The sclerotic ring [1] ( Latin Anulus ossicularis sclerae ) is an annular bone structure found in the eyes of several modern and extinct groups of vertebrates , such as birds , dinosaurs , pterosaurs and ichthyosaurs , with the exception of mammals and crocodiles . It may consist of a single bone or several segments.
The sclerotic ring is located directly behind the iris visible from the outside, but in front of the lens . Usually has no contact with other bones. The visible iris of the eye is located on the outside of the sclerotic ring, and the lens hangs on the inside. For this reason, the diameter of the pupil can not be larger than the central opening of the sclerotic ring. Sclerotic rings allow more accurate focusing of the eyes, and also perform a supporting function, especially in those animals whose eyes are not spherical or living under water.
Notes
- ↑ Fundamentals of Paleontology (in 15 volumes) / ed. Yu. A. Orlova . - M .: Publishing House of the Academy of Sciences of the USSR, 1959-1963. - V. 12. Amphibians, reptiles and birds. - p. 590.
Literature
- Hummel G. Anatomie und Physiologie der Vögel. Kompendium für Studium und Praxis (= UTB für Wissenschaft. Agrarwissenschaften, Veterinärmedizin 2144). - Stuttgart: Eugen Ulmer, 2000. - ISBN 3-8252-2144-X .