Having a concave surface on both ends, used to describe the shape of certain bones or vertebrae.
From Greek 'amphi-' (both sides) + 'koilos' (hollow). This anatomical term developed in the 19th century when paleontologists were classifying fossilized vertebrae.
Fish and many amphibians have these double-concave vertebrae, but mammals like us moved away from this design—our vertebrae are flat in front and rounded in back, which gives us more flexibility for complex movements.
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