Retailer Antique Shadowbox Frame Unusual Joinery 8.5x6 Photo

retailer Antique shadowbox frame with an unusual bit of joinery. The corners are held together with a mortised strip of wood set on the diagonal across the corner joints. See the photos of the back. The frame is a deep shadowbox style. The hardwood is finished in warm reddish tones, maybe walnut or cherry. The frame has a glass cover and a botanical print.
There is some scuffing here and there and a piece has a small broken area and it looks like it is split a little on the inner edge bordering the photo.

Frame Size: 11 1/4" x 9" x 1 5/8"
Frame Width Profile approx 2"
Image Size: 8.5" x 6"
Wall Hanging Picture Frame