Histology of the African ostrich lungs. A, the lung parenchyma and artery; B, the tertiary bronchus; C, atria; D, respiratory capillaries. TB, tertiary bronchus; RC, respiratory capillaries; Ar, artery; SM, smooth muscle; EL, epithelial layer; A, atria; BC, blood capillary; MC, macrophage; V, vein. Scale bar: A=500 μm; B, C and D=50 μm, Stain: haematoxylin and eosin.