coussinet

A stone placed on the impost of a pier for receiving the first stone of an arch or vault.

The intrados of a simple vault is generally formed of the portion of the surface of a cylinder, cylindroid, or sphere, never greater than that of half the solid; and the springing lines of the coussinet, which terminate the walls from which the vault rises, are generally straight lines, parallel to the axis of the cylinder or cylindroid.

It is to be observed that in most of , if not in all , their bridges , the ancients did not increase the dimensions of their voussoirs from the crown towards the springing or coussinet, but made them of an equal thickness throughout; in this they were followed by Palladio, and all the Italian architects.

Part of the Ionic capital between the abacus and quarter round, which forms the volute.

The term balteus is also used by Vitruvius to denote the strap which seems to bind up the coussinet or cushion of the Ionic capital.

Many details merely painted on in the Doric order, like the leaves on the molding, the coussinet, etc., are presented plastically in the Ionic.