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Fig. 2. Methods used to quantify the posture of the snake one frame before bridging
a gap. The image is a tracing of a right lateral view of a video of a snake
with SVL=57 cm crossing a 30 cm gap. The pegs in the large horizontal
cylinder are inclined approximately 45° relative to the horizontal plane,
and the tips of those in the foreground were oriented towards the camera. The
origin of the coordinate system used for kinematic analysis was the top center
end of the perch upon which the snake was initially placed. The longitudinal
positions were measured or calculated for the most posterior location of the
snake (Xposterior), mid-way between the end of the initial
perch and Xposterior (Xmid-perch) and
the most anterior location of the snake that was underneath part of the
initial perch or one of its pegs (third right peg from the edge in this
example) so that upward forces could be applied (Xanchor).
The x and y coordinates were digitized for the lowest
location of the mid-dorsal line and center of mass (COM) for the portion of
the body suspended in the gap between the two perches.
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