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BONES. 87

of the bone, where it articulates with its fellow of the opposite side. It
is broader behind than in front, and composed principally of cancellous
or spongy tissue. It is curved in outline, corresponding to some extent
to the body of the bone above. This curve varies in different bones,
the extent of variation depending in great measure on the race and tem-
perament of the individual from which the bone is taken. With its
fellow in well-formed mouths its axis is parabolic. It is composed of
two plates of bone—an inner and an outer—with numerous septa of can-
cellous tissue uniting them and forming the alveoli for the accommoda-
tion or reception of the roots of the teeth.
The Older Plate of the alveolar process is continuous with the facial
and zygomatic surfaces of the bone. It is the thinner and weaker of
the two, whicli accounts for the fact that a healthy tooth is more easily
pressed outward than inward. After a tooth has been extracted the
outer plate absorbs much more quickly and to a greater extent than the
inner.
The Inner Plate is well defined superiorly, where it forms an angle
wath the palate process. It is thicker and stronger than the outer plate.
The Outer Surface is marked by eminences corresponding to the roots
of the teeth, and depressions marking the position of the interspaces.
The eminence over the canine tooth is more prominent than the others.
This surface at or near its superior margin, over the second bicuspid and
three molar teeth, gives origin to the buccinator muscle.
Fig. 37.

Alveoli of Permanent Teeth.
The Alveoli (Fig. 37) in the normal adult bone are eight in number,
and correspond in shape and size with the roots of the teeth which they