Figures 42–45: Scanning electron microscope views of the branching pattern and anastomoses of the airways in the mature lung of the domestic fowl, Gallus gallus variant domesticus . Figure 42: Medial view of latex cast of the lung showing the different sizes, orientations and anastomoses of the tertiary bronchi (parabronchi). Dashed square, paleopulmonic parabronchi which are long and lie parallel to each other; dashed circles, neopulmonic parabronchi which are short and anastomose profusely; PB, primary bronchus; SB secondary bronchi. Figure 43: Close-up of a stack of cast of paleopulmonic parabronchi (Pr) showing areas which they anastomose (arrows). Figure 44: Close-up of cast of a parabronchus showing atria (At) which give rise to infundibula (If) which anastomose (arrows). AC, air capillaries; dashed lines, interatrial septa. Figure 45: Close-up of cast of air capillaries (AC), the terminal gas exchange units, which profusely anastomose (arrows). Scale bars: Figure 42, 1 cm; Figure 43, 1 mm; Figure 44, 0.5 mm; Figure 45, 8 μm.