On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal bones. Separates from Berardius and Ziphius.
No sulcus exists in middle if the combined antero-dorsal surface of the nasals. Separates from Mesoplodon and Hyperoodon.
Frontal bones occupy an area of the vertex of the skull approximating or exceeding that occupied by the nasal bones. Separates from Berardius, Ziphius, Tasmacetus, and Hyperoodon.