Fig. 12. External and internal anatomy of the I1/I3/jaw complex, and measurement of the circumference of the jaw cartilage during a bite. (A) Fiber directions in the I1 muscle visualized by staining with hematein (see Materials and methods). White lines have been added that closely follow discrete I1 fibers. A schematic view of fiber positions during the biting cycle is shown in Fig. 2A. (B) Fiber directions in the I3 muscle visualized by staining with Fast Green (see Materials and methods). Two white lines have been added that closely follow discrete I3 bands. (C) Dissected view of jaw cartilage within the I1/I3/jaw complex. Lines point to folds in the cartilage of the jaw. Note that the jaw cartilage only occupies approximately half of the full antero-posterior length of the I1/I3/jaw complex both dorsally and ventrally. Scale bar (1 cm) applies to A-C. (D-G) Measurement of circumference of jaw cartilage during a bite. Images are oriented so that the dorsal surface of the animal is at the top, as in Figs 1 and 2. Compare with the line drawings in fig. 2A of Morton and Chiel (Morton and Chiel, 1993a). (D) Circumference at peak protraction; the radula has just closed. Arrow indicates the dorsal region of the jaws that are not in contact with the dorsal surface of the radula. (E) Circumference just after peak protraction, as radula begins to rotate and retract posteriorly into the buccal cavity (0.5 s after image shown in D; arrow indicates the dorsal region of the jaws that is not in contact with the dorsal surface of the radula). (F) Circumference at the onset of folds in the cartilage (folds are indicated by arrows; 1.0 s after image shown in D). (G) Circumference as the jaws close (1.3 s after image shown in D).