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BONES. 107

bone, the condyloid processes being short and inclined slightly back-
Avard. The rami are short, and but slightly deflected upward from the
axis of the body of the bone.
After birth the body of the bone becomes elongated (Fig. 52), increas-
ing backward behind the anterior (mental) foramen to a greater extent
than it does in front of it. This dilierence is to giye greater space for
the accommodation of the permanent molar teeth.
The growth of the body of the bone aboye the oblique line is made
up principally of its alyeolar process, which sustains the teeth. The
growth below the oblique line, both in extent and thickness, .giyes
strength to the bone and space for the attachment of muscles, lodg-
ment of glands, etc. The rami and condyles of the bone increase in
length, and the angles between the rami and the body of the bone
become less obtuse ; finally, they are almost at right angles with the
body (Fig. 53), the diiference in direction being due to the gradual sep-
aration of the jaws by the growth of the teeth. As the teeth wear
away, the jaws approach each other more closely again, and the angles
between the rami and the body of the bone begin to reassume their
Fig. 56.

Engraving showing Absorption of Alveolar Process in upper and lower jaw after loss of all the
tseth.
former shape (Fig. 54). AVhen the teeth are lost by decay or otherwise,
the alyeolar process is absorbed (Fig. 55), the depth of the bone thereby
diminishes, the mental foramen being nearly on a level with the supe-
rior border of the bone, the dental canal becoming superficial. The
buccinator, levator labii inferioris, and the genio-glossus muscles ara