rugae

n. wrinkle, fold, crease

Rugae is a term used in anatomy that refers to a series of ridges produced by folding of the wall of an organ. Most commonly the term is applied to the internal surface of the stomach. The stomach rugae may be seen during esophagogastroduodenoscopy or in radiological studies. They provide the stomach with a higher amount of surface area for food. When food enters the stomach, these rugae unfold and become stretched out.
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Rugae, n.pl the irregular ridges in the mucous membrane covering the anterior part of the hard palate. rugae area, n See area, rugae. [more]Rugae - Community and Resources

Noun
1. (anatomy) a fold or wrinkle or crease; "rugae of the stomach"
(hypernym) fold, plica
(classification) anatomy, general anatomy

(pl. )
of Ruga