Fig. 2. Head profile and cross-section of rostrum and baleen. Fin, Sei and Bowhead illustrate the range of curvature of the rostrum, the sei being intermediate with a slightly arched rostrum and mandible, raised lip relative to the fin whale, with a greater curvature near the tip of the mandible. This modification would create an opening immediately under the shorter baleen plates and fibre bundles at the tip of the rostrum at partial gape. The rostrum cross-sections indicate the greater outward angle of the fin (and blue) baleen, as well as the greater prominence of the vomer relative to the sei. The sei has relatively longer baleen plates which hang at a more vertical angle from the rostrum, and which may allow the lips of the mandible to slide to a partial gape with less resistance against the baleen rack, similar to the Balaenids.