Technical Abstract: Cephalization and seamless fusion of the anterior body segments during development obscure the segmental origins of the insect head. Most of the visible seams are thought to reflect infolding for structural reinforcement rather than a merger of segmental or cuticular plate borders. Incomplete fusions, partial deletions or other modifications of segments associated with eight Tribolium mutations affecting the adult head indicate that the frontal and gular sutures are true sutures that mark borders between adjacent cuticular plates, and suggest that the anterior facial shelf is a composite of three segmental surfaces: ocular, antennal, and labro-intercalary. Additionally, midline splits of the clypeo-labrum and gula, and membranous lesions on the dorsal and lateral head capsule of mutant beetles reveal probable borders of adjacent cuticular plates where visible sutures are normally absent. The anterio-lateral lesions seen in certain mutations mark the border between ocular and antennal plates and appear to reveal the site of the often cryptic postfrontal sutures that separate these segments. While revealing or clarifying intersegmental borders between ocular, antennal and clypeo-labral plates, the various modified or unfused surfaces of the head mutations described here do not suggest the existence of a separate acronal plate at the anterior extreme of the insect head.