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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).
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