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'Annulus' (or 'anulus'), being the Latin for "ring", is a term used to describe various ring-shaped objects:

★ Annulus (entomology), an antennal unit in simple antennae, or a ring-like marking or structure surrounding a joint or segment

★ Annulus (anatomy) refers to several structures in human anatomy. The spelling "anulus" is preferred under Terminologia Anatomica, but both spellings are commonly found. Examples include:

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★ Annulus fibrosus cordis, the ring-like structure on a heart valve where the valve leaflets are anchored

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★ Annulus fibrosus disci intervertebralis, the outer wall of the invertebral disc

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★ Annulus femoralis

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★ Annulus inguinalis superficialis

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★ Annulus inguinalis profundus

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★ Annulus tendineus communis

★ Annulus (ichthyology), the annual rings that form in fish scales or bone sections

★ Annulus (mycology), the "ring" on a mushroom stem

★ Annulus (astronomy), the ring of light from the visible part of the photosphere seen at the greatest extent of an annular eclipse

★ Annulus (cosmology), the ring around the lens on which strong gravitationally lensed images of one source appear

★ Annulus (mathematics), a ring-shaped geometric figure

★ Annulus (firestop), the space in a penetration seal surrounding a penetrant, i.e. between a pipe or electrical conduit, or cable and a sleeve, with or without a firestop

★ Annulus (oil well), the tube shaped void between the drill string and the formation when drilling an oil well

★ Annulus (microscopy), a circular opening "disk" below a specimen slide, required for Phase Contrast microscopy

★ Annular hurricane, a hurricane that is nearly symmetrical and takes longer to weaken than normal hurricanes.