An ornamented or painted ball or boss fastened at each
end of the stick on which manuscripts were rolled.

The hilum.

A depression or opening in the center of the base of
many spiral shells.

Either one of the two apertures in the calamus of a
feather.

One of foci of an ellipse, or other curve.

A point of a surface at which the curvatures of the
normal sections are all equal to each other. A sphere may be osculatory
to the surface in every direction at an umbilicus. Called also umbilic.