Fig. 4. Measurements on high-temporal-resolution magnetic resonance images. The same image is shown in A-D. (A) Radular stalk outline (see Fig. 3 and text) and a line indicating the axis of the radular stalk. (B) The angle of the anterior margin of the odontophore, determined by the margin of the I6 muscle just posterior to the prow (see Fig. 6 and text). (C) Outline of the odontophore including the prow. (D) Image showing all the measurements shown in A-C and, in addition, an outline of the entire buccal mass (excluding the pharyngeal tissue), the line of the jaws and the line of the lateral groove (the dorsal and ventral border between the I1/I3/jaw musculature and the posterior I2 muscle).