Anulus fibrosus - Anulus fibrosus
Each intervertebral disc is composed, at its circumference, of laminæ of fibrous tissue and fibrocartilage, forming the annulus fibrosus.
The laminæ are arranged concentrically; the outermost consist of ordinary fibrous tissue, the others of white fibrocartilage. The laminæ are not quite vertical in their direction, those near the circumference being curved outward and closely approximated; while those nearest the center curve in the opposite direction, and are somewhat more widely separated. The fibers of which each lamina is composed are directed, for the most part, obliquely from above downward, the fibers of adjacent laminæ passing in opposite directions and varying in every layer; so that the fibers of one layer are directed across those of another, like the limbs of the letter X. This laminar arrangement belongs to about the outer half of each fibrocartilage.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).