This reminds me of an antique "side-by-side" cabinet which typically have a desk element. But yours DEFINITELY has a music sheet element to it! NICE!
Let's see what someone else chimes in on this one. Are there any tags, stamps, etc on it anywhere?
Sheet music cabinets were the craze in the mid 1800's onwards to around 1920. They can be plain to flat-out fancy. Yours is a very unique and nice piece! Sheet music was usually made wider than the bench seats that came about and prior to that they were small round claw foot stools. So the cabinet was made to keep the coveted music sheets clean and crisp (without bends or folds).