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686 ORTHODONTIA AS AN OPERATIVE PROCEDURE.

An upper protrusion may be described as a distal occlusiou of the
lower jaw on both sides (or a bilateral distal occlusiou).
Mesial Occlusion.—If the key tooth closes anteriorly or uiesially
to the normal position to any degree, even to the width of a bicuspid
or more, the occlusion of the jaws is shown to be mesial (Fig. 602).
This may occur on one or both sides of the mouth and may be the fault
of the teeth themselves, if the abnormality is slight. It may be due
to lack of development of the upper maxilla, as in Fig. 779 ; or abnor-
mal development of the lower maxilla, as shown in Fig. 780, both

Fig. 002.
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