Anatomy of the scleral ossicles in brazilian bird

ABSTRACT

The sclera is the outermost layer of the eye. In some vertebrates, it consists of a scleral ring of osseous plates that afford protection against pressure and help maintain the shape of the eyeball. The morphology, number, development and position of the scleral ossicles differ in distinct groups of vertebrates. Therefore, the objective here was to examine the number, shape and arrangement of the scleral ossicles in Brazilian birds of different orders. The study involved 208 birds of 18 orders, which died from causes unrelated to eye infections. The birds’ eyeballs were removed and subjected to diaphanization and staining of the ossicles with Alizarin red S. All the eyeballs analyzed presented scleral ossicles in a fixed position in the central portion of the eyeball, but which varied in size, shape and number. The number of bony plates in the various bird species varied from 11 to 16, with a modal number of 14, and their shape was predominantly quadrangular, showing a similar pattern in species of the same order. Some specimens presented differences in the number of ossicles in the right and left eyeball, as in Spheniscus magellanicus, Elanus leucurus, Ramphastos toco and others and Leptodon cayanensisalso presented a scleral sesamoid bone. The distribution and morphology of the ossicles vary according to the taxonomic group, although species of the same order present a similar pattern.