The Side-Lying Extension-Rotation works your thoracic spine.
You may also see this exercise as the Side Lying Archer.
There are 2 slight variations here.
The first variation is demonstrated by Eric Cressey. He keeps his bottom hand up and adds a PNF to the moving arm.
Notice how the thump rotates towards the floor as he comes to the front.
The second variation is more typical.
One hand is reaching out in front along the floor. The other rotates around the spine to touch the floor behind you.
Because you’re lying on your side, you’ll notice that the head is supported in this variation.
In both variations it’s important to keep your knee in contact with the ball or foamroller. Pillow, yoga block, or medicine-ball all work if you don’t have a foam roller.