everting

Everting is the act or process of turning something inside-out or turning outward from its normal orientation. It is the present participle form of the verb evert, which derives from Latin externus meaning outside. In use, everting emphasizes the ongoing action of turning outward rather than the final state.

In anatomy and physiology, everting describes movements or positional changes where a part is turned outward. The most familiar example is eversion of the foot, in which the sole faces away from the midline. Eyelid eversion is another documented use, where the eyelid is turned outward to inspect the conjunctiva. In developmental biology and related fields, tissues or organs may undergo eversion as part of morphogenesis, resulting in surfaces that face outward.

In mathematics and topology, everting appears in the study of surfaces. Sphere eversion is a well-known theoretical phenomenon in which a sphere can be turned inside-out through a continuous deformation in three-dimensional space without tearing or gluing, though the surface may intersect itself during the process. This counterintuitive result is tied to broader concepts in geometry and was popularized through discussions of Smale’s paradox.

See also: evert, eversion (general term), inversion, topology, Smale’s paradox.