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Other Terms: Anulus fibrosus (diskus intervertebralis)
The annulus consists of consecutive rings of collagen fibers, called lamellae, arranged in a highly ordered pattern. Anywhere from ten to twenty lamellae are present in the annulus. They resemble the growth rings of a tree and surround the central nucleus pulposus. The annulus is formed of strong fibrocartilage. The collagen fibers in each lamellae alternate, one to the right the next to the left, but their orientation with respect to the vertical is always approximately 65 to 70 degrees. The lamellae are thicker in the anterior and lateral portions of the disc and thin posteriorly.