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).
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an·nu·lus 'an-yə-ləs n,
pl -li -.lī also -lus·es a ringlike part, structure, or marking
esp any of various ringlike anatomical parts (as the inguinal ring)
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n.
(in anatomy) a circular opening or ring-shaped structure.
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an·nu·lus (anґu-ləs) gen. and pl. anґnuli [L., from anus ring] a ring or ringlike structure; in official anatomical terminology, spelled anulus [TA], q.v. for terms not found here.
Medical dictionary.
2011.