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MICTIIODS OF TAKrNG TM PRKSSIONS. 13
tlniily into position. At tlie same time direet the patient to
thrust the toni;;ue upward and forward. In tliis way an
impression of that portion of tlie mylolnoid muscle and tlie
cord (tni?num lin^u.v) which is attached to the ridge just
beneath tlie ti]) of llie ton^-ue. is secureih while they are
ekwated and tense; the}' will then not disturb the plate while
Fic. 5.
they are in motion, as in speech and mastication. It wdll
sometimes be found that a perfect low'er impression will
offer considerable resistance to removal, on account of the
adhesion and undercuts. Where this is the case, air can
reachly be admitted by drawing away the lips and cheeks.
For partial impressions, cups of a different pattern are
required. Fig. 5 shows the general form of cups used for
