The part under the bowl

The underside of the basin is decorated with a large torus covered at the corners by a lanceolate leaf-shaped « griffe ». These large « griffe » are characteristic of the Tournais tradition. 

Lexicon:

Lanceolate « griffe » : decorative motif that transforms the square shape of the base into the circular shape of a column shaft (here in the shape of a spearhead).