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142 DENTAL lUSrOLOGY AND OPERATIVE DENTISTRY.

uninterruptedly from the eementuni to tlie bono (Fi^s. 119 and 122).
In the middle third the fibers are inclined occlusally, and this inclina-
tion increases as the apical third is approached. In the apical third
the inclination is greatest, and the fibers as they arise from the cemen-
tum are very large and break up into fim-sha])ed fiisciculi as they pass
across to the bone. In the apical portion the fibers radiate from the
apex in all directions across the apical region and spread out in fan-
shaped bundles like those in the apical third of the alveolar portion.
In a transverse section near the border of the alveolus (Fig. 12.'}), at
the centre of the labial surface of the root, the fibers are seen to extend
directly out from the surface of the root to the bone of the process, ex-
cepting where they are diverted to pass around bloodvessels. Passing
around distally at the corner of the root, the fibers swing laterally so as
to be almost at a tangent to the surface of the root, and are inserted
much farther to the distal on the wall of the alveolus. A similar ar-
rangement is noticed at the other corners of the root, though these
tangential fibers are usually more marked at the distal than at the
mesial corners.
Studying the arrangement of the fibers with reference to the physical
function of the membrane, it is seen to be the best that could be
devised to support the teeth against the force of mastication and to
support the tissues about them. In the gingival portion the fibers
passing from tooth to tooth form the foundation for the gingivae between
the teeth filling the interproximal spaces ; so that if these fibers are
cut off from the cementum, by extending a crown band too far, or by
the encroachment of calculary deposits beginning in the gingival space,
the gingivus drops down and no longer fills the interproximal S])ace. In
the alveolar portion the fibers at the border of the process and those
at the apex of the root together su])])ort the tooth against lateral
strain, while those in the rest of the alveolar portion are so arranged
as to swing the tooth in its socket and support it against the force
of occlusion (Fig. 118). As seen from the transverse section, the fibers
of the occlusal third of the alveolar portion are so arranged as to sup-
port the tooth against forces tending to rotate it in its socket.

CELLULAR ELEMENTS OF THE MEMBRANE.

The fibroblasts are spindle-shaped or stellate connective-tissue cells
which are found between the fibers as they are arranged in bundles. In
sections stained with hematoxylin they take the stain deeply, and the
fibers, which are unstained, are differentiated by the cells lying in rows
between them. The number of fibroblasts in the membrane decreases
with age. They are large and numerous in the membrane of a newly