Fig. 5. Summary of corpus and isthmus motions. For simulation, muscle motions were assumed to be piecewise linear as diagrammed here (i.e. the extent of contraction varies linearly with time, except at discrete breakpoints where its rate of change with time abruptly changes.) The corpus contracts from 0 to 133 ms and relaxes from 133 to 150 ms. C indicates the fully contracted position and R the fully relaxed position. The entire corpus contracts and relaxes as a unit. The anterior isthmus contracts from 83 to 150 ms and relaxes from 150 to 167 ms; the middle of the isthmus (the most posterior region included in the simulation) contracts from 150 to 183 ms and relaxes from 183 to 200 ms. Between the anterior and middle isthmus the times at which contraction starts, relaxation starts, and relaxation ends vary linearly. These times are based on the video sequence from which Fig. 3 was abstracted, but the precise times of pharyngeal motions are quite variable. Important features consistently seen are the delay of isthmus motions with respect to the corpus, and the progression of motion from the anterior to the middle isthmus.