Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
Walking of Chrysemys has been studied by cinephotography and x-rays. The lateral sequence, diagonal couplet gait, limb support sequence, and wide track provide great stability, yet a slight pitch and roll cause some plastral drag. Velocity ranges from 28 mm to 51 mm/second, and fluctuates within a stride. Limb movements and structure resemble those of other ectotherms, but incorporate modifications reflecting the animal's short, broad trunk encased in a shell and carried close to the ground. The triradiate pectoral girdle so articulates with the shell as to act as a truss for weight transfer to the ground. Girdle rotation increases the efficiency of the girdle as a truss, and contributes to locomotor efficiency. The glenoid cavities are more than twice as far apart as the acetabula, so a thrust from the pectoral girdle has less propulsive efficiency on the center of gravity than one from the acetabulum. The humerus and femur are protracted to a greater extent than in other ectotherms and their horizontal arcs of retraction are less. Rotation of these elements about their longitudinal axes contributes to the length of a stride and to foot placement and withdrawal. Differences in the movements of comparable segments of front and hind limbs correlate with differences in the width of the girdles, a crus longer than the antebrachium, and different capacities for joint rotation.
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