Fig. 4. Three-dimensional kinematic model of the buccal mass during a biting cycle. The I1/I3 muscles are shown as a continuous blue mesh, the odontophore is shown as a continuous yellow mesh, and the radular stalk is shown as a red solid. Views are shown in orthographic projection. (A) Right lateral views of transition, protraction and retraction. The central panel shows a side view of protraction; the arrows to the left indicate the contact between the posterior I3 muscle and the posterior of the radula/odontophore. The arrow to the right indicates a gap between the dorsal surface of the odontophore and the dorsal portion of the anterior I3 muscle; compare the views shown in Fig. 12D,E. (B) Dorso-ventral views of transition, protraction and retraction. The lateral groove (posteriormost edge of the I1/I3/jaw complex) has been rotated so that it is vertical. (C) Antero-posterior views of transition, protraction and retraction. The left, middle and right columns are based on frames 26, 34 and 39, respectively, of bite 3213. Compare with fig. 11 of Neustadter et al. (Neustadter et al., 2002b).