Markings on base os scales

[Jarrod_H]

G'day I have a albino Darwin with some markings on the base of his scales that run along his back. His enclosure hasn't changed for the past 2 years so I don't believe they have been getting caught/ rubbing on anything.
He hasn't been soaking in his water bowl.
Opinions would be helpful please.

 

[caliherp]

It looks like rub marks to me. Is there something it could be rubbing on?

 

[Jarrod_H]

It looks like rub marks to me. Is there something it could be rubbing on?

I really don't thing it is coz his enclosure hasn't changed in years and all there is in there is kritter crumble with two large Exo hides and all the marks are only at the base of the scales.

 

[caliherp]

I don't know what critter crumble is but maybe is is under its scales.

edit: It looks deep enough that it may be able to burrow. Is it tanbark like material?

Edit#2: is that a light cover on the top right side? Are you sure it is not rubbing on that? It kinda looks like a cheese grater.