Fig. 9. Odontophore-centric model of a polyethylene tube swallow, magnetic resonance imaging (MRI) sequence 7732-S3, frames 15-38. (A—C) Mid-sagittal MR images; (D—F) schematic tracings of the anatomical structures in A—C; (G—L) corresponding odontophore-centric model representations (orthographic projection). G—I are latero-medial views and J—L are dorso-ventral views. The left-hand column is rest (MRI frame 15), the centre column is peak protraction (MRI frame 26) and the right-hand column is peak retraction (MRI frame 35). Buccal mass rotation has been removed from the MR images (buccal mass angle 0°). Note the apparent stretching of the ventral I1/I3 muscle at the hinge region between rest and peak protraction (dotted line, A and B). The plane of the lateral groove tilts anteriorly at peak protraction (arrowheads, B), but in the model representation, the plane of the first I1/I3 muscle ring remains vertical (H; arrowheads indicate the in vivo lateral groove plane). The right or left halves of the I1/I3 rings have been cut away in G—L to reveal internal details. e, esophagus; r, radula; rs, radular stalk; rt, radular tip. Each frame is 310 ms (real time).