Fig. 3. Anterior isthmus motions. Non-consecutive series of video fields shows the motions of the metacorpus and anterior isthmus during a pump. Black lines show the lumen; time in ms is in the upper right corner of each image. (A) The pharynx is fully relaxed, the lumen closed. At 33 ms (B) contraction (opening) of the metacorpus is barely visible, and at 100 ms (C) contraction is complete and the corpus lumen fully open. Only at 117 ms (D), after the corpus has fully contracted, does the anteriormost part of the isthmus open. The metacorpus remains fully contracted until 150 ms (E), then goes from fully open to fully closed between two consecutive video fields at 150 and 167 ms (F). In the meantime the isthmus contraction proceeds, gradually opening more posteriorly until at 183 ms (G) the entire anterior half of the isthmus is open. At 233 ms (H) the isthmus is fully relaxed.