Fig. 13. Estimate of forces of I1/I3/jaw complex on odontophore. (A) Graph of estimated net forces for successive frames of sequence 3213, images 26-43. See Materials and methods for description of force calculation. Nominal model force units are plotted against time (ms). Positive force values imply that the odontophore will be protracted; negative force values imply that the odontophore will be retracted. The four lines are plotted using the assumption that the ratio of force in the anterior half to the posterior half of the I1/I3/jaw muscle complex is 0.0 (top line), 0.3 (second from top), 0.6 (third from top), or 1.0 (bottom line). Whenever the data for different force ratios lies above the zero line (as it does for ratios of 0.3 and 0.0), this indicates that the structures are kinematically configured such that with this differential excitation ratio, the I3 muscle can function as a protractor. (B) Three-dimensional model right lateral views of the I1/I3/jaw complex (blue mesh) and odontophore (yellow solid), corresponding to the arrows above A (images 31, 33 and 35, respectively). Top row: I1/I3/jaw complex and odontophore. Bottom row: odontophore alone. In the center top image, the antero-dorsal I1/I3 mesh is not in contact with the dorsal surface of the odontophore, but it is in contact with the dorsal surface of the posterior part of the odontophore. Also note that, in the central bottom image, the posterior part of the odontophore widens towards its midpoint. (C) Three-dimensional model dorso-ventral views of the I1/I3/jaw complex corresponding to the arrows above A (images 31, 33 and 35, respectively). Top row: I1/I3/jaw complex and odontophore. Bottom row: odontophore alone. In the center top image, note that the posterior I1/I3 mesh is in contact with the posterior surface of the odontophore. In the center bottom image, note that the posterior part of the odontophore widens towards its midpoint.