel organ ; 2, showing Tomes' processes : 2, layer of formed
stratum intermedium ; 3, internal epithe- dentin; 3, odontoblasts 4, pulp tissue. (Sec-
;
lium of enamel organ (ameloblasts); 4, tion by Dr. Sudduth.)
forming odontoblasts ; 5, pulp tissue.
dentin, and it frequently happens that the layer of odontoblasts is
slightly separated from the dentin in making a section, when these
processes, which constitute the dentinal fibrils, may be seen stretching
across the interval in great numbers. Intermediate between the per-
manently soft central fibrils and the general calcified matrix is that
portion which immediately surrounds the fibril, namely, the dentinal
sheath.
In 1891 Mr. Mummery noted, as the dentin was forming, the
appearance of connective-tissue fibers, or bundles of fibers, just in ad-
vance of the main line of calcification. Their high refractive index
suggested their partial calcification, the processes being continuous from
the formed dentin to the general connective tissue of the dentin germ.
He found in a young developing tooth a distinct reticulum of fine fibers
passing between and enveloping the odontoblasts. By careful focussing,
he saw these fibers gathered into bundles and incorporated with the
matrix substance of the dentin, out of which they seemed to spring.
The origin of these fibers seems to be from connective-tissue cells, which
are found everywhere in the formative pulp next the odontoblastic layer,
and also, as he has demonstrated, between the odontoblasts themselves.
These fibers are the scaffolding on whicli the tooth matrix is built up
;
they are incorporated in the matrix of the dentin, and form really the
basis of its substance.