anulus fibrosus

anulus /anu·lus/ (an´u-lus) pl. a´nuli   [L.] a small ring or encircling structure; spelled also annulus.

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anulus fibro´sus 

1. fibrous ring of heart: one of the dense fibrous rings that surround the right and left atrioventricular (tricuspid and mitral) orifices and to which are attached the atrial and ventricular muscle fibers.

2. fibrous ring of intervertebral disk; the circumferential ringlike portion of an intervertebral disk.

anulus of nuclear pore  a circular filamentous structure surrounding a nuclear pore in the nuclear membrane of a cell.

anulus of spermatozoon  an electron-dense body at the caudal end of the neck of a spermatozoon.

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anulus fibrosus,

an outer ring of collagen in an intervertebral disk arranged in a lamellar configuration that surrounds a wider zone of fibrocartilage.

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anulus [an´u-lus] (pl. a´nuli) (L.)

a small ring or encircling structure; also spelled annulus.

anulus fibro´sus

1. fibrous ring of heart; any of four dense fibrous rings, one of which surrounds each of the major cardiac orifices.

2. fibrous ring of intervertebral disk; the circumferential ringlike portion of an intervertebral disk.

anulus of spermatozoon a dark ringlike structure at the posterior end of the middle piece of a spermatozoon. Called also ring centriole.