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144 DKSTAL HISTOLOGY AND OPERATIVE DENTISTHY

are very irregular in (itilliiie. This irregularity of outline; is eaused by
the cells fitting around the attached fibers of the membrane so as to
cover the entire surface of the eementum between the fibers. Ficr. 125
from a drawing by Dr. Black,' shows several cementoblasts as seen
when isolated by teasing. The cementoblasts have a central mass of
protoplasm containing an oval nucleus, and short irregular processes
which fit around the fibers as these spring from the surface of the
eementum. Fig. 126 shows them in section perpendicularly to the

Fig. 126.

Ti-aii.-iVLr.sc section, sliowinc; the rcllulnr elements: Fh, fihrcililasts ; Er, ejiithelial structures;
Cti, cementoblasts ; C;», eementum ; />, tlentin. (About 'JOO X-)
surface of the root, where they are crowded between the fibers. The
cementoblasts often have processes projecting into the eementum like
those from the osteoblast, but processes projecting into the membrane
have never been demonstrated.
In the formation of the eementum occasionally a cementoblast be-
comes inclosed in the formed tissue filling one of the lacunae, in which
position it becomes a cement corpuscle. i
^ Periosteum and Peridental Membrane.