A "Stitching Pony" is a leatherworking tool used to hold leather securely, freeing up both hands for doing the actual stitching. In woodworking parlance, it's comparable to a vise or a clamp.
The construction is a flat base, with one fixed jaw extending vertically, and the second jaw being connected to the base with a hinge, so that it may open and close.
To protect the leather being clamped from indentations, the jaws themselves are covered with some leather offcuts, which were simply attached with contact cement. Brass tacks were used to hold the leather in place while the glue dried (and help to add to the aesthetic of the piece).
|The jaws of the clamp.|
The bookend woodgrain was a fortunate coincidence