The squared jaw and flat chin sparkso much joy, its such a distinctive facial shape, and I love the stripes over his lips. It could probably help deflect sunlight away from his face, also, it reminds me of mimicry in nature, like a butterfly's eyespots. The lines give him the look of skinless teeth and gums, and a skeletal look could give the illusion of bad health or danger to an unintelligent enemy.

Multi-purpose markings! Deflecting light, scaring enemies, possibly even helps attract mates?