Hello SandorToaso
You can right-click on the body to view the Hide options as shown in Red box in the image below.
Under 'Faces' you have options to Hide Faces as well.
You can also, make the solid geometry 'Transparent' by toggling the symbol highlighted with a blue box in the image. This will allow you to view the internal geometry without hiding faces. You can then, either box select or you can also place your mouse over the region and scroll to select them.
You are navigating away from the AIS Discovery experience