Canon EOS-1D X Mark III Advanced User's Manual page 385

[ 5]
AF point selection movement
When AF points are selected, you can set whether selection stops at the outermost AF point
or continues to the first AF point on the opposite side.
[ ] Stops at AF area edges
Useful if you often use the outermost AF point.
[ ] Continuous
Instead of stopping at the outer edge, the selection of AF point continues to the opposite
side.
Note
Also applies when the initial AF point for AI Servo AF is selected with [
Servo AF pt, / ] set to [Initial Servo AF pt, /
385
: Initial
].