So I won't go into the details of this neat gun, but this is a Lignose Einhand (one hand) .25 caliber handgun. (Note that I don't own this, I got the image online). The gun was made in the very early 1900s. It has a cocking spur in the front of the trigger guard. It is meant to be cocked and fired with one hand. You would use your trigger finger and middle finger to cock the spur, which racks the slide with it. It's a pretty neat design. It would be cool for such a design, today, but it would require a LOT of strength.