Video 1

Movie S1. In vivo visualization of synthetic smoke showing unidirectional flow. Endoscopic video (left circle) of synthetic smoke moving in the caudal chamber of a lung at the location illustrated in Fig. 2 B and C, and a recording of the direction of airflow at the nares (right panel) from a dual thermistor flow meter. Expiration occurs as the trace becomes positive. Airflow is craniad during both inspiration and expiration, indicated by the particles of smoke moving from lower right toward the upper left hand side of the screen. The red line in the background is a blood vessel in the wall of the lung. Several of the pockets illustrated in Fig. 1 can also be seen in the background. The head of the animal is toward the left and dorsal is toward the top of the page.