Medical Definition of pronephros
plural pro·neph·roi \-ˌrȯi\play
: either member of the first and most anterior pair of the three paired vertebrate renal organs that functions in the adults of amphioxus and some lampreys, functions temporarily in larval fishes and amphibians, and is present but nonfunctional in embryos of reptiles, birds, and mammals—compare mesonephros, metanephros
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