Meniscus

The meniscus is not a bone. It is a cartilage, a flexible, elastic tissue.

And from Crabbe's own forehead sweat dripped or gathered into a kind of meniscus to be scooped off.

He opened wide both casements; they gave on a parking place four floors below; the thin meniscus overhead was too wan to illumine the roofs of the houses descending toward the invisible lake [...].