FIG. 1 is a front perspective view of a portion of a respiratory mask frame showing our design, with the lower portion of the frame with clip receptacles portrayed in broken lines;

FIG. 2 is a reverse perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof;

FIG. 7 is a right side view thereof; and

FIG. 8 is a left side view thereof;

FIG. 9 is a front perspective view of a portion of a respiratory mask frame showing an embodiment of our design, with the vent portions and the lower portion of the frame with clip receptacles portrayed in broken lines;

FIG. 10 is a reverse perspective view thereof;

FIG. 11 is a front view thereof;

FIG. 12 is a rear view thereof;

FIG. 13 is a top view thereof;

FIG. 14 is a bottom view thereof;

FIG. 15 is a right side view thereof; and,

FIG. 16 is a left side view thereof.

Where included, the use of broken lines are for illustrative purposes only to indicate environmental surroundings and does not constitute a portion of the claimed design.

Where included, the use of dotted lines represents the border between claimed and unclaimed subject matter and does not constitute a portion of the claimed design.