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Fig. 4. Pelvic fin motion. Paired pelvic fins oscillated in a regular contralateral
cycle. (A–D) Four stages of left pelvic fin oscillation are drawn in
lateral, transverse and ventral views. The left fin is coloured green, the
dorsal side of the fin in light green and the ventral side of the fin in dark
green. (A) Column A is arbitrarily assigned as the start of the oscillating
cycle when the fin is adducted against the body relative to the transverse
plane (phase=0 deg.). (B) As the fin started its cycle the fin's lateral edge
began abducting toward the transverse plane and supinated away from the
sagittal plane where it reached maximum lateral excursion (phase=120 deg.).
(C) As the fin continued abducting toward the transverse plane, the fin's
lateral edge started pronating medially toward the fish's mid-sagittal plane
(phase=180 deg.). (D) The fin began adducting away from the transverse plane
as the fin's lateral edge was pronated maximally toward the mid-sagittal plane
(phase=300 deg.). Finally, the fin made its return stroke back to a fully
adducted, partially supinated starting position (A, phase=360 deg./0 deg.).
Arrows in each of the images note the direction in which the fin is moving or
about to move. Background colours of each panel correspond with those in
Fig. 3.