FIGURE 2.

Measurement systems for joint kinematics. Joint coordinate systems in the reference pose (all rotations and translations equal zero) for the (a) Helmeted Guineafowl and (b) American alligator. Red, green, and blue correspond to X, Y, and Z axes, respectively. Scale cubes represent 1 cm. Prism‐based hinge joint translation measurement system shown on a right guineafowl knee joint in anterolateral view (c) at flexion–extension rotation = 40 degrees with (X, Y, Z) translations = (0.8, 0.7, 1.0) cm and (D) at flexion–extension rotation = 80 degrees with (X, Y, Z) translations = (1.1, 0.8, −0.4) cm. Red, green, and blue cylinders reflect translations along X, Y, and Z axes, respectively; black spheres represent positions of the proximal and distal ACS origins. Note that the red X axis captures pure distraction–compression translation, and the green Y captures pure anterior–posterior translation, with separate degrees of freedom. See also Movie S1