In the room with two statues to fight drop down to the left and fight the statue. After destroying use avifors on the thing left behind. This will open the first gate. Notably this gate goes down into the floor as opposed to up into the ceiling. You can use this to your advantage of coarse. Go up to the gate that is still closed. Turn towards the avifors statue that opened the first gate. Use avifors on it and hold the stick towards the second gate. the first gate will come back up push you out of bounds and above the second gate where you'll jump over it and into the room with the spellbook.

(Not tested on the ps2 and xbox versions)

I use it in my run, you can watch it for a better example as to how to do it. ( It happens at 2:15:20)