Lens (vertebrate anatomy)
Development

Additional fibers are derived from lens epithelial cells located at the lens equator. These cells lengthen towards the front and back wrapping around fibers already laid down. The new fibers need to be longer to cover earlier fibers but as the lens gets larger the ends of the newer fibers no longer reach as far towards the front and back of the lens. The lens fibers that do not reach the poles form tight, interdigitating seams with neighboring fibers. These seams being less crystalline than the bulk of the lens are more visible and are termed "sutures". The suture patterns become more complex as more layers of lens fibers are added to the outer portion of the lens.
oulipo:avoid_letter[e]