Fig. 4. Schematic representation of the skull of three species of Paleognathae. (A) Ostrich Struthio camelus, (B) emu Dromaius novaehollandiae, (C) rhea Rhea americana. (D) Model of the rhea drawn into a outline of the actual skull, indicating the relationship between the model and the actual skull. Arrows in A–C indicate the line of action and the approximate length of the muscles: 1, musculus depressor mandibulae; 2, musculus pterygoideus; 3, musculus adductor mandibulae externus; 4, adductor muscle complex of the quadrate; 5, musculus protractor pterygoidei et quadrati. Gray areas represent the quadrate and the lower bill. Circles represent rotation points. Scale bar, 2 cm.