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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 AC 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.