Select boundaries inside a cube

Hi all,

I use COMSOL 5. My geometry is a cube and inside of the cube there is a small sphere. To perform my model, I need to select the boundaries of the sphere. The problem is that I cannot select the boundaries crossing the cube...I can select only the boundaries of the cube...

Have you a method to select the boundaries of the sphere crossing the cube ?

Thank you for your help.

Kevin Bartoloni (PhD)