When kept in non-metallic vessels they take the shape of a convex meniscus.
The area of a lune or meniscus is expressible as the difference or sum of two segments, and the circumference as the sum of two arcs.
Sometimes the pad is reduced to a ventral semi-ring or meniscus; it retains its largest almost original shape and size in the second vertebra, the axis or epistropheus, where it forms a separately ossifying piece which connects, and coossifies with, the odontoid process (the centrum of the atlas) and the centrum of the second vertebra.
- Biconcave, biconvex and concavo-convex (meniscus) lenses are employed in ophthalmic practice in the treatment of errors of refraction.
4) in which the field-lens is changed into a meniscus having radii in about the ratio of +I to - 9 gives still better results, but still not quite so good as the results obtained by using the combination of two convexo-plane lenses of the focal ratio 2 to I.