outter ring design question.

Ricopotamus,

With its irregularity along the curved lines and the appearance of being part of something with lines of (certain) different directions and thicknesses and round endings (as the one at the top left and some others), I believe you could, given the two curved lines:

0) If not already, create the two curved lines (maybe starting with one and Object>Path>Offset Path with the right offset);

1) Create a background consisting of such lines with different directions and positions all having Round Caps, some of which may end at/between the curved lines so the roundings are visible; you can select them all and turn them into filled paths (Object>Path>Outline Stroke), for the two first possible uses in 3);

2) Turn the curved lines into a Compound Path (you can use Object>Compound Path>Make;

3) You can then Select 1) and 2) and use the Shape Builder or one of the Pathfinders to delete the unwanted bits, or you can Ctrl/Cmd+7 to form a Clipping Mask which will be fully reversible and just leave the unwanted bits invisible.

Outer*