What are these holes in my late 1800s home’s windows?

Been wondering about this for a while. These windows are in a sunroom and are in hard shape. I’m assuming due to the fact there are massive holes in the window frame that allow rain & snow to build up and rot the wood, as well as allow bugs and other pests inside. These windows become moist in the winter as well and will mold any curtains, ect placed against them. I cannot fathom a purpose for this design but it must have been for some reason?

Been wondering about this for a while. These windows are in a sunroom and are in hard shape. I’m assuming due to the fact there are massive holes in the window frame that allow rain & snow to build up and rot the wood, as well as allow bugs and other pests inside. These windows become moist in the winter as well and will mold any curtains, ect placed against them. I cannot fathom a purpose for this design but it must have been for some reason?