The view from the top
Sometimes it looks like the badly drawn picture A (above) and sometimes like picture B. My last scan confirmed that Baby had flipped over, and is now in the recommended "head down" position.
So that large bump is the nice little rounded bottom, which Baby keeps moving from side to side in a sort of slow but enthusiastic rumba... :)
Darling says what ever Baby's other features may be, Baby has certainly inherited my posterior! Lol!