Firstly, the mostly obvious difference is that the Caucasoid top skull has a very flat profile, while the negroid bottom skull is ‘prognathic’, meaning it’s jaws protrude out. Although not obvious from this image, the nose aperture of the Caucasian skull has a narrower triangle shape; with a longer, thinner bony protrusion at the point where the nose comes out from between the eyes (nuchal ridge). Caucasian skulls also posess a nasil sill (unless you see this shown, no explanation will make sense), Asian and African skulls don’t.