Fig. 4. Diagrammatic frontal section through the balaenid oral cavity for the model of continuous ram filtration powered by forward locomotion, showing the relationships of tongue, lips and baleen, and the flow of water-borne prey through the mouth: inward through the anterior subrostral gap between baleen racks, rearward to the center of mouth, and outward through the fringed medial side of baleen (filtration step) into the gutter-like channel inside lip (orolabial sulcus). Areas of mouth's anterior and posterior (paired) openings (AO and PO, respectively; see Fig. 2) are used in modeling. Incurrent/excurrent flow through AO and PO are shown by open arrows.