Volume Containing a Solid Foot

Puzzle

Mathematicians affirm that of all bodies contained under the same superficies, a sphere is the most capacious;

but they have never considered the amazing capaciousness of a body,

the name of which is now required,

of which it may be truly affirmed that supposing:

its greatest length $9$ inches,

greatest breadth $4$ inches,

and greatest depth $3$ inches,

yet under these dimensions it contains a solid foot.

A shoe.