Fig. 5. Medial view of the left lung of the ostrich Struthio camelus showing the hilus and the three medioventral secondary bronchi (filled circles) arising from the primary bronchus (marked with a pencil). a, pulmonary artery; the arrow indicates ostium opening to the abdominal air sac. Each gradation on the scale bar, 1 cm. Open circles, parabronchi.