Using sphere and box as tools to represent human torso is a good way to organize and clarify the structural relationship between rib cage and pelvis. When you are drawing the sphere, you should try to feel and show its round volume. Simply giving it a little bit of form shadow and core shadow will show the form. The center lines on both sphere and box shows the direction each structure facing. The connection part between the two structures is soft and it can be bended, stretched or twisted.