FIG. 1 is a front perspective view of a portion of a mask assembly according to our design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof, with the right side view being a mirror image thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

Throughout the various figures of the drawings, certain views may not be provided. The omission of a particular view is intended to convey that the element(s) depicted is/are plain and unornamented in that omitted view, or that the particular ornamental appearance in the view is not claimed.

Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design.