Fig. 13. Kinematics of the antero-posterior lengths of the I3 muscle compared with measurements in the same magnetic resonance images (MRIs). Data in A—D are plotted as length (mm) as a function of time (ms). Data from the model are plotted using a black line; data measured from the MRIs are plotted using a grey line. On the left side are plots of the antero-posterior I3 length on the dorsal side of the model. On the right side are plots of the antero-posterior I3 length on the ventral side of the model. The match to the lengths on the ventral surface is good but, in three out of the four swallows, the match to the antero-posterior length of I3 on the dorsal surface is poor, especially during late protraction and most of retraction. (A) I3 antero-posterior kinematics in the first swallow. (B) I3 antero-posterior kinematics in the second swallow. (C) I3 antero-posterior kinematics in the third swallow. (D) I3 antero-posterior kinematics in the fourth swallow. (E) Normalized, averaged and smoothed I3 antero-posterior kinematics during a swallowing cycle. Values are means ±1 S.D. (N=4). At the protraction/retraction transition and early in retraction (t4/t1 transition and early t1), the model underestimates the length of the ventral surface because of its inability to represent stretch of the ventral I3 muscle around the prow.