From the "Sessions and Maps" option, select "Add Map Window."
Enter a name "TIN Data" for the new Map Window in the dialog that pops up and press OK.
Expand this new "TIN" Map Window node in the "Bald Eagle" Session.
In the "active mapping files" node, right-click on Bald Eagle and select "Make Background Map," because the next step will involve adding data sets that cover different areas in the U.S. mostly outside the range of the Bald Eagle watershed.
You are now ready to add TIN data to the "TIN Data" map panel.