Fig. 1. Morphology of balaenid head. Schematic lateral views showing the narrow, arched rostrum and huge, scoop-shaped, lower jaw with mouth closed (A) and open, in feeding position, with abducted lips (B). (A) When the mouth closes the baleen folds back, the lip overlaps the upper jaw, and the central furrow of tongue (light broken lines) contacts the palate. Heavy broken lines indicate the orolabial sulcus between tongue and lip; the dotted line denotes oropharynx and esophageal orifice. (B) In the less streamlined open-gape feeding profile, note the large lower lip above the mandible (broken line) and the overlapping extent of the freely suspended baleen rack (dotted line), with the shortest plates at rear. The arrow indicates where filtered water exits posterior to the lip after passing along the gutter-like orolabial sulcus.