Annulus
A ringlike structure, or any body part that is shaped like a ring.
Applied to many small ring-shaped structures.
The base of a heart valve that supports the valve's leaflets is called the annulus.
A ring-shaped pancreas that encircles the duodenum is an annular pancreas.
'Annulus' is a misspelling of the Latin 'anulus' (a little ring), the diminutive of the Latin 'anus' (a ring of more substantial size).