Help with a J.O Anderson print.

Hello all,
I found this amazing J.O Anderson print today that was about to go in the dumpster and I couldn't believe it.
The print is around 31 inches by 18 inches, it seems to have a few dark spots on it maybe from matting or something over the years. The frame is beautiful as well but it is in pretty rough shape. It is hand signed in pencil, in the top left corner it says-copyrighted J.O Anderson New York 1894.
I wanted to put a new matte in it so I took it out and flipped it over and I don't see how to get it out, maybe I can't. When you flip the matting over you can see a thin piece of paper that covers the lrint and goes all the way to edges the matting. So I peeled a little away, because the paper is glued to the matting and it crumbles. I don't know if its the print im crumbling or just the old paper, i wouldn't think the print would go all the way to the edges of the matting. I took some photos of the back corner and what peeled off.
Please help on how I should proceed with this if at all possible.
Thanks to all of your help in advance.

 

Would you be kind enough to post photographs, Bobby, so we can see what you're seeing?

Debora

 

Sorry guys, its not letting me upload the pics for some reason, when I click upload file and the prompt pops up nothing happens when I click choose file. I'm trying to fix it.

 

I have no idea why it won't let me choose a file to upload, I've never had this problem before.

 

If its tissue covering the back of the mat, you ought to be able to feel the outer edge of the actual print through it.

One unmounted Anderson print I found online had a band of adhesive residue across the top suggesting that it had been fastened to the mat.