Scleral ring
The scleral ring (also sclerotal ring , ancient Greek σκληρός sklēros "hard", Latin annulus ossicularis sclerae ) is a ring-shaped, bony reinforcement of the eyes of birds , the extinct dinosaurs , pterosaurs and ichthyosaurs , but also some modern reptiles such as the iguanas . On average, it consists of 14–15 bone platelets that are embedded in a ring in the dermis at the transition to the cornea . They are arranged in an overlapping manner and can also be completely fused.
The scleral ring is located directly behind the externally visible iris , but in front of the lens . It usually has no contact with other bones. The visible iris is attached to the outside of the scleral ring and the lens is attached to it on the inside. Since the iris is attached to the scleral ring, the diameter of the pupil can never be larger than the central hole of the scleral ring. When reconstructing extinct species, this allows a precise statement to be made about the maximum pupil size of the species in question. The scleral ring is flat u. a. in chickens and songbirds , but it is z. B. in the case of the owls tubular, which means that their elongated eyes have a longer focal length and therefore more vision in the dark. The scleral ring supports the eyeball and gives the accommodation apparatus a starting point.
literature
- Gerhard Hummel: anatomy and physiology of birds. Compendium for study and practice (= UTB for science. Agricultural sciences, veterinary medicine 2144). Eugen Ulmer, Stuttgart 2000, ISBN 3-8252-2144-X .
Individual evidence
- ↑ Palæos - Eureptilia: Euichthyosauria ( Memento of December 21, 2010 in the Internet Archive ). Palaeos.com as of January 20, 2009