Medical Definition of annulus fibrosus
: a ring of fibrous tissue (such as that surrounding a heart valve); especially : the outer portion of an intervertebral disk that surrounds the nucleus pulposus and is composed chiefly of layers of collagen fibers Disks between the vertebrae have a soft center—a nucleus pulposus—and a tougher exterior, annulus fibrosus.—Matthew Sturdevant, The Hartford (Connecticut) Courant, 30 May 2010 The nucleus pulposus can bulge out or herniate the anulus fibrosus, but the disk itself does not “slip.”—John Palo, Newsday, 21 Feb. 1990
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