Great work! Regarding the yellow ball I think it's good. Shadow of balls look sometimes weird, but are still right lol. Well, that's what I think. As to the anatomy diagrams I think the chest goes to low. The nipples usually are 2 heads down and the pecs don't go TOO far down bellow the nipples anymore. The shoulders are to broad I'd say. they usually fit in 3 heads (idealiyed), but here it's more like 4.
You're improving overall I see, keep at it!