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Inside the great egret’s eye: a detailed anatomical portrait

Research · Anatomy & morphology

What does a great egret’s eye look like in detail? Researchers examined six great egrets (Ardea alba) and described the structure of their eyes and the glands around them. The study offers a detailed anatomical portrait, rather than a test of how each feature affects vision.

The right and left eyes had similar measurements. The eyeballs accounted for about 11.2% of head mass. The eyes were flat, with yellow irises and circular pupils. The authors note that flat eye morphology has previously been associated with daytime-active birds.

The study also describes structures within and around the eye. A ring of 14 small bones, or ossicles, was associated with hyaline cartilage in the sclera, the outer supporting layer of the eyeball. The cornea had a distinct Bowman’s membrane, and the retina had 10 identifiable layers. A pleated structure called the pecten extended from the optic nerve towards the vitreous body, the gel-like material inside the eye.

Three accessory glands had different shapes. The Harderian gland was the largest; the lacrimal gland, which produces tears, was shaped like a hockey stick; and the supraorbital nasal, or salt, gland was pyramidal.

Detailed anatomical descriptions provide a basis for comparing the eyes of different bird species. This study documents features of the great egret’s eye and surrounding glands, but its observations come from six specimens and do not establish how much those features vary across the species.

Sources and image credit

  1. Ocular morphology and morphometry of the great egret (Ardea alba): A comprehensive anatomical descriptionPrimary source; the verified evidence was the published abstract.

Image: Giles Laurent / Wikimedia Commons, CC BY-SA 4.0. Representative photograph. · CC BY-SA 4.0 · Source

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Anatomy & morphology

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