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SURGICAL ANATOMY. 577

the relations of the teeth of the upper jaw with the floor of the nasal
chamber and the maxillary sinus are fully understood. In the lower
jaw the relations of the teeth with the inferior dental canal and the
position of the roots, especially those of the third molar, must also be
thorouijldv known.
Fig. 506.

Hewitt's mouth props (half size).

The alveolar process of both jaws is made up of two plates, external
and internal, consisting of dense compact bone without a true line of de-

FiG. 507.

Mechanical mouth-opener (half size).
markation between the process and maxilla proper. The interspaces be-
tween these plates form the sockets for the teeth and are surrounded by a
Fir,. oOS.

I'haryngeal forceps (half .size).

very thin cribriform plate of cortical bone. The remaining space is filled
with cancellated tissue, small bony channels, connective tissue, nerves,
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